PROJECT EOS October 1, 2019

EARTHS IN OTHER SOLAR SYSTEMS

Recent Publications

Constraining Stellar Photospheres as an Essential Step for Transmission Spectroscopy of Small ………………………………. A Statistical Comparative PROJECT EOS Planetology Approach to Maximize the Scientific Return of Future Characterization Efforts ………………………………. Planetary Habitability Informed by Planet Earths in Other Solar Systems is part of NASA’s Nexus for Formation and Exoplanet Exoplanetary System Science program, which carries out Demographics coordinated research toward to the goal of searching for and ………………………………. determining the frequency of habitable extrasolar planets with Wotan: Comprehensive atmospheric in the Solar neighborhood. time-series de-trending in Python Our interdisciplinary EOS team includes astrophysicists, planetary scientists, cosmochemists, material scientists, ……………………………….. chemists and physicists. The newborn planet population emerging from The Principal Investigator of EOS is Daniel Apai (University of ring-like structures in discs ). The project’s lead institutions are The University of ……………………………….. Arizona‘s and Lunar and Planetary Double-peaked [O I] Profile: Laboratory. A Likely Signature of the The EOS Institutional Consortium consists of the Steward Gaseous Ring around KH Observatory and the Lunar and Planetary Laboratory of the 15D , the National Optical Astronomy ……………………………….. Observatory, the Department of Geophysical Sciences at the Combining high contrast University of Chicago, the Institute, and the imaging and radial velocities Catholic University of Chile. to constrain the planetary

architecture of nearby stars For a complete list of publications, please visit the EOS Library on the SAO/NASA Data System. eos-nexus.org 1 PROJECT EOS October 1, 2019

EARTHS IN OTHER SOLAR SYSTEMS

Recent Publications (cont.)

A Thousand Earths: A Very Large Aperture, Ultralight Space Telescope Array for Atmospheric PROJECT EOS Surveys ………………………………. Systematic Variations of CO Gas Abundance with Radius in Gas-rich Protoplanetary Disks ………………………………. The impact of stripped cores on the frequency of Earth- size planets in the habitable zone ………………………………. Dust spreading in debris discs: do small grains cling on their birth environment? ……………………………….. Thermal Infrared Imaging of MWC 758 with the Large Binocular Telescope: Planetary-driven Spiral Arms? ……………………………….. Dust Transport and Some members of the EOS Team at the 2019 All Hands Meeting in Tucson Processing in Centrifugally Driven Winds ……………………………….. Compact Disks in a High- resolution ALMA Survey of Dust Structures in the Taurus Molecular Cloud

eos-nexus.org 2 PROJECT EOS October 1, 2019

Constraining Stellar Photospheres as an Essential Step for Transmission Spectroscopy of Small Exoplanets

Rackham, Benjamin; Pinhas, Arazi; Apai, Dániel; Haywood, Raphaëlle; Cegla, Heather; Espinoza, Néstor; Teske, Johanna; Gully-Santiago, Michael; Rau, Gioia; Morris, Brett M.; Angerhausen, Daniel; Barclay, Thomas; Carone, Ludmila; Cauley, P. Wilson; de Wit, Julien; Domagal-Goldman, Shawn; Dong, Chuanfei; Dragomir, Diana; Giampapa, Mark S.; Hasegawa, Yasuhiro Hinkel, Natalie R.; Hu, Renyu; Jordán, Andrés; Kitiashvili, Irina; Kreidberg, Laura; Lisse, Carey; Llama, Joe; López-Morales, Mercedes; Mennesson, Bertrand; Molaverdikhani, Karan; Osip, David J.; Quintana, Elisa V.

Bulletin of the American Astronomical Society, Vol. 51, Issue 3

Transmission spectra probe the atmospheres of transiting exoplanets, but these observations are also subject to signals introduced by magnetic active regions on host stars. We outline scientific opportunities in the next decade for providing useful constraints on stellar photospheres for the purposes of exoplanet transmission spectroscopy.

