333 — 15 September 2020 Editor: Bo Reipurth (Reipurth@Ifa.Hawaii.Edu) List of Contents

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THE STAR FORMATION NEWSLETTER An electronic publication dedicated to early stellar/planetary evolution and molecular clouds

No. 333 — 15 September 2020 Editor: Bo Reipurth ([email protected]) List of Contents

The Star Formation Newsletter Editorial ...... 3 Interview ...... 4 Editor: Bo Reipurth [email protected] My Favorite Object ...... 7

Associate Editor: Anna McLeod Perspective ...... 14 [email protected] Abstracts of Newly Accepted Papers ...... 18 Technical Editor: Hsi-Wei Yen Abstracts of Newly Accepted Major Reviews .. 51 [email protected] Dissertation Abstracts ...... 52

Editorial Board New Jobs ...... 56 Short Announcements ...... 58 Joao Alves Alan Boss Meetings ...... 59 Jerome Bouvier Summary of Upcoming Meetings ...... 60 Lee Hartmann Thomas Henning New Books ...... 61 Paul Ho Passings ...... 63 Jes Jorgensen Charles J. Lada Thijs Kouwenhoven Michael R. Meyer Ralph Pudritz Luis Felipe Rodríguez Cover Picture Ewine van Dishoeck Hans Zinnecker The image shows the active star forming regions of M8 and M20 and associated giant molecular clouds, The Star Formation Newsletter is a vehicle for together with the hidden Galactic Center to the fast distribution of information of interest for as- lower left. The small Bok globule Barnard 86 is tronomers working on star and planet formation seen near the center of the image against the rich and molecular clouds. You can submit material star ﬁelds of Sagittarius. The vertical axis is 10◦, for the following sections: Abstracts of recently with north up and east left. accepted papers (only for papers sent to refereed journals), Abstracts of recently accepted major re- Image by Bo Reipurth (Canon EOS Ra, 30 sec, views (not standard conference contributions), Dis- 135mm lens at f/2, ISO 6400). sertation Abstracts (presenting abstracts of new Ph.D dissertations), Meetings (announcing meetings broadly of interest to the star and planet formation and early solar system community), New Jobs (advertising jobs speciﬁcally aimed towards persons within the areas of the Newsletter), and Submitting your abstracts Short Announcements (where you can inform or re- quest information from the community). Addition- Latex macros for submitting abstracts ally, the Newsletter brings short overview articles and dissertation abstracts (by e-mail to on objects of special interest, physical processes or [email protected]) are appended to theoretical results, the early solar system, as well each Call for Abstracts. You can also as occasional interviews. submit via the Newsletter web interface at http://www2.ifa.hawaii.edu/star- Newsletter Archive formation/index.cfm www.ifa.hawaii.edu/users/reipurth/newsletter.htm Editorial

After 28 years and 333 issues of the Star Formation Newsletter, I have decided that the time has come for me to step down as Editor of the Newsletter. While it has been wonderful to interact with our community and I am thankful for the many expressions of appreciation I have received over the years, it has also been a challenge every month to find the time to prepare an issue, no matter what other things I was doing, or where I was. Technology inexorably advances, and new means of communication appear. 28 years ago the world looked very different, as we were only at the beginning of the information age, and it may be difficult for young people today to understand that information was not so easy to get hold of as it is now. Back then many institutes still issued preprints and mailed them to other institutes. The process of publishing a paper was much slower, and people actually went to the library and (gasp) read the journals as they came in. It was in that environment that the Star Formation Newsletter was launched as the first electronic newsletter in astronomy, offering rapid dissemination not only of abstracts, but also of news about meetings, jobs, dissertations, and new books. This soon led to more such newsletters being circulated in other fields of astronomy, most of which unfortunately had short lives, although some still exist. About 8 years ago I expanded the Newsletter to also include interviews with leading researchers, and short articles meant to give quick overviews about particular subjects or specially interesting objects. Although I step down as Editor, it does not mean that the Newsletter ceases to exist. I am very happy to announce that João Alves at the University of Vienna, Austria, has agreed to take the helm. Joao will gradually introduce changes to the Newsletter, and in next month’s issue he will lay out his vision. I will continue to prepare interviews for the Newsletter, since they have been universally welcomed by readers. I have come to realize that, subsequent to publication, the interviews have been buried in the archives on the webpage for the Newsletter, and while still accessible it is a major effort to find any specific one. Hence, I have decided to make a compilation of all 77 interviews so far,. This facilitates finding particular ones, but - perhaps more importantly - allows young researchers to see more globally how star formation has developed into its present state. The compilation, which will be augmented yearly, is further described in the section on New Books in this issue, and it can be downloaded from this URL: http://bit.ly/77interviews It has always been a puzzle to me that I only receive about 50% of the abstracts of relevant papers. Given that we all publish to be read, it seems logical that, after spending many months to prepare research results for publication, one should also spend 5 minutes to circulate an abstract to potential readers. I therefore urge readers to submit their abstracts to João in the spirit of a shared community. If we all do this, we all can benefit from a near-complete monthly compilation. The Newsletter is a creation of the star formation community for the star formation community. So please support João in his future efforts on behalf of our community. In closing, I would like to thank all the readers who have submitted their abstracts and announcements to the Newsletter. I would like to extend special thanks to my Associate Editors Hsi-Wei Yen and Anna McLeod who have been steadfast in their support of the Newsletter. Finally, on a practical note, please continue to submit your abstracts to the Newsletter website at its current location until further notice.

Bo Reipurth

3 replace George Coyne on my Ph.D. Committee as Charlie was transitioning to become an Assistant Professor at Uni- Bruce Wilking versity of Arizona (Coyne had left to become the Director in conversation with Bo Reipurth of the Vatican Observatory). Q: Your PhD from 1981 focused on star formation in the ρ Ophiuchi cloud. How did you choose that subject? A: I was fortunate that Charlie Lada arrived at the Uni- versity of Arizona as a Bok Fellow in 1978. He wanted to do infrared surveys of molecular clouds and I assisted him with infrared observations of Barnard 35 at the Mt. Lem- mon 28-inch telescope. In return, he offered to take me observing at the Millimeter Wave Observatory (MWO) in West Texas. We had done some near-infrared polarization measurements of stars toward the ρ Oph cloud and I thought I was seeing two cloud components. So I began observing 12C16O emission in the direction of these stars and found the line profiles to be very complex and very optically thick. So Charlie suggested tuning to 13C16O, Q: While you were still a student you led a study on the but we found these too looked optically thick. So right 12 18 wavelength dependence of interstellar linear polarization. before we were to return to Tucson, we tuned to C O This has remained a highly cited paper for 40 years, what and found a single strong emission line. On subsequent 12 18 accounts for this longevity? trips we started mapping the cloud in C O only to find that the resident astronomer, Bob Loren, was already do- A: As near-infrared polarization data of stars were becom- ing so. When Bob found out I was hoping to make this ing more available, a more versatile functional form for part of my dissertation, he graciously stepped aside and the wavelength dependence of polarization was needed. gave me the project. George and Marcia Rieke had already measured a large 12 18 sample of field stars with one of the first near-infrared po- Once we had done a higher resolution C O map of the larimeters, built by James Kemp, and I joined the effort. L1688 cloud with the NRAO 12-meter telescope, I carried With the help of Peter Martin, who was visiting the Uni- out a near-infrared survey of the highest column density versity of Arizona at the time, we added an additional region using George and Marcia’s InSb detector at the 61- free parameter to the lognormal Serkowski Law and pro- inch telescope on Mt. Bigelow. This multi-wavelength posed some physical significance to this addition. Kristof approach to studying star formation was relatively new. I Serkowski was also at the University of Arizona and was surveyed a 10’ x 10’ region by raster scanning with a single supportive of us tinkering with his “Law". The relation- detector across the region over 4 nights. ship we proposed in 1980, and in a follow-up study of Back when I was a student, observational astronomy was sources with more extreme values of λmax, was confirmed very hands-on. There were no telescope operators at MWO by subsequent studies and became a standard marker for or Mt. Bigelow. At MWO, you had to tune the klystron interstellar dust in the Galaxy. The narrowing of the nor- and microwave cavities to the desired frequency and at Mt. malized polarization curve with λmax has been the target Bigelow all of the observations were done in the dome with of studies modeling how the wavelength dependence of po- the telescope and instrument. Fortunately, summer nights larization varies with grain shape, alignment mechanisms, in the Catalinas were warm and relatively short and ob- and composition. It is used to compare Milky Way inter- serving time was easy to get with the “monsoons" lurking stellar dust with that in diverse environments including to the south. Things got much easier when infrared cam- other galaxies. eras became available. Tom Greene made the first infrared I was in the Planetary Science Department and approached camera survey of the entire L1688 region with a 128x128 George about doing an observational planetary project. HgCdTe array. I told him that he could have done my sur- George’s office and the Infrared lab where he worked were vey in about 6 minutes but he pointed out that his data in the same building as Planetary Science, the Lunar and reduction was much more involved. Planetary Lab. He suggested a project unrelated to plan- Q: The ρ Ophiuchi region has become a lifelong passion for ets (polarimetry) and ultimately on the emerging field of you, and at the latest count you have written or co-written star formation. My department was supportive of this for 27 refereed papers on this region. Please tell about key my dissertation research. After all, star formation is re- points in these many studies and how our view of ρ Oph lated to planet formation. They even let Charlie Lada

4 has developed over the last 40 years. line, that it was “an instrument to detect heat radiation A: There was always more to learn about this region since, from young stars", was usually met with blank stares. Of over 40 years, we have seen the emergence of infrared cam- course this would never happen today given the increased eras, infrared astronomical satellites, multi-object spectro- scrutiny of airport security not to mention the size of cur- graphs, and large aperture ground-based telescopes. There rent infrared detector systems. are some properties of ρ Oph that make it unique - the Q: Another region you have focused on is the R CrA cloud. high visual extinctions and its proximity to us and to the What are the similarities and differences with ρ Ophiuchi? Sco-Cen association. But of course it is now just one of A: I find the two regions very similar. They both are many young clusters that have been studied in detail. nearby low-mass star forming regions with centrally con- As one of the closest star-forming regions, the ρ Oph clus- densed molecular cores. The near-infrared image of the ter presented an opportunity to get a complete census Coronet cluster is strikingly beautiful. I was never able to of the young population with which to investigate global identify as many YSOs or any young brown dwarfs in this properties such as timescales for pre-main sequence evo- region, partly since I used mostly northern hemisphere lution, disk frequency, cluster dynamics, and the mass telescopes, and thus I never attempted a mass function. function. This required a multi-wavelength approach to But this will be done, with help from the Gaia database catch all stages of PMS evolution. IRAS was a real break- to get a more complete census of cluster members and through. With Charlie and Erick Young, we were able to multi-object spectrographs. It will be interesting to see locate the young stars associated with the IRAS sources in how the mass functions compare particularly in the sub- ρ Oph and start building and classifying spectral energy stellar range. distributions which have become a proxy for the evolu- Q: You joined the faculty at the University of Missouri-St. tionary states. Starting about 20 years ago, I began fo- Louis in 1984 and worked with Dick Schwartz on several cusing more on spectroscopy, both optical and infrared, projects. for a more direct comparison with PMS models. This began with a 1999 grism study of water bands in low mass A: Dick was a great colleague and mentor. I had worked objects with Tom Greene and Michael Meyer and the iden- with him and Martin Cohen as they were guest observers tification of young brown dwarfs in ρ Oph. Optical spectra with Paul’s instrument on the KAO. His specialty was were obtained using the multi-object spectrographs Hydra Herbig-Haro objects/protostellar jets and we collaborated in both the northern and southern hemispheres resulting on several projects including a survey of Hα emission line in over a hundred YSOs with spectral classifications. We objects and Herbig-Haro objects in ρ Oph and shocked made our best attempt at a mass function in a 2011 paper molecular hydrogen emission associated with Herbig-Haro with Ph.D. student Kryss Erikson, Tom, and Michael, and objects and their exciting stars. The latter observations found it to be consistent with the Initial Mass Function were made at CTIO in April 1987 and were memorable with a possible deficit of brown dwarfs. With a bit more since we had the opportunity to see and observe SN1987A. work one may be able to fill in the substellar piece of the Q: You have also studied the mm emission from cold IRAS mass function. sources. This was back in 1989/1990 when molecular out- Q: You spent your postdoc at the University of Texas work- flows were intensely studied. What did you learn? ing in Paul Harvey’s infrared group with experiments on A: The initial survey of cold IRAS sources with Lee Mundy the Kuiper Airborne Observatory. was a follow-up to our interferometric mapping of IRAS A: This was a great experience and I have great respect 16293, one of the first “Class 0" sources. We were hoping for groups that not only build instruments, but know the that this sample of objects would reveal similar objects astrophysical questions to apply them to, and publish the and spur some follow-up observations. As it was a flux- results. I was involved with the first far-infrared detection limited survey, many of the sources were more luminous of a quasar (3C 345) and the detection of the debris disk objects in more distant star-forming regions and the sur- of Vega. I was part of the KAO’s second southern hemi- vey did not reveal any sources analogous to IRAS 16293. sphere deployment in 1983 and took the opportunity to However, as we were hoping, a larger fraction were associ- map the R CrA cloud at 50 and 100 µm. The flight series ated with high velocity gas compared to visible YSOs. We were exhausting and the flight schedules always chang- did follow-up observations of several of these sources in- ing. When flying to NASA Ames we used to take our cluding mapping some of the outflows. Other groups have infrared photometer, which was a gold dewar with electri- continued to study some of the higher mass protostars like cal feedthroughs and a bracket with gears and motors for IRAS 20126+4104 and IRAS 21391+5802. the filter wheels, through airport security and place it on Q: In addition to the ρ Oph cluster, you have also ex- the floor in front of our seat in coach. The security people plored the mass functions in the NGC 1333 and Serpens were often skeptical about letting us on the plane. Our clusters.

5 A: Following our identification of young brown dwarfs in dynamics of the cluster. The velocity dispersions were ρ Oph, we did a similar study in NGC 1333 with the consistent with virial equilibrium but only when we as- grism at the IRTF and with the Hubble Space Telescope. sumed that the relative proper motions in each infrared We were able to identify 21 young brown dwarfs. Subse- frame (subcluster) had the same mean. I was invited to quent studies have doubled this number and identifying join Elisabetta and Michael Meyer in analysing the radial young brown dwarfs, “rogue" planets, and the end of the velocities of optically-visible YSOs obtained in support of mass function will be the target of a JWST program with the Gaia mission and again we found a dispersion con- NIRISS. Using a multi-object spectrograph, Kryss Erick- sistent with virial equilibrium. However in a follow-up son and I attempted a study in the Serpens cluster similar study with Ph.D. student Tim Sullivan and Tom Greene, to that in ρ Oph and found working in the Galactic plane we measured the radial velocity dispersion of less evolved very challenging. Plus, during the course of our observa- YSOs and after accounting for all known sources of er- tions, the distance to the Serpens cluster doubled thanks ror, their dispersion was much higher. While we would to VLBI, which explained why we saw no stars at or below like to see this confirmed with a larger sample, a super- the hydrogen-burning limit. virial state for the youngest cluster members is predicted Q: Over the years you and your collaborators have studied in simulations due to the initial collapse and expansion of water maser emission from young low-mass stars, includ- subclusters. This interpretation would be consistent with ing a recent study of the T Tauri binary Haro 6-10.What a radial velocity gradient observed along the major axis of is the information you can extract from such masers? the ρ Oph cluster. A: When Mark Claussen and I did our water maser survey of ρ Oph in 1986, few outflows had been discovered in this region due in part to the high visual extinctions and source confusion. Using the VLA to observe water maser emission, these selection effects could be overcome. We then expanded our survey to monthly monitoring of 45 low-mass YSOs with the Haystack telescope. Prior to this survey, water maser emission was mainly associated with massive stars. While weaker and highly variable, we found water masers were common among low-mass young stars and were collisionally pumped by their winds. The monitoring of these low mass stars was then used to trigger VLBI observations during periods of high activity. Multi-epoch observations could measure the proper motions of these shock excited clumps, get the 3-D geometry of the outflows, and trace the outflow’s formation and ac- celeration within 10s of AU from the source. The VLBI observations were also helpful in sorting out multiple outflows since, as you might expect, many of the objects we observed were in multiple systems. In the case of Haro 6- 10, a known binary, the masers’ proper motions aligned with a giant HH flow and the visible T Tauri star Haro 6- 10S. And yet a blue-shifted HH jet with a different orientation is also associated with Haro 6-10S which is believed to have a face-on disk. We concluded that the masers and giant HH flow originated from a yet undiscovered companion within 150 mas (20 AU) of Haro 6-10S. This would be consistent with the idea that giant HH flows are due to the interaction of close binary companions. Q: Most recently, you worked with Elisabetta Rigliaco and with Timothy Sullivan on Gaia proper motions and radial velocities, respectively, of young stars in the ρ Oph clouds. A: This started with a decade-long proper motion study that Fred Vrba and I started in 2001 to investigate the

6 and multiples see for instance Dûchene & Kraus 2013 and Reipurth et al. 2014). For these systems we are able to My Favorite Object directly measure the 3-dimensional orbits and dynamical GW Orionis: masses of the perturbing bodies and can image how the disk responds to the perturbation. A pre-main-sequence triple with a warped disk and a torn-apart ring One system that has the potential to serve as such a “rosetta stone” for hydrodynamic studies, is the PMS triple Stefan Kraus GW Orionis. This system is one of the brightest and best- studied T Tauri multiple systems. It is located in the λ Orionis star-forming region (388 pc; Kounkel et al. 2017) and has an age of ∼ 1 million years (Calvet et al. 2004). With orbital periods of ∼ 9 months and 11 years, the orbital periods and separations are just in the right range to enable a full orbit characterisation, while expecting at the same time strong interactions between the disk and the stars.

The triple star system

GW Ori is long known to be a single-lined spectroscopic binary with a 242 day period (Mathieu et al. 1991). Prato et al. (2018) reported the detection of lines associated with Pre-main-sequence multiples as benchmark the secondary. Observations with the IOTA infrared interferometer resolved the inner binary and discovered a third for disk hydrodynamics component (Berger et al. 2011). Building on the work by Mathieu and coworkers, Czekala et al. presented in Understanding how bodies interact with each other and 2017 an impressive set of spectra that were obtained over with disk material holds the key to understanding the 35 years with the Fred L. Whipple Observatory and Oak architecture of stellar systems and of planetary systems. Ridge Observatory and that provide radial velocities for While the interactions between point sources can be de- the primary and secondary. Using these radial velocities scribed by simple gravity, interactions with disk material and the IOTA astrometry, Czekala and colleagues derived require further knowledge about viscosity and gas+dust first orbit solutions for all 3 stars. These orbit solutions in- microphysics that need to be included when simulating dicated a 11.5 year orbit period for the tertiary and hinted disk-body interactions. As a result of our limited knowl- at a signficant misalignment between the stellar orbits and edge in these areas it is, for instance, still difficult to esti- the disk, although the small orbital arc covered by the mate the mass of a gap-opening planet from the morphol- IOTA astrometry resulted in degeneracies in the orbit fits. ogy of a gap observed in a protoplanetary disk, or, to de- Between 2008 and 2019, the VLT Interferometer and the rive with certainty whether a gap is opened by a planet in- CHARA array were used to monitor the astrometric orbit stead of by other processes. Furthermore, numerical sim- of the inner binary and the tertiary (Kraus et al. 2020a). ulations continue to unveil new dynamical processes that The resulting orbits are shown in Figure 1 and correspond might shape protoplanetary disk structures and affect the to a near-circular (e =0.069±0.009), 241.62±0.05 day or- planet populations forming from these disks. One example bit for the inner binary and a 4216.8±4.6 day orbit for the is disk tearing that might occur in the disks around mul- tertiary with significant eccentricity (e = 0.379 ± 0.003), tiple stars whose orbital angular momentum vectors are where the mutual inclination between the orbital planes is misaligned with respect to the rotation axis of the disk. 13.9 ± 1.1◦. Based on computer simulations it has been proposed in 2012 that the resulting gravitational torques could tear The precise masses of the components in the GWOri sys- the disk apart and cause rings to separate from the disk tem has long been a matter of debate. Mathieu et al. and to precess independently around the central objects (1995) estimated the mass using evolutionary tracks, yield- (Nixon et al. 2012, 2013, Facchini et al. 2013, 2018). In ing 2.5 M⊙ and 0.5 M⊙ for the primary and secondary, order to test such theories and to calibrate the fundamen- respectively. Other workers estimated the mass from the tal parameters involved in hydrodynamic simulations, pre- H-band flux ratio and derived more equal mass ratios (e.g. main-sequence (PMS) multiple systems provide us with a 3.2 M⊙ and 2.7 M⊙; Prato et al. 2018). These discrepan- unique laboratory (for general reviews on PMS binaries cies can likely be explained by the non-negligle & time-

7 20 20 2010.0 C D 2009.9 2011.0 4 A B 2009.0 10 10 2005.9 2011.9 2003.9 2009.9

2019.7 [km/s] [km/s] 2011.9 0 0 A,A-B 2 A,AB-C RV 2010.0 C RV 2012.8 -10 -10 2019.7 A A+B 0 -20 -20 2015.0 B E F 2018.1 2015.0 30 30 dDEC[mas] 2003.9 20 20 2011.0 -2 10 10

2005.9 [km/s] [km/s] 0 0 2005.0 2018.1 B,A-B 2009.0 2012.8 2005.0 -10 -10 B,AB-C RV RV -20 -20 -4 GWOriC GWOriB GWOriB -30 -30 4 2 0 -2 -4 30 20 10 0 -10 -20 -30 0 0.2 0.4 0.6 0.8 1 1.2 1.4 0 0.2 0.4 0.6 0.8 1 1.2 1.4 Phase A-B Phase AB-C dRA [mas] dRA [mas]

Figure 1: GW Ori orbit ﬁt to the astrometry of the inner binary (A-B; panel A) and the tertiary (AB-C; panel C), where the primary is in the origin of the coordinate system (Kraus et al. 2020a). Panels C-F show the ﬁt to the radial velocity data presented by Czekala et al. 2017.

variable contributions from circumbinary/circumtertiary 43.0±2.5 kms−1) and estimates of the stellar radius, Bou- dust emission biasing the near-infrared ﬂux ratio (Kraus vier & Bertout 1989 estimated the inclination of the sys- et al. 2020a). The dynamical masses resulting from the tem to ∼ 15◦, i.e. close to face-on. Using a similar method, orbit solution are MA = 2.47 ± 0.33, MB = 1.43 ± 0.18, but other observational data, Mathieu et al. 1995 obtained ◦ and MC =1.36 ± 0.28 M⊙ (Kraus et al. 2020a). an inclination of 30 . However, photometric observations also reported Algol-like eclipses (e.g. Shevchenko et al. 1992, Lamzin et al. 1998, Czekala et al. 2017) that have A highly dynamical environment in the in- been interpreted as evidence for a nearly edge-on disk ori- ner few au entation.

The spectral energy distribution (SED) of GW Ori fea- Variability on longer time scales has been reported as well, tures strong excess emission from mid-infrared to millime- including dramatic changes in the near-infrared SED on ter wavelengths, indicating the presence of circumstellar timescales of ∼ 20 yrs (Fang et al. 2014). This variabil- dust. SED modeling suggested the presence of a circumbi- ity might be linked with a 0.2 mag-amplitude sinusoidal nary disk extending from around 1.2 au (Fang et al. 2017), variation in the V-band light curve (Czekala et al. 2017) 2.1 au (Artymowicz & Ludow 1994) or 3.3 au (Mathieu et that is phased with the orbital period of the tertiary. The al. 1995) outwards. This circumbinary disk was also re- origin of the long-term variability has not been answered solved spatially, where the VLTI and CHARA visibilities conclusively yet, but might be due to changes in the view- associate 16 ± 2% of the H-band flux with circumbinary ing geometry or accretion rate on the circumtertiary disk. +2.5 The circumtertiary disk has been detected as submillime- material located 2−0.8 au from the inner binary (Kraus et al. 2020a). ter emission in the ALMA 0.02” images (Fig. 2B) and as near-infrared excess emission near the location of the ter- To fit the mid-infrared SED, Fang et al. (2014, 2017) de- tiary in infrared interferometry data (Kraus et al. 2020a). rived a dust-depleted gap at ∼ 45 au. Further evidence for a truncated or gapped disk structure comes from the line profile of the CO fundamental lines, where Najita Misaligned rings et al. (2003) noted that the line profile exhibits a narrow+broad emission component and that the line width The intermediate/outer dust disk has been probed with increases towards the more energetic transitions. The sys- JCMT (Mathieu et al. 1995) and SMA millimeter interfer- tem also shows signposts of active accretion, in particular ometry, where Fang et al. 2017 highlighted the large spa- Brγ-emission (Folha & Emerson 2001) and strong UV veil- tial extent (∼ 400 au) and high mass (0.12 M⊙) of the disk. −7 −1 ing (M˙ acc =3 × 10 M⊙ yr , Calvet et al. 2004). Bi et al. 2020 and Kraus et al. 2020a acquired ALMA data with different baseline configurations and detected three There has been a long debate on the viewing geometry dust rings. The two outer rings, R1 and R2, have radii of the system: Based on measurements of the stellar rota- of about 350 and 180au and are oriented North-South tion period (P =3.25 days), the rotation velocity (v sin i = and seen under intermediate inclination 37 ± 1◦ (Fig. 2A),

8 A Thermal!dust!emission!1.3mm B Thermal!dust!emission!1.3mm

R3asym

DAB

R3 R1 R2

100!au 20!au E

C 12CO!moment!0! D 12CO!moment!1! Bi!et!al.!2020 +!continuum!(contours) +!continuum!(contours) 12CO!mom.!1

Figure 2: ALMA observations of GW Ori at 0.12” (right, Bi et al. 2020a) and 0.02” resolution (left, panels A-D, Kraus et al. 2020a). The top row shows continuum images, while the bottom row shows 12CO moment maps.

representing the angular moment vector of the cloud that al. 2020a, Fig. 2D). feeds the disk. The Eastern side of the disk is tilted to- (b) Warm gas at the inner surface of the ring: wards us, as indicated by the strong forward-scattered 12 light from that side of the disk (Fig. 3). The CO moment 0 map shows that the CO surface brightness is low at the location of the ring R3, The inner submillimeter ring, R3, appears much more cir- which can be explained with the high optical depth cular in the images – which could be interpreted as a more and low gas temperature within the ring. However, face-on viewing geometry. However, from extrapolating there is strong CO emission near the inner edge of the center of the outer rings (Bi et al. 2020) and from direct ring R3 on the Eastern side (labeled C1 in Fig. 2C), imaging (Kraus et al. 2020a) it is evident that the inner indicating that the Eastern side of the ring is farther ring is not centered on the position of the stars (Fig. 2B). away from the observer and that we see warm gas This can be explained best if the ring is intrinsically ec- at the illuminated inner surface of the ring (Fig. 3, centric but seen under signiﬁcant inclination and appears bottom-right; Kraus et al. 2020a). near-circular in projection. The following additional information can be used to derive the 3-dimensional shape (c) Shadows cast by the ring: SPHERE scattered and orientation of the ring: light imagery (Figs. 3 and 4, top) exhibits several shadows, including narrow shadows in south-east and (a) Gas kinematics: 12CO moment 1 maps show that north-west direction (S1 and S2; Fig. 3, top) and the rotation axis of the outer disk is oriented roughly broader shadows extending in north and south-west in East-West direction (position angle 90◦; e.g. Fang direction (S3 and S4). Remarkably, shadow S1 does et al. 2017, Czekala et al. 2017) with a ’twist’ in the not follow a straight line but changes direction at velocity ﬁeld in the inner 0.2” (Bi et al. 2020; Fig. 2, ∼ 100 au separation (Fig. 3, top-right), indicating right). The twist might follow a spiral-arm pattern, that the shadow falls onto a curved surface in the with the position angle of the rotation axis changing inner 100 au. Simultaneous modeling of the shadow to 180◦ at 100 au and ∼ 210◦ at ∼ 30 au (Kraus et morphology and of the ALMA continuum geometry