Science white paper submitted in response to the the U.S. National Academies of Science, Engineering, and Medicine's call for community input to the Astro2020 Decadal Survey

Figure 1: Schematic of the transit light source effect. Inhomogeneities in a stellar photosphere introduce a spectral difference between the light that illuminates the exoplanet atmosphere during a transit and the disk- integrated stellar spectrum, which provides the reference for measuring transit depths. This spectral mismatch produces apparent transit depth variations that can mimic or mask exoplanetary atmospheric features. From Rackham et al. (2018).

eos-nexus.org 3 PROJECT EOS October 1, 2019

A Statistical Comparative Planetology Approach to Maximize the Scientific Return of Future Exoplanet Characterization Efforts

Checlair, Jade; Abbot, Dorian S.; Webber, Robert J.; Feng, Y. Katherina; Bean, Jacob L.; Schwieterman, Edward W.; Stark, Christopher C.; Robinson, Tyler D.; Kempton, Eliza; Alcabes, Olivia D. N.; Apai, Daniel; Arney, Giada; Cowan, Nicolas; Domagal-Goldman, Shawn; Dong, Chuanfei; Fleming, David P.; Fujii, Yuka; Graham, R. J.; Guzewich, Scott D.; Hasegawa, Yasuhiro Hayworth, Benjamin P. C.; Kane, Stephen R.; Kite, Edwin S.; Komacek, Thaddeus D.; Kopparapu, Ravi K.; Mansfield, Megan; Marounina, Nadejda; Montet, Benjamin T.; Olson, Stephanie L.; Paradise, Adiv; Popovic, Predrag; Rackham, Benjamin V.; Ramirez, Ramses M.; Rau, Gioia; Reinhard, Chris; Renaud, Joe; Rogers, Leslie; Walkowicz, Lucianne M.; Warren, Alexandra; Wolf, Eric. T.

Bulletin of the American Astronomical Society, Vol. 51, Issue 3

Provided that sufficient resources are deployed, we can look forward to an extraordinary future in which we will characterize potentially habitable planets. Until now, we have had to base interpretations of observations on habitability hypotheses that have remained untested. To test these theories observationally, we propose a statistical comparative planetology approach to questions of planetary habitability. The key objective of this approach will be to make quick and cheap measurements of critical planetary characteristics on a large sample of exoplanets, exploiting statistical marginalization to answer broad habitability questions. This relaxes the requirement of obtaining multiple types of data for a given planet, as it allows us to test a given hypothesis from only one type of measurement using the power of an ensemble. This approach contrasts with a “systems science” approach, where a few planets would be extensively studied with many types of measurements. A systems science approach is associated with a number of difficulties which may limit overall scientific return, including: the limited spectral coverage and noise of instruments, the diversity of exoplanets, and the extensive list of potential false negatives and false positives. A statistical approach could also be complementary to a systems science framework by providing context to interpret extensive measurements on planets of particular interest. We strongly recommend future missions with a focus on exoplanet characterization, and with the capability to study large numbers of Figure 2: The silicate-weathering feedback: planets in a homogenous way, rather than Atmospheric CO2 dissolves in rainwater, forming carbonic acid, which reacts with continental silicate exclusively small, intense studies directed at a small rocks to form products that move into the oceans, sample of planets. and are then carried down subduction zones, where they release gaseous CO2 which returns to the atmosphere through volcanoes. Kasting (1993). eos-nexus.org 4 PROJECT EOS October 1, 2019

Planetary Habitability Informed by Planet Formation and Exoplanet Demographics

Apai, Daniel; Banzatti, Andrea; Ballering, Nicholas P.; Bergin, Edwin A.; Bixel, Alex; Birnstiel, Til; Bose, Maitrayee; Brittain, Sean; Cadillo-Quiroz, Hinsby; Carrera, Daniel; Ciesla, Fred; Close, Laird; Desch, Steven J.; Dong, Chuanfei; Dressing, Courtney D.; Fernandes, Rachel B.; France, Kevin; Gharib-Nezhad, Ehsan; Haghighipour, Nader; Hartnett, Hilairy E. Hasegawa, Yasuhiro; Jang- Condell, Hannah; Kalas, Paul; Kane, Stephen R.; Kim, Jinyoung Serena; Krijt, Sebastiaan; Lisse, Carey; López-Morales, Mercedes; Malhotra, Renu; Morrison, Sarah; Mulders, Gijs D.; Pontoppidan, Klaus M.; Scharf, Caleb; Schwarz, Kamber R.; Schwieterman, Edward W.; Stassun, Keivan G.; Turner, Neal; Wagner, Kevin; Young, Patrick