9 Figure 3: Top-left: Overlay of the ALMA continuum image (blue) and the SPHERE scattered light image (red; credit: ESO/Exeter/Kraus et al.). Top-right: SPHERE H-band polarimetric image and model image. Bottom: Sketch of the 3-dimensional disk geometry of GWOri. From Kraus et al. 2020a.

yields an eccentricity e =0.3 and a semi-major axis surface that is facing away from Earth and that appears of 43 au radius for ring R3 and that the ring is seen bright in scattered light due to the direct illumination from under inclination of 155◦ (Fig. 3; Kraus et al. 2020a). the stars. Arc A4 corresponds to the side facing towards us, where we see only the self-shadowed outer side of the warped surface (Fig. 3). The shadows from the misaligned Broken & warped disk geometry ring are cast onto this warped surface and appear as shadows S1 and S2, while the broad shadows S3 and S4 cor- Shadows have been observed in several protoplanetary disks, respond to the regions where the break orbit crosses the but GW Ori is (to my knowledge) the ﬁrst case where the plane of the outer disk, which coincides with the direction ring casting the shadow has been spatially resolved. This in the warp with the highest radial column density. enables tight constraints on the shape and 3-dimensional orientation of the misaligned ring as well as the curva- ture of the warped disk surface inside of the middle ring Origin of the disk misalignments < R2 (r ∼ 182 au). The scattered-light morphology shows a strong East-West asymmetry, where the bright Eastern To determine the origin of the extreme disk misalignments arc A3 and the fainter Western arc A4 form together an observed in GW Ori, two teams recently presented smoothed apparent ellipse with semi-major axis of 90 au and high particle hydrodynamic simulations. Bi et al. conducted eccentricity (e = 0.65; Fig. 4). Kraus et al. (2020a) iden- SPH simulations using the ’phantom’ code and concluded tiﬁes this ellipse as the point where the disk breaks due that the gravitational torque of the stars alone cannot ex- to the gravitational torque from the central triple system. plain the observed large misalignment between the dust The bright arc A3 constitutes the side of the warped disk ring. Instead, they propose that an undiscovered compan-

10 Artist! impression (adopting! derived! 3D! geometry) SPHERE! (H−band)

Figure 4: Artist impression of the 3-dimensional geometry of the GW Ori disk (left) and comparison with the SPHERE image (right). Credit: ESO/Calçada, Exeter/Kraus et al.

ion located between the inner and middle ring that might Outlook have broken the disk and induced the misalignments. Over the last few decades several exciting pre-main-sequence The ’sphNG’ simulation presented in Kraus et al. (2020a), multiple systems have been found and extensively stud- on the other hand, shows the disk tearing effect, where the ied, including GG Tau, HD142527, HD98800, and T Tauri. gravitational torque of the three stars tears the disk apart GW Ori stands out with respect to the tight constraints into distinct rings that precess independently around the on the full 3-dimensional orbits for all components in the central objects. After letting the dust distribution evolve system, the dynamical masses, and our knowledge on the for a few thousand years, a ring breaks out of the disk 3-dimensional geometry of the strongly distorted disk (for plane, whose radius (∼ 40 au), eccentricity (e ∼ 0.2), and a visualization of the deduced disk geometry & orbits, extreme misalignment agree well with the observed prop- see the interactive 3-dimensional model in Fig. 6). Due erties of ring R3. Also, the disk breaks and a warp forms to this unique information, the system could serve as a just beyond the break radius, whose dimension, geometry, valuable benchmark for calibrating hydrodynamic mod- and low column density agree reasonably well with the els and fundamental parameters under well-defined condi- properties of the warp derived from the GWOri observations. This could provide the validation & refinement that tions (Fig. 5). is needed before applying the models to the much less-well- Both simulations adopt similar Shakura-Sunyaev viscosi- constrained planet formation case, where the masses and ties (αSS =0.008 − 0.013 for Bi et al.; 0.01-0.02 for Kraus orbits of the gap-opening bodies are not known in general. et al.). Therefore, it appears more likely that the different The disk-tearing effect that we might witness in GW Ori in outcomes might be related to the setup of the simulation. action, constitutes an important new mechanism for mov- There are differences concerning the number of stars in- ing disk material onto highly oblique or retrograde orbits, cluded in the simulation (2 stars in Bi et al. simulation; even at very wide separations from the star. At the same 3 stars in Kraus et al. simulation) and the orbit solution time, the observed torn ring seems to be sufficiently mas- that is adopted for the simulation (Czekala et al. 2017 sive and might be sufficiently stable for planet formation solution and Kraus et al. 2020a solution, respectively). to occur, potentially giving rise to an yet-undiscovered population of circum-multiple planets on highly oblique, long-period orbits.

11 A B C

Warp

100! au 100! au 100! au Dec z z

RA RA RA

0 2 4 6 −1 0 1 2 −17 −15 −13 −11 column! density! /! g! cm−2 log! (column! density! /! g! cm−2 ) log! (density! /! g! cm−3 )

Figure 5: SPH model, computed with the sphNG code developed by Matthew Bate and collaborators. The simulation adopts the triple star orbits shown in Fig. 1 and an initial disk orientation that corresponds to the outer ALMA rings R1+R2. The snapshot shows the gas density after 9500 years. Panel (A) shows the column density along the line-of- sight seen from Earth; in (B) and (C) the z-axis indicates the direction towards the observer.

An important open question concerns the origin of the out- References: ermost ring in GW Ori. The high submillimeter brightness Artymowicz & Ludow 1994, ApJ 421, 651 of the inner and middle ring can likely be explained by disk Bate, M.R., et al. 2010, MNRAS 401, 1505 tearing and dust filtration processes near the disk warp re- Bate, M.R., 2018, MNRAS 475, 5618 Berger, J.-P., et al. 2011, A&A 529, L1 gion. It is unclear whether the outer-most ring can also be Bi, J., et al. 2020, ApJL 895, L18 explained by the dynamical interplay between the central Bouvier, J. & Bertout, C. 1989, A&A 211, 99 triple system and the disk, or whether dust trapping near Calvet, N., et al. 2004, AJ 128, 1294 a planet-induced density gap might be required to explain Clarke, C.J., & Pringle, J.E. 1991, MNRAS 249, 588 Clarke, C.J., & Pringle, J.E. 1993, MNRAS 261, 190 the high submillimeter surface brightness in this region. Czekala, I., et al. 2017, ApJ 851, 132 But what caused the misalignment between the disk and Dûchene, G. & Kraus, A. 2013, ARAA, 51, 269 Facchini, S., et al. 2013, MNRAS 433, 2142 the orbits in the first place? Possibilities include turbulent Facchini, S., et al. 2018, MNRAS 473, 4459 disk fragmentation (Offner et al. 2010), perturbation by Fang, M., et al. 2017, A&A 603, 132 other stars in a stellar cluster (Clarke & Pringle 1993), the Fang, M., et al. 2014, A&A 570, 118 capture of disk material during a stellar flyby (Clarke & Folha, D.F.M. & Emerson, J.P., 2001, A&A 365, 90 Kraus, S., et al. 2019, zenodo.3356286 Pringle 1991), or the infall of material with a different an- Kraus, S., et al. 2020a, Science 369, 6508 gular momentum vector from that of the gas that formed Kraus, S., et al. 2020b, ApJ 897, 8 the stars initially (Bate et al. 2010, Bate 2018). To answer Kounkel, M., et al. 2017, AJ 834, 142 this question, statistical information will be of essence, Lamzin, S., et al. 1998, Ap&SS, 261, 167 Mathieu, R.D., et al. 1991, AJ, 101, 2184 both on the disk-orbit misalignment in pre-main-sequence Mathieu, R.D., et al. 1995, AJ, 109, 2655 multiples and on the orbital architecture and spin-orbit Najita, J., et al. 2003, ApJ 589, 931 alignment in main-sequence systems. Obtaining such con- Nixon, C., et al. 2012, ApJ 757, L24 Nixon, C., et al. 2013, MNRAS 434, 1946 straints on a large sample of stars is a key science objec- Offner, S., et al. 2010, ApJ 725, 1485 tive for the proposed VLTI instrument BIFROST (Kraus Prato, L., et al. 2018, ApJ 852, 38 et al. 2019, 2020b) and could offer important new insights Reipurth, B. et al. 2014, Protostars and Planets V, p. 267 on both the star- and planet-formation processes. Shevchenko, V.S., et al. 1992, IBVS 3746, 1 Acknowledgement: I would like to thank my collaborators on our recent paper on GW Ori and the members of the team around Jiaqing Bi for delightful dis- cussions on this fascinating object. Also I acknowledge support from an ERC Starting Grant (Grant Agreement No. 639889).

12 Figure 6: Interactive 3-dimensional model of the disk geometry in GWOri, as derived in Kraus et al. 2020a. Open with Adobe Acrobat Reader, click on the graphics, and select ’trust this document’ at the top of the window. Then click & drag with the mouse to change the viewing angle. You can use the toolbar elements or mouse/trackpad gestures (e.g. pinch gesture on trackpad; or shift key and swipe up/down) to zoom into the graphics and to display the triple star orbits.

13 retical evolutionary models did not agree and there was no agreed upon conversion scale for observed spectral types Perspective to Teff . The Prologue: In the late 1990’s Lisa Prato (Lowell Masses and Ages of Pre-Main Obs.), Gail Schaefer (CHARA, GSU), and I set out to Sequence Stars measure Mdyn of spectroscopic and visual binaries (SB Michal Simon and VB) in the Taurus and the Ophiuchus SFRs. We knew that at the average distances of these regions, VBs and SBs whose parameters would be measurable in a rea- sonable amount of time (for us, and hopefully not exceed- ing the patience of TACs and funding agencies), would have separations of a few tens of milli-arc seconds and their components would orbit at few to 10s of km/s. This meant that the observations would have to be made at very high angular and spectral resolutions. These requirements eventually led us to competing for the share of observing time funded by NASA at the Keck Observatory. Schaefer et al. (2020) describes results of this work applied to the T Tau triple system. We were able to measure the Mdyn T Tau Sa and Sb and estimate the mass of T Tau N.

An approach to measuring Mdyn, that could be applied to single stars, resulted from my good fortune to spend 1 The Past is Prologue the last half of 1998 on sabbatical leave at Observatoire de Grenoble. Stéphane Guilloteau and Anne Dutrey had just shown that using a 12CO J=1 to 0 line interferomet- I take the liberty of writing this Perspective as a personal ric image of the circumstellar disk associated with the sin- history. In a long, productive, and fun collaboration with gle star DM Tau, they could extract the disk’s rotation wonderful colleagues I have pursued dynamical mass mea- velocity, inclination, and other parameters (Guilloteau & surements of PMS stars for more than a quarter of a cen- Dutrey, 1998). Since the disk mass is small compared to tury. that of the central star, the rotation is Keplerian and de- The Past: Why dynamical? Dynamical masses, Mdyn, termines DM Tau’s mass dynamically. On a memorable depend only on gravity and are the gold standard of mass walk to lunch, Stéphane and I decided to embark on Mdyn measurement. Usually they have been determined by the measurements of the PMS stars with disks in the Taurus orbital parameters of binaries. A star’s mass is an intrin- SFR. sic property. It determines everything about its evolution Dynamical mass determined by the circumstellar disk tech- from formation to end. A large sample of masses in a star nique can be obtained in a single observation while the SB forming region (SFR) such as Taurus provides informa- and VB techniques require many observations distributed tion about its distribution of masses, the IMF. But there’s over the orbital period of the binary, usually several years. more to our work than mass: Age also matters. By plac- Measurement of M by disk rotation can therefore pro- ing a PMS star with well-determined T and luminosity dyn eff ceed more rapidly than by observation of binaries. The on an HR diagram (HRD) with evolutionary tracks and techniques are complementary because the disk technique isochrones, we can estimate its age and learn about its is limited to Class II T Tauri stars while the VB and SB history and the formation of its associated exoplanets. techniques may be applied to both Class II and III T Tauri The HRD-ﬁtting approach works reliably when applied to stars. This turned out to be important because we slowly main-sequence stars because the accuracy of theoretical learned from experience that very low mass PMS stars models of their properties has been well tested and cali- (M < 0.4M⊙) with disks extensive and massive enough brated by dynamical measurements of their masses. Un- for measurement of their rotation are rare (Schaefer et al. fortunately, when we applied the HRD-ﬁtting approach to 2009, Simon et al. 2019). PMS stars, we quickly found that we were standing on Using data from IRAM’s Plateau de Bure interferome- quicksand. In addition to the expected problems associ- ter, by 1999 we had measured M for 7 singles in Tau- ated with observing PMS stars, principally their variabil- dyn Aur. With values of M in hand, the next step was ity, extinction, veiling, and spectral energy distributions, dyn to place them on HRDs showing the evolutionary tracks we faced two other obstacles: the several available theo- and isochrones of four available theoretical evolutionary

14 3 12 MESA BHAC15 10 F16

8 2 Disk Rotation

1.4 6 VBSB2

VBSB2 Rphot/Rsun Number of Stars 4 Astrom 1 1.0

0.2 0.5 2

Eclipsing Binaries 0.1 M(msun) 0 0 0.0 0.5 1.0 1.5 2.0 6.0 6.5 7.0 7.5 8.0 Mass (Msun) Log Age(yr)

Figure 1: Mdyn good to 5% that had been measured by Figure 2: Photospheric radius vs log Age for the MESA, mid-2019 (G. Schaefer, priv. comm.) BHAC15, and non-magnetic F16 models.

models (Simon et al 2000). This paper shows vividly the • Discrepancies among the evolutionary models needed to quicksand we were walking in. We found differences as be resolved. large as 0.2 M⊙ between the Mdyn and Mhrd. For a given • Given that PMS stars are very variable, probably ow- star the models indicate ages discrepant by as much as 3 ing to active regions driven by their convective interiors MY. and episodic accretion, we needed at least a conservative Hillenbrand & White (2004) confirmed and quantified these estimate of the uncertainty of the measured luminosity. discrepancies. Using 27 Mdyn for PMS stars in the north- • The Taurus SFR spans about ∼ 50 × 50 pc in RA and ern and southern hemispheres and the available evolution- Dec; its depth probably extends ∼ 50 pc as well. To avoid ary models they found that Mhrd underestimated Mdyn by an uncertainty as large as ∼ 60% attributable to unknown 10 − 30% for Mdyn in the range 0.3 to 1.2 M⊙ in all age distance we needed precise distances to individual stars. ranges considered. The mass and age discrepancies meant that we could not trust the theoretical models to provide The wheels of progress turn slowly, but through the efforts estimates of the masses and ages of PMS stars and that of theorists and observers they did turn. Fig. 1 shows our understanding of the earliest years of star and planet G. Schaefer’s compilation of 67 PMS M measured to formation were very uncertain. dyn precision ≤ 5.0%. The compilation includes stars in the mass range 0.1 to 2.0 M⊙. It is complete to mid-2019. Three of the Mdyn measured by disk rotation are from 2 The Devil is in the Details - Sheehan et al. (2019); the others are drawn from Simon Beating Back the Devil et al. (2019) and references therein.

Spectral Type to Teff conversions are now in good agree- The way forward was clear but achieving clarity took two ment down to the Teff of the late M SpTy PMS stars decades. To accomplish our over-all goals, we needed: (Luhman (2003); Pecaut and Mamajek (2013); Herczeg and Hillenbrand (2014)). • A large database of PMS Mdyn distributed over a range of spectral types. Agreement among recent models of PMS evolution that do • The majority of known PMS stars in Taurus are M spec- not include magnetic fields is now much improved (Fig. 2). For M > 0.5 M⊙ and age > 1 MY, the models of Baraffe tral type stars. Unfortunately the SpTy to Teff conversion for M stars differed among the look-up tables avail- et al. (2015, BHAC15), MESA (Paxton et al. 2015 and able in the early 2000s and most did not extend to SpTy Choi et al. 2016), and the non-magnetic models of Feiden M9 (understandably because on the main sequence M9’s (2016), the models are in excellent agreement (Simon & Toraskar 2017). Moreover, models that included the effect were brown dwarfs.) We needed a reliable SpTy to Teff look-up table for PMS stars. of magnetic fields on the convection in low mass stars and their public availability (Feiden 2016) would enable their

15 application to PMS stars (Richert et al. 2018; Simon et al. 2019). Gaia DR2 in 2018 meant that precision distances became available. The time was ripe to apply the advances of the ﬁrst two decades of this millenium to the stars for which we had measured Mdyn.

3 Putting It All Together

By 2019 we had measured Mdyn by disk rotation for 45 stars in Taurus. The stars are singles and components of binaries that are sufficiently wide that the disk rotation of one component can be measured without confusion from the other. The sample includes 33 stars with previously published dynamical masses and 12 stars for which we obtained new dynamical masses using archival ALMA data. Of the 12 stars, 5 did not have dynamical masses published previously. Our sample consisted of well known T Tauri stars, all Class II objects. By Gaia standards all are bright and distances with precisions better than ±2 pc are available for nearly all (Bailer-Jones et al. 2018). We selected 29 stars with dynamical mass precisions better than 10% for analysis. We placed the stars on two HRDs, one using evolutionary models of Baraffe et al. 2015 and the other Feiden’s (2016) magnetic models. We derived Mhrd for both and compared them to the Mdyn. Figures 3 (left and right) show the results. Fig. 3 right provided the Eureka! moment. Figure 3: Top: (Mdyn − Mhrd) vs Mdyn for Mhrd derived Fig. 3 (top) shows that track masses derived using the from an HRD using Baraffe et al.’s (2015) evolutionary non-magnetic, “standard”, model of Baraffe et al. (2015) models. Bottom: Same as (a) but for Mhrd derived from are smaller than most of the dynamical masses. The av- Feiden (2016)’s magnetic evolutionary models (see Fig. 4). erage difference (Mdyn - Mhrd) is 0.19 ± 0.02 M⊙. In the All masses are in units of M⊙. Mdyn mass range 0.4 to 1.0 M⊙, the normalized difference (Mdyn - Mhrd)/Mdyn is about 0.3. Our finding that masses derived from an HRD that uses a standard evolutionary star at log (Teff ) = 3.58 and log (L/L⊙) = -0.30. Its model tend to underestimate the Mdyn is completely con- mass and age measured with respect to the non-magnetic sistent with Hillenbrand and White’s (2004) result. model would be ∼ 0.5M⊙ and ∼ 2 MY while relative to On the other hand, the Mhrd evaluated using an HRD the magnetic model its mass and age would be greater, with Feiden’s magnetic evolutionary tracks and isochrones ∼ 0.7 M⊙, and older, ∼ 3 MY. The older age is the (Fig. 4) provide values much closer to the Mdyn, Fig. 3 result of the star’s slower contraction owing to additional bottom. The average difference (Mdyn - Mhrd) is 0.01 ± magnetic pressure. It takes longer for the star to collapse 0.02 M⊙. The magnetic models provide mass estimates to the photospheric radius determined by its luminosity that are more consistent with actual masses of the stars. and effective temperature. Further, in the presence of the Fig. 4 also shows that the stars appear older (roughly 3 to combined gas and magnetic pressures, a stronger gravi- 10 MY) than the 1 to 3 MY usually quoted for the Taurus tational field than in the standard model is necessary to SFR based on standard models. The average age of the support the star at the given photospheric radius. stars evaluated with respect to Feiden’s magnetic models CI Tau, a Classic T Tauri star in our sample with mass is 5.8 ± 0.8 MY (Simon and Prato, 2019). +6.8 0.90 ± 0.02 M⊙ and age 7.8−4.0 MY hosts a well-studied Fig. 5 illustrates why magnetic models represent the mass hot Jupiter (Flagg et al., 2019). The fact that the ex- of a PMS star better than non-magnetic models and also oplanet is bright enough that Flagg et al. were able to produce an older age. The blue dot represents a PMS unravel the exoplanet’s K-band emission from that of the

16 Figure 4: Mdyn on an HRD using Feiden’s (2016) mag- Figure 5: Comparison of Feiden’s standard and magnetic netic evolutionary models. The luminosities and Teff are models on the HRD. derived from Herczeg & Hillenbrand (2014).

ity of the magnetic models with measured Mdyn smaller host star rules out a “cold start” model for its formation. than 0.4 M⊙. My colleagues and I are working on this. Apparently a “hot start” did it. This illustrates the po- The pressure of internal magnetic fields increases the star’s tential of age determination to inform planet formation photospheric radius over that predicted by the non-magnetic scenarios. models. The acid test will come from measurements of the diameters of the T Tauri stars. This measurement may be The material in this section is described in more detail in possible soon with the next generation of O/IR interfer- Simon et al. (2019). ometers. References: 4 “It’s Tough to Make Predictions Bailer-Jones, C. A. L., Rybizki, J., Fouesneau, M., et al. 2018, AJ, 156, 58 - Especially about the Future”, Baraffe, I.; Homeier, D., Allard, F. & Chabrier, G., 2015, A&A, 577, 42 Yogi Berra Choi, J., Dotter, A., Conroy, C., Cantiello, M. Paxton, B., Johnson, B. 2016, ApJ, 823, 102 Feiden, G. A. 2016, A&A, 593, A99 Where do we stand today? The work I have described Flagg, L., Johns-Krull, C. M., Nofi, L., et al. 2019, ApJL, 878, L37 points the way out of the quicksand. We have learned that Luhman, K.L.; Stauffer, J.R., Muench, A.A.; et al. 2003, ApJ, 593, when ages and masses of low mass PMS stars are needed 1093 Herczeg, Gregory J.; Hillenbrand, Lynne A. 2014, ApJ, 786, 97 and dynamical masses are not available, magnetic mod- Hillenbrand, Lynne A.; White, Russel J. 2004, ApJ, 604, 741 els of stellar evolution will provide trust-worthy results Paxton, B.; Marchant,P.; Schwab, J. et al. 2015, ApJS, 220, 15 for masses > 0.4 M⊙. Simon and Prato (2019) placed 9 Pecaut, M. J.& Mamajek, E. E., 2013, ApJS, 208, 9 Class III stars, stars without disks in the Taurus SFR and Schaefer, G.H.; Dutrey, A.; Guilloteau, S. et al. 2008, ApJ, 701, 698 Schaefer, G.H.; Beck, Tracy L., Prato, L. & Simon, M. 2020, AJ, found their age, 5.4 ± 0.4 MY, is indistinguishable from 160, 35 that of the Class II stars. Obviously, the same procedure Simon, M.; Dutrey, A. & Guilloteau 2000, ApJ, 545, 1034 can be applied to other SFRs whose PMS stars have well- Simon. M.; Toraskar, J. 2017, ApJ, 841, 95 determined luminosities and T . Simon, M., Guilloteau, S., Beck, T. L., et al. 2019, ApJ, 884, 42 eff Simon, M. & Prato, L. 2019, RNAAS, 3, 168. Two advances are necessary. We need to test the reliabil-

17 Abstracts of recently accepted papers

A Novel Survey for Young Substellar Objects with the W-band Filter. I. Filter Design and New Discoveries in Ophiuchus and Perseus K.N. Allers1,2 and Michael C. Liu3 1 Department of Physics and Astronomy, Bucknell University, Lewisburg, PA 17837, USA; 2 Visiting Astronomer at the Infrared Telescope Facility, which is operated by the University of Hawaii under contract NNH14CK55B with the National Aeronautics and Space Administration; 3 Institute for Astronomy, University of Hawai’i, 2680 Woodlawn Drive, Honolulu, HI 96822, USA E-mail contact: mliu at ifa.hawaii.edu We present the design and implementation of a medium-band near-IR filter tailored for detecting low-mass stars and brown dwarfs from the summit of Maunakea. The W-band filter is centered at 1.45 µm with a bandpass width of 6%, designed to measure the depth of the H2O water absorption prominent in objects with spectral types of M6 and later. When combined with standard J- and H-band photometry, the W-band filter is designed to determine spectral types to ≈1.4 subtypes for late-M and L dwarfs, largely independent of surface gravity and reddening. This filter’s primary application is completing the census of young substellar objects in star-forming regions, using W-band selection to greatly reduce contamination by reddened background stars that impede broad-band imaging surveys. We deployed the filter on the UH 88-inch telescope to survey ≈3 sq. deg. of the NGC 1333, IC 348, and rho Ophiuchus star-forming regions. Our spectroscopic followup of W-band selected candidates resulted in the confirmation of 48 ultracool dwarfs with a success rate of 89%, demonstrating the efficacy of this new filter and selection method. Accepted by PASP http://arxiv.org/pdf/2008.00010

Selected aspects of the analysis of molecular line observation of edge-on circumbinary disks Roman Avramenko1, Sebastian Wolf1, Tobias F. Illenseer1 and Stig Rehberg1 1 University of Kiel, Institute of Theoretical Physics and Astrophysics, Leibnizstrasse 15, 24118 Kiel, Germany E-mail contact: ravramenko at astrophysik.uni-kiel.de Context: Inner cavities, accretion arms and density waves are characteristic structures in the density distribution of circumbinary disks. They are the result of the tidal interaction of the non-axisymmetric gravitational forces of the central binary with the surrounding disk and are most prominent in the inner region, where the asymmetry is most pronounced. Aims: The goal of this study is to test the feasibility of reconstructing the gas density distribution and quantifying properties of structures in the inner regions of edge-on circumbinary disks using multiple molecular line observations. Methods: The density distribution in circumbinary disks is calculated with two-dimensional hydrodynamic simulations. Subsequently, molecular line emission maps are generated with 3D radiative transfer simulations. Based on these, we investigate the observability of characteristic circumbinary structures located in the innermost region for spatially resolved and unresolved disks. Results: We ﬁnd that it is possible to reconstruct the inner cavity, accretion arms and density waves from spatially resolved multi- wavelength molecular line observation of circumbinary disks seen edge-on. For the spatially unresolved observation only an estimate for the density gradient in the transition area from cavity to inner disk rim can be derived. Accepted by Astronomy & Astrophysics http://arxiv.org/pdf/2008.10499

18 On the Nature of the T Tauri Triple System Tracy L. Beck1, G. H. Schaefer2, S. Guilloteau3, M. Simon4, A. Dutrey3, E. Di Folco3 and E. Chapillon3,5 1 The Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA; 2 The CHARA Array of Georgia State University, Mount Wilson Observatory, Mount Wilson, CA 91023, USA; 3 Laboratoire dAstrophysique de Bordeaux, Universit de Bordeaux, CNRS, B18N, Alle Geoffroy Saint-Hilaire, 33615 Pessac, France; 4 Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY 11794, USA; 5 IRAM, 300 Rue de la Piscine, 38406 Saint Martin dHres Cedex, France E-mail contact: tbeck at stsci.edu We present a multi-wavelength analysis to reveal the nature of the enigmatic T Tauri triple star system. New optical and infrared measurements are coupled with archival X-ray, UV and mm datasets to show morphologies of disk material and outflow kinematics. A dark lane of obscuring material is seen in silhouette in several emission lines and in model-subtracted ALMA mm continuum dust residuals near the position of T Tau Sa+Sb, revealing the attenuating circumbinary ring around T Tau S. The flux variability of T Tau S is linked in part to the binary orbit; T Tau Sb brightens near orbital apastron as it emerges from behind circumbinary material. Outflow diagnostics confirm that T Tau N powers the blue-shifted western outflow, and the T Tau S binary drives the northwest-southeastern flow. Analysis of the southern outflow shows periodic arcs ejected from the T Tau system. Correlation of these arc locations and tangential kinematics with the orbit timing suggests that launch of the last four southern outflow ejections is contemporaneous with, and perhaps triggered by, the T Tau Sa+Sb binary periastron passage. We present a geometry of the T Tau triple that has the southern components foreground to T Tau N, obscured by a circumbinary ring, with misaligned disks and interacting outflows. Particularly, a wind from T Tauri Sa that is perpendicular to its circumstellar disk might interact with the circumbinary material, which may explain conflicting high contrast measurements of the system outflows in the literature. T Tauri is an important laboratory to understand early dynamical processes in young multiple systems. We discuss the historical and future characteristics of the system in this context. Accepted by The Astrophysical Journal https://arxiv.org/pdf/2009.03861

Spectroscopic characterization of the known O-star population in Cygnus OB2. Evi- dence of multiple star-forming bursts S.R. Berlanas1,2,3, A. Herrero2,3, F. Comerón4, S. Simón-Díaz2,3, D.J. Lennon2 et al. 1 Departamento de Física Aplicada, Universidad de Alicante, 03690 San Vicente del Raspeig, Alicante, Spain; 2 Instituto de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Spain; 3 Departamento de Astrofísica, Universidad de La Laguna, Tenerife, Spain; 4 ESO, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany E-mail contact: sara.rb at ua.es Cygnus OB2 provides a unique insight into the high-mass stellar content in one of the largest groups of young massive stars in our Galaxy. Although several studies of its massive population have been carried out over the last decades, an extensive spectroscopic study of the whole known O-star population in the association is still lacking. In this work, we created the most complete spectroscopic census of O stars carried out so far in Cygnus OB2 using already existing and new spectroscopy. We present the spectra for 78 O-type stars, from which we identify new binary systems, obtain the distribution of rotational velocities, and determine the main stellar parameters for all the stars in the region that have not been detected as double-line spectroscopic binaries. We also derive radii, luminosities, and masses for those stars with reliable Gaia astrometry, in addition to creating the Hertzsprung-Russell Diagram to interpret the evolutionary status of the association. This work has shown the improvement reached when using accurate spectroscopic parameters and astrometry for the interpretation of the evolutionary status of a population, revealing, in the case of Cygnus OB2, at least two star-forming bursts at ∼3 and ∼5 Myr. We ﬁnd an apparent deﬁcit of very fast rotators in the distribution of rotational velocities. The inspection of the dynamical distribution of the sample has allowed us to identify nine O stars with peculiar proper motions and discuss a possible dynamical ejection scenario or past supernova explosions in the region. Accepted by A&A http://arxiv.org/pdf/2008.09917

19 Dense gas formation in the Musca filament due to the dissipation of a supersonic converging flow L. Bonne1, N. Schneider2, S. Bontemps1, S. D. Clarke2, A. Gusdorf3,4, A. Lehmann3, M. Steinke2, T. Csengeri1,5, S. Kabanovic2, R. Simon2, C. Buchbender2 and R. Guesten5 1 Laboratoire d’Astrophysique de Bordeaux, Université de Bordeaux, CNRS, B18N, alle Geoffrey Saint-Hilaire, 33615 Pessac, France; 2 I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany; 3 Laboratoire de Physique de l’Ecole Normale Supérieure, ENS, Université PSL, CNRS Sorbonne Université de Paris, Paris, France; 4 Observatoire de Paris, PSL University, Sorbonne Université, LERMA, 75014 Paris, France; 5 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany E-mail contact: lars.bonne at u-bordeaux.fr Observations with the Herschel Space Telescope have established that most star forming gas is organised in filaments, a finding that is supported by numerical simulations of the supersonic interstellar medium (ISM) where dense filamentary structures are ubiquitous. We aim to understand the formation of these dense structures by performing observations covering the 12CO(4→3), 12CO(3→2), and various CO(2-1) isotopologue lines of the Musca filament, using the APEX telescope. The observed CO intensities and line ratios cannot be explained by PDR (photodissociation region) emission because of the low ambient far-UV field that is strongly constrained by the non-detections of the [CII] line at 158 µm and the [OI] line at 63 µm, observed with the upGREAT receiver on SOFIA, as well as a weak [CI] 609 µm line detected with APEX. We propose that the observations are consistent with a scenario in which shock excitation gives rise to warm and dense gas close to the highest column density regions in the Musca filament. Using shock models, we find that the CO observations can be consistent with excitation by J-type low-velocity shocks. A qualitative comparison of the observed CO spectra with synthetic observations of dynamic filament formation simulations shows a good agreement with the signature of a filament accretion shock that forms a cold and dense filament from a converging flow. The Musca filament is thus found to be dense molecular post-shock gas. Filament accretion shocks that dissipate the supersonic kinetic energy of converging flows in the ISM may thus play a prominent role in the evolution of cold and dense filamentary structures. Accepted by A&A https://www.aanda.org/articles/aa/pdf/2020/09/aa37104-19.pdf

A High Angular Resolution Survey of Massive Stars in Cygnus OB2: JHK Adaptive Optics Results from the Gemini Near-InfraRed Imager S.M. Caballero-Nieves1, D.R. Gies2, E.K. Baines3, A.H. Bouchez4,5, R.G. Dekany6 et al. 1 Department of Physics and Space Sciences, Florida Institute of Technology 150 University Blvd, Melbourne, FL 32901, USA; 2 Center for High Angular Resolution Astronomy, Department of Physics and Astronomy, Georgia State University, P. O. Box 5060, Atlanta, GA 30302-5060, USA; 3 Remote Sensing Division, Naval Research Laboratory, 4555 Overlook Avenue SW, Washington, DC 20375, USA 4GMTO Corporation, 251 South Lake Avenue, Pasadena, CA 91101,USA; 5 Observatories of the Carnegie Institution for Science, 813 Santa Barbara Street, Pasadena, CA 91101, USA; 6 California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125, USA E-mail contact: scaballero at fit.edu We present results of a high angular resolution survey of massive OB stars in the Cygnus OB2 association that we conducted with the NIRI camera and ALTAIR adaptive optics system of the Gemini North telescope. We observed 74 O- and early B-type stars in Cyg OB2 in the JHK infrared bands in order to detect binary and multiple companions. The observations are sensitive to equal-brightness pairs at separations as small as 0′′. 08, and progressively fainter companions are detectable out to ∆K = 9 mag at a separation of 2′′. This faint contrast limit due to readnoise continues out to 10′′ near the edge of the detector. We assigned a simple probability of chance alignment to each companion based upon its separation and magnitude difference from the central target star and upon areal star counts for the general star field of Cyg OB2. Companion stars with a field membership probability of less than 1% are assumed to be physical companions. This assessment indicates that 47% of the targets have at least one resolved companion that is probably gravitationally bound. Including known spectroscopic binaries, our sample includes 27 binary, 12 triple, and 9 systems with four or more components. These results confirm studies of high mass stars in other environments that find that massive stars are born with a high multiplicity fraction. The results are important

20 for the placement of the stars in the H-R diagram, the interpretation of their spectroscopic analyses, and for future mass determinations through measurement of orbital motion. Accepted by AJ http://arxiv.org/pdf/2008.00064

The observational impact of dust trapping in self-gravitating discs James Cadman1,2, Cassandra Hall3,4,5, Ken Rice1,2, Tim J. Harries6 and Pamela D. Klaassen7 1 SUPA, Institute for Astronomy, University of Edinburgh, Blackford Hill, Edinburgh, EH9 3HJ, Scotland, UK; 2 Centre for Exoplanet Science, University of Edinburgh, Edinburgh, UK; 3 Department of Physics and Astronomy, University of Leicester, University Road, Leicester, LE1 7RH, UK; 4 Department of Physics and Astronomy, The University of Georgia, Athens, GA 30602, USA; 5 Center for Simulational Physics, The University of Georgia, Athens, GA 30602, USA; 6 Department of Physics and Astronomy, University of Exeter, Stocker Road, Exeter, EX4 4QL, UK; 7 UK Astronomy Technology Center, Royal Observatory Edinburgh, Blackford Hill, Edinburgh, EH9 3HJ, UK E-mail contact: cadman at roe.ac.uk We present a 3D semi-analytic model of self-gravitating discs, and include a prescription for dust trapping in the disc spiral arms. Using Monte-Carlo radiative transfer we produce synthetic ALMA observations of these discs. In doing so we demonstrate that our model is capable of producing observational predictions, and able to model real image data of potentially self-gravitating discs. For a disc to generate spiral structure that would be observable with ALMA requires that the disc’s dust mass budget is dominated by millimetre and centimetre-sized grains. Discs in which grains have grown to the grain fragmentation threshold may satisfy this criterion, thus we predict that signatures of gravitational instability may be detectable in discs of lower mass than has previously been suggested. For example, we find that discs with disc-to-star mass ratios as low as 0.10 are capable of driving observable spiral arms. Substructure becomes challenging to detect in discs where no grain growth has occurred or in which grain growth has proceeded well beyond the grain fragmentation threshold. We demonstrate how we can use our model to retrieve information about dust trapping and grain growth through multi-wavelength observations of discs, and using estimates of the opacity spectral index. Applying our disc model to the Elias 27, WaOph 6 and IM Lup systems we find gravitational instability to be a plausible explanation for the observed substructure in all 3 discs, if sufficient grain growth has indeed occurred. Accepted by MNRAS http://arxiv.org/pdf/2008.09826

Colliding in the shadows of giants: Planetesimal collisions during the growth and migration of gas giants Philip J. Carter1 and Sarah T. Stewart1 1 Department of Earth and Planetary Sciences, University of California, Davis, One Shields Avenue, Davis, CA 95616, USA E-mail contact: pjcarter at ucdavis.edu Giant planet migration is an important phenomenon in the evolution of planetary systems. Recent works have shown that giant planet growth and migration can shape the asteroid belt, but these works have not considered interactions between planetesimals. We have calculated the evolution of planetesimal disks, including planetesimal-planetesimal collisions, during gas giant growth and migration. The numbers, locations, and impact velocities of these collisions depend on the specific growth and migration path. We find that giant planet growth alone has little effect on impact velocities, and most of the planetesimals scattered by growing giants do not undergo collisions with each other during the growth period. In contrast, we find that giant planet migration induces large numbers of high velocity collisions between planetesimals. These impacts have sufficient velocities to cause shock-induced vaporization for both water ice and silicate components of planetesimals, and to cause catastrophic disruption of the bodies. New bodies may form from impact debris. Collisional evolution reduces the efficiency of planetesimal implantation into the asteroid belt via giant planet growth and migration. A small fraction of the largest planetesimals implanted into the asteroid belt would have been processed via collisions. We identify important consequences of planetesimal collisions that have not been considered in planet accretion models. The prevalence of high velocity collisions during giant planet migration,

21 and their potential links to the properties of meteorites, and the formation of chondrules, makes impact vaporization a critically important phenomenon. The consequences of vaporizing planetesimal constituents require further detailed study. New collision outcome models for impacts within the nebula, and models for new planetesimal formation are needed. Accepted by The Planetary Science Journal http://arxiv.org/pdf/2008.05549

The GAPS Programme at TNG XXVII. Reassessment of a young planetary system with HARPS-N: is the hot Jupiter V830 Tau b really there? M. Damasso1, A.F. Lanza2, S. Benatti3, V.M. Rajpaul4, M. Mallonn5 et al. 1 INAF — Osservatorio Astrofisico di Torino, Via Osservatorio 20, I-10025, Pino Torinese (TO), Italy; 2 INAF — Osservatorio Astrofisico di Catania, Via S. Sofia,78 - 95123 Catania, Italy; 3 INAF — Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, I-90134, Palermo, Italy; 4 Astrophysics Group, Cavendish Laboratory, JJ Thomson Avenue, CB3 0HE Cambridge, UK; 5 Leibniz-Institut für Astrophysik Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany E-mail contact: mario.damasso at inaf.it Detecting and characterising exoworlds around very young stars (age <10 Myr) are key aspects of exoplanet de- mographic studies, especially for understanding the mechanisms and timescales of planet formation and migration. However, detection using the radial velocity method alone can be very challenging, since the amplitude of the signals due to magnetic activity of such stars can be orders of magnitude larger than those induced even by massive planets. We observed the very young (∼2 Myr) and very active star V830 Tau with the HARPS-N spectrograph −1 to independently confirm and characterise the previously reported hot Jupiter V830 Tau b (Kb = 68 ± 11 ms ; −1 mb sin ib = 0.57 ± 0.10 Mjup; Pb = 4.927 ± 0.008 d). Due to the observed ∼1 kms radial velocity scatter clearly attributable to V830 Tau’s magnetic activity, we analysed radial velocities extracted with different pipelines and modelled them using several state-of-the-art tools. We devised injection-recovery simulations to support our results and characterise our detection limits. The analysis of the radial velocities was aided by using simultaneous photometric and spectroscopic diagnostics. Despite the high quality of our HARPS-N data and the diversity of tests we performed, we could not detect the planet V830 Tau b in our data and confirm its existence. Our simulations show that a statistically-significant detection of the claimed planetary Doppler signal is very challenging. Much as it is important to continue Doppler searches for planets around young stars, utmost care must be taken in the attempt to overcome the technical difficulties to be faced in order to achieve their detection and characterisation. This point must be kept in mind when assessing their occurrence rate, formation mechanisms and migration pathways, especially without evidence of their existence from photometric transits. Accepted by A&A http://arxiv.org/pdf/2008.09445

Inferring (Sub)millimeter Dust Opacities and Temperature Structure in Edge-on Pro- tostellar Disks From Resolved Multi-Wavelength Continuum Observations: The Case of the HH 212 Disk Zhe-Yu Daniel Lin1,2,3, Chin-Fei Lee2,4, Zhi-Yun Li1, John Tobin5 and Neal Turner6 1 Department of Astronomy, University of Virginia, Charlottesville, VA 22904, USA; 2 Academia Sinica Institute of Astronomy and Astrophysics, P.O. Box 23-141, Taipei 106, Taiwan; 3 Department of Physics, National Chung Cheng University, No.168, Sec. 1, University Rd., Minhsiung, Chiayi 62102, Taiwan; 4 Graduate Institute of Astronomy and Astrophysics, National Taiwan University, No. 1, Sec. 4, Roosevelt Rd., Taipei 10617, Taiwan; 5 National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903, USA; 6 Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109, USA E-mail contact: zdl3gk at virginia.edu (Sub)millimeter dust opacities are required for converting the observable dust continuum emission to the mass, but their values have long been uncertain, especially in disks around young stellar objects. We propose a method to

22 constrain the opacity κν in edge-on disks from a characteristic optical depth τ0, ν, the density ρ0 and radius R0 at the disk outer edge through κν = τ0,ν /(ρ0R0) where τ0,ν is inferred from the shape of the observed ﬂux along the major axis, ρ0 from gravitational stability considerations, and R0 from direct imaging. We applied the 1D semi-analytical model to the embedded, Class 0, HH 212 disk, which has high-resolution data in ALMA Band 9, 7, 6, and 3 and VLA Ka band (λ=0.43, 0.85, 1.3, 2.9, and 9.1 mm). The modeling of the HH 212 disk is extended to 2D through −2 −2 −3 RADMC-3D radiative transfer calculations. We ﬁnd a dust opacity of κν ≈ 1.9 × 10 , 1.3 × 10 , and 4.9 × 10 cm2 g−1 of gas and dust for ALMA Bands 7, 6, and 3, respectively with uncertainties dependent on the adopted −2 2 −1 stellar mass. The inferred opacities lend support to the widely used prescription κλ =2.3 × 10 (1.3 mm/λ) cm g advocated by Beckwith et al. (1990). We inferred a temperature of ∼45 K at the disk outer edge which increases radially inward. It is well above the sublimation temperatures of ices such as CO and N2, which supports the notion that the disk chemistry cannot be completely inherited from the protostellar envelope. Accepted by MNRAS http://arxiv.org/pdf/2008.08627

Making massive stars in the Galactic Centre via accretion onto low-mass stars within an accretion disc Melvyn B. Davies1 & Doug N. C. Lin2 1 Lund Observatory, Department of Astronomy and Theoretical Physics, Box 43, Lund, Sweden; 2 UCO/Lick Obser- vatory, Board of Studies in Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064, USA E-mail contact: mbd at astro.lu.se The origin of the population of very massive stars observed within ∼0.4 pc of the supermassive black hole in the Galactic Centre is a mystery. Tidal forces from the black hole would likely inhibit in situ star formation whilst the youth of the massive stars would seem to exclude formation elsewhere followed by transportation (somehow) into the Galactic centre. Here we consider a third way to produce these massive stars from the lower-mass stars contained in the nuclear stellar cluster which surrounds the supermassive black hole. A passing gas cloud can be tidally shredded by the supermassive black hole forming an accretion disc around the black hole. Stars embedded within this accretion 2 disc will accrete gas from the disc via Bondi-Hoyle accretion, where the accretion rate onto a star, M˙ ⋆ ∝ M⋆ . This super-exponential growth of accretion can lead to a steep increase in stellar masses, reaching the required 40–50 M⊙ in some cases. The mass growth rate depends sensitively on the stellar orbital eccentricities and their inclinations. The evolution of the orbital inclinations and/or their eccentricities as stars are trapped by the disc, and their orbits are circularised, will increase the number of massive stars produced. Thus accretion onto low-mass stars can lead to a top heavy stellar mass function in the Galactic Centre and other galactic nuclei. The massive stars produced will pollute the environment via supernova explosions and potentially produce compact binaries whose mergers may be detectable by the LIGO-VIRGO gravitational waves observatories. Accepted by MNRAS http://arxiv.org/pdf/2008.10033

Tidal tails of open star clusters as probes to early gas expulsion II: Predictions for Gaia Frantiˇsek Dinnbier1 and Pavel Kroupa2,3 1 I.Physikalisches Institut, Universität zu Köln, Zülpicher Strasse 77, D-50937 Köln, Germany; 2 Helmholtz-Institut für Strahlen- und Kernphysik, University of Bonn, Nussallee 14-16, 53115 Bonn, Germany; 3 Charles University in Prague, Faculty of Mathematics and Physics, Astronomical Institute, V Holesovickách 2, 180 00 Praha 8, Czech Republic E-mail contact: dinnbier at ph1.uni-koeln.de We study the formation and evolution of the tidal tail released from a young star Pleiades-like cluster, due to expulsion of primordial gas in a realistic gravitational ﬁeld of the Galaxy. The tidal tails (as well as clusters) are integrated from their embedded phase for 300 Myr. We vary star formation eﬃciencies (SFEs) from 33% to 100% and the timescales of gas expulsion as free parameters, and provide predictions for the morphology and kinematics of the evolved tail for each of the models. The resulting tail properties are intended for comparison with anticipated Gaia observations in order to constrain the poorly understood early conditions during the gas phase and gas expulsion. The simulations are

23 performed with the code nbody6 including the gravitational potential of the Galaxy, and an analytical approximation for the natal gaseous potential. Assuming that the Pleiades formed with rapid gas expulsion and an SFE of ≈ 30 %, the current Pleiades are surrounded by a rich tail extending from ≈ 150 to ≈ 350pc from the cluster and containing 0.7× to 2.7× the number of stars in the present-day cluster. If the Pleiades formed with an SFE close to 100%, then the tail is shorter (∼<90pc) and substantially poorer with only ≈ 0.02× the number of present-day cluster stars. If the Pleiades formed with an SFE of ≈ 30 %, but the gas expulsion was adiabatic, the tail signatures are indistinguishable from the case of the model with 100% SFE. The mass function of the tail stars is close to that of the canonical mass function for the clusters including primordial gas, but it is slightly depleted of stars more massive than ≈ 1 M⊙ for the cluster with 100% SFE, a diﬀerence that is not likely to be observed. The model takes into account the estimated contamination due to the ﬁeld stars and the Hyades-Pleiades stream, which constitutes a more limiting factor than the accuracy of the Gaia measurements. Accepted by Astronomy & Astrophysics http://arxiv.org/pdf/2007.00036

How fast do young star clusters expel their natal gas?: Estimating the upper limit of the gas expulsion time-scale Frantiˇsek Dinnbier1,2 and Stefanie Walch1,3 1 I.Physikalisches Institut, Mathematisch-Naturwissenschaftliche Fakultät, Universität zu Köln, Zülpicher Strasse 77, D-50937 Köln, Germany; 2 Charles University in Prague, Faculty of Mathematics and Physics, Astronomical Institute, V Holesovickách 2, 180 00 Praha 8, Czech Republic; 3 Center for Data and Simulation Science, University of Cologne, Germany E-mail contact: dinnbier at ph1.uni-koeln.de Formation of massive stars within embedded star clusters starts a complex interplay between their feedback, inflowing gas and stellar dynamics, which often includes close stellar encounters. Hydrodynamical simulations usually resort to substantial simplifications to model embedded clusters. Here, we address the simplification which approximates the whole star cluster by a single sink particle, which completely neglects the internal stellar dynamics. In order to model the internal stellar dynamics, we implement a Hermite predictor-corrector integration scheme to the hydrodynamic code flash. As we illustrate by a suite of tests, this integrator significantly outperforms the current leap-frog scheme, and it is able to follow the dynamics of small compact stellar systems without the necessity to soften the gravitational potential. We find that resolving individual massive stars instead of representing the whole cluster by a single energetic 3 source has a profound influence on the gas component: for clusters of mass less than ≈ 3 × 10 M⊙, it slows gas expulsion by a factor of ≈ 5 to ≈ 1Myr, and it results in substantially more complex gas structures. With increasing 3 cluster mass (up to ≈ 3 × 10 M⊙), the gas expulsion time-scale slightly decreases. However, more massive clusters > 3 (∼5 × 10 M⊙) are unable to clear their natal gas with photoionising radiation and stellar winds only if they form with a star formation efficiency (SFE) of 1/3. This implies that the more massive clusters are either cleared with another feedback mechanism or they form with a SFE higher than 1/3 Accepted by MNRAS https://arxiv.org/pdf/2008.08602

Strong H-alpha emission and signs of accretion in a circumbinary planetary mass companion from MUSE Simon C. Eriksson1, Rubén Asensio Torres2, Markus Janson1, Yuhiko Aoyama3,4, Gabriel-Dominique Marleau5,6,2, Mickael Bonnefoy7 and Simon Petrus7 1 Institutionen för astronomi, Stockholms universitet, AlbaNova universitetscentrum, 106 91 Stockholm, Sweden; 2 MPIA, Königstuhl 17, 69117 Heidelberg, Germany; 3 Institute for Advanced Study, Tsinghua University, Beijing 100084, PR China; 4 Dept of Astronomy, Tsinghua University, Beijing 100084, PR China; 5 Institut für Astronomie und Astrophysik, Auf der Morgenstelle 10, 72076 Tübingen, Germany; 6 Physikalisches Institut, Universität Bern, Gesellschaftsstr. 6, 3012 Bern, Switzerland; 7 Univ. Grenoble Alpes, IPAG, Grenoble, France E-mail contact: simon.eriksson at astro.su.se

24 Context: Intrinsic Hα emission can be advantageously used to detect substellar companions because it improves contrasts in direct imaging. Characterising this emission from accreting exoplanets allows for the testing of planet formation theories. Aims: We characterise the young circumbinary planetary mass companion 2MASS J01033563-5515561 (AB)b (Delorme 1 (AB)b) through medium-resolution spectroscopy. Methods: We used the new narrow-field mode for the MUSE integral-field spectrograph, located on the ESO Very Large Telescope, during science verification time to obtain optical spectra of Delorme 1 (AB)b. Results: We report the discovery of very strong Hα and Hβ emission, accompanied by He I emission. This is consistent with an active accretion scenario. We provide accretion rate estimates obtained from several independent methods and find a likely mass of 12?15 MJup for Delorme 1 (AB)b. This is also consistent with previous estimates. Conclusions: Signs of active accretion in the Delorme 1 system might indicate a younger age than the ∼ 30 − 40 Myr expected from a likely membership in Tucana-Horologium (THA). Previous works have also shown the central binary to be overluminous, which gives further indication of a younger age. However, recent discoveries of active discs in relatively old (∼40 Myr), very low-mass systems suggests that ongoing accretion in Delorme 1 (AB)b might not require in and of itself that the system is younger than the age implied by its THA membership. Accepted by Astronomy & Astrophysics https://doi.org/10.1051/0004-6361/202038131

The chemical structure of young high-mass star-forming clumps: (II) parsec-scale CO depletion and deuterium fraction of HCO+ S. Feng1,2,3, D. Li1,4, P. Caselli5, F. Du6,7, Y. Lin8 et al. 1 National Astronomical Observatories, Chinese Academy of Science, Beijing 100101, People’s Republic of China; 2 ASIAA, No.1, Sec. 4, Roosevelt Rd, Taipei 10617, Taiwan, Republic of China; 3 NAOJ, National Institutes of Natural Sciences, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan; 4 NAOC-UKZN Computational Astrophysics Cen- tre, University of KwaZulu-Natal, Durban 4000, South Africa; 5 Max-Planck-Institut für Extraterrestrische Physik, Gießenbachstraße 1, Garching bei München, Germany; 6 Purple Mountain Observatory and Key Laboratory of Radio Astronomy, Chinese Academy of Sciences, Nanjing 210023, People’s Republic of China; 7 School of Astronomy and Space Science, University of Science and Technology of China, Hefei 230026, People’s Republic of China; 8 Max Planck Institute for Radio Astronomy, Auf dem Hügel 69, D-53121 Bonn, Germany E-mail contact: siyi.s.feng at gmail.com The physical and chemical properties of cold and dense molecular clouds are key to understanding how stars form. Using the IRAM 30 m and NRO 45 m telescopes, we carried out a Multiwavelength line-Imaging survey of the 70 µm- dArk and bright clOuds (MIAO). At a linear resolution of 0.1–0.5 pc, this work presents a detailed study of pc-scale CO depletion and HCO+ deuterium (D-) fractionation toward four sources (G11.38+0.81, G15.21−0.43, G14.49−0.13, and 4 5 −3 G34.74−0.12) included in our full sample. In each source with T < 20 K and nH ∼ 10 –10 cm , we compared pairs of neighboring 70 µm bright and dark clumps and ﬁnd that: (1) The H2 column density and dust temperature of each source show strong spatial anti-correlation; (2) The spatial distribution of CO isotopologue lines and dense gas tracers such as 1–0 lines of H13CO+ and DCO+ are anti-correlated; (3) The abundance ratio between C18O and DCO+ shows a strong correlation with the source temperature; (4) Both the C18O depletion factor and D-fraction of HCO+ show robust decrease from younger clumps to more evolved clumps by a factor of more than 3; (5) Preliminary chemical modeling indicates chemical ages of our sources are ∼8×104 yr, which is comparable to their free-fall timescales and smaller than their contraction timescales, indicating that our sources are likely dynamically and chemically young. Accepted by ApJ http://arxiv.org/pdf/2008.03531

GIARPS High-resolution Observations of T Tauri stars (GHOsT) II. Connecting atomic and molecular winds in protoplanetary disks M. Gangi1, B. Nisini1, S. Antoniucci1, T. Giannini1, K;. Biazzo1, J.M. Alcalà2, A. Frasca3, U. Munari4, A.A. Arkharov5, A. Harutyunyan6, C.F. Manara7, E. Rigliaco8 and F. Vitali1 1 INAF - Osservatorio Astronomico di Roma - Via Frascati 33, 00078 Monte Porzio Catone, Italy; 2 INAF - Osservatorio