Bulletin of the American Astronomical Society, Vol. 51, Issue 3

Dozens of habitable zone, approximately earth-sized exoplanets are known today and many more are set to be discovered in the next decade. An emerging frontier of exoplanet studies is identifying which of these habitable zone, small planets are actually habitable (have all necessary conditions for life) and, of those, which are earth-like. Many parameters and processes influence habitability, ranging from the planet’s orbit, to its detailed composition (including volatiles and organics), to the presence of geological activity and even plate tectonics. While some properties will soon be directly observable, others cannot be probed by remote sensing for the foreseeable future. Thus, statistical understanding of planetary systems’ formation and evolution is a key supplement to the direct measurements of planets’ properties. With over four thousand exoplanets discovered it is now possible to systematically test planet formation models against the emerging exoplanet demographics information. Probabilistically assessing the parameters we cannot directly measure is essential for reliably assessing habitability, for prioritizing habitable zone planets for follow-up, and for interpreting possible biosignatures. Here we review the key questions in planet formation that must be addressed to improve the predictive power of planet formation models. We will also discuss how Bayesian assessment of a planet’s habitability provides a tool for combining statistical contextual knowledge on the exoplanet population with specific – but necessarily uncertain and incomplete – information on the individual planet.

RELATIONSHIP TO THE NAS EXOPLANET STRATEGY REPORT: This white paper is consistent with the general recommendations of the NAS Exoplanet Strategy Report, but focuses on a different, novel approach for integrating multi-disciplinary and multi-field knowledge in a consistent framework to provide Bayesian assessment for planetary habitability.

eos-nexus.org 5 PROJECT EOS October 1, 2019

Wotan: Comprehensive time-series de-trending in Python Michael Hippke, Trevor J. David, Gijs D. Mulders, Réne Heller

Accepted for publication in The Astrophysical Journal

The detection of transiting exoplanets in time-series photometry requires the removal or modeling of instrumental and stellar noise. While instrumental systematics can be reduced using methods such as pixel level decorrelation, removing stellar trends while preserving transit signals proves challenging. Due to vast archives of light curves from recent transit surveys, there is a strong need for accurate automatic detrending, without human intervention. A large variety of detrending algorithms are in active use, but their comparative performance for transit discovery is unexplored. We benchmark all commonly used detrending methods against hundreds of Kepler, K2, and TESS planets, selected to represent the most difficult cases for systems with small planet-to-star radius ratios. The full parameter range is explored for each method to determine the best choices for planet discovery. We conclude that the ideal method is a time-windowed slider with an iterative robust location estimator based on Tukey's biweight. This method recovers 99% and 94% of the shallowest Kepler and K2 planets, respectively. We include an additional analysis for young stars with extreme variability and conclude they are best treated using a spline-based method with a robust Huber estimator. All stellar detrending methods explored are available for public use in wotan, an open-source Python package on GitHub (see this https URL).

Figure 1. Light curve of EPIC211995398 (black points, Pope et al. 2016) with a Savitzky-Golay filter (red) as used in the lightkurve package (Barentsen et al. 2019) with a default of w = 101 cadences, polynomial order p = 2, and a time-windowed estimator (orange, Tukey's biweight, w = 0:5 d). The latter represents a reasonable fit to the data, while the Savitzky-Golay overfits the in-transit points and reduces the transit depth by ~ 15 %, making detection more difficult (although in this example still trivial). eos-nexus.org 6 PROJECT EOS October 1, 2019