25 Astronomico di Capodimonte - Salita Moiariello 16, 80131 Napoli, Italy; 3 INAF - Osservatorio Astrofisico di Catania - Via S. Sofia 78, 95123 Catania, Italy; 4 INAF - Osservatorio Astronomico di Padova, via dell’Osservatorio 8, 36012 Asiago (VI), Italy; 5 Central Astronomical Observatory of Pulkovo, Pulkovskoe shosse 65, 196140 St. Petersburg, Russia; 6 Fundacion Galileo Galilei - INAF - Telescopio Nazionale Galileo, 38700 Brena Baja, Santa Cruz de Tenerife, Spain; 7 European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei Munchen, Germany; 8 INAF - Osservatorio Astronomico di Padova, vicolo dell’Osservatorio 5, 35122, Padova, Italy E-mail contact: manuele.gangi at inaf.it Disk winds play a fundamental role in the evolution of protoplanetary systems. The complex structure and dynamics can be investigated through the emission of atomic and molecular lines detected in high-resolution optical/IR spectra of young stellar objects. Despite their great importance, however, studies connecting the atomic and molecular components are lacking so far. In the framework of the GIARPS High-resolution Observations of T Tauri stars (GHOsT) project, we aim to characterize the atomic and molecular winds in a sample of classical T Tauri stars (CTTs) of the Taurus-Auriga region, focusing on a statistical analysis of the kinematic properties of the [OI] 630 nm and H2 2.12 µm lines and their mutual relationship. We analyzed the flux calibrated [OI] 630 nm and H2 2.12 µm lines in a sample of 36 CTTs observed at the Telescopio Nazionale Galileo with the HARPS-N spectrograph (resolving power of R = 115000) and with the GIANO spectrograph (R = 50000). We decomposed the line profiles into different kinematic Gaussian components and focused on −1 the most frequently detected component, the narrow low-velocity (vp < 20 km s ) component (NLVC). We found that the H2 line is detected in 17 sources (∼ 50% detection rate), and [OI] is detected in all sources but one. The NLV components of the H2 and [OI] emission are kinematically linked, with a strong correlation between the peak velocities and the full widths at half maximum of the two lines. Assuming that the line width is dominated by Keplerian broadening, we found that the [OI] NVLC originates from a disk region between 0.05 and 20 au and that of H2 in a region from 2 and 20 au. We also found that H2 is never detected in sources where [OI] originates in regions below 1 au, as well as in sources of early (∼ F-G) spectral type with a luminosity > 1L⊙. Moreover, in seven sources, both H2 and [OI] have clear blueshifted peaks and prominent [OI] high-velocity components. These components have also been detected in sources with no relevant centroid shift. Finally, we did not find any clear correlation between vp of the H2 and [OI] NVLC and the outer disk inclination. This result is in line with previous studies. Our results suggest that molecular and neutral atomic emission in disk winds originate from regions that might overlap, and that the survival of molecular winds in disks strongly depends on the gas exposure to the radiation from the central star. The presence of jets does not necessarily affect the kinematics of the low-velocity winds. Our results demonstrate the potential of wide-band high-resolution spectroscopy in linking tracers of different manifestations of the same phenomenon. Accepted by A&A https://arxiv.org/pdf/2008.01977

The µ Tau Association: A 60 Myr-Old Coeval Group at 150 pc from the Sun Jonathan Gagné1,2, Trevor J. David3,4, Eric E. Mamajek4,5, Andrew W. Mann6, Jacqueline K. Faherty7 and Antoine Bédard8 1 Planétarium Rio Tinto Alcan, Espace pour la Vie, 4801 av. Pierre-de Coubertin, Montréal, Québec, Canada; 2 Institute for Research on Exoplanets, Université de Montréal, Département de Physique, C.P. 6128 Succ. Centre-ville, Montréal, QC H3C 3J7, Canada; 3 Center for Computational Astrophysics, Flatiron Institute, New York, NY 10010, USA; 4 Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA; 5 Department of Physics & Astronomy, University of Rochester, Rochester, NY 14627, USA; 6 Department of Physics and Astronomy, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3255, USA; 7 Department of Astrophysics, American Museum of Natural History, Central Park West at 79th St., New York, NY 10024, USA; 8 Département de Physique, Université de Montréal, C.P. 6128 Succ. Centre-ville, Montréal, QC H3C 3J7, Canada E-mail contact: gagne at astro.umontreal.ca We present an analysis of the newly identiﬁed µ Tau Association (MUTA) of young stars at ∼150 pc from the Sun that is part of the large Cas-Tau structure, coeval and co-moving with the α Persei cluster. We identify more than 500 candidate members using Gaia DR2 data and the BANYAN Σ tool (Gagné et al. 2018) and we determine an age

26 of 62±7 Myr for its population based on an empirical comparison of its color-magnitude diagram sequence with those of other nearby young associations. The MUTA is related to the Theia 160 group of Kounkel & Covey (2019) and corresponds to the e Tau group of Liu et al. (2020). As part of this analysis, we introduce an iterative method based on spectral templates to perform an accurate correction of interstellar extinction of Gaia DR2 photometry, needed because of its wide photometric bandpasses. We show that the members of the MUTA display an expected increased rate of stellar activity and faster rotation rates compared with older stars, and that literature measurements of the lithium equivalent width of nine G0 to K3-type members are consistent with our age determination. We show that the present-day mass function of the MUTA is consistent with other known nearby young associations. We identify WD 0340+103 as a hot, massive white dwarf remnant of a B2 member that left its planetary nebula phase only 270,000 +8 years ago, posing an independent age constraint of 60−6 Myr for the MUTA. Accepted by ApJ http://arxiv.org/pdf/2008.06139

A measure of the size of the magnetospheric accretion region in TW Hydrae R. Garcia Lopez1,2,3, A. Natta1, A. Caratti o Garatti1,2,3, T. Ray1, R. Fedriani4, M. Koutoulaki5 et al.6,7 1 Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, D02 XF86 Dublin, Ireland; 2 Max Planck Institute for Astronomy, Königstuhl 17, Heidelberg, Germany, D-69117; 3 University College Dublin, School of Physics, Belfield, Dublin 4, Ireland; 4 Department of Space, Earth & Environment, Chalmers University of Technology, SE-412 93 Gothenburg, Sweden; 5 European Southern Observatory, Karl-Schwarzschild-Str. 2, D-85748, Garching, Germany; 6 Univ. Grenoble Alpes, CNRS, IPAG, F-38000 Grenoble, France; 7 Universidade do Porto - Faculdade de Engenharia, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal E-mail contact: rebeca.garcialopez at ucd.ie Stars form by accreting material from their surrounding disks. There is a consensus that matter flowing through the disk is channelled onto the stellar surface by the stellar magnetic field. This is thought to be strong enough to truncate the disk close to the corotation radius, at which the disk rotates at the same rate as the star. Spectro-interferometric studies in young stellar objects show that hydrogen emission (a well known tracer of accretion activity) mostly comes from a region a few milliarcseconds across, usually located within the dust sublimation radius. The origin of the hydrogen emission could be the stellar magnetosphere, a rotating wind or a disk. In the case of intermediate-mass Herbig AeBe stars, the fact that Brγ emission is spatially resolved rules out the possibility that most of the emission comes from the magnetosphere because the weak magnetic fields (some tenths of a gauss) detected in these sources result in very compact magnetospheres. In the case of T Tauri sources, their larger magnetospheres should make them easier to resolve. The small angular size of the magnetosphere (a few tenths of a milliarcsecond), however, along with the presence of winds make the interpretation of the observations challenging. Here we report optical long-baseline interferometric observations that spatially resolve the inner disk of the T Tauri star TW Hydrae. We find that the near-infrared hydrogen emission comes from a region approximately 3.5 stellar radii across. This region is within the continuum dusty disk emitting region (7 stellar radii across) and also within the corotation radius, which is twice as big. This indicates that the hydrogen emission originates in the accretion columns (funnel flows of matter accreting onto the star), as expected in magnetospheric accretion models, rather than in a wind emitted at much larger distance (more than one astronomical unit). Accepted by Nature, Volume 584, Issue 7822, p.547-550 https://www.nature.com/articles/s41586-020-2613-1

Quantitative inference of the H2 column densities from 3 mm molecular emission: A case study towards Orion B Pierre Gratier1, Jérôme Pety2,3, Emeric Bron4, Antoine Roueﬀ5, Jan H. Orkisz6 et al. 1 Laboratoire d’Astrophysique de Bordeaux, Univ. Bordeaux, CNRS, B18N, Allee Geoﬀroy Saint-Hilaire,33615 Pessac, France; 2 IRAM, 300 rue de la Piscine, 38406 Saint Martin d’Hères, France; 3 LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, 75014 Paris, France; 4 LERMA, Observatoire de Paris, PSL

27 Research University, CNRS, Sorbonne Universités, 92190 Meudon, France; 5 Aix Marseille Univ, CNRS, Centrale Marseille, Institut Fresnel, Marseille, France; 6 Chalmers University of Technology, Department of Space, Earth and Environment, 412 93 Gothenburg, Sweden E-mail contact: pierre.gratier at u-bordeaux.fr Molecular hydrogen being unobservable in cold molecular clouds, the column density measurements of molecular gas currently rely either on dust emission observation in the far-IR or on star counting. (Sub-)millimeter observations of numerous trace molecules are effective from ground based telescopes, but the relationships between the emission of one molecular line and the H2 column density (NH2 ) is non-linear and sensitive to excitation conditions, optical depths, abundance variations due to the underlying physico-chemistry. We aim to use multi-molecule line emission to infer NH2 from radio observations. We propose a data-driven approach to determine NH2 from radio molecular line observations. We use supervised machine learning methods (Random Forests) on wide-field hyperspectral IRAM-30m observations of the Orion B molecular cloud to train a predictor of NH2 , using a limited set of molecular lines as input, and the Herschel-based dust-derived NH2 as ground truth output. For conditions similar to the Orion B molecular cloud, we obtain predictions of NH2 within a typical factor of 1.2 from the Herschel-based estimates. An analysis of the contributions of the different lines to the predictions show that the most important lines are 13CO(1–0), 12CO(1–0), C18O(1–0), and HCO+(1–0). A detailed analysis distinguishing between diffuse, translucent, filamentary, and dense core conditions show that the importance of these four lines depends on the regime, and that it is recommended to + add the N2H (1–0) and CH3OH(20–10) lines for the prediction of NH2 in dense core conditions. This article opens a promising avenue to directly infer important physical parameters from the molecular line emission in the millimeter domain. The next step will be to try to infer several parameters simultaneously (e.g., NH2 and far-UV illumination field) to further test the method. Accepted by A&A http://arxiv.org/pdf/2008.13417

The GRAVITY young stellar object survey III. The dusty disk of RY Lup GRAVITY Collaboration: Y.-I. Bouarour1,2,3, K. Perraut1, F. Ménard1, W. Brandner5 et al. 1 Univ. Grenoble Alpes, CNRS, IPAG, F-38000 Grenoble, France; 2 Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, D02 XF86 Dublin, Ireland; 3 School of Physics, University College Dublin, Belfield, Dublin 4, Ireland; 4 I. Physikalisches Institut, Universität zu Köln, Zülpicher Strasse 77, 50937, Köln, Germany; 5 Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany E-mail contact: youcef.bouarour at ucdconnect.ie We use PIONIER data from the ESO archive and GRAVITY data that were obtained in June 2017 with the four 8m telescopes. We use a parametric disk model and the 3D radiative transfer code MCFOST to reproduce the Spectral Energy Distribution and match the interferometric observations. To match the SED , our model requires a stellar luminosity of 2.5 L⊙, higher than any previously determined values. Such a high value is needed to accommodate the circumstellar extinction caused by the highly inclined disk, which has been neglected in previous studies. While using an effective temperature of 4800 K determined through high-resolution spectroscopy, we derive a stellar radius of 2.29 R⊙. These revised fundamental parameters, when combined with the mass estimates available , lead to an age of 0.5–2.0 Ma for RY Lup, in better agreement with the age of the Lupus association than previous determinations. Our disk model nicely reproduces the interferometric GRAVITY data and is in good agreement with the PIONIER ones. We derive an inner rim location at 0.12 au from the central star. This model corresponds to an inclination of the inner disk of 50◦, which is in mild tension with previous determinations of a more inclined outer disk from SPHERE (70◦ in NIR) and ALMA(67◦±5◦) images, but consistent with the inclination determination from the ALMA CO spectra (55◦±5◦). Increasing the inclination of the inner disk to 70◦ leads to a higher line-of-sight extinction and therefore requires a higher stellar luminosity of 4.65 L⊙ to match the observed flux levels. This luminosity would translate to a stellar radius of 3.13 R⊙, leading to an age of 2–3 Ma, and a stellar mass of about 2 M⊙, in disagreement with the observed dynamical mass estimate of 1.3–1.5 M⊙. Critically, this high-inclination inner disk model also fails to reproduce the visibilities observed with GRAVITY. Accepted by A&A http://arxiv.org/pdf/2008.08527

28 The Gaia-ESO Survey: Calibrating the lithium-age relation with open clusters and associations. I. Cluster age range and initial membership selections. M.L. Gutiérrez Albarrán1, D. Montes1, M. Gómez Garrido1,2, H.M. Tabernero1,3, J.I. Gónzalez Hernández4,5, E. Marfil1, A. Frasca6, A. C. Lanzafame7,6, A. Klutsch8,6, E. Franciosini9, S. Randich9, R. Smiljanic10, A. J. Korn11, G. Gilmore12, E.J. Alfaro23, M. Baratella24, A. Bayo20,21, T. Bensby13, R. Bonito14, G. Carraro15, E. Delgado Mena3, S. Feltzing13, A. Gonneau12, U. Heiter11, A. Hourihane12, F. Jiménez Esteban16, P. Jofre22, T. Masseron4, L. Monaco17, L. Morbidelli9, L. Prisinzano14, V. Roccatagliata18, S. Sousa3, M. Van der Swaelmen9, C.C. Worley12 and S. Zaggia19 1 Departamento de Física de la Tierra y Astrofísica and IPARCOS-UCM (Instituto de Física de Partículas y del Cosmos de la UCM), Facultad de Ciencias Físicas, Universidad Complutense de Madrid, E-28040, Madrid, Spain; 2 Observatorio Astronómico Nacional (OAN-IGN), Apdo 112, 28803 Alcalá de Henares, Madrid, Spain; 3 Instituto de Astrofísica e Ciências do Espaçø, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal; 4 Instituto de Astrofísica de Canarias (IAC), E-38205 La Laguna, Tenerife, Spain; 5 Universidad de la Laguna, Dept. Astrofísica, E-38206 La Laguna, Tenerife, Spain; 6 INAF - Osservatorio Astrofisico di Catania, via S. Sofia, 78, 95123 Catania, Italy; 7 Università di Catania, Dipartimento di Fisica e Astronomia, Sezione Astrofisica, Via S. Sofia 78, I-95123 Catania, Italy; 8 Institut für Astronomie und Astrophysik, Eberhard Karls Universität, Sand 1, D-72076 Tübingen, Germany; 9 INAF - Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125, Firenze, Italy; 10 Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences, ul. Bartycka 18, 00-716, Warsaw, Poland; 11 Observational Astrophysics, Division of Astronomy and Space Physics, Department of Physics and Astronomy, Uppsala University, Box 516, SE-751 20 Uppsala, Sweden; 12 Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, United Kingdom; 13 Lund Observatory, Department of Astronomy and Theoretical Physics, Box 43, SE-221 00 Lund, Sweden; 14 INAF - Osservatorio Astronomico di Palermo, Piazza del Parlamento, 1, 90134 Palermo, Italy; 15 Dipartimento di Fisica e Astronomia, Università di Padova, Vicolo dell’Osservatorio 3, 35122 Padova, Italy; 16 Spanish Virtual Observatory, Centro de Astrobiología (INTA-CSIC), P.O. Box 78, 28691 Villanueva de la Canada, Madrid, Spain; 17 Departamento de Ciencias Físicas, Universidad Andrés Bello, Fernández Concha 700, Las Condes, Santiago, Chile; 18 Dipartimento di Fisica “E. Fermi", Università di Pisa, Largo Bruno Pontecorvo 3, 56127 Pisa, Italy; 19 INAF - Padova Observatory, Vicolo dell’Osservatorio 5, 35122 Padova, Italy; 20 Instituto de Física y Astronomía, Universidad de Valparaíso, Chile; 21 Núcleo Milenio Formación Planetaria - NPF, Universidad de Valparaíso; 22 Núcleo de Astronomía, Facultad de Ingeniería y Ciencias, Universidad Diego Portales (UDP), Santiago de Chile; 23 Instituto de Astrofísica de Andalucía (CSIC), Glorieta de la Astronomía s/n, Granada 18008, Spain; 24 Dipartimento di Fisica e Astronomia Galileo Galilei, Vicolo Osservatorio 3, I-35122, Padova, Italy E-mail contact: mlgutierrez at ucm.es Previous studies of open clusters have shown that lithium depletion is not only strongly age dependent but also shows a complex pattern with other parameters that is not yet understood. For pre- and main-sequence late-type stars, these parameters include metallicity, mixing mechanisms, convection structure, rotation, and magnetic activity. We perform a thorough membership analysis for a large number of stars observed within the Gaia-ESO survey (GES) in the field of 20 open clusters, ranging in age from young clusters and associations, to intermediate-age and old open clusters. Based on the parameters derived from the GES spectroscopic observations, we obtained lists of candidate members for each of the clusters in the sample by deriving RV distributions and studying the position of the kinematic selections in the EW(Li) versus Teff plane to obtain lithium members. We used gravity indicators to discard field contaminants and studied [Fe/H] metallicity to further confirm the membership of the candidates. We also made use of studies using recent data from the Gaia DR1 and DR2 releases to assess our member selections. We identified likely member candidates for the sample of 20 clusters observed in GES (iDR4) with UVES and GIRAFFE, and conducted a comparative study that allowed us to characterize the properties of these members, as well as identify field contaminant stars, both lithium-rich giants and non-giant outliers. This work is the first step towards the calibration of the lithium- age relation and its dependence on other GES parameters. During this project we aim to use this relation to infer the ages of GES field stars, and identify their potential membership to young associations and stellar kinematic groups of different ages. Accepted by Astronomy & Astrophysics http://arxiv.org/pdf/2009.00610

29 Emission-Line Datacubes of the HH 32 Stellar Jet Patrick Hartigan1, Lynne Hillenbrand2, Matuesz Matuszewski3, Arlindo Chan Borges2, James D. Neill3, D. Christopher Martin3, Patrick Morrissey3 and Anna M. Moore4 1 Physics and Astronomy Dept., Rice University, 6100 S. Main, Houston, TX 77005-1892; 2 Department of Astronomy, MC 249-17, California Institute of Technology, Pasadena, California 91125; 3 Cahill Center for Astrophysics, California Institute of Technology, 1216 East California Boulevard, Pasadena, California 91125; 4 Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2611, Australia E-mail contact: hartigan at sparky.rice.edu We analyze datacubes of over 60 emission lines in the HH 32 stellar jet acquired with the Keck Cosmic Web Imager (KCWI). The data cover the less-explored blue portion of the spectrum between 3586Å and 6351Å, and have both high spectral (R ∼ 10000) and spatial (<∼ 1") resolution. The study includes all three major ionization states of oxygen, three Balmer lines, multiple lines of Fe II and Fe III, as well as the first datacubes ever acquired for important unblended diagnostic lines such as He II λ4686, Ca I λ3933, and Mg I] λ4571. The data cubes generally sort according to excitation, and have a relatively continuous progression from the highest-excitation ions (He II, O III) through the intermediate-excitation ions (O I and H I) to the lowest-excitation ions (Ca II and Mg I). Merging the KCWI cubes with HST images leads to several new insights about the flow, including evidence for bow shocks, partial bow shocks, spur shocks, Mach disks, jet deflection shocks, a wiggling jet, and potential shock precursors. The most surprising result is that one of the velocity components of Fe II in the Mach disk suddenly increases in flux relative to other lines by a factor of two, implying that the Mach disk vaporizes dust in the jet. Hence, jets must accelerate or entrain dust to speeds of over 300 km/s without destroying the grains. Accepted by Astronomical Journal https://arxiv.org/pdf/2008.03466

A JWST Preview: Adaptive-Optics Images of H2, Br-gamma, and K-continuum in Carina’s Western Wall Patrick Hartigan1, Turlough Downes2 and Andrea Isella1 1 Rice University; 2 Dublin City University E-mail contact: hartigan at sparky.rice.edu We present the first wide-field near-infrared adaptive optics images of Carina’s Western Wall (G287.38-0.62), one of the brightest and most well-defined irradiated interfaces known in a region of massive star formation. The new narrowband H2 2.12µm, Br-γ and K-continuum images from Gemini South trace the photoevaporative flow from the cloud and identify locations where UV-radiation from the surrounding massive stars excites molecular hydrogen to fluoresce. With a field of view of ∼ 1.5’ × 2.9’ and spatial resolution between 60 − 110 mas, the new images show a spectacular level of detail over a large area, and presage what JWST should achieve. The Wall is convex in shape, with a large triangular-shaped extension near its apex. The interface near the apex consists of 3 − 4 regularly-spaced ridges with projected spacings of ∼ 2000 AU, suggestive of a large-scale dynamically-important magnetic field. The northern edge of the Wall breaks into several swept-back fragments of width ∼ 1800 AU that resemble Kelvin-Helmholtz instabilities, and the southern part of the Wall also shows complex morphologies including a sinusoidal-like variation with a half- wavelength of 2500 AU. Though the dissociation front must increase the density along the surface of the Wall, it does not resolve into pillars that point back to the ionization sources, as could occur if the front triggered new stars to form. We discovered a new H2 jet with no clear driving source, MHO 1630, in the northern portion of the Wall, visible as a series of bow shocks arrayed in a line. Accepted by ApJ Letters http://arxiv.org/pdf/2008.01364

Searching for wide-orbit gravitational instability protoplanets with ALMA in the dust continuum J. Humphries1, C. Hall1,2,3, T.J. Haworth4 & S. Nayakshin1 1 Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UK; 2 Department of Physics

30 and Astronomy, The University of Georgia, Athens, GA 30602, USA; 3 Center for Simulational Physics, The University of Georgia, Athens, GA 30602, USA; 4 Astronomy Unit, School of Physics and Astronomy, Queen Mary University of London, London E1 4NS, UK E-mail contact: cassandra.hall at uga.edu Searches for young gas giant planets at wide separations have so far focused on techniques appropriate for compact (Jupiter sized) planets. Here we point out that protoplanets born through Gravitational Instability (GI) may remain in an initial pre-collapse phase for as long as the first 105–107 years after formation. These objects are hundreds of times larger than Jupiter and their atmospheres are too cold (T ∼ tens of K) to emit in the NIR or Hα via accretion shocks. However, it is possible that their dust emission can be detected with ALMA, even around Class I and II protoplanetary discs. In this paper we produce synthetic observations of these protoplanets. We find that making a detection in a disc at 140 parsecs would require a few hundred minutes of ALMA band 6 observation time. Protoplanets with masses of 3–5 MJ have the highest chance of being detected; less massive objects require unreasonably long observation times (1000 minutes) while more massive ones collapse into giant planets before 105 years. We propose that high resolution surveys of young (105–106 years), massive and face on discs offer the best chance for observing protoplanets. Such a detection would help to place constraints on the protoplanet mass spectrum, explain the turnover in the occurrence frequency of gas giants with system metallicity and constrain the prevalence of GI as a planet formation mechanism. Consistent lack of detection would be evidence against GI as a common planet formation mechanism. Accepted by MNRAS http://arxiv.org/pdf/2008.04014

Observing protoplanetary discs with the Square Kilometre Array – I. Characterising pebble substructure caused by forming planets John D. Ilee1, Cassandra Hall2,3,4, Catherine Walsh1, Izaskun Jimenez-Serra5, Christophe Pinte6,7, Jason Terry3,4, Tyler L. Bourke8 and Melvin Hoare1 1 School of Physics and Astronomy, University of Leeds; 2 Department of Physics and Astronomy, University of Leicester; 3 Department of Physics and Astronomy, The University of Georgia; 4 Center for Simulational Physics, The University of Georgia; 5 Departamento de Astrofisica, Centro de Astrobiologia CSIC-INTA; 6 School of Physics and Astronomy, Monash University; 7 Univ. Grenoble Alpes, CNRS; 8 SKA Organisation, Jodrell Bank E-mail contact: j.d.ilee at leeds.ac.uk High angular resolution observations of discs at mm wavelengths (on scales of a few au) are now commonplace, but there is a current lack of a comparable angular resolution for observations at cm wavelengths. This presents a significant barrier to improving our understanding of planet formation, in particular how dust grains grow from mm to cm sizes. In this paper, we examine the ability of the Square Kilometre Array (SKA) to observe dust substructure in a young, planet-forming disc at cm wavelengths. We use dusty hydrodynamics and continuum radiative transfer to predict the distribution and emission of 1 cm dust grains (or pebbles) within the disc, and simulate continuum observations with the current SKA1-MID design baseline at frequencies of 12.5 GHz (Band 5b, 2.4 cm) on 5-10 au scales. The SKA will provide high-fidelity observations of the cm dust emission substructure in discs for integration times totalling 100’s of hours. Radial structure can be obtained at a sufficient resolution and S/N from shorter (10’s of hours) integration times by azimuthal averaging in the image plane. By modelling the intensity distribution directly in the visibility plane, it is possible to recover a similar level of (axisymmetric) structural detail from observations with integration times 1-2 orders of magnitude lower than required for high-fidelity imaging. Our results demonstrate that SKA1-MID will provide crucial constraints on the distribution and morphology of the raw material for building planets, the pebbles in protoplanetary discs. Accepted by MNRAS https://arxiv.org/pdf/2009.00562

Revisiting the Magnetic Field of the L183 Starless Core Janik Karoly1,2, Archana Soam2, B-G Andersson2, Simon Coudé2, Pierre Bastien3 et al. 1 Dept of Physics, Santa Clara University, Santa Clara, 500 El Camino Real, Santa Clara, CA, USA; 2 SOFIA Science Center, Universities Space Research Association, NASA Ames Research Center, M.S. N232-12, Moﬀett Field, CA

31 94035, USA; 3 Institut de Recherche sur les Exoplanètes (iREx) & Centre de Recherche en Astrophysique du Québec (CRAQ), Université de Montréal, Département de Physique, C.P. 6128 Succ. Centre-ville, Montréal, Canada E-mail contact: jkaroly at alumni.scu.edu We present observations of linear polarization from dust thermal emission at 850 µm towards the starless cloud L183. These data were obtained at the James Clerk Maxwell Telescope (JCMT) using the Submillimetre Common-User Bolometer Array 2 (SCUBA-2) camera in conjunction with its polarimeter POL-2. Polarized dust emission traces the plane-of-sky magnetic field structure in the cloud, thus allowing us to investigate the role of magnetic fields in the formation and evolution of its starless core. To interpret these measurements, we first calculate the dust temperature and column density in L183 by fitting the spectral energy distribution obtained by combining data from the JCMT and the Herschel space observatory. We used the Davis-Chandrasekhar-Fermi technique to measure the magnetic field strength in five sub-regions of the cloud, and we find values ranging from ∼120±18 µG to ∼270±64 µG in agreement 22 −2 with previous studies. Combined with an average hydrogen column density (NH2 ) of ∼1.5×10 cm in the cloud, we also find that all five sub-regions are magnetically subcritical. These results indicate that the magnetic field in L183 is sufficiently strong to oppose the gravitational collapse of the cloud. Accepted by ApJ http://arxiv.org/pdf/2008.02841

First L band detection of hot exozodiacal dust with VLTI/MATISSE Florian Kirchschlager1, Steve Ertel2,3, Sebastian Wolf4, Alexis Matter5 and Alexander V. Krivov6 1 Dept of Physics and Astronomy, University College London, Gower Street, WC1E 6BT London, UK; 2 Large Binocular Telescope Observatory, 933 North Cherry Avenue, Tucson, AZ 85721, USA; 3 Steward Observatory, Dept of Astronomy, University of Arizona, 993 N. Cherry Ave, Tucson, AZ, 85721, USA; 4 Institute of Theoretical Physics and Astrophysics, Kiel University, Leibnizstraße 15, 24118, Kiel, Germany; 5 Laboratoire Lagrange, Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, 06304 Nice Cedex 4, France; 6 Astrophysical Institute and University Observatory, Friedrich Schiller University Jena, Schillergäßchen 2-3, 07745 Jena, Germany E-mail contact: f.kirchschlager at ucl.ac.uk For the first time we observed the emission of hot exozodiacal dust in L band. We used the new instrument MATISSE at the Very Large Telescope Interferometer to detect the hot dust around κ Tuc with a significance of 3σ to 6σ at wavelengths between 3.37 and 3.85 µm and a dust-to-star flux ratio of 5 to 7 %. We modelled the spectral energy distribution based on the new L band data alone and in combination with H band data published previously. In all cases we find 0.58 µm grains of amorphous carbon to fit the κ Tuc observations the best, however, also nanometre or micrometre grains and other carbons or silicates reproduce the observations well. Since the H band data revealed a temporal variability, while our L band data were taken at a different epoch, we combine them in different ways. Depending on the approach, the best fits are obtained for a narrow dust ring at a stellar distance in the 0.1 to 0.29 au range and thus with a temperature between 940 and 1430 K. Within the 1σ uncertainty dust location and temperature are confined to 0.032 − 1.18 au and 600 − 2000 K. Accepted by MNRAS Letters https://arxiv.org/pdf/2009.02334

Interferometric study on the temporal variability of the brightness distributions of protoplanetary disks J. Kobus1, S. Wolf1, T. Ratzka2,3 and R. Brunngräber1 1 Institute of Theoretical Physics and Astrophysics, University of Kiel, Leibnizstraße 15, 24118 Kiel, Germany; 2 Institute for Physics/IGAM, NAWI Graz, University of Graz, Universitätsplatz 5/II, 8010 Graz, Austria; 3 Planetarium im Museum am Schölerberg, Klaus-Strick-Weg 10, 49082 Osnabrück, Germany E-mail contact: jkobus at astrophysik.uni-kiel.de Context. Optical and infrared spatially unresolved multi-epoch observations have revealed the variability of pre-main sequence stars and/or their environment. Moreover, structures in orbital motion around the central star, resulting from planet-disk interaction, are predicted to cause temporal variations in the brightness distributions of protoplanetary

32 disks. Through repeated observations of pre-main sequence stars with the Very Large Telescope Interferometer (VLTI) over nearly two decades, the ESO Archive has become a treasure chest containing unprecedented high-resolution multi- epoch near- and mid-infrared observations of the potential planet-forming regions in protoplanetary disks. Aims. We aim to investigate whether the existing multi-epoch observations provide evidence for the variability of the brightness distributions of the innermost few astronomical units of protoplanetary disks and to quantify any variations detected. Methods. We present different approaches to search for evidence of temporal variations based on multi-epoch observations obtained with the VLTI instruments PIONIER, AMBER, and MIDI for 68 pre-main sequence stars. Results. For nine objects in our sample, multi-epoch data obtained using equal baselines are available that allow us to directly detect variations in the visibilities due to temporally variable brightness distributions. Significant variations of the near-infrared visibilities obtained in different epochs with PIONIER and/or AMBER for HD 50138, DX Cha, HD 142527, V856 Sco, HD 163296, and R CrA were found. HD 37806, TW Hya, and CPD-36 6759 show no significant variations. By estimating the impact of a small variation of the baseline on the measured squared visibilities, we are able to compare the data of another 12 pre-main sequence stars. Thereby, we find evidence for temporal variations of the brightness distribution of one additional object, AK Sco. Besides the two binaries DX Cha and AK Sco, HD 50138 and V856 Sco also show signs of variability caused by variations of asymmetric structures in the brightness distribution. Accepted by A&A https://arxiv.org/pdf/2008.08374

A triple-star system with a misaligned and warped circumstellar disk shaped by disk tearing Stefan Kraus1, Alexander Kreplin1, Alison K. Young1,2, Matthew R. Bate1, John D. Monnier3, Tim J. Harries1, Henning Avenhaus4, Jacques Kluska1,5, Anna S. E. Laws1, Evan A. Rich3, Matthew Willson1,6, Alicia N. Aarnio7, Fred C. Adams3, Sean M. Andrews8, Narsireddy Anugu1,3,9, Jaehan Bae3,10, Theo ten Brummelaar11, Nuria Calvet3, Michel Curé12, Claire L. Davies1, Jacob Ennis3, Catherine Espaillat13, Tyler Gardner3, Lee Hartmann3, Sasha Hinkley1, Aaron Labdon1, Cyprien Lanthermann5, Jean- Baptiste LeBouquin3,14, Gail H. Schaefer11, Benjamin R. Setterholm3, David Wilner7 and Zhaohuan Zhu15 1 School of Physics and Astronomy, University of Exeter, Exeter EX4 4QL,UK; 2 School of Physics and Astronomy, University of Leicester, Leicester LE17 RH, UK; 3 Dept of Astronomy, University of Michigan, Ann Arbor, MI 48109, USA; 4 no academic aﬃliation; 5 Instituut voor Sterrenkunde, Katholieke Universiteit Leuven, 3001 Leuven, Belgium; 6 Dept of Physics and Astronomy, Georgia State University, Atlanta, GA 30302,USA; 7 Dept of Physics and Astronomy, University of North Carolina Greensboro, Greensboro, NC 27402, USA; 8 CfA, Harvard and Smithsonian, Cambridge, MA 02138, USA; 9 Steward Observatory, University of Arizona, Tucson, AZ 85721, USA; 10 Carnegie Institution for Science, Washington, DC 20015, USA; 11 Center for High Angular Resolution Astronomy Array of Georgia State University, Mount Wilson, CA 91023, USA; 12 Instituto de Fisica y Astronomia, Universidad de Valparaiso, 12 Casilla 5030, Valparaiso, Chile; 13 Dept of Astronomy, Boston University, Boston, MA 02215, USA; 14 Université Grenoble Alpes, Institut de Planétologie et d’Astrophysique, 38000; 15 Dept of Physics and Astronomy, University of Nevada, Las Vegas, NV 89154, USA E-mail contact: s.kraus at exeter.ac.uk Young stars are surrounded by a circumstellar disk of gas and dust, within which planet formation can occur. Gravi- tational forces in multiple star systems can disrupt the disk. Theoretical models predict that if the disk is misaligned with the orbital plane of the stars, the disk should warp and break into precessing rings, a phenomenon known as disk tearing. We present observations of the triple-star system GW Orionis, ﬁnding evidence for disk tearing. Our images show an eccentric ring that is misaligned with the orbital planes and the outer disk. The ring casts shadows on a strongly warped intermediate region of the disk. If planets can form within the warped disk, disk tearing could provide a mechanism for forming wide-separation planets on oblique orbits. Accepted by Science (369, 1233-1238) https://arxiv.org/pdf/2004.01204, https://science.sciencemag.org/content/369/6508/1233

33 Physicochemical models: source-tailored or generic? Beatrice M. Kulterer1, Maria N. Drozdovskaya1, Audrey Coutens2, Sébastien Manigand3 and Gwen- doline Stéphan4 1 Center for Space and Habitability, University of Bern, 3012 Bern, Switzerland; 2 Laboratoire d’astrophysique de Bordeaux, Univ. Bordeaux, CNRS, 33615 Pessac, France; 3 Center for Star and Planet Formation, Niels Bohr Institute & Natural History Museum of Denmark, University of Copenhagen, 1350 Copenhagen K., Denmark; 4 Dept of Chemistry, University of Virginia, Charlottesville, VA 22904, USA E-mail contact: beatrice.kulterer at csh.unibe.ch Physicochemical models can be powerful tools to trace the chemical evolution of a protostellar system and allow to constrain its physical conditions at formation. The aim of this work is to assess whether source-tailored modelling is needed to explain the observed molecular abundances around young, low-mass protostars or if, and to what extent, generic models can improve our understanding of the chemistry in the earliest stages of star formation. The physical conditions and the abundances of simple, most abundant molecules based on three models are compared. After establishing the discrepancies between the calculated chemical output, the calculations are redone with the same chemical model for all three sets of physical input parameters. With the differences arising from the chemical models eliminated, the output is compared based on the influence of the physical model. Results suggest that the impact of the chemical model is small compared to the influence of the physical conditions, with considered timescales having the most drastic effect. Source-tailored models may be simpler by design; however, likely do not sufficiently constrain the physical and chemical parameters within the global picture of star-forming regions. Generic models with more comprehensive physics may not provide the optimal match to observations of a particular protostellar system, but allow a source to be studied in perspective of other star-forming regions. Accepted by MNRAS https://arxiv.org/pdf/2008.04798

SCExAO/CHARIS Near-IR Integral Field Spectroscopy of the HD 15115 Debris Disk Kellen Lawson1, Thayne Currie2,3,4, John P. Wisniewski1, Motohide Tamura5,6,7, Glenn Schneider8 et al. 1 Dept of Physics and Astronomy, Univ. of Oklahoma, Norman, OK; 2 Subaru Telescope, NAOJ, Hilo, HI 96720, USA; 3 NASA-Ames Research Center, Moffett Field, CA, USA; 4 Eureka Scientific, Oakland, CA, USA; 5 Astrobiology Center of NINS, Tokyo, Japan; 6 Dept of Astronomy, Graduate School of Science, Univ. of Tokyo, 113-0033, Japan; 7 NAOJ, Tokyo 181-8588, Japan; 8 Steward Obs., Univ. of Arizona, Tucson, AZ 85721, USA E-mail contact: kellenlawson at gmail.com We present new, near-infrared (1.1–2.4 µm) high-contrast imaging of the debris disk around HD 15115 with the Subaru Coronagraphic Extreme Adaptive Optics system (SCExAO) coupled with the Coronagraphic High Angular Resolution ′′ Imaging Spectrograph (CHARIS). SCExAO/CHARIS resolves the disk down to ρ ∼ 0. 2 (rproj ∼ 10 au), a factor of ∼3–5 smaller than previous recent studies. We derive a disk position angle of PA ∼279◦.4–280◦.5 and an inclination of i ∼ 85◦.3–86◦.2. While recent SPHERE/IRDIS imagery of the system could suggest a significantly misaligned two ring disk geometry, CHARIS imagery does not reveal conclusive evidence for this hypothesis. Moreover, optimizing models of both one and two ring geometries using differential evolution, we find that a single ring having a Hong-like scattering ′′ phase function matches the data equally well within the CHARIS field of view (ρ ∼< 1 ). The disk’s asymmetry, well- evidenced at larger separations, is also recovered; the west side of the disk appears on average around 0.4 magnitudes brighter across the CHARIS bandpass between 0′′. 25 and 1′′. Comparing STIS/50CCD optical photometry (2000– 10500 Å) with CHARIS NIR photometry, we find a red (STIS/50CCD–CHARIS broadband) color for both sides of the disk throughout the 0′′. 4–1′′ region of overlap, in contrast to the blue color reported at similar wavelengths for regions exterior to ∼2′′. Further, this color may suggest a smaller minimum grain size than previously estimated at larger separations. Finally, we provide constraints on planetary companions, and discuss possible mechanisms for the observed inner disk flux asymmetry and color. Accepted by AJ http://arxiv.org/pdf/2008.00309

34 A 3 mm Chemical Exploration of Small Organics in Class I YSOs Romane Le Gal1, Karin I. Öberg1, Jane Huang1, Charles J. Law1, François Ménard2, Bertrand Lefloch2, Charlotte Vastel3, Ana Lopez-Sepulcre2,4, Cécile Favre2, Eleonora Bianchi2, Cecilia Ceccarelli2 1 Center for Astrophysics |Harvard & Smithsonian, 60 Garden St., Cambridge, MA 02138, USA; 2 Université Grenoble Alpes, CNRS, IPAG, F-38000 Grenoble, France; 3 IRAP, Université de Toulouse, CNRS, UPS, CNES, 31400 Toulouse, France 4 IRAM, 300 rue de la piscine, F-38406 Saint-Martin d’Heres, France E-mail contact: romane.le_gal at cfa.harvard.edu There is mounting evidence that the composition and structure of planetary systems are intimately linked to their birth environments. During the past decade, several spectral surveys probed the chemistry of the earliest stages of star formation and of late planet-forming disks. However, very little is known about the chemistry of intermediate protostellar stages, i.e., Class I Young Stellar Objects (YSOs), where planet formation may have already begun. We present here the first results of a 3mm spectral survey performed with the IRAM-30m telescope to investigate the chemistry of a sample of seven Class I YSOs located in the Taurus star-forming region. These sources were selected to embrace the wide diversity identified for low-mass protostellar envelope and disk systems. We present detections + + and upper limits of thirteen small (Natoms ≤ 3) C, N, O, and S carriers - namely CO, HCO , HCN, HNC, CN, N2H , + 13 15 18 17 34 C2H, CS, SO, HCS , C2S, SO2, OCS - and some of their D, C, N, O, O, and S isotopologues. Together, these species provide constraints on gas-phase C/N/O ratios, D- and 15N-fractionation, source temperature and UV exposure, as well as the overall S-chemistry. We find substantial evidence of chemical differentiation among our source sample, some of which can be traced back to Class I physical parameters, such as the disk-to-envelope mass ratio (proxy for Class I evolutionary stage), the source luminosity, and the UV-field strength. Overall, these first results allow us to start investigating the astrochemistry of Class I objects, however, interferometric observations are needed to differentiate envelope versus disk chemistry. Accepted by ApJ (898,131) https://iopscience.iop.org/article/10.3847/1538-4357/ab9ebf/pdf

Wind-MRI interactions in local models of protoplanetary discs: I. Ohmic resistivity Philip K C. Leung1, Gordon I. Ogilvie1 1 Department of Applied Mathematics and Theoretical Physics, Centre for Mathematical Sciences, University of Cambridge, Wilberforce Road, Cambridge CB3 0WA E-mail contact: pkcl2 at cam.ac.uk A magnetic disc wind is an important mechanism that may be responsible for driving accretion and structure formation in protoplanetary discs. Recent numerical simulations have shown that these winds can take either the traditional ‘hourglass’ symmetry about the mid-plane, or a ‘slanted’ symmetry dominated by a mid-plane toroidal field of a single sign. The formation of this slanted symmetry state has not previously been explained. We use radially local 1D vertical shearing box simulations to assess the importance of large-scale MRI channel modes in influencing the formation and morphologies of these wind solutions. We consider only Ohmic resistivity and explore the effect of different magnetisations, with the mid-plane β parameter ranging from 105 to 102. We find that our magnetic winds go through three stages of development: cyclic, transitive and steady, with the steady wind taking a slanted symmetry profile similar to those observed in local and global simulations. We show that the cycles are driven by periodic excitation of the n =2 or 3 MRI channel mode coupled with advective eviction, and that the transition to the steady wind is caused by a much more slowly growing n = 1 mode altering the wind structure. Saturation is achieved through a combination of advective damping from the strong wind, and suppression of the instability due to a strong toroidal field. A higher disc magnetisation leads to a greater tendency towards, and more rapid settling into the slanted symmetry steady wind, which may have important implications for mass and flux transport processes in protoplanetary discs. Accepted by MNRAS http://arxiv.org/pdf/2008.00906

35 Evidence for dense gas heated by the explosion in Orion KL Dalei Li1,2, Xindi Tang1,2, Christian Henkel3,4,1, Karl M. Menten3, Friedrich Wyrowski3, Yan Gong3, Gang Wu1,2, Yuxin He1,2, Jarken Esimbek1,2 and Jianjun Zhou1,2 1 Xinjiang Astronomical Observatory, Chinese Academy of Sciences, 830011 Urumqi, PR China; 2 Key Laboratory of Radio Astronomy, Chinese Academy of Sciences, 830011 Urumqi, PR China; 3 MPIfR, Auf dem Hügel 69, 53121 Bonn, Germany; 4 Astron. Dept, King Abdulaziz Univ., 21589 Jeddah, Saudi Arabia E-mail contact: tangxindi at xao.ac.cn ′′ We mapped the kinetic temperature structure of Orion KL in a ∼20 (∼8000AU) sized region with para-H2CS 707−606, 726 −625, and 725 −624 making use of ALMA Band 6 Science Verification data. The kinetic temperatures obtained with a resolution of 1 ′′. 65×1 ′′. 14 (∼550 AU) are deduced by modeling the measured averaged velocity-integrated intensity ratios of para-H2CS 726−625/707−606 and 725−624/707−606 with a RADEX non-LTE model. The kinetic temperatures 7 −3 of the dense gas, derived from the para-H2CS line ratios at a spatial density of 10 cm , are high, ranging from 43 to >500 K with an unweighted average of ∼170 K. There is no evidence for internal sources playing an important role in the heating of the various structures identified in previous work, namely the elongated ridge, the northwestern clump, and the eastern region of the compact ridge, while the high temperatures in the western region of the compact ridge may be dominated by internal massive star formation. Significant gradients of kinetic temperature along molecular filaments traced by H2CS indicate that the dense gas is heated by the shocks induced by the enigmatic explosive event, which occurred several hundred years ago greatly affecting the energetics of the Orion KL region. Thus, with the notable exception of the western region of the compact ridge, the high temperatures of the dense gas in Orion KL are probably caused by shocks from the explosive event, leading to a dominant component of externally heated dense gas. Accepted by ApJ http://arxiv.org/pdf/2008.04564

The family of amide molecules toward NGC 6334I Niels F.W. Ligterink1, Samer J. El-Abd2,3, Crystal L. Brogan3, Todd R. Hunter3 et al. 1 Center for Space and Habitability, Univ. of Bern, Sidlerstrasse 5, 3012 Bern, Switzerland; 2 Dept of Astronomy, Univ. of Virginia, Charlottesville, VA 22904, USA; 3 NRAO, Charlottesville, VA 22903, USA E-mail contact: niels.ligterink at csh.unibe.ch Amide molecules produced in space could play a key role in the formation of biomolecules on a young planetary object. However, the formation and chemical network of amide molecules in space is not well understood. In this work, ALMA observations are used to study a number of amide(-like) molecules toward the high-mass star-forming region NGC 6334I. The ﬁrst detections of cyanamide (NH2CN), acetamide (CH3C(O)NH2) and N-methylformamide (CH3NHCHO) are presented for this source. These are combined with analyses of isocyanic acid (HNCO) and formamide (NH2CHO) and a tentative detection of urea (carbamide; NH2C(O)NH2). Abundance correlations show that most amides are likely formed in related reactions occurring in ices on interstellar dust grains in NGC 6334I. However, in an expanded sample of sources, large abundance variations are seen for NH2CN that seem to depend on the source type, which suggests that the physical conditions within the source heavily inﬂuence the production of this species. The rich amide inventory of NGC 6334I strengthens the case that interstellar molecules can contribute to the emergence of biomolecules on planets. Accepted by ApJ http://arxiv.org/pdf/2008.09157

Gas-grain model of carbon fractionation in dense molecular clouds Jean-Christophe Loison1, Valentine Wakelam2, Pierre Gratier2 and Kevin M. Hickson1 1 Institut des Sciences Moléculaires (ISM), CNRS, Univ. Bordeaux, 351 cours de la Libération, 33400, Talence, France; 2 Laboratoire d’astrophysique de Bordeaux, Univ. Bordeaux, CNRS, B18N, 33615 Pessac, France E-mail contact: jean-christophe.loison at u-bordeaux.fr

36 Carbon containing molecules in cold molecular clouds show various levels of isotopic fractionation through multiple observations. To understand such effects, we have developed a new gas-grain chemical model with updated 13C fractionation reactions (also including the corresponding reactions for 15N, 18O and 34S). For chemical ages typical of dense clouds, our nominal model leads to two 13C reservoirs: CO and the species that derive from CO, mainly s-CO and s-CH3OH, as well as C3 in the gas phase. The nominal model leads to strong enrichment in C3, c-C3H2 and C2H in contradiction with observations. When C3 reacts with oxygen atoms the global agreement between the various observations and the simulations is rather good showing variable 13C fractionation levels which are specific to each species. Alternatively, hydrogen atom reactions lead to notable relative 13C fractionation effects for the two non-equivalent isotopologues of C2H, c-C3H2 and C2S. As there are several important fractionation reactions, some carbon bearing species are enriched in 13C, particularly CO, depleting atomic 13C in the gas phase. This induces a 13C depletion in CH4 formed on grain surfaces, an effect that is not observed in the CH4 in the solar system, in particular on Titan. This seems to indicate a transformation of matter between the collapse of the molecular clouds, leading to the formation of the protostellar disc, and the formation of the planets. Or it means that the atomic carbon sticking to the grains reacts with the species already on the grains giving very little CH4. Accepted by MNRAS http://arxiv.org/pdf/2008.13411

Herbig-Haro flows around BBWo 192E (GM 1-23) nebula T.Yu. Magakian1, T.A. Movsessian1, H.R. Andreasyan1, J.Bally2 and A.S. Rastorguev3,4 1 Byurakan Observatory of the Nat.Acad.Sci. of Armenia, Byurakan, Aragatsotn prov., 0213, Armenia; 2 Department of Astrophysical and Planetary Sciences, University of Colorado, Boulder, CO,USA; 3 Faculty of Physics, Lomonosov Moscow State University, Leninskie Gory 1, bldg.2, Moscow, Russia; 4 Sternberg Astronomical Institute, Lomonosov Moscow State University, Universitetskii prospect, 13, Moscow, Russia E-mail contact: tigmag at sci.am We studied a small comet-shape reflection nebula, located in the dark cloud SL 4 in the Vela Molecular Ridge cloud C, known as BBWo 192E (GM 1-23), and a young infrared cluster embedded into the nebula, for the evidences of recent star formation. We obtained the images of BBWo 192E in Hα and [SII] lines and in SDSS i’ with Blanco telescope at the Cerro Tololo Interamerican Observatory to discover new Herbig-Haro (HH) flows. 2MASS and WISE surveys were used for the search of the additional member stars of the cluster. We also studied proper motions and parallaxes of the cluster members with the aid of GAIA DR2. Five new groups containing at least 9 HH objects tracing several distinct outflows were revealed. A previously unreported reflection nebula and a number of probable outflow sources were found in the infrared range. The proper motions allowed selecting eight probable member stars in the visual range. Their parallaxes correspond to a mean distance 800 ± 100 pc for this cluster. The bolometric luminosities of the brightest cluster members are 1010 L⊙ (IRAS 08513−4201, the strong source in the center of the cluster) and 2 to 6 L⊙ for the five other stars. The existence of the optical HH flows around the infrared cluster of YSOs suggests that star formation in this cloud is on-going around the more massive HAeBe star. By its morphology and other features this star-forming region is similar to the zone of star formation near CPM 19. Accepted by MNRAS http://arxiv.org/pdf/2009.00642

Accretion discs with non-zero central torque Chris Nixon1 and Jim Pringle1,2 1 School of Physics and Astronomy, University of Leicester, Leicester, LE1 7RH, UK; 2 Institute of Astronomy, Madingley Road, Cambridge, CB3 0HA, UK E-mail contact: cjn at leicester.ac.uk We present analytical and numerical solutions for accretion discs subject to a non-zero central torque. We express this in terms of a single parameter, f, which is the ratio of outward viscous ﬂux of angular momentum from the inner boundary to the inward advected ﬂux of angular momentum there. The standard “accretion” disc, where the central boundary condition is zero-torque, is represented by f =0. A “decretion” disc, where the radial velocity at the inner

37 boundary is zero, is represented by f → ∞. For f > 0 a torque is applied to the disc at the inner boundary, which feeds both angular momentum and energy into the disc. This can arise, for example, in the case of a circumbinary disc where resonances transfer energy and angular momentum from the binary to the disc orbits, or where the disc is around a rotating magnetic star which can allow the disc orbits to be accelerated outwards at the magnetospheric radius. We present steady-state solutions to the disc structure as a function of f, and for arbitrary kinematic viscosity ν. For time-dependent discs, we solve the equations using a Green’s function approach for the specific case of ν ∝ R and provide an example numerical solution to the equations for the case of ν ∝ R3/2. We find that for values of f < 0.1 the disc solutions closely resemble “accretion” discs. For values of f > 10 the solutions initially resemble “decretion” discs, but at sufficiently late times exhibit the properties of “accretion” discs. We discuss the application of this theory to different astrophysical systems, and in particular the values of the f parameter that are expected in different cases. Accepted by New Astronomy https://arxiv.org/pdf/2008.07565

Solving grain size inconsistency between ALMA polarization and VLA continuum in the Ophiuchus IRS 48 protoplanetary disk Satoshi Ohashi1, Akimasa Kataoka2, Nienke Van der Marel3, Charles L. H. Hull4,5, William R. F. Dent5, Adriana Pohl6, Paola Pinilla6, Ewine F. van Dishoeck7 and Thomas Henning6 1 RIKEN Cluster for Pioneering Research, 2-1, Hirosawa, Wako-shi, Saitama 351-0198, Japan; 2 National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan; 3 Department of Physics and Astronomy, University of Victoria 3800 Finnerty Road, Victoria, BC, V8P 5C2, Canada; 4 National Astronomical Observatory of Japan, NAOJ Chile, Alonso de Córdova 3788, Oﬃce 61B, 7630422, Vitacura, Santiago, Chile; 5 Joint ALMA Observatory, Alonso de Córdova 3107, Vitacura, Santiago, Chile; 6 Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany; 7 Leiden Observatory, Leiden University, P.O. Box 9513, NL-2300 RA Leiden, The Netherlands E-mail contact: satoshi.ohashi at riken.jp The protoplanetary disk around Ophiuchus IRS 48 shows an azimuthally asymmetric dust distribution in (sub- )millimeter observations, which is interpreted as a vortex, where millimeter/centimeter-sized particles are trapped at the location of the continuum peak. In this paper, we present 860 µm ALMA observations of polarized dust emission of this disk. The polarized emission was detected toward a part of the disk. The polarization vectors are parallel to the disk minor axis, and the polarization fraction was derived to be 1 − 2%. These characteristics are consistent with models of self-scattering of submillimeter-wave emission, which indicate a maximum grain size of ∼ 100 µm. However, this is inconsistent with the previous interpretation of millimeter/centimeter dust particles being trapped by a vortex. To explain both, ALMA polarization and previous ALMA and VLA observations, we suggest that the thermal emission at 860 µm wavelength is optically thick (τabs ∼ 7.3) at the dust trap with the maximum observable grain size of ∼ 100 µm rather than an optically thin case with ∼ cm dust grains. We note that we cannot rule out that larger dust grains are accumulated near the midplane if the 860 µm thermal emission is optically thick. Accepted by ApJ https://arxiv.org/pdf/2007.15014.pdf