The newborn planet population emerging from ring-like structures in discs G. Lodato, G. Dipierro, E. Ragusa, F. Long, G.J. Herczeg, I. Pascucci, P. Pinilla, C. F. Manara, M. Tazzari, Y. Liu, G. D. Mulders, D. Harsono, Y. Boehler, F. Menard, D. Johnstone, C. Salyk, G. van der Plas, S. Cabrit, S. Edwards, W. J. Fischer, N. Hendler, B. Nisini, E. Rigliaco, H. Avenhaus, A. Banzatti, M. Gully-Santiago

Monthly Notices of the Royal Astronomical Society, Volume 486, Issue 1

ALMA has observed a plethora of ring-like structures in planet forming discs at distances of 10-100 au from their host star. Although several mechanisms have been invoked to explain the origin of such rings, a common explanation is that they trace new-born planets. Under the planetary hypothesis, a natural question is how to reconcile the apparently high frequency of gap-carving planets at 10-100 au with the paucity of Jupiter mass planets observed around main sequence stars at those separations. Here, we provide an analysis of the new-born planet population emerging from observations of gaps in discs, under the assumption that the observed gaps are due to planets. We use a simple estimate of the planet mass based on the gap morphology, and apply it to a sample of gaps recently obtained by us in a survey of Taurus with ALMA. We also include additional data from recent published surveys, thus analysing the largest gap sample to date, for a total of 48 gaps. The properties of the purported planets occupy a distinctively different region of parameter space with respect to the known exo-planet population, currently not accessible Plot of mass (y-axis) Mp versus separation from the central through planet finding methods. Thus, no star R (x-axis) of the (empty circles) currently known exo- discrepancy in the mass and radius distribution of planets (retrieved from the exoplanet.org data base) compared to those obtained from the sample in Long the two populations can be claimed at this stage. et al. (2018) (red points) and Zhang et al. (2018) (green We show that the mass of the inferred planets points) using equation (2), and those collected by Bae conforms to the theoretically expected trend for et al. (2018) (blue points). Error bars in the planet masses the minimum planet mass needed to carve a dust indicate the uncertainty in the proportionality factor between gap width and planet’s Hills radius, assumed to be gap. Finally, we estimate the separation and mass in the range [4.5–7]. of the putative planets after accounting for migration and accretion, for a range of evolutionary times, finding a good match with the distribution of cold Jupiters. eos-nexus.org 7 PROJECT EOS October 1, 2019

Double-peaked [O I] Profile: A Likely Signature of the Gaseous Ring around KH 15D Lodato, Giuseppe; Dipierro, Giovanni; Ragusa, Enrico; Long, Feng; Herczeg, Gregory J.; Pascucci, Ilaria; Pinilla, Paola; Manara, Carlo F.; Tazzari, Marco; Liu, Yao; Mulders, Gijs D.; Harsono, Daniel; Boehler, Yann; Ménard, François; Johnstone, Doug; Salyk, Colette; van der Plas, Gerrit; Cabrit, Sylvie; Edwards, Suzan; Fischer, William J. Hendler, Nathan; Nisini, Brunella; Rigliaco, Elisabetta; Avenhaus, Henning; Banzatti, Andrea; Gully-Santiago, Michael

The Astrophysical Journal Letters, Volume 879, Number 1

KH 15D is a well-known spectroscopic binary because of its unique and dramatic photometric variability. The variability is explained by a circumbinary dust ring, but the ring itself was never directly detected. We present a new interpretation of the double- peaked [O I] λ6300 profiles as originating from the hot disk surface of KH 15D. By modeling these profiles, we measure emitting radii between ~0.5 and 5 au, basically a gaseous ring very similar in radial extent to the dust ring inferred from modeling the system's photometric variability. We also discuss the possibility that external photoevaporation driven by ultraviolet photons from the nearby massive star HD 47887 has truncated the outer edge of the disk to the observed value.

Figure 1. [O I] λ6300 line profile (gray line) in the system’s reference

frame obtained on 2001 December 21. The profile is compared with the H2 1-0 S(1) digitally extracted from Figure 2 of Deming et al. (2004; red line). The best-fit model profile is also shown in the panel (blue line). The gray filled region marks the wavelength range contaminated by the sky line and thus excluded in the fitting (see the discussion in Section 2). eos-nexus.org 8 PROJECT EOS October 1, 2019

Combining high contrast imaging and radial velocities to constrain the planetary architecture of nearby stars

Boehle, A.; Quanz, S. P.; Lovis, C.; Sègransan, D.; Udry, S.; Apai, D.

Accepted for pulication in Astronomy & Astrophysics

Nearby stars are prime targets for exoplanet searches and characterization using a variety of detection techniques. Combining constraints from the complementary detection methods of high contrast imaging (HCI) and radial velocity (RV) can further constrain the planetary architectures of these systems because these methods place limits at different regions of the companion mass and semi-major axis parameter space. We aim to constrain the planetary architectures from the combination of HCI and RV data for 6 nearby stars within 6 pc: τ Ceti, Kapteyn's star, AX Mic, 40 Eri, HD 36395, and HD 42581. We compiled the sample from stars with available archival VLT/NACO HCI data at L′ band (3.8 μm). The NACO data were fully reanalyzed using the state-of-the-art direct imaging pipeline PynPoint and combined with RV data from HARPS, Keck/HIRES, and CORALIE. A Monte Carlo approach was used to assess the completeness in the companion mass/semi-major axis parameter space from the combination of the HCI and RV data sets. We find that the HCI data add significant information to the RV constraints, increasing the completeness for certain companions masses/semi-major axes by up to 68 - 99% for 4 of the 6 stars in our sample, and by up to 1 - 13% for the remaining stars. The improvements are strongest for intermediate semi-major axes (15 - 40 AU), corresponding to the semi-major axes of the ice giants in our own solar system. The HCI mass limits reach 5 - 20 MJup in the background-limited regime, depending on the age of the star. Through the combination of HCI and RV data, we find that stringent constraints can be placed on the possible substellar companions in these systems. Applying these methods systematically to nearby stars will quantify our current knowledge of the planet population in the Fig. 2. PSF-subtracted images for each star in the sample, where the PSF solar neighborhood and was subtracted using classical ADI. These images were used to search for inform future observations. companions from 200 out to 6.500 (the maximum separation allowed by the NACO field of view and the dithering observing strategy). The white circle indicates the extent of the PCA images shown in Fig. 1 (200 radius). The white bar in the lower left of each image corresponds to 5 AU at the distance of the star. The images are plotted with a linear stretch. eos-nexus.org 9 PROJECT EOS October 1, 2019

A Thousand Earths: A Very Large Aperture, Ultralight Space Telescope Array for Atmospheric Biosignature Surveys

Apai, Dániel; Milster, Tom D.; Kim, Dae Wook; Bixel, Alex; Schneider, Glenn; Liang, Ronguang; Arenberg, Jonathan

The Astronomical Journal, Volume 158, Issue 2

An outstanding, multidisciplinary goal of modern science is the study of the diversity of potentially Earth-like planets and the search for life in them. This goal requires a bold new generation of space telescopes, but even the most ambitious designs yet hope to characterize several dozen potentially habitable planets. Such a sample may be too small to truly understand the complexity of exo-earths. We describe here a notional concept for a novel space observatory designed to characterize 1000 transiting exo-earth candidates. The Nautilus concept is based on an array of inflatable spacecraft carrying very large diameter (8.5 m), very low weight, multiorder diffractive optical elements (MODE lenses) as light-collecting elements. The mirrors typical to current space telescopes are replaced by MODE lenses with a 10 times lighter areal density that are 100 times less sensitive to misalignments, enabling lightweight structure. MODE lenses can be cost-effectively replicated through molding. The Nautilus mission concept has a potential to greatly reduce fabrication and launch costs and mission risks compared to the current space telescope paradigm through replicated components and identical, lightweight unit telescopes. Nautilus is designed to survey transiting exo-earths for biosignatures up to a distance of 300 pc, enabling a rigorous statistical exploration of the frequency and properties of life-bearing planets and the diversity of exo-earths.