Modeling disk fragmentation and multiplicity in massive star formation G. André Oliva1 and Rolf Kuiper1 1 Institute for Astronomy and Astrophysics, University of Tübingen, Auf der Morgenstelle 10, 72076, Tübingen, Germany E-mail contact: andree.oliva at uni-tuebingen.de Context: There is growing evidence that massive stars grow by disk accretion similar to their low-mass counterparts. Early in evolution, these disks can achieve masses which are comparable to the current stellar mass, and hence, the forming disks are highly susceptible for gravitational fragmentation. Aims: We investigate the formation and early evolution of an accretion disk around a forming massive protostar, focussing on its fragmentation physics. For this, we follow the collapse of a molecular cloud of gas and dust, the

38 formation of a massive protostar, the formation of its circumstellar disk, and the formation and evolution of the disk fragments. Methods: We use a grid-based self-gravity-radiation-hydrodynamics code including a sub-grid module for stellar evolution and dust evolution. On purpose, we do not use a sub-grid module for fragmentation such as sink particles to allow for all paths of fragment formation and destruction, but instead keeping the spatial grid resolution high enough to properly resolve the physical length scales of the problem, namely the pressure scale height and Jeans length of the disk. Simulations are performed on a grid in spherical coordinates with a logarithmic spacing of the grid cells in the radial direction and a cosine-distribution of the grid cells in the polar direction, focusing the spatial resolution on the disk midplane. Because of that, roughly 25% of the total number of grid cells, corresponding to ∼ 26 million grid cells, are used to model the disk physics. They constitute the highest resolution simulations performed up to now on disk fragmentation around a forming massive star with the physics considered here. For a better understanding of the effects of spatial resolution and to compare our high-resolution results with previous lower resolution studies in the literature, we perform the same simulation for five different resolutions, each of them with a factor of two lower resolution than the predecessor run. Results: The cloud collapses and a massive (proto)star is formed in its center, surrounded by a fragmenting Keplerian- like accretion disk with spiral arms. The fragments have masses of ∼ 1 M⊙, and their continuous interactions with the disk, spiral arms and other fragments results in eccentric orbits. Fragments form hydrostatic cores, surrounded by secondary disks with spiral arms that also produce new fragments. We identified several mechanisms of fragment formation, interaction and destruction. Central temperatures of the fragments can reach the hydrogen dissociation limit, form second Larson cores and evolve into companion stars. Based on this, we study the multiplicity predicted by the simulations and find ∼ 6 companions at different distances from the primary: from possible spectroscopic multiples, to companions at distances between 1000 and 2000 au. Accepted by Astronomy & Astrophysics https://arxiv.org/pdf/2008.13653

Different Fates of Young Star Clusters After Gas Expulsion Xiaoying Pang1,2, Yuqian Li1, Shih-Yun Tang3,4, Mario Pasquato5,6 and M.B.N. Kouwenhoven1 1 Department of Physics, Xi’an Jiaotong-Liverpool University, 111 Renai Road, Dushu Lake Science and Education Innovation District, Suzhou 215123, Jiangsu Province, P. R. China; 2 Shanghai Key Laboratory for Astrophysics, Shanghai Normal University, 100 Guilin Road, Shanghai 200234, P. R. China; 3 Lowell Observatory, 1400 W. Mars Hill Road, Flagstaff, AZ 86001, USA; 4 Department of Astronomy and Planetary Sciences, Northern Arizona University, Flagstaff, AZ 86011, USA; 5 INAF-Osservatorio Astronomico di Padova, Vicolo dellOsservatorio 5, 35122 Padova, Italy; 6 INFN- Sezione di Padova, Via Marzolo 8, I35131 Padova, Italy E-mail contact: Xiaoying.Pang at xjtlu.edu.cn We identify structures of the young star cluster NGC 2232 in the solar neighborhood (323.0 pc), and a newly discovered star cluster LP 2439 (289.1 pc). Member candidates are identified using the Gaia DR2 sky position, parallax and proper motion data, by an unsupervised machine learning method, StarGO. Member contamination from the Galactic disk is further removed using the color magnitude diagram. The four identified groups (NGC 2232, LP 2439 and two filamentary structures) of stars are coeval with an age of 25 Myr and were likely formed in the same giant molecular cloud. We correct the distance asymmetry from the parallax error with a Bayesian method. The 3D morphology shows the two spherical distributions of clusters NGC 2232 and LP 2439. Two filamentary structures are spatially and kinematically connected to NGC 2232. Both NGC 2232 and LP 2439 are expanding. The expansion is more significant in LP 2439, generating a loose spatial distribution with shallow volume number and mass density profiles. The expansion is suggested to be mainly driven by gas expulsion. NGC 2232, with 73 percent of the cluster mass bound, is currently experiencing a process of re-virialization, However, LP 2439, with 52 percent cluster mass being unbound, may fully dissolve in the near future. The different survivability traces different dynamical states of NGC 2232 and LP 2439 prior to the onset of gas expulsion. NGC 2232 may have been substructured and subvirial, while LP 2439 may either have been virial/supervirial, or it has experienced a much faster rate of gas removal. Accepted by ApJL http://arxiv.org/pdf/2008.02803

39 Magnetic torques on T Tauri stars: accreting vs. non-accreting systems G. Pantolmos1, C. Zanni2 and J. Bouvier1 1 Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France; 2 INAF - Osservatorio Astrofisico di Torino, Strada Osservatorio 20, 10025 Pino Torinese, Italy E-mail contact: george.pantolmos at univ-grenoble-alpes.fr Classical T Tauri stars (CTTs) magnetically interact with their surrounding disks, a process that is thought to regulate their rotational evolution. In this work, we compute torques acting onto the stellar surface of CTTs arising from different accreting (accretion funnels) and ejecting (stellar winds and magnetospheric ejections) flow components. Furthermore, we compare the magnetic braking due to stellar winds in two different systems: isolated and accreting stars. 2.5D magnetohydrodynamic, time-dependent, axisymmetric simulations are employed. For both systems the stellar wind is thermally driven. In the star-disk-interaction (SDI) simulations the accretion disk is Keplerian, viscous, and resistive. Two series of simulations are presented, one for each system. We find that in classical T Tauri systems the presence of magnetospheric ejections confines the stellar-wind expansion, resulting in an hourglass-shaped geometry of the outflow. In addition, the formation of the accretion columns modifies the amount of open magnetic flux exploited by the stellar wind. These effects have a strong impact on the stellar wind properties and we show that the stellar-wind braking is more efficient in the star-disk-interacting systems than in the isolated ones. We also derive torque scalings, over a wide range of magnetic field strengths, for each flow component in a SDI system that directly applies a torque on the stellar surface. In all the performed SDI simulations the stellar wind extracts less than 2% of the mass accretion rate and the disk is truncated up to 66% of the corotation radius. All the simulations show a net spin-up torque. In order to achieve a stellar-spin equilibrium we need either more massive stellar winds or disks being truncated closer to the corotation radius, which increases the torque efficiency by the magnetospheric ejections. Accepted by A&A http://arxiv.org/pdf/2009.00940

Gas trapping of hot dust around main-sequence stars Tim D. Pearce1, Alexander V. Krivov1 and Mark Booth1 1 Astrophysikalisches Institut und Universitätssternwarte, Friedrich-Schiller-Universität Jena, Schillergäßchen 2-3, D- 07745 Jena, Germany E-mail contact: timothy.pearce at uni-jena.de In 2006 Vega was discovered to display excess near-infrared emission. Surveys now detect this phenomenon for one ﬁfth of main-sequence stars, across various spectral types and ages. The excesses are interpreted as populations of small, hot dust grains very close to their stars, which must originate from comets or asteroids. However, the presence of such grains in copious amounts is mysterious, since they should rapidly sublimate or be blown out of the system. Here we investigate a potential mechanism to generate excesses: dust migrating inwards under radiation forces sublimates near the star, releasing modest quantities of gas which then traps subsequent grains. This mechanism requires neither specialised system architectures nor high dust supply rates, and could operate across diverse stellar types and ages. The model naturally reproduces many features of inferred dust populations, in particular their location, preference for small grains, steep size distribution, and dust location scaling with stellar luminosity. For Sun-like stars the mechanism can produce 2.2 µm excesses that are an order of magnitude larger than those at 8.5 µm, as required by observations. However, for A-type stars the simulated near-infrared excesses were only twice those in the mid infrared; grains would have to be 5 − 10 times smaller than those trapped in our model to be able to explain observed near-infrared excesses around A stars. Further progress with any hot dust explanation for A stars requires a means for grains to become very hot without either rapidly sublimating or being blown out of the system. Accepted by MNRAS https://arxiv.org/pdf/2008.07505.pdf

40 Linking ice and gas in the Serpens low-mass star-forming region G. Perotti1, W. R. M. Rocha1, J. K. Jørgensen1, L.E. Kristensen1, H. J. Fraser2 and K. M. Pontoppidan3 1 Niels Bohr Institute & Centre for Star and Planet Formation, University of Copenhagen, Øster Voldgade 5−7, 1350 Copenhagen K., Denmark; 2 School of Physical Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA, United Kingdom; 3 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA E-mail contact: giulia.perotti at nbi.ku.dk The interaction between dust, ice, and gas during the formation of stars produces complex organic molecules. While observations indicate that several species are formed on ice-covered dust grains and are released into the gas phase, the exact chemical interplay between solid and gas phases and their relative importance remain unclear. Our goal is to study the interplay between dust, ice, and gas in regions of low-mass star formation through ice- and gas-mapping and by directly measuring gas-to-ice ratios. This provides constraints on the routes that lead to the chemical complexity that is observed in solid and gas phases. We present observations of gas-phase methanol (CH3OH) and carbon monoxide (13CO and C18O) at 1.3 mm towards ten low-mass young protostars in the Serpens SVS 4 cluster from the SubMillimeter Array (SMA) and the Atacama Pathfinder EXperiment (APEX) telescope. We used archival data from the Very Large Telescope (VLT) to derive abundances of ice H2O, CO, and CH3OH towards the same region. Finally, we constructed gas-ice maps of SVS 4 and directly measured CO and CH3OH gas-to-ice ratios. The SVS 4 cluster is characterised by a global temperature of 15 ± 5 K. At this temperature, the chemical behaviours of CH3OH and CO are anti-correlated: larger variations are observed for CH3OH gas than for CH3OH ice, whereas the opposite is seen −4 −3 for CO. The gas-to-ice ratios (Ngas/Nice) range from 1 − 6 for CO and 1.4 × 10 − 3.7 × 10 for CH3OH. The CO gas-maps trace an extended gaseous component that is not sensitive to the effect of freeze-out. Because of temperature variations and dust heating around 20 K, the frozen CO is efficiently desorbed. The CH3OH gas-maps, in contrast, probe regions where methanol is predominantly formed and present in ices and is released into the gas phase through non-thermal desorption mechanisms. Combining gas- and ice-mapping techniques, we measure gas-to-ice ratios of CO and CH3OH in the SVS 4 cluster. The CH3OH gas-to-ice ratio agrees with values that were previously reported for embedded Class 0/I low-mass protostars. We find that there is no straightforward correlation between CO and CH3OH gas with their ice counterparts in the cluster. This is likely related to the complex morphology of SVS 4: the Class 0 protostar SMM 4 and its envelope lie in the vicinity, and the outflow associated with SMM 4 intersects the cluster. This study serves as a pathfinder for future observations with ALMA and the James Webb Space Telescope (JWST) that will provide high-sensitivity gas-ice maps of molecules more complex than methanol. Such comparative maps will be essential to constrain the chemical routes that regulate the chemical complexity in star-forming regions. Accepted by Astronomy and Astrophysics https://arxiv.org/pdf/2008.02827

ALMA chemical survey of disk-outflow sources in Taurus (ALMA-DOT) II: Vertical stratification of CO, CS, CN, H2CO, and CH3OH in a Class I disk L. Podio1, A. Garufi1, C. Codella1,2, D. Fedele1, E. Bianchi2, F. Bacciotti1, C. Ceccarelli2, C. Favre2, S. Mercimek1,4, K. Rygl3 and L. Testi5,6,1 1 INAF - Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy; 2 Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France; 3 INAF - Istituto di Radioastronomia & Italian ALMA Regional Centre, via P. Gobetti 101, 40129 Bologna, Italy; 4 Università degli Studi di Firenze, Dipartimento di Fisica e Astronomia, Via G. Sansone 1, 50019 Sesto Fiorentino, Italy; 5 European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany; 6 Excellence Cluster Origins, Boltzmannstrasse 2, 85748 Garching bei München, Germany E-mail contact: lpodio at arcetri.astro.it The chemical composition of planets is inherited from the one of protoplanetary disks at the time of their formation. Increasing observational evidence suggests that planet formation occurs in less than 1−2 Myr. This motivates the need for spatially resolved spectral observations of young Class I disks, as carried out by the ALMA-DOT campaign in Taurus. In the context of ALMA-DOT, we observe the edge-on disk around the Class I source IRAS 04302+2247 (the butterfly star) in the 1.3 mm continuum and five molecular lines. We report the first tentative detection of methanol (CH3OH) in a Class I disk and resolve for the first time the vertical structure of a disk with multiple molecular tracers. The bulk of the emission in the CO 2 − 1, CS 5 − 4, and o-H2CO 31,2 − 21,1 lines originates from the warm molecular

41 layer, with the line intensity peaking at increasing disk heights, z, for increasing radial distances, r. Molecular emission is vertically stratiﬁed, with CO observed at larger disk heights (aperture z/r ∼ 0.41 − 0.45) compared to both CS and H2CO, which are nearly co-spatial (z/r ∼ 0.21 − 0.28). In the outer midplane, the line emission decreases due to molecular freeze-out onto dust grains (freeze-out layer) by a factor of > 100 (CO) and 15 (CS). H2CO decreases by a factor of only about 2, possibly due to H2CO formation on icy grains, followed by non-thermal release into gas-phase. The inferred [CH3OH]/[H2CO] abundance ratio is 0.5 − 0.6, which is 1 − 2 orders of magnitude lower than for Class 0 hot-corinos, a factor ∼ 2.5 lower than the only other value inferred for a protoplanetary disk (in TW Hya, 1.3 − 1.7), and at the lower edge but still consistent with the values in comets. This may indicate that some chemical reprocessing occurs in disks before the formation of planets and comets. Accepted by Astronomy & Astrophysics Letters https://arxiv.org/pdf/2008.12648

Magnetospheric accretion in the intermediate-mass T Tauri star HQ Tau K. Pouilly1, J. Bouvier1, E. Alecian1, S. H. P. Alencar2, A. -M. Cody3, J. -F. Donati4, K. Grankin5, G. A. J. Hussain6, L. Rebull7 and C. P. Folsom4 1 Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France; 2 Dept de Fisica - ICEx - UFMG, Av. Antonio Carlos 6627, 30270-901 Belo Horizonte, MG, Brazil; 3 Bay Area Environmental Research Institute, 625 2nd St Ste. 209, Petaluma, CA 94952; 4 Univ. de Toulouse, CNRS, IRAP, 14 avenue Belin, 31400 Toulouse, France; 5 Crimean Astrophysical Observatory, Nauchny, Crimea 298409; 6 ESO, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany; 7 Infrared Science Archive, IPAC, California Institute of Technology, 1200 E. California Blvd, MS 100-22, Pasadena, CA91125 USA E-mail contact: kim.pouilly at univ-grenoble-alpes.fr Context: Classical T Tauri stars (cTTs) are pre-main sequence stars surrounded by an accretion disk. They host a strong magneticfield, and both magnetospheric accretion and ejection processes develop as the young magnetic star interacts with its disk. Studyingthis interaction is a major goal toward understanding the properties of young stars and their evolution. Aims: The goal of this study is to investigate the accretion process in the young stellar system HQ Tau, an intermediate- mass T Tauristar (1.9 M⊙). Methods: The time variability of the system is investigated both photometrically, using Kepler-K2 and complementary light curves,and from a high-resolution spectropolarimetric time series obtained with ESPaDOnS at CFHT. Results: The quasi-sinusoidal Kepler-K2 light curve exhibits a period of 2.424 d, which we ascribe to the rotational period of thestar. The radial velocity of the system shows the same periodicity, as expected from the modulation of the photospheric line profilesby surface spots. A similar period is found in the red wing of several emission lines (e.g., HI, CaII, NaI), due to the appearance ofinverse P Cygni components, indicative of accretion funnel flows. Signatures of outflows are also seen in the line profiles, some beingperiodic, others transient. The polarimetric analysis indicatesa complex, moderately strong magnetic field which is possibly sufficientto truncate the inner disk close to the corotation radius,rcor ∼ 3.5 R⋆. Additionally, we report HQ Tau to be a spectroscopic binarycandidate whose orbit remains to be determined. Conclusions: The results of this study expand upon those previously reported for low-mass T Tauri stars, as they indicate that themagnetospheric accretion process may still operate in intermediate-mass pre-main sequence stars, such as HQ Tau. Accepted by Astronomy & Astrophysics https://arxiv.org/pdf/2008.12531.pdf

Interpreting high spatial resolution line observations of planet-forming disks with gaps and rings - The case of HD 163296 Ch. Rab1,5, I. Kamp1, C. Dominik2, C. Ginski2,3, G. A. Muro-Arena2, W.-F. Thi5, L. B. F. M. Waters4,2 and P. Woitke6,7 1 Kapteyn Astronomical Institute, Univ. of Groningen, P.O. Box 800, 9700 AV Groningen, The Netherlands; 2 Anton Pannekoek Inst. for Astronomy, Univ. of Amsterdam, 1098 XH Amsterdam, The Netherlands; 3 Leiden

42 Observatory, Leiden Univ., 2300 RA Leiden, The Netherlands; 4 SRON Netherlands Institute for Space Research, 3584 CA Utrecht, The Netherlands; 5 Max-Planck-Institut für extraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching, Germany; 6 SUPA, School of Physics & Astronomy, Univ. of St. Andrews, North Haugh, St. Andrews KY16 9SS, UK; 7 Centre for Exoplanet Science, Univ. of St Andrews, North Haugh, St Andrews, KY169SS, UK E-mail contact: rab at mpe.mpg.de Spatially resolved continuum observations of planet-forming disks show prominent ring and gap structures in their dust distribution. However, the picture from gas observations is much less clear and constraints on the radial gas density structure (i.e. gas gaps) remain rare and uncertain. We want to investigate the importance of thermo- chemical processes for the interpretation of high-spatial-resolution gas observations of planet-forming disks and their impact on derived gas properties. We apply the radiation thermo-chemical disk code ProDiMo (PROtoplanetary DIsk MOdel) to model self-consistently the dust and gas disk of HD 163296, using the DSHARP (Disk Substructure at High Angular Resolution) gas and dust observations. With this model we investigate the impact of dust gaps and gas gaps, considering chemistry and heating/cooling processes, on the observables and the derived gas properties. We find distinct peaks in the radial line intensity profiles of the CO line data of HD 163296 at the location of the dust gaps. Our model indicates that those peaks are not only a consequence of a gas temperature increase within the gaps but are mainly caused by the absorption of line emission from the back side of the disk by the dust rings. For two of the three prominent dust gaps in HD 163296, we find that thermo-chemical effects are negligible for deriving density gradients via measurements of the rotation velocity. However, for the gap with the highest dust depletion, the temperature gradient can be dominant and needs to be considered to derive accurate gas density profiles. Self-consistent gas and dust thermo-chemical modelling in combination with high-quality observations of multiple molecules are necessary to accurately derive gas gap depths and shapes. This is crucial to determine the origin of gaps and rings in planet-forming disks and to improve the mass estimates of forming planets if they are the cause of the gap. Accepted by A&A https://arxiv.org/pdf/2008.05941

Illuminating a tadpole’s metamorphosis III: quantifying past and present environmental impact Megan Reiter1, Thomas J. Haworth2, Andres E. Guzman3, Pamela D. Klaassen1, Anna F. McLeod4,5 and Guido Garay6 1 UK Astronomy Technology Centre, Blackford Hill, Edinburgh, EH9 3HJ, UK; 2 Astronomy Unit, School of Physics and Astronomy, Queen Mary University of London, London E1 4NS, UK; 3 NAOJ, National Institutes of Natural Sciences, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan; 4 Dept of Astronomy, Univ. of California, Berkeley, CA 94720, USA; 5 Dept of Physics and Astronomy, Texas Tech University, Lubbock, TX 79409, USA; 6 Dept de Astronomia, Universidad de Chile, Camino el Observatorio 1515, Las Condes, Santiago, Chile E-mail contact: megan.reiter at stfc.ac.uk We combine MUSE and ALMA observations with theoretical models to evaluate how a tadpole-shaped globule located in the Carina Nebula has been influenced by its environment. This globule is now relatively small (radius ∼ 2500 au), hosts a protostellar jet+outflow (HH 900) and, with a blue-shifted velocity of ∼ 10 km s−1, is travelling faster than it should be if its kinematics were set by the turbulent velocity dispersion of the precursor cloud. Its outer layers are currently still subject to heating, but comparing the internal and external pressures implies that the globule is in a post-collapse phase. Intriguingly the outflow is bent, implying that the YSO responsible for launching it is comoving with the globule, which requires that the star formed after the globule was up to speed since otherwise it would have been left behind. We conclude that the most likely scenario is one in which the cloud was much larger before being subject to radiatively-driven implosion, which accelerated the globule to the high observed speeds under the photoevaporative rocket effect and triggered the formation of the star responsible for the outflow. The globule may now be in a quasi-steady state following collapse. Finally, the HH 900 YSO is likely > 1 M⊙ and may be the only star forming in the globule. It may be that this process of triggered star formation has prevented the globule from fragmenting to form multiple stars (e.g., due to heating) and has produced a single higher mass star. Accepted by MNRAS https://arxiv.org/pdf/2007.10341

43 AB Aur, a Rosetta stone for studies of planet formation (I): chemical study of a planet- forming disk P. Riviére-Marichalar1, A. Fuente1, R. Le Gal2, C. Baruteau3, R. Neri4 et al. 1 Observatorio Astronómico Nacional (OAN,IGN), Calle Alfonso XII, 3. 28014 Madrid, Spain; 2 Center for Astro- physics, Harvard & Smithsonian, 60 Garden St, Cambridge, MA 02138, USA; 3 CNRS / Institut de Recherche en Astrophysique et Planétologie, 14 avenue Edouard Belin, F-31400 Toulouse, France; 4 Institut de Radioastronomie Millimétrique, 300 rue de la Piscine, F-38406 Saint-Martin d’Héres, France E-mail contact: p.riviere at oan.es AB Aur is a Herbig Ae star that hosts a prototypical transition disk. The disk shows a plethora of features connected with planet formation mechanisms. Understanding the physical and chemical characteristics of these features is crucial to advancing our knowledge of planet formation. We aim to characterize the gaseous disk around the Herbig Ae star AB Aur. A complete spectroscopic study was performed using NOEMA to determine the physical and chemical 12 13 18 conditions. We present new observations of the continuum and CO, CO, C O, H2CO, and SO lines. We used the integrated intensity maps and stacked spectra to derive estimates of the disk temperature. By combining our 13CO and C18O observations, we computed the gas-to-dust ratio along the disk. We also derived column density maps for the different species and used them to compute abundance maps. The results of our observations were compared with Nautilus astrochemical models. We detected continuum emission in a ring that extends from 0′′. 6 to 2′′. 0, peaking at 0′′. 97 and with a strong azimuthal asymmetry. The molecules observed show different spatial distributions, and the peaks of the distributions are not correlated with the binding energy. Using H2CO and SO lines, we derived a mean disk temperature of 39 K. We derived a gas-to-dust ratio that ranges from 10 to 40. The comparison with Nautilus models favors a disk with a low gas-to-dust ratio (40) and prominent sulfur depletion. From a very complete spectroscopic study of the prototypical disk around AB Aur, we derived, for the first time, the gas temperature and the gas-to-dust ratio along the disk, providing information that is essential to constraining hydrodynamical simulations.Moreover, we explored the gas chemistry and, in particular, the sulfur depletion. The derived sulfur depletion is dependent on the assumed C/O ratio. Our data are better explained with C/O ∼ 0.7 and S/H = 8×10−8. Accepted by A&A http://arxiv.org/pdf/2008.00751

A dusty origin for the correlation between protoplanetary disc accretion rates and dust masses Andrew D. Sellek1, Richard A. Booth1 and Cathie J. Clarke1 1 Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK E-mail contact: ads79 at cam.ac.uk Recent observations have uncovered a correlation between the accretion rates (measured from the UV continuum excess) of protoplanetary discs and their masses inferred from observations of the sub-mm continuum. While viscous evolution models predict such a correlation, the predicted values are in tension with data obtained from the Lupus and Upper Scorpius star forming regions; for example, they underpredict the scatter in accretion rates, particularly in older regions. Here we argue that since the sub-mm observations trace the discs’ dust, by explicitly modelling the dust grain growth, evolution, and emission, we can better understand the correlation. We show that for turbulent viscosities with α ≤ 10−3, the depletion of dust from the disc due to radial drift means we can reproduce the range of masses and accretion rates seen in the Lupus and Upper Sco datasets. One consequence of this model is that the upper locus of accretion rates at a given dust mass does not evolve with the age of the region. Moreover, we ﬁnd that internal photoevaporation is necessary to produce the lowest accretion rates observed. In order to replicate the −9 −1 correct dust masses at the time of disc dispersal, we favour relatively low photoevaporation rates ≤ 10 M⊙ yr for most sources but cannot discriminate between EUV or X-ray driven winds. A limited number of sources, particularly in Lupus, are shown to have higher masses than predicted by our models which may be evidence for variations in the properties of the dust or dust trapping induced in substructures. Accepted by MNRAS https://arxiv.org/pdf/2008.07530

44 Reading between the lines: Disk emission, wind, and accretion during the ZCMa NW outburst A. Sicilia-Aguilar1, J. Bouvier2, C. Dougados2, K. Grankin3 and J.-F. Donati4 1 SUPA, School of Science and Engineering, University of Dundee, Nethergate, Dundee DD1 4HN, UK; 2 Université Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France; 3 Crimean Astrophysical Observatory, 298409 Nauchny, Crimea; 4 IRAP Observatoire Midi-Pyrénées, 14 Avenue E Belin, 31400 Toulouse, France E-mail contact: asiciliaaguilar at dundee.ac.uk Aims: We use optical spectroscopy to investigate the disk, wind, and accretion during the 2008 Z CMa NW outburst. Methods: The emission lines are used to constrain the locations, densities, and temperatures of the structures around the star. Results: Over 1000 optical emission lines reveal accretion, a variable, multi-component wind, and double-peaked lines of disk origin. The variable, non-axisymmetric, accretion-powered wind has slow (∼0 km s−1), intermediate (∼−100 km s−1) and fast (≥−400 km s−1) components. The fast components are of stellar origin and disappear in quiescence, while the slow component is less variable and could be related to a disk wind. The changes in the optical depth of the lines between outburst and quiescence are consistent with increased accretion being responsible for the observed −4 outburst. We derive an accretion rate of 10 M⊙/yr in outburst. The Fe I and weak Fe II lines arise from an irradiated, flared disk at ∼0.5-3 ×M∗/16M⊙ au with asymmetric upper layers, revealing that the energy from the accretion burst is deposited at scales below 0.5 au. Some line profiles have redshifted asymmetries, but the system is unlikely sustained by magnetospheric accretion, especially in outburst. The accretion-related structures extend over several stellar radii and, like the wind, are likely non-axisymmetric. The stellar mass may be ∼6-8 M⊙, lower than previously thought (∼16 M⊙). Conclusions: Emission line analysis is found to be a powerful tool to study the innermost regions and accretion in stars within a very large range of effective temperatures. The density ranges in the disk and accretion structures are higher than in late-type stars, but the overall behavior, including the innermost disk emission and variable wind, is very similar independently of the spectral type. Our work suggests a common outburst behavior for stars with spectral types ranging from M-type to intermediate-mass stars. Accepted by A&A https://arxiv.org/pdf/2008.13678