Figure 4. (a) 5 m diameter Eyeglass prototype using 72 single-order diffractive optical elements (e.g., Hyde 1999; photo credit: R. Hyde). (b) Ball’s MOIRE test segment, using single-order diffractive optics replicated to membranes (photo credit: Atcheson et al. 2014). (c) MODE lens prototype developed at the University of Arizona by our team. eos-nexus.org 10 PROJECT EOS October 1, 2019

Systematic Variations of CO Gas Abundance with Radius in Gas-rich Protoplanetary Disks

Zhang, Ke; Bergin, Edwin A.; Schwarz, Kamber R.; Krijt, Sebastiaan; Ciesla, Fred

Accepted for publication in the Astrophysical Journal

CO is the most widely used gas tracer of protoplanetary disks. Its abundance is usually assumed to be an interstellar ratio throughout the warm molecular layer of the disk. But recent observations of low CO gas abundance in many protoplanetary disks challenge our understanding of physical and chemical evolutions in disks. Here we investigate the CO abundance structures in four well-studied disks and compare their structures with predictions of chemical processing of CO and transport of CO ice-coated dust grains in disks. We use spatially resolved CO isotopologue line observations and detailed thermo-chemical models to derive CO abundance structures. We find that the CO abundance varies with radius by an order of magnitude in these disks. We show that although chemical processes can efficiently reduce the total column of CO gas within 1 Myr under an ISM level of cosmic-ray ionization rate, the depletion mostly occurs at the deep region of a disk. Without sufficient vertical mixing, the surface layer is not depleted enough to reproduce weak CO emissions observed. The radial profiles of CO depletion in three disks are qualitatively consistent with predictions of pebble formation, settling, and drifting in disks. But the dust evolution alone cannot fully explain the high depletion observed in some disks. These results suggest that dust evolution may play a significant role in transporting volatile materials and a coupled chemical-dynamical study is necessary to understand what raw materials are available for planet formation at different distances from the central star.

Figure 1. Left column: Moment zero map (integrated intensity) of CO isotopologue line observations (continuum subtracted). The axes are labeled with angular offsets from the disk center, and the synthesized beam is shown in the lower-left corner of each panel. RIght column: deprojected radial line intensity profiles of each line. The shaded areas indicate a 1σ uncertainty. The deprojections used the disk geometric parameters listed in Table 3. eos-nexus.org 11 PROJECT EOS October 1, 2019

The impact of stripped cores on the frequency of Earth-size planets in the habitable zone Pascucci, I; Mulders, G; Lopez, E.

Astrophysics - Earth and Planetary Astrophysics

The frequency of Earth-size planets in the habitable zone of Sun-like stars, hereafter η⊕, is a key parameter to evaluate the yield of nearby Earth analogues that can be detected and characterized by future missions. Yet, this value is poorly constrained as there are no reliable exoplanet candidates in the habitable zone of Sun-like stars in the Kepler field. Here, we show that extrapolations relying on the population of small (<1.8R⊕) short- period (<25days) planets bias η⊕ to large values. As the radius distribution at short orbital periods is strongly affected by atmospheric loss, we re-evaluate η⊕ using exoplanets at larger separations. We find that η⊕ drops considerably, to values of only ∼5−10%. Observations of young (<100 Myr) clusters can probe short-period sub-Neptunes that still retain most of their envelope mass. As such, they can be used to quantify the contamination of sub-Neptunes to the population of Kepler short-period small planets and aid in more reliable estimates of η⊕.

Figure 1. Upper panel: DR25+Gaia candidate list, color coded by survey completeness. The sample includes only dwarfs and planet candidates with a Robovetter score > .9. The grey rectangle delineates the HZ, no reliable planet candidate is detected inside the HZ. Occurrence rates using the inverse detection efficiency method are also provided for nine period and two radius bins (black rectangles). For clarity these values are also plotted in the lower panel with the number of planets per bin for the five bins at largest orbital periods.

eos-nexus.org 12 PROJECT EOS October 1, 2019

Dust spreading in debris discs: do small grains cling on their birth environment? Pawellek, Nicole; Moór, Attila; Pascucci, Ilaria; Krivov, Alexander V.

Monthly Notices of the Royal Astronomical Society, Volume 487, Issue 4

Debris discs are dusty belts of planetesimals around main-sequence stars, similar to the asteroid and Kuiper belts in our Solar system. The planetesimals cannot be observed directly, yet they produce detectable dust in mutual collisions. Observing the dust, we can try to infer properties of invisible planetesimals. Here, we address the question of what is the best way to measure the location of outer planetesimal belts that encompass extrasolar planetary systems. A standard method is using resolved images at millimetre wavelengths, which reveal dust grains with sizes comparable to the observational wavelength. Smaller grains seen in the infrared (IR) are subject to several non-gravitational forces that drag them away from their birth rings, and so may not closely trace the parent bodies. In this study, we examine whether imaging of debris discs at shorter wavelengths might enable determining the spatial location of the exo-Kuiper belts with sufficient accuracy. We find that around M-type stars the dust best visible in the mid-IR is efficiently displaced inwards from their birth location by stellar winds, causing the discs to look more compact in mid-IR images than they actually are. However, around earlier- type stars where the majority of debris discs is found, discs are still the brightest at the birth ring location in the mid-IR regime. Thus, sensitive IR facilities with good angular resolution, such as MIRI on James Webb Space Telescope, will enable tracing exo-Kuiper belts in nearby debris disc systems.

Radiation pressure efficiency as a function of grain size.

eos-nexus.org 13 PROJECT EOS October 1, 2019

Thermal Infrared Imaging of MWC 758 with the Large Binocular Telescope: Planetary-driven Spiral Arms? Wagner, Kevin; Stone, Jordan M.; Spalding, Eckhart; Apai, Daniel; Dong, Ruobing; Ertel, Steve; Leisenring, Jarron; Webster, Ryan

The Astrophysical Journal, Volume 882, Issue 1

Theoretical studies suggest that a giant planet around the young star MWC 758 could be responsible for driving the spiral features in its circumstellar disk. Here, we present a deep imaging campaign with the Large Binocular Telescope with the primary goal of imaging the predicted planet. We present images of the disk in two epochs in the L′ filter (3.8 μm) and a third epoch in the M′ filter (4.8 μm). The two prominent spiral arms are detected in each observation, which constitute the first images of the disk at M′, and the deepest yet in L′ (∆L′ = 12.1 exterior to the disk at 5σ significance). We report the detection of an S/N ∼ 3.9 source near the end of the Southern arm, and, from the source’s detection at a consistent position and brightness during multiple epochs, we establish a ∼90% confidence-level that the source is of astrophysical origin. We discuss the possibilities that this feature may be (a) an unresolved disk feature, and (b) a giant planet responsible for the spiral arms, with several arguments pointing in favor of the latter scenario. We present additional detection limits on companions exterior to the spiral arms, which suggest that a ≲4 M Jup planet exterior to the spiral arms could have escaped detection. Finally, we do not detect the companion candidate interior to the spiral arms reported recently by Reggiani et al., although forward modeling suggests that such a source would have likely been Figure 1. Top: Lʹ image of MWC 758 taken on 2017 February 11. Bottom: Mʹ image taken on 2018 December detected. 25. Both data sets were taken in dual-aperture mode with the LBT and then combined. The images shown here are smoothed by a 5 pixel Gaussian kernel.

eos-nexus.org 14 PROJECT EOS October 1, 2019

Dust Transport and Processing in Centrifugally Driven Protoplanetary Disk Winds Giacalone, Steven; Teitler, Seth; Königl, Arieh; Krijt, Sebastiaan; Ciesla, Fred J.