The history of dynamics and stellar feedback revealed by the HI filamentary structure in the disk of the Milky Way J. D. Soler1, H. Beuther1, J. Syed1, Y. Wang1, L. D. Anderson2, S. C. O. Glover3, P. Hennebelle4,M. Heyer5, Th. Henning1, A. F. Izquierdo6,7, R. S. Klessen2, H. Linz1, N. M. McClure-Griffiths8, J. Ott9, S. Ragan10, M. Rugel11, N. Schneider12, R. J. Smith6, M. C. Sormani3, J. M. Stil13, R. Treß3 and J. S. Urquhart14 1 MPIA, Königstuhl 17, 69117, Heidelberg, Germany.; 2 Dept of Physics and Astronomy, West Virginia University, Morgantown, WV 26506, USA; 3 Universität Heidelberg, Zentrum für Astronomie, Institut für Theoretische Astro- physik, 69120, Heidelberg, Germany; 4 Lab. AIM, Paris-Saclay, CEA/IRFU/SAp - CNRS - Univ Paris Diderot, 91191, Gif-sur-Yvette Cedex, France.; 5 Dept of Astronomy, Univ of Massachusetts, Amherst, MA 01003-9305, USA; 6 Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, Univ of Manchester, Manchester M13 9PL, UK; 7 ESO, Karl Schwarzschild str. 2, 85748, Garching bei München, Germany; 8 Research School of Astronomy and Astro- physics, The Australian National University, Canberra, ACT, Australia; 9 NRAO, PO Box O, 1003 Lopezville Road, Socorro, NM 87801, USA; 10 School of Physics and Astronomy, Cardiff University, Queen’s Buildings, The Parade, Cardiff, CF24 3AA, UK; 11 MPIfR, Auf dem Hügel 69, 53121 Bonn, Germany; 12 Univ zu Köln, I. Physikalisches Institut, Zülpicher Str. 77, 50937, Köln, Germany; 13 Dept of Physics and Astronomy, Univ of Calgary, Calgary, AB T2N 1N4, Canada; 14 Centre for Astrophysics and Planetary Science, Univ of Kent, Canterbury CT2 7NH, UK E-mail contact: soler at mpia.de We present a study of the filamentary structure in the emission from the neutral atomic hydrogen (HI) at 21 cm across velocity channels in the 40” and 1.5-km/s resolution position-position-velocity cube resulting from the combination of the single-dish and interferometric observations in The HI/OH/Recombination (THOR) line survey. Using the Hessian

45 matrix method in combination with tools from circular statistics, we find that the majority of the filamentary structures in the HI emission are aligned with the Galactic plane. Part of this trend can be assigned to long filamentary structures that are coherent across several velocity channels. However, we also find ranges of Galactic longitude and radial velocity where the HI filamentary structures are preferentially oriented perpendicular to the Galactic plane. These are located ◦ ◦ (i) around the tangent point of the Scutum spiral arm, l ≈ 28 and vLSR ≈ 100 km/s, (ii) toward l ≈ 45 and vLSR ≈ 50 km/s, (iii) around the Riegel-Crutcher cloud, and (iv) toward the terminal velocities. Comparison with numerical simulations indicates that the prevalence of horizontal filamentary structures is most likely the result of the large-scale dynamics and that vertical structures identified in (i) and (ii) may arise from the combined effect of supernova (SN) feedback and strong magnetic fields. The vertical filamentary structures in (iv) can be related to the presence of clouds from extra-planar HI gas falling back into the Galactic plane after being expelled by SNe. Our results indicate that a systematic characterization of the emission morphology toward the Galactic plane provides an unexplored link between the observations and the dynamical behaviour of the interstellar medium, from the effect of large-scale Galactic dynamics to the Galactic fountains driven by SNe. Accepted by Astronomy & Astrophysics https://arxiv.org/pdf/2007.07285

Low Level Carbon Monoxide Line Polarization in two Protoplanetary Disks: HD 142527 and IM Lup Ian W. Stephens1, Manuel Fernández-López2, Zhi-Yun Li3, Leslie W. Looney4 and Richard Teague1 1 Center for Astrophysics | Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA; 2 Instituto Ar- gentino de Radioastronomía (CCT-La Plata, CONICET; CICPBA), C.C. No. 5, 1894, Villa Elisa, Buenos Aires, Argentina; 3 Astronomy Department, University of Virginia, Charlottesville, VA 22904, USA; 4 Department of As- tronomy, University of Illinois, 1002 West Green Street, Urbana, IL 61801, USA E-mail contact: ian.stephens at cfa.harvard.edu Magnetic fields are expected to play an important role in accretion processes for circumstellar disks. Measuring the magnetic field morphology is difficult, especially since polarimetric (sub)millimeter continuum observations may not trace fields in most disks. The Goldreich-Kylafis (GK) effect suggests that line polarization is perpendicular or parallel to the magnetic field direction. We attempt to observe CO(2–1), 13CO(2–1), and C18O(2–1) line polarization toward HD 142527 and IM Lup, which are large, bright protoplanetary disks. We use spatial averaging and spectral integration to search for signals in both disks, and detect a potential CO(2–1) Stokes Q signal toward both disks. The total CO(2–1) polarization fractions are 1.57±0.18% and 1.01±0.10% for HD 142527 and IM Lup, respectively. Our Monte Carlo simulations indicate that these signals are marginal. We also stack Stokes parameters based on the Keplerian rotation, but no signal was found. Across the disk traced by dust of HD 142527, the 3σ upper limits for ′′ 13 18 Pfrac at 0. 5 (∼80 au) resolution are typically less than 3% for CO(2–1) and CO(2–1) and 4% for C O(2–1). For IM Lup, the 3σ upper limits for these three lines are typically less than 3%, 4%, and 12%, respectively. Upper limits based on our stacking technique are up to a factor of ∼10 lower, though stacking areas can potentially average out small-scale polarization structure. We also compare our continuum polarization at 1.3 mm to observations at 870 µm from previous studies. The polarization in the northern dust trap of HD 142527 shows a significant change in morphology and an increase in Pfrac as compared to 870 µm. For IM Lup, the 1.3 mm polarization may be more azimuthal and has a higher Pfrac than at 870 µm. Accepted by ApJ http://arxiv.org/pdf/2008.04952

Atomic and molecular gas properties during cloud formation J. Syed1, Y. Wang1, H. Beuther1, J. D. Soler1, M. R. Rugel2, J. Ott3, A. Brunthaler2, J. Kerp4,M. Heyer5, R. S. Klessen6,7, Th. Henning1, S. C. O. Glover6, P. F. Goldsmith8, H. Linz1, J. S. Urquhart9, S. E. Ragan10, K. G. Johnston11 and F. Bigiel4 1 Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany; 2 Max-Planck-Institut für Ra- dioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany; 3 National Radio Astronomy Observatory, PO Box O, 1003 Lopezville Road, Socorro, NM 87801, USA; 4 Argelander-Institut für Astronomie, Auf dem Hügel 71, 53121

46 Bonn, Germany; 5 Department of Astronomy, University of Massachusetts, Amherst, MA01003, USA; 6 Universität Heidelberg, Zentrum für Astronomie, Institut für Theoretische Astrophysik, Albert-Ueberle-Str. 2, 69120 Heidelberg, Germany; 7 Universität Heidelberg, Interdisziplinäres Zentrum für Wissenschaftliches Rechnen, INF 205, 69120 Hei- delberg, Germany; 8 Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA; 9 Centre for Astrophysics and Planetary Science, University of Kent, Canterbury CT2 7NH, UK; 10 School of Physics and Astronomy, Cardiff University, Queen’s Buildings, The Parade, Cardiff CF24 3AA, UK; 11 School of Physics and Astronomy, E.C. Stoner Building, The University of Leeds, Leeds LS2 9JT, UK E-mail contact: syed at mpia.de Molecular clouds, which harbor the birthplaces of stars, form out of the atomic phase of the interstellar medium (ISM). To understand this transition process, it is crucial to investigate the spatial and kinematic relationships between atomic and molecular gas. We aim to characterize the atomic and molecular phases of the ISM and set their physical properties into the context of cloud formation processes. We studied the cold neutral medium (CNM) by means of HI self-absorption (HISA) toward the giant molecular filament GMF20.0-17.9 (distance=3.5kpc, length ∼170 pc) and compared our results with molecular gas traced by 13CO emission. We fitted baselines of HISA features to HI emission spectra using first and second order polynomial functions. The CNM identified by this method spatially correlates with the morphology of the molecular gas toward the western region. However, no spatial correlation between HISA and 13CO is evident toward the eastern part of the filament. The distribution of HISA peak velocities and line widths agrees well with 13CO within the whole filament. The column densities of the CNM probed by HISA are on the order of 1020 cm−2 while those of molecular hydrogen traced by 13CO are an order of magnitude higher. The column density probability density functions (N-PDFs) of HISA (CNM) and HI emission (tracing both the CNM and the warm neutral medium, WNM) have a log-normal shape for all parts of the filament, indicative of turbulent motions as the main driver for these structures. The H2 N-PDFs show a broad log-normal distribution with a power-law tail −2 suggesting the onset of gravitational contraction. The saturation of HI column density is observed at ∼25 M⊙ pc . We conjecture that different evolutionary stages are evident within the filament. In the eastern region, we witness the onset of molecular cloud formation out of the atomic gas reservoir while the western part is more evolved, as it reveals pronounced H2 column density peaks and signs of active star formation. Accepted by A&A http://arxiv.org/pdf/2008.13502

Salt, Hot Water, and Silicon Compounds Tracing Massive Twin Disks Kei E. I. Tanaka1,2, Yichen Zhang3, Tomoya Hirota1,4, Nami Sakai3, Kazuhito Motogi5, Kengo Tomida6, Jonathan C. Tan7,8, Viviana Rosero9, Aya E. Higuchi1, Satoshi Ohashi3, Mengyao Liu8 and Koichiro Sugiyama10,1 1 National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588, Japan; 2 Department of Earth and Space Science, Osaka University, Toyonaka, Osaka 560-0043, Japan; 3 Star and Planet Formation Laboratory, RIKEN Cluster for Pioneering Research, Wako, Saitama 351-0198, Japan; 4 Department of Astronomical Sciences, SOKENDAI (The Graduate University for Advanced Studies), Mitaka, Tokyo 181-8588, Japan; 5 Graduate School of Sciences and Technology for Innovation, Yamaguchi University, Yamaguchi 753-8512, Japan; 6 Astronomical Institute, Tohoku University, Sendai 980-8578, Japan; 7 Department of Space, Earth & Environment, Chalmers University of Technology, SE-412 96 Gothenburg, Sweden; 8 Department of Astronomy, University of Virginia, Charlottesville, VA 22904- 4325, USA; 9 National Radio Astronomy Observatory, 1003 Lopezville Rd., Socorro, NM 87801, USA; 10 National Astronomical Research Institute of Thailand, 260 Moo 4, T. Donkaew, A. Maerim, Chiang Mai 50180, Thailand E-mail contact: kei.tanaka at nao.ac.jp We report results of 0.05′′-resolution observations toward the O-type proto-binary system IRAS 16547–4247 with the Atacama Large Millimeter/submillimeter Array (ALMA). We present dynamical and chemical structures of the circumbinary disk, circumstellar disks, outﬂows and jets, illustrated by multi-wavelength continuum and various molecular lines. In particular, we detect sodium chloride, silicon compounds, and vibrationally-excited water lines as probes of the individual protostellar disks at a scale of 100 au. These are complementary to typical hot-core molecules tracing the circumbinary structures on a 1000-au scale. The H2O line tracing inner-disks has an upper-state energy of Eu/k > 3000 K, indicating a high temperature of the disks. On the other hand, despite the detected transitions of NaCl, SiO, and SiS not necessarily having high upper-state energies, they are enhanced only in the vicinity of the

47 protostars. We interpret that these molecules are the products of dust destruction, which only happens in the inner disks. This is the second detection of alkali metal halide in protostellar systems after the case of the disk of Orion Source I, and also one of few massive protostellar disks associated with high-energy transition water and silicon compounds. These new results suggest these “hot-disk" lines may be common in innermost disks around massive protostars, and have great potential for future research of massive star formation. We also tentatively ﬁnd that the twin disks are counter-rotating, which might give a hint of the origin of the massive proto-binary system IRAS 16547–4247. Accepted by ApJ Letters https://arxiv.org/pdf/2007.02962.pdf

Secular Gravitational Instability of Drifting Dust in Protoplanetary Disks: Formation of Dusty Rings without Significant Gas Substructures Ryosuke T. Tominaga1, Sanemichi Z. Takahashi2 and Shu-ichiro Inutsuka1 1 Department of Physics, Nagoya University, Nagoya, Aichi 464-8692, Japan; 2 National Astronomical Observatory of Japan, Osawa, Mitaka, Tokyo 181-8588, Japan E-mail contact: tominaga.ryosuke at a.mbox.nagoya-u.ac.jp Secular gravitational instability (GI) is one of the promising mechanisms for creating annular substructures and planetesimals in protoplanetary disks. We perform numerical simulations of the secular GI in a radially extended disk with inward drifting dust grains. The results show that, even in the presence of the dust diffusion, the dust rings form via the secular GI while the dust grains are moving inward, and the dust surface density increases by a factor of ten. Once the secular GI develops into a nonlinear regime, the total mass of the resultant rings can be a significant fraction of the dust disk mass. In this way, a large amount of drifting dust grains can be collected in the dusty rings and stored for planetesimal formation. In contrast to the emergence of remarkable dust substructures, the secular GI does not create significant gas substructures. This result indicates that observations of a gas density profile near the disk midplane enable us to distinguish the mechanisms for creating the annular substructures in the observed disks. The resultant rings start decaying once they enter the inner region stable to the secular GI. Since the ring-gap contrast smoothly decreases, it seems possible that the rings are observed even in the stable region. We also discuss the likely outcome of the non-linear growth and indicate the possibility that a significantly developed region of the secular GI may appear as a gap-like substructure in dust continuum emission since dust growth into larger solid bodies and planetesimal formation reduce the total emissivity. Accepted by ApJ http://arxiv.org/pdf/2008.02564

Temperature structures of embedded disks: young disks in Taurus are warm Merel L.R. van ’t Hoff1,2, Daniel Harsono3, John J. Tobin4, Arthur D. Bosman1,2, Ewine F. van Dishoeck1,5, Jes K. Jørgensen6, Anna Miotello7, Nadia M. Murillo1,8 and Catherine Walsh9 1 Leiden Observatory, Leiden University, P.O. box 9513, 2300 RA Leiden, The Netherlands; 2 Department of As- tronomy, University of Michigan, 1085 S University Ave, Ann Arbor, MI 48109, USA; 3 Institute of Astronomy and Astrophysics, Academia Sinica, No. 1, Sec. 4, Roosevelt Road, Taipei 10617, Taiwan, R. O. C.; 4 National Radio Astronomy Observatory, 520 Edgemont Rd., Charlottesville, VA 22903, USA; 5 Max-Planck-Institut für Extrater- restrische Physik, Giessenbachstrasse 1, D-85748 Garching bei München, Germany; 6 Niels Bohr Institute, University of Copenhagen, Øster Voldgade 5-7, DK-1350 Copenhagen K., Denmark; 7 European Southern Observatory, Karl- Schwarzschild-Str. 2, D-85748 Garching bei München, Germany; 8 The Institute of Physical and Chemical Research (RIKEN), 2-1, Hirosawa, Wako-shi, Saitama 351-0198, Japan; 9 School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK E-mail contact: mervth at umich.edu The chemical composition of gas and ice in disks around young stars set the bulk composition of planets. In contrast to protoplanetary disks (Class II), young disks that are still embedded in their natal envelope (Class 0 and I) are predicted to be too warm for CO to freeze out, as has been confirmed observationally for L1527 IRS. To establish whether young disks are generally warmer than their more evolved counterparts, we observed five young (Class 0/I

48 and Class I) disks in Taurus with the Atacama Large Millimeter/submillimeter Array (ALMA), targeting C17O 2 − 1, ′′ ′′ H2CO 31,2 −21,1, HDO 31,2 −22,1 and CH3OH 5K −4K transitions at 0.48 ×0.31 resolution. The diﬀerent freeze-out 17 temperatures of these species allow us to derive a global temperature structure. C O and H2CO are detected in all −4 disks, with no signs of CO freeze-out in the inner ∼100 au, and a CO abundance close to ∼10 . H2CO emission originates in the surface layers of the two edge-on disks, as witnessed by the especially beautiful V-shaped emission pattern in IRAS 04302+2247. HDO and CH3OH are not detected, with column density upper limits more than 100 times lower than for hot cores. Young disks are thus found to be warmer than more evolved protoplanetary disks around solar analogues, with no CO freeze-out (or only in the outermost part of ∼>100 au disks) or CO processing. However, they are not as warm as hot cores or disks around outbursting sources, and therefore do not have a large gas-phase reservoir of complex molecules. Accepted by Astrophysical Journal https://arxiv.org/pdf/2008.08106.pdf

Observations of edge-on protoplanetary disks with ALMA. I. Results from continuum data M. Villenave1,2, F. Ménard1, W. R. F. Dent3, G. Duchêne4,1, K. R. Stapelfeldt5, M. Benisty6,1, Y. Boehler1, G. van der Plas1, C. Pinte7,1, Z. Telkamp4, S. Wolff8, C. Flores9, G. Lesur1, F. Louvet10, A. Riols1, C. Dougados1, H. Williams11,4 and D. Padgett5 1 Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France.; 2 European Southern Observatory, Alonso de Cordova 3107, Vitacura, Casilla 19001, Santiago 19, Chile; 3 Joint ALMA Observatory, Alonso de Cordova 3107, Vitacura 763- 0355, Santiago, Chile; 4 Astronomy Department, University of California, Berkeley, CA 94720, USA; 5 Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA; 6 Unidad Mixta Internacional Franco-Chilena de Astronomia (CNRS, UMI 3386), Departamento de Astronomia, Universidad de Chile, Camino El Observatorio 1515, Las Condes, Santiago, Chile; 7 Monash Centre for Astrophysics (MoCA) and School of Physics and Astronomy, Monash University, Clayton Vic 3800, Australia; 8 Leiden Observatory, Leiden University, 2300 RA Leiden, The Netherlands; 9 Institute for Astronomy, University of Hawaii, 640 N. Aohoku Place, Hilo, HI 96720, USA; 10 AIM Paris-Saclay Departement d’Astrophysique, CEA, CNRS, Univ. Paris Diderot, CEA-Saclay, F-91191 Gif-sur- Yvette Cedex, France; 11 School of Physics and Astronomy, University of Minnesota, 116 Church Street SE, Minneapolis, MN 55455 USA E-mail contact: marion.villenave at univ-grenoble-alpes.fr Aims. We aim to study vertical settling and radial drift of dust in protoplanetary disks from a different perspective: an edge-on view. An estimation of the amplitude of settling and drift is highly relevant to understanding planet formation. Methods. We analyze a sample of 12 HST-selected edge-on protoplanetary disks (i.e., seen with high inclinations) for which the vertical extent of the emission layers can be constrained directly. We present ALMA high angular resolution continuum images (∼0.1 arcsec) of these disks at two wavelengths, 0.89 mm and 2.06 mm (respectively ALMA bands 7 and 4), supplemented with archival band 6 data (1.33 mm) where available. Results. Several sources show constant brightness profiles along their major axis with a steep drop at the outer edges. Two disks have central holes with additional compact continuum emission at the location of the central star. For most sources, the millimeter continuum emission is more compact than the scattered light, both in the vertical and radial directions. Six sources are resolved along their minor axis in at least one millimeter band, providing direct information on the vertical distribution of the millimeter grains. For the second largest disk of the sample, Tau042021, the significant difference in vertical extent between band 7 and band 4 suggests efficient size-selective vertical settling of large grains. Furthermore, the only Class I object in our sample shows evidence of flaring in the millimeter. Along the major axis, all disks are well resolved. Four of them are larger in band 7 than in band 4 in the radial direction, and three have a similar radial extent in all bands. These three disks are also the ones with the sharpest apparent edges (between 80% and 20% of the peak flux, ∆r/r ∼ 0.3), and two of them are binaries. For all disks, we also derive the millimeter brightness temperature and spectral index maps. We find that all edge-on disks in our sample are likely optically thick and that the dust emission reveals low brightness temperatures in most cases (brightness temperatures ≤ 10 K). The integrated spectral indices are similar to those of disks at lower inclination. Conclusions. The comparison of a generic radiative transfer disk model with our data shows that at least three disks

49 are consistent with a small millimeter dust scale height, of a fewau (measured at r=100au). This is in contrast with the more classical value of hg ∼10 au derived from scattered light images and from gas line measurements. These results conﬁrm, by direct observations, that large (millimeter) grains are subject to signiﬁcant vertical settling in protoplanetary disks. Accepted by Astronomy and Astrophysics https://arxiv.org/pdf/2008.06518.pdf

The effect of luminosity outbursts on the protoplanetary disk dynamics Eduard Vorobyov1,2, Vardan Elbakyan2, Michihiro Takami3 and Hauyu Baobab Liu3 1 Department of Astrophysics, University of Vienna, Vienna, Austria; 2 Research Institute of Physics, Southern Federal University, Rostov-on-Don, 344090 Russia; 3 Institute of Astronomy and Astrophysics, Academia Sinica, 11F of Astronomy-Mathematics Building, AS/NTU No.1, Sec. 4, Roosevelt Rd, Taipei 10617, Taiwan, R.O.C. E-mail contact: eduard.vorobiev at univie.ac.at Response of a protoplanetary disk to luminosity bursts of various duration is studied with the purpose to determine the effect of the bursts on the strength and sustainability of gravitational instability in the disk. A special emphasis is paid to the spatial distribution of gas and grown dust (from 1 mm to a few cm) during and after the burst. Numerical hydrodynamics simulations using the FEOSAD code were employed to study the dynamics of gas and dust in the thin-disk limit. Dust-to-gas friction including back reaction and dust growth were also considered. Bursts of various duration (from 100 to 500 yr) were initiated in accordance with a thermally ignited magnetorotational instability. Luminosity curves for constant- and declining-magnitude bursts were adopted to represent two typical limiting cases for FU-Orionis-type eruptions. The short-term effect of the burst is to reduce the strength of gravitational instability by heating and expanding the disk. The longest bursts with duration comparable to the revolution period of the spiral can completely dissolve the original two-armed spiral pattern in the gas disk by the end of the burst, while the shortest bursts only weaken the spiral pattern. The reaction of grown dust to the burst is somewhat different. The spiral-like initial distribution with deep cavities in the inter-armed regions transforms into a ring-like distribution with deep gaps. This transformation is most expressed for the longest-duration bursts. The long-term effect of the burst depends on the initial disk conditions at the onset of the burst. In some cases, vigorous disk fragmentation sets in several thousand years after the burst, which was absent in the model without the burst. Several clumps with masses in the giant-planet mass range form in the outer disk regions. After the disk fragmentation phase, the spatial distribution of grown dust is characterized by multiple sharp rings located from tens to hundreds of astronomical units. The arrangement and sharpness of the rings depends on the strength of dust turbulent diffusion. The wide-orbit rings are likely formed as the result of dust-rich clump dispersal in the preceding gravitationally unstable phase. Luminosity bursts similar in magnitude to FU-Orionis-type eruptions can have a profound effect on the dynamics of gas and dust in protoplanetary disks if the burst duration is comparable to or longer than the dynamical timescales. In this context, the spatial morphology of the gas-dust disk of V883 Ori, a FUor-like object that is thought to be in the outburst phase for more than a century with the unknown onset date, may be used as test case for the burst models considered here. A potential relation of the obtained ring structures to a variety of gaps and rings observed in T Tauri disks remains to be established. Accepted by Astronomy & Astrophysics http://arxiv.org/pdf/2009.01888

High-resolution survey for planetary companions to young stars in the Taurus Molecular Cloud A.L. Wallace1, J. Kammerer1,2, M.J. Ireland1, C. Federrath1, A.L. Kraus3 et al. 1 Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2611, Australia; 2 European Southern Observatory, Karl-Schwarzschild-Str 2, 85748, Garching, Germany; 3 Department of Astronomy, University of Texas, Austin, TX 78712, United States of America E-mail contact: alexander.wallace at anu.edu.au

50 Direct imaging in the infrared at the diffraction limit of large telescopes is a unique probe of the properties of young planetary systems. We survey 55 single class I and class II stars in Taurus in the L′ filter using natural and laser guide star adaptive optics and the near-infrared camera (NIRC2) of the Keck II telescope, in order to search for planetary mass companions. We use both reference star differential imaging and kernel phase techniques, achieving typical 5σ contrasts of ∼6 magnitudes at separations of 0′′. 2 and ∼8 magnitudes beyond 0′′. 5. Although we do not detect any new faint companions, we constrain the frequency of wide separation massive planets, such as HR 8799 analogues. We find that, assuming hot-start models and a planet distribution with power-law mass and semi-major axis indices of −0.5 and −1, respectively, less than 20% of our target stars host planets with masses >2 MJ at separations >10 AU. Accepted by MNRAS http://arxiv.org/pdf/2008.06065

Abstracts of recently accepted major reviews

Magnetohydrodynamics of protoplanetary discs Geoffroy R.J. Lesur1 1 Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France E-mail contact: geoffroy.lesur at univ-grenoble-alpes.fr Protoplanetary discs are made of gas and dust orbiting a young star. They are also the birth place of planetary systems, which motivates a large amount of observational and theoretical research. In these lecture notes, I present a review of the magnetic mechanisms applied to the outer regions R> 1 AU of these discs, which are the planet-formation regions. In contrast to usual astrophysical plasmas, the gas in these regions is noticeably cold (T < 300 K) and dense, which implies a very low ionisation fraction close to the disc midplane. In these notes, I deliberately ignore the innermost R 0.1 AU region which is influenced by the star-disk interaction and various radiative effects. I start by presenting a short overview of the observational evidence for the dynamics of these objects. I then introduce the methods and approximations used to model these plasmas, including non-ideal MHD, and the uncertainties associated with this approach. In this framework, I explain how the global dynamics of these discs is modelled, and I present a stability analysis of this plasma in the local approximation, introducing the non-ideal magneto-rotational instability. Following this mostly analytical part, I discuss numerical models which have been used to describe the saturation mechanisms of this instability, and the formation of large-scale structures by various saturation mechanisms. Finally, I show that local numerical models are insufficient since magnetised winds are also emitted from the surface of these objects. After a short introduction on winds physics, I present global models of protoplanetary discs, including both a large-scale wind and the non-ideal dynamics of the disc. Accepted by the lecture notes series of the Journal of Plasma Physics http://arxiv.org/pdf/2007.15967

51 Dissertation Abstracts

A closer look at protoplanetary discs: the inner few au probed with spectroscopy and optical interferometry

Maria Kalliopi Koutoulaki

Thesis work conducted at: Dublin Institute for Advanced Studies & University College Dublin, Ireland Address as of 1 October 2020: European Southern Observatory, 85748 Garching bei München, Germany Electronic mail: [email protected] Ph.D dissertation directed by: Dr. Rebeca Garcia-Lopez, Prof. Antonella Natta, Dr. Deirdre Coﬀey and Prof. Tom Ray Ph.D degree awarded: June 2020

A first step towards understanding planetary formation is the characterisation of the structure and evolution of protoplanetary discs. Although the large scale disc is understood in some detail, much less is known about the inner 5 au in which the main physical processes take place: accretion, ejection, and planetary formation. Even in the nearest sites of star formation, this region cannot be spatially resolved by stand-alone telescopes; only in recent years have optical and infrared interferometers been able to achieve this, and only in the case of the brightest sources. Hydrogen recombination lines are present in the spectra of young stars. In particular, the Brackett-γ line is the brightest line in the K-band. HD 50138 is a target that exhibits bright Brackett-γ and faint high-n Pfund (from level n=24 to n=19) emission. Our results show that the circumstellar environment of the target is complex and shows asymmetries in both the Brackett-γ and the continuum emitting regions. The Brackett-γ is more compact than the continuum emitting region and originates from a wind with a wide opening angle. The origin of the Brackett-γ line is still controversial, and it has been found to be associated with both accretion and ejection processes. Thus, more tracers are needed to better constrain the inner gaseous disc properties. Molecules are also present in this part of the disc. In particular, the CO overtone emission at 2.3 mµ is a good tracer of the inner disc properties. This emission is not common and in the case of T Tauri stars it has been observed in only three sources. RWAur A is a CTTS that exhibits irregular dimming events. It shows CO overtone emission in both the bright and dim states. Modelling this emission with an LTE CO ring in Keplerian rotation, we find that the CO conditions do not change during the dimming events. Moreover, no significant accretion variation is detected between the two states, leading to the conclusion that the dimmings are caused by occulting material very close to the star (within 1 au). The CO ro-vibrational emission at 2.3 mµ observed with the second generation interferometer VLTI/GRAVITY opens a new window on constraining the physical properties of the inner gaseous disc, by spatially resolving the CO emission. 51 Oph is a target which shows bright CO overtone emission. By modelling the CO emission, the CO is found to emitt very close to the star from a warm and dense gas. This is the first observational evidence of the physical properties so close to the star (∼0.1 au) where there is no dust. This is consistent with previous LTE models of the physical conditions in the dust-free disc.