The Astrophysical Journal, Volume 882, Issue 1

There is evidence that protoplanetary disks—including the protosolar one—contain crystalline dust grains on spatial scales where the dust temperature is lower than the threshold value for their formation through thermal annealing of amorphous interstellar silicates. We interpret these observations in terms of an extended, magnetocentrifugally driven disk wind that transports grains from the inner disk—where they are thermally processed by the stellar radiation after being uplifted from the disk surfaces—to the outer disk regions. For any disk radius r, there is a

maximum grain size a max(r) that can be uplifted from that location: grains of size

a ≪ a max are carried away by the wind,

whereas those with a ≲ a max reenter the disk at larger radii. A significant portion of the reentering grains converge to—and subsequently accumulate in—a narrow

region just beyond r max(a), the maximum radius from which grains of size a can be uplifted. We show that this model can account for the inferred crystallinity fractions in classical T Tauri and Herbig Ae disks and for their indicated near constancy after being established early in the disk evolution. It is also consistent with the reported radial gradients in the mean grain size, crystallinity, and crystal composition. In addition, this model yields the properties of the grains that remain embedded in the outflows from protoplanetary disks and naturally explains the inferred persistence of small grains in the surface layers of these disks.

Figure 1. Trajectories of uplifted 1 μm grains in the (r, z/r) plane for four illustrative profiles of the gas temperature in the wind (see Table 1). The dashed red curve represents the locus of points where the grain velocity component normal to the disk surface vanishes (vd,⊥ = 0), whereas the dotted blue curve represents the locus of points where vd,z = 0. The background cells depict the computational grid in the region under consideration. eos-nexus.org 15 PROJECT EOS October 1, 2019

Compact Disks in a High-resolution ALMA Survey of Dust Structures in the Taurus Molecular Cloud

Long, Feng; Herczeg, Gregory J.; Harsono, Daniel; Pinilla, Paola; Tazzari, Marco; Manara, Carlo F.; Pascucci, Ilaria; Cabrit, Sylvie; Nisini, Brunella; Johnstone, Doug; Edwards, Suzan; Salyk, Colette; Menard, Francois; Lodato, Giuseppe; Boehler, Yann; Mace, Gregory N.; Liu, Yao; Mulders, Gijs D.; Hendler, Nathanial; Ragusa, Enrico; Fischer, William J.; Banzatti, Andrea; Rigliaco, Elisabetta; van de Plas, Gerrit; Dipierro, Giovanni; Gully-Santiago, Michael; Lopez-Valdivia, Ricardo

The Astrophysical Journal, Volume 882, Issue 1

We present a high-resolution (∼0.″12, ∼16 au, mean sensitivity of 50 μJy beam-1 at 225 GHz) snapshot survey of 32 protoplanetary disks around young stars with spectral type earlier than M3 in the Taurus star-forming region using the Atacama Large Millimeter Array. This sample includes most mid-infrared excess members that were not previously imaged at high spatial resolution, excluding close binaries and objects with high extinction, thereby providing a more representative look at disk properties at 1–2 Myr. Our 1.3 mm continuum maps reveal 12 disks with prominent dust gaps and rings, 2 of which are around primary stars in wide binaries, and 20 disks with no resolved features at the observed resolution (hereafter smooth disks), 8 of which are around the primary star in wide binaries. The smooth disks were classified based on their lack of resolved substructures, but their most prominent property is that they are all compact

with small effective emission radii (R eff,95% ≲ 50

au). In contrast, all disks with R eff,95% of at least 55 au in our sample show detectable substructures. Nevertheless, their inner emission cores (inside the resolved gaps) have similar peak brightness, power-law profiles, and transition radii to the compact smooth disks, so the primary difference between these two categories is the lack of outer substructures in the latter. These compact disks may lose their outer disk through fast radial drift without dust trapping, or they might be born with small sizes. The compact dust disks, as well as the inner disk cores of extended ring disks, that look smooth Figure 2. H–R diagram of Taurus sources. Our ALMA at the current resolution will likely show small- sample is labeled with colors as in Figure 1, while the other Taurus members listed in Andrews et al. (2013) are scale or low-contrast substructures at higher shown in gray dots. We use the non-magnetic resolution. The correlation between disk size evolutionary tracks from Feiden (2016) to cover our ALMA sample, with gray-dotted lines representing and disk luminosity correlation demonstrates evolutionary tracks for different stellar masses. that some of the compact disks are optically thick at millimeter wavelengths. eos-nexus.org 16