52 The Dynamics of Star Cluster Formation

Juan Pablo Farias

Chalmers University of Technology, Department of Space, Earth and Environment, SE-412 96, Gothenburg, Sweden Electronic mail: juanfariaso at gmail.com Ph.D dissertation directed by: Prof. Dr. Jonathan C. Tan Ph.D degree awarded: August 2020

How do star clusters form? We care, since these are the birth sites of most stars, perhaps including our own Sun. There are a great variety of different theoretical models of cluster formation and our main goal in this thesis is to examine the implications of these for the dynamical evolution of a cluster’s stellar population, including the ejected stars. In contrast to the majority of previous cluster formation studies, the focus of this work is on detailed modeling, using the Nbody6 code, of stellar dynamics, including binaries, with the structure, kinematics and star formation of the natal gas cloud explored with simple analytic prescriptions. In particular, we adopt the Turbulent Clump Model of pressure-truncated singular polytropic spheres, which sets global and local initial conditions of the newly formed stars. In a first paper, exploring a fiducial 3,000 solar mass clump, we investigated the effects of overall clump density, global star formation efficiency, degree of primordial mass segregation, degree of primordial binarity and binary population properties on the dynamical evolution of the cluster. Here, like most previous works, we assumed stars are formed very quickly, i.e., approximated as instantaneously, compared to the free-fall time of the clump. In our next work, after implementing a major code development to Nbody6 that allows modeling of gradual formation of stars, we investigated how the timescale of cluster formation, parameterized via the star formation efficiency per free-fall time, ǫff , affects its early dynamical evolution. This is the first time that such a study, including a realistic binary population, has been carried out. We showed that star clusters that form rapidly, e.g., with ǫff = 1, expand more quickly after they emerge from the gas, while slowly-formed clusters, e.g., with ǫff < 0.03, evolve into a much more stable configuration during the gas rich phase. We also showed how the stellar population is affected by the timescale of formation, including the frequency of runaway/walkaway stars, stellar age gradients and primordial binary processing. We have then carried out preliminary explorations of a broad range of star-forming clump parameters, i.e., with masses from 300 to 30,000 solar masses and background cloud mass surface densities from 0.1 to 1 g cm−2. For the largest clusters simulated, we make use of a GPU-enabled version of the code. Further improvements to the modeling that have been implemented include global elongation of the clump so that nonspherical, including very filamentary, initial conditions can be studied. Models with internal spatial and kinematic substructure for the birth locations of the stars, based on hydrodynamic simulations of supersonic turbulence, have also been studied. In parallel, we have also carried out two projects that focus on observed systems related to dynamical ejections within the Orion Nebula Cluster (ONC). First, we examined a particular set of runaway stars associated with the Orion KL massive star forming region and carried out a systematic exploration of N-body simulations to understand the properties of the dynamical ejection that produced them. Second, we have performed a census of runaway stars from the ONC using Gaia data, estimating the total unbound population from the cluster. We have compared these results with our cluster formation simulations leading to new constraints on the star formation rate and dynamical age of the system. https://research.chalmers.se/en/publication/518158

53 From parsec to au scales: zooming-in on the formation of high-mass young stellar objects

Rubén Fedriani

Thesis work conducted at: Dublin Institute for Advanced Studies and University College Dublin, Ireland Current address: Chalmers University of Technology, Gothenburg, Sweden Electronic mail: [email protected] Ph.D dissertation directed by: Alessio Caratti o Garatti, Deirdre Coﬀey, and Tom Ray Ph.D degree awarded: June 2020

In this thesis, I investigate the formation of high-mass young stellar objects (HMYSOs) and the properties of their protostellar jets.

My ﬁrst science chapter is a study of the kinematic and dynamic properties of the 20 M⊙ HMYSO IRAS 13481-6124 −4 −1 −2 −1 −1 (Fedriani et al. 2018). I measured mass-loss and momentum rates on the order of 10 M⊙ yr and 10 M⊙ yr kms , respectively. I used HI emission lines to perform spectro-astrometry to probe the massive protostellar jet at au-scales and connect it with the parsec-scale jet.

In the second science chapter, I study the unique case of G35.2-0.74N, a 10 M⊙ HMYSO Fedriani et al. 2019. I observe, spatially coincident atomic near-infrared (NIR) and ionised radio jet emission. For the ﬁrst time, the ionisation fraction from a jet driven by a massive protostar has been measured. The value obtained (∼ 10%) is similar to that found in jets driven by low-mass protostars. This suggests a common launching mechanism, i. e., the jet is launched −5 −1 magneto-centrifugally. It was possible to measure mass-loss and momentum rates on the order of 10 M⊙ yr and −2 −1 −1 10 M⊙ yr kms , respectively, without relying on assumptions on the ionisation fraction. This study also conﬁrms that the ionisation mechanism is related to shocks instead of UV radiation from the central source. The new method used in this paper, which combines NIR and radio measurements, opens up a new way to measure ionisation fraction of jets for both the low- and high-mass regime.

Lastly, the jet and the accretion disc of the driving source of the Herbig-Haro object 135/136, IRAS 11101-5829, was investigated in the third science chapter (Fedriani et al. 2020). I found disc emission, for the first time, in this object revealed by the NIR CO overtone bandhead emission at 2.29 − 2.5 µm. By using our own developed LTE model, I 22 −2 infer that the emission is consistent with a relatively warm (T ∼ 3000 K) and dense (NCO ∼ 10 cm ) disc. Notably, the model also suggests a geometry different from that inferred in the jet, retrieved from both spectral emission lines and imaging. This implies that the disc emission is reflected off the outflow cavity walls. This approach has been used for the first time in this thesis and indicates that to obtain the correct geometry of the system, one needs both high spectral and spatial resolution to avoid retrieving possible erroneous results. The results presented in this thesis show further observational evidence that the formation of high-mass protostars and their jets are a scaled-up version of their low-mass counterparts and that their properties scale with mass. In light of these results, we are then one step closer to confirm that star formation proceeds in a similar fashion independently of mass.

54 Searching for gas in debris disks Daniela Iglesias

Instituto de Fisica y Astronomia, Facultad de Ciencias, Universidad de Valparaiso, Valparaiso, Chile Electronic mail: dpiglesi at uc.cl Ph.D dissertation directed by: Amelia Bayo – Ph.D degree awarded: April 2020 A debris disk is commonly described as a second generation circumstellar disk composed of dust grains, planetesimals and possibly already formed giant planets. It was long thought that debris disks were systems fully depleted of gas, but in the last few years the presence of gas has been detected in a increasing number of them. The nature of this gas is still under debate; it may be residual gas (leftover from earlier stages of the disk) or second generation gas (generated by the sublimation of exocomets or collisions of icy bodies), however, both possibilities would have great implications in the process of planet formation and evolution. An efficient way to search for this gas in debris disks is monitoring gas tracers using multi-epoch high-resolution UV-optical spectroscopy. A detection of gas in the line of sight of the star shows up as a very narrow absorption feature superposed to the photospheric absorption of lines such as Ca ii or Na i, which are very sensitive gas tracers. This Thesis is devoted to the search for gas via high-resolution spectroscopy in a sample of 301 debris disks with the purpose of estimating the frequency of gas in debris disks. We collected high-resolution UV-optical spectroscopic data from our own observations and the ESO archive for 273 objects, completing 91% of our sample. We analysed the multi-epoch spectra of each object searching for variable and stable non-photospheric absorption features of circumstellar origin. Firstly, we performed a detailed analysis of a sub-sample of 27 objects having multiple stable absorption features with the aim of determining whether their features were of circumstellar or interstellar origin. In this group we found two objects; c Aql and HR 4796, with variable absorption features attributable to the presence of star-grazing exocomets, and one object; HD110058 with a stable circumstellar gas absorption. We concluded from these preliminary results that the presence of gas in debris disks might be a common phenomenon. Secondly, we studied the presence of unusually large non-photospheric absorption features found in several ionized lines of the object HD 37306, that lasted for several days. After analysing different possibilities we concluded that the most likely explanation might be an exocometary break-up releasing a stream of gas that remained in orbit for at least a week around the star. Then, we analyzed the variability found in the Ca ii K lines of 97 objects with the purpose of distinguishing variable absorption features most likely produced by exocometary activity from variability of a different nature, like stellar pulsations, spots or radial velocity shifts, for instance. We found five candidates with variability consistent with exocometary activity: c Aql, 49 Cet, gam Tri, HR4796 and HD37306, two of them with no previous reports of exocomets besides this work. Finally, we studied a sub-sample of 107 objects presenting stable non-photospheric features in their Ca ii K lines within our updated database of observations in addition to those in our first sub-sample of analysis. Similarly, the absorption features observed in these objects were analysed in order to determine whether they were of circumstellar or interstellar origin. We confirmed an interstellar origin for the features in 104 of these objects, one of them, 49 Cet having a blended feature of combined circumstellar and interstellar origin. In addition, we found three candidates with features of yet inconclusive origin that might be circumstellar but need further study to confirm it. Putting together our results, we found six debris disks with presence of circumstellar gas, five of them presenting variable absorption features attributable to exocometary activity and one of them with a stable circumstellar gas component. Considering that our sample is unbiased with respect to inclination, that the gas is more likely to be detected when the disk is observed close to edge-on, more easily detected in the spectra of early-type stars, the many detection challenges related to the sporadical nature of exocometary transits, and the interlopers of gas detection, then the evidence of circumstellar gas is significant. Taking into account the currently increasing number of detections, this imply the possibility that most debris disks may harbor some gas, challenging the current paradigm of debris disks.

55 New Jobs

KIAA-SHAO Joint Postdocs in Star Formation

The Kavli Institute for Astronomy and Astrophysics (KIAA) at Peking University and the Shanghai Astronomical Observatory (SHAO), Chinese Academy of Sciences invite applications for 1-2 postdocs, as part of a new Joint Center of Astrophysics that establishes close links between KIAA and SHAO. The postdocs will work in projects on star formation using ALMA, JVLA, SMA, FAST and other telescopes, led by Dr. Ke Wang (KIAA) and Dr. Tie Liu (SHAO). Independent research is also encouraged. The salary and research budget are competitive and commensurate with qualifications and experience. Generous research grants are available from national and regional funding resources. The postdocs are strongly encouraged and fully supported to apply, and grant proposals written in English are acceptable. Our postdocs have been very successful in obtaining grants as principle investigator: http://kiaa.pku.edu.cn/People/Postdoctoral_Research_Fellows.htm. The postdocs will spend 1-2 years at SHAO and 1-2 years at KIAA in either order, with the second part pending satisfactory performance. The postdoc positions are open to applicants of any nationality who will graduate prior to their appointment, with a preference for those who received their PhD after January 2017, per requirement by the China Postdoctoral Office. KIAA is located on the historic grounds of Peking University in China, has English as the working language, and regularly sponsors thematic workshops and conferences to provide a platform for national and international scientific exchanges. Astronomy at PKU includes 25 faculty, 35 postdocs, 60 graduate students, 120 undergraduates, and many visiting scholars. SHAO is located in the downtown of Shanghai, one of the most international and developed cities of China. SHAO provides a diverse setting and research facilities. In addition to the involvement of some domestic and international projects such as SKA, EHT, LAMOST, CSST, FAST and HUBS, the institute also possesses its own facilities, such as the 65-m radio telescope, and excellent computational facilities. Astronomy at SHAO includes 174 faculty, 17 postdocs, and 103 PhD students. Start date: negotiable, as soon as possible Application process: Applicants should send a single PDF file which includes (1) CV with list of publications, (2) 3- page research statement, to the contacts. Applicants should also arrange three confidential letters of recommendation to be sent to the same contacts. Deadline: Applications will be evaluated until the positions are filled. However, applications received prior to October 15, 2020 will be given full consideration. Related URLs: PKU-SHAO Joint Research Center for Astrophysics: http://kavli.pku.edu.cn/pkushao/ KIAA: http://kiaa.pku.edu.cn/ SHAO: http://english.shao.cas.cn/ Application Deadline: Thursday, October 15, 2020 Inquiries To: Ke Wang; Tie Liu Email: [email protected]; [email protected]

56 PhD Position in experimental astrochemistry and planetary science

Full-time, 4 years, 47 000 - 50 000 CHF per year (Brutto, as set by the SNSF). Starting date: between November 1st, 2020 and April 1st, 2021 Under the supervision of Dr. Niels Ligterink, a PhD project is available on the investigation of molecules in ices that are present in star-forming regions and on Solar System bodies. Using laboratory experiments that make use of Laser Desorption Mass Spectrometry and cryogenic cooling techniques, these molecules are analysed and their chemical reactions and physical processes are studied. The results of this work will provide insight into how molecules form in ice, evolve over time, and contribute to the chemical complexity seen in star-forming regions and on Solar System bodies. The main activities of the position are: laboratory work with advanced Laser Desorption Mass Spectrometry equip- ment, active participation in the scientific life of the Space Research and Planetary Sciences division, the Center for Space and Habitability (CSH), and the Bern Astrochemistry Research (BEAR) group, teaching assistant assignments, participation in national and international conferences, possibility to be involved in astrobiology projects, instrument development for planetary science missions, and/or radio telescope observations (e.g., ALMA observations). Skills of the candidate: The candidate must be in possession of a Master-level degree (or equivalent) in a relevant field (e.g., chemistry, physics, astronomy) by the starting date. Experience with laboratory experiments and techniques relevant to this position (e.g., vacuum technology, laser systems, mass spectrometry, cryogenics) is preferred. The candidate must be competent in spoken and written English. How to apply: Applicants should send all application materials in English in one PDF file to [email protected] by the deadline of November 1st, 2020. Note that applications are considered on a rolling basis meaning that the position may be filled earlier. A complete application consists of: a cover letter (max. 1 page), curriculum vitae (CV), a personal statement detailing (but not limited to): past research experience and the skills obtained, reasons for pursuing a 4-year PhD research project, aspirations for the future (max. 2 pages in total), full list and transcripts (grades) of all university-level courses (Bachelor- and Master-level) and a translated version if not in English, German, or Dutch (notarised translation is not needed), preferably two, but at least one reference letter. University of Bern: The Space Research and Planetary Sciences division is involved in the experimental and theoretical investigation of our Solar System and extra-solar planets. The division participates in NASA, ESA, and Roscosmos spacecraft missions through the provision of instruments for both remote-sensing and in situ mass spectrometry. Any question can be addressed to Dr. Niels Ligterink - [email protected]

57 Discs and planet formation - Ens de Lyon (postdoctoral position)

Applications are invited for one or several 2+1-year Postdoctoral Research Fellows to work with Dr. Guillaume Laibe on discs and planet formation (ERC-CoG project PODCAST) at the Ecole Normale Supérieure de Lyon (AstroENS team, Centre de Recherche Astrophysique de Lyon). The project includes any of the following aspects: - Formation and evolution of protostellar discs, - Dust dynamics and evolution inside the disc, - Numerical simulations of discs, - Theoretical aspects of planet formation. The successful candidate should have a Ph.D. in Astrophysics, Physics or Applied mathematics in relation with hydrodynamics with experience computational or theoretical discs or star and planet formation. By Nov, 15, enthusiastic candidates should send: i) a CV including a publication list, ii) a statement of research interests, iii) arrange for three letters of reference to be provided separately (to be sent to [email protected]). Later applications will be considered until the position has been ﬁlled. Included Beneﬁts: The initial monthly net salary is around 2000Euro and is commensurate with experience. Included : National medical insurance, maternity/paternity leaves, family supplement for children, participation to public transport fees, pension contributions. School is free in France for children above 3. The Université de Lyon provides support for settling in Lyon and France. Miscellaneous : Since 2016, the Ecole Normale Supérieure de Lyon appears in the world’s Top 5 small universities of the Times Higher Education ranking. Lyon is a vibrant city with high quality of life. The project is funded by the ERC-CoG project PODCAST (contract n?864965). Application Deadline: Sunday, November 15, 2020 Selection Deadline: Tuesday, December 1, 2020 Attention To: Dr Guillaume Laibe Phone: +33472728917 Email: [email protected]

Short Announcements

Dear colleagues, A new website for the UV Legacy Library of Young Stars as Essential Standards (ULLYSES) Director’s Discretionary program is now live at https://ullyses.stsci.edu. In particular, the ULLYSES website contains the program ID and scheduling information for targets already observed or in the long-range plan; currently this includes stars in the Large and Small Magellanic Clouds, and the Orion T Tauri stars scheduled to be observed in November-December 2020 to coincide with TESS observations. The ULLYSES website will continue to be updated with additional program and scheduling information as it becomes available. The ULLYSES implementation team at STScI

58 Meetings

Chemical processes in Solar-type star forming regions 13 - 17 September 2021 - Torino, Italy https://sites.google.com/inaf.it/aco-conference

How the chemical complexity evolves during the process leading to the formation of a Sun and its planetary system? Is the chemical richness of a Solar-like planetary system, at least partially, inherited from the earliest stages or is there a complete chemical reset? A powerful way to answering these questions is by comparing the chemical content in young protostars and primitive bodies of the Solar System, using astrochemistry as a tool. Yet, to do so, we need to fully understand the processes that govern the chemical evolution of a molecular cloud into a young planetary system. The goal of the conference is to gather together the actors of this intrinsically interdisciplinary endeavor: astronomers, chemists and modelers. The recent huge progresses in the three areas make the time ripe for these communities to join and ride this scientiﬁc wave. The conference aims to review:

• The new results from the powerful observing facilities, such as the IRAM-NOEMA, ALMA and VLA interferometers, and the chemical composition during the youngest phases of Solar-like planetary systems, from prestellar cores to protoplanetary disks, with particular emphasis on the interstellar complex organic molecules;

• The recent progresses due to the enhancement of high-performance computing facilities combined with eﬃcient quantum chemistry algorithms, which allow for the in-silico simulation of many chemical processes occurring both in gas-phase and at grain surfaces;

• The latest laboratory experiments which have provided new insights on the possible processes occurring in the interstellar conditions;

• The new generation astrochemical models as well as the innovative tools to interpret the astronomical observations that have seen the light in the last few years;

• The most recent results on the chemical composition of the small bodies of the Solar System.

This will naturally pave the way for discussing the future developments in front of us. The meeting will consist of invited reviews, invited and contributed talks, and posters. A limited amount of ﬁnancial support will be dedicated to students and young researchers. SOC: P. Ugliengo (Chair, Università di Torino, Italy), C. Codella (Co-chair, INAF - Osservatorio Astroﬁsico di Arcetri, Italy) A. Barucci (LESIA, Observatoire de Paris, Université PSL, CNRS, Université de Paris, Sorbonne Université, France), C. Ceccarelli (Univ. Grenoble Alpes, CNRS, Institut de Planétologie et d’Astrophysique de Grenoble, France), L. Piccirillo (Univ. of Manchester - School of Physics and Astronomy, UK), A. Rimola (Univ. Autonoma Barcelona - Dept. of Chemistry, Spain), C. Vastel (Univ. Paul Sabatier, Toulouse 3 - IRAP, France), S. Viti (Univ. College of London, UK), S. Yamamoto (University of Tokyo, Department of Physics, Japan)

59 Summary of Upcoming Meetings

Check the websites of these meetings for the latest information on how they are aﬀected by Covid-19 Conditions and Impact of Star Formation - Across Times and Scales 28 September - 2 October 2020, Chile https://astro.uni-koeln.de/symposium-star-formation-2020.html From Clouds to Planets II: The Astrochemical Link 28 September - 2 October 2020, Berlin, Germany https://events.mpe.mpg.de/event/12/ Threats from the Surroundings – VIRTUAL MEETING 10 - 12 November 2020 http://www.eso.org/sci/meetings/2020/tfts2020.html Five Years after HL Tau: A New Era in Planet Formation – VIRTUAL MEETING 7 - 11 December 2020 https://www.eso.org/sci/meetings/2020/hltau2020.html Protostars & Planets VII 1 - 7 April 2021, Kyoto, Japan http://www.ppvii.org Gordon Conference on Origins of Solar Systems 19 - 25 June 2021, MA, USA https://www.grc.org/origins-of-solar-systems-conference/2021 Cool Stars, Stellar Systems, and the Sun 21 5 - 9 July 2021, Toulouse, France https://coolstars21.github.io/ Star Formation: From Clouds to Discs - A Tribute to the Career of Lee Hartmann 16 - 19 August 2021, Malahide, Ireland https://www.dias.ie/cloudstodiscs/ Chemical Processes in Solar-type Star Forming Regions 13 - 17 September 2021, Torino, Italy https://sites.google.com/inaf.it/aco-conference Wheel of Star Formation: A conference dedicated to Prof. Jan Palouˇs 20 - 24 September 2020, Prague, Czech Republic https://janfest2020.asu.cas.cz The Physics of Star Formation: From Stellar Cores to Galactic Scales ∼June - July 2022, Lyon, France http:/staratlyon.univ-lyon1.fr/en

60 New Books

The Physics of the Interstellar Medium A. C. Raga, J. Cantó, and A. Rodríguez-González

This book about the interstellar medium is based on the ISM course that the authors have taught at Universidad Nacional Autónoma de México for over 25 years. All three authors are theoreticians, and the book is primarily dealing with theoretical concepts. The subject of the ISM is enormous and so all books emphasize somewhat diﬀerent subjects. The present book broadly focuses on three areas: a) the ionized ISM and static models, b) dynamics of the ISM, and c) astrophysical jets. These are areas where the authors have made major contributions of their own. At the same time, subjects such as magnetic ﬁelds, stellar winds, dust, and accretion disks are omitted. The book is directed to master’s and PhD students, or researchers interested in calculating dynamical models of the ISM. The authors have also made the book freely available at the website listed below, instead of publishing another very expensive textbook. This implies that changes and additions are easily made, and the authors welcome feedback for future editions.

The following lists the chapters of the book: 1. General comments 2. Observational characteristics of the ISM 3. Photoionized regions 4. The emitted spectrum 5. The equations of gasdynamics 6. Sound waves and linear stability analysis 7. Shock waves 8. 1D, stationary, radiative shocks 9. The hydrodynamic expansion of an HII region 10. Wind-driven HII regions 11. Supernova remnants 12. Gravitational collapse

61 13. Astrophysical and laboratory jets 14. Hypersonic, variable velocity jets 15. The centre of mass equation of motion 16. The uniformly accelerating jet in a homogeneous environment 17. Time-dependent ejection direction 18. Steady jet in a sidewind 19. Bullets The book can be downloaded from this URL: https://bigbang.nucleares.unam.mx/astroplasmas/index.php/the-physics-of-the-interstellar-medium-book

Studies in Star Formation - 77 Perspectives Edited by Bo Reipurth

Since 2012, the Star Formation Newsletter has brought interviews with scientists working in the field of star and planet formation, molecular clouds, and the early solar system. While the interviews have remained accessible on the Newsletter webpage, they have not been easy to find. I have therefore decided to compile all the 77 interviews done so far into a single compendium, which will be expanded once a year with new interviews. The compilation can be downloaded from this link: http://bit.ly/77interviews Each interview provides a glimpse into the scientific lives of researchers who have made important contributions to our field. But taken together, the 77 interviews also provide an overview of the past 40-50 years of tremendous development in our understanding of star and planet formation. As such, it may be helpful for new generations of astronomers in understanding how different topics have come to their present state. The compendium could also serve as supplementary material for courses on star formation. The current 2020 version is 199 pages.

62 Passings

Martin Cohen 1950-2020

Martin Cohen, a native of Manchester, England and pioneer in infrared astronomy and studies of pre-Main Sequence stars, passed away on March 7, 2020, of a rare form of Alzheimer’s disease. He was born in 1950. His interest in astronomy was kindled in Manchester Grammar School and strengthened in high school, both institutions having small telescopes that Martin was allowed to use and restore to working order. This early interest led him to a personal quest for ever bigger and sophisticated telescopes in pursuit of his career in astronomy. That journey was described in detail in his book ’In Quest of Telescopes’ published in 1979 and continued to the present day as he made use of the Kuiper Airborne Observatory, the Hubble and Spitzer Space Telescopes. Martin was a summer student at the Royal Greenwich Observatory in 1968 and earned his undergraduate degree in mathematics from the University of Cambridge in 1969. He became interested in the new field of infrared astronomy and was one of three British students sent to the University of Minnesota to pursue their graduate studies. He helped build the 60-inch metal mirror infrared telescope at Mt. Lemmon and received his PhD in 1975 observing the spectral energy distributions of pre-Main Sequence stars. The study of young stars fascinated him for most of his life and led to the publication of another book in 1988, ’In Darkness Born-The Story of Star Formation’. It was a subject he loved to talk about and was the focus of many of his lectures popularizing astronomy. After his graduate degree he embarked upon a long time association with the University of California at Berkeley and NASA Ames. I was fortunate to work with him for several years, using the Wampler Scanner at Lick Observatory combined with his infrared observations to undertake a massive study of the properties of ∼500 pre-Main Sequence stars resulting in the HR diagrams for the Taurus-Auriga complex, Orion, NGC 2264, NGC 7000/IC 5070, and the Rho Ophiuchi association. His dedication to hard work and his enthusiasm for research were inspiring. We would observe all night and he would search for additional objects on the Palomar sky survey prints during the day. He was indefatigable as his collaborators will attest to. Martin continued his infrared observations which extended to ever longer wavelengths as the instrumentation improved. Many papers were published dealing with T Tauri stars, Herbig Haro objects, bipolar nebulae, bipolar flows, jets, carbon stars, planetary nebulae, Wolf Rayet stars, cometary nebulae and other objects of interest that were detected by AFCRL rocket infrared observations and later IRAS observations. His infrared work on T Tauri stars detected ice around HL Tauri and eventually led to the conclusion that about one third of T Tauri stars had circumstellar dust disks. His prolific research laid the groundwork for our understanding of the nature of very young stars and their early evolution. In later years he devoted his energies to the problem of absolute calibration at infrared wavelengths, and published a series of highly cited papers on the subject.

Len Kuhi