THE STAR FORMATION NEWSLETTER An electronic publication dedicated to early stellar/planetary evolution and molecular clouds No. 331 — 15 July 2020 Editor: Bo Reipurth ([email protected]) List of Contents The Star Formation Newsletter Interview ...................................... 3 Abstracts of Newly Accepted Papers ........... 6 Editor: Bo Reipurth [email protected] Abstracts of Newly Accepted Major Reviews .. 38 Associate Editor: Anna McLeod Dissertation Abstracts ........................ 40 [email protected] Meetings ..................................... 41 Technical Editor: Hsi-Wei Yen Summary of Upcoming Meetings .............. 43 [email protected] Short Announcements ........................ 44 Editorial Board Joao Alves Alan Boss Jerome Bouvier Cover Picture Lee Hartmann Thomas Henning The cover shows a region of the Serpens star form- Paul Ho ing cloud as imaged by HST. A disk around the Jes Jorgensen young star HBC 672 = EC82 (to the upper right) Charles J. Lada casts a large shadow over its surroundings. See the Thijs Kouwenhoven abstract by Pontoppidan et al. in this issue. Michael R. Meyer Image courtesy NASA, ESA, and Klaus Pontoppi- Ralph Pudritz dan (STScI). Luis Felipe Rodríguez Ewine van Dishoeck Hans Zinnecker The Star Formation Newsletter is a vehicle for fast distribution of information of interest for as- tronomers working on star and planet formation Submitting your abstracts and molecular clouds. You can submit material for the following sections: Abstracts of recently Latex macros for submitting abstracts accepted papers (only for papers sent to refereed and dissertation abstracts (by e-mail to journals), Abstracts of recently accepted major re- [email protected]) are appended to views (not standard conference contributions), Dis- each Call for Abstracts. You can also sertation Abstracts (presenting abstracts of new submit via the Newsletter web inter- Ph.D dissertations), Meetings (announcing meet- face at http://www2.ifa.hawaii.edu/star- ings broadly of interest to the star and planet for- formation/index.cfm mation and early solar system community), New Jobs (advertising jobs specifically aimed towards persons within the areas of the Newsletter), and Short Announcements (where you can inform or re- quest information from the community). Addition- ally, the Newsletter brings short overview articles on objects of special interest, physical processes or theoretical results, the early solar system, as well as occasional interviews. Newsletter Archive www.ifa.hawaii.edu/users/reipurth/newsletter.htm familiar with Kippenhahn’s code, and when I returned to Germany in the second half of 1967, I joined his theory Immo Appenzeller group. Kippenhahn’s code was hydrostatic and Newto- in conversation with Bo Reipurth nian, but the quasar model required a dynamical and rel- ativistic code. Therefore, I modified Kippenhahn’s code in two steps: First I replaced the hydrostatic equation with a Newtonian equation of motion. After the resulting New- tonian dynamical code was running, I replaced the New- tonian equations by the corresponding relativistic equa- tions. The numerical results showed that Fowler’s quasar model could not explain the quasars. Therefore, I retired the relativistic code and applied the Newtonian version to various problems of stellar physics, including star for- mation via the contraction and collapse of interstellar gas clouds. A few years earlier Richard Larson and others had demonstrated that the outcome of such computations was a ’protostar’, consisting of a hydrostatic core, which was accreting matter from an extended envelope. Sim- ulations, carried out together with Werner Tscharnuter, Q: First of all, congratulations on your 80th birthday. You confirmed this result for different parameters and differ- have witnessed essentially the whole development of the ent initial conditions. As our code included the energy subject of star formation. How did your own involvement production by nuclear reactions, we could simulate the with the subject start? evolution of more massive protostars, where the hydro- A: Thanks, Bo, for the congratulations and for inviting me static evolutionary time scale of the core becomes shorter to your interview series. To your question: I got involved than the accretion time scale. For an initially 60 M⊙ pro- in star formation as a by-product of work on quasars. I tostar we found that the mass accretion was halted and had studied physics at the universities of Tübingen and the remaining envelope was blown away, soon after hydro- Göttingen. After graduating in 1966 with a thesis on the gen burning had started in the core. Our code did not the local interstellar magnetic field, as traced by the inter- include rotation, but we expected that with rotation the stellar polarization, I spent some time at the University outcome would have been qualitatively similar. of Chicago. There I built a new and more sensitive po- Q: You then returned to observations and wrote a series of larimeter, which I used at the telescopes of the McDonald papers on the so-called YY Orionis-type stars, like S CrA Observatory in Texas. Among my targets were the newly and RW Aur. discovered quasars, which were the most discussed objects of that time. To test one of the mechanisms, which had A: I enjoyed doing theoretical work in Kippenhan’s group, been proposed to explain quasars, I carried out numeri- but I never completely abandoned observational astron- cal model computations, and as a by-product I obtained omy. When ESO’s La Silla Observatory in Chile was offi- a computer code that was suitable for simulating star for- cially opened in 1969, I started using the first small tele- mation. scopes there. With larger telescopes under construction at ESO and the creation of the German-Spanish Astronom- Q: Could you explain this in more detail? Why did you ical Center on Calar Alto in Spain, observational astron- switch to theory and how did this lead to your investiga- omy became attractive again in Germany. Thus, when tions of massive protostars? And what were your conclu- I was offered a professorship at the University of Heidel- sions? berg in 1975, I accepted with the aim of forming a research A: My initial aim was to investigate a quasar model, which group, which combined theory and observations. One of had been proposed in 1966 by William Fowler. He had sug- our first programs in Heidelberg was identifying observa- gested that quasars resulted from relaxation oscillations of tional counterparts of the predicted protostars. Among 5 unstable supermassive (M ≥ 10 M⊙) stars. To test this the prime candidates were the T Tauri stars. They were scenario I planned numerical simulations using the stellar known to be young, and they showed chromospheric emis- evolution code of Rudolf Kippenhahn. Kippenhahn had sion spectra which resembled those predicted for the cool- started developing this code at the Max-Planck-Institute ing zones of protostellar accretion shocks. Already in 1948 for Astrophysics in Munich, but in 1965 he had moved to Jesse Greenstein had suggested that the properties of the Göttingen, where he formed a new group for theoretical as- T Tauri stars resulted from mass infall on forming stars. trophysics. To earn money, I had done some programming This suggestion was supported by Merle Walker, who in for his group while working on my thesis. Therefore, I was 3 1972 identified a subclass of the T Tauri stars, which he A: This was a joint project with an astronomy group, called ‘YY Ori stars’, and which were characterized by a which at that time existed at the Norwegian University strong UV excess at the U band and redward displaced of Tromsø. Tromsø is located about 350 km north of the absorption components at the higher Balmer lines. The Arctic Circle. Thus, at midwinter the sun remains be- observed velocity shifts were close to the expected free-fall low the horizon for about 50 days, and the sky remains velocities of low-mass PMS stars. To investigate the sug- dark for about three weeks. Tromsø itself is not a suit- gested protostellar nature of the T Tauri stars, we com- able observatory site, as the winters bring fog, clouds, and bined non-LTE line profile calculations, done mainly by heavy snowfall. But its University operated a 50 cm Tele- Claude Bertout and Ulrich Bastian, with spectroscopic scope about 50 km east of Tromsø, in the Skibotn valley, observations, carried out by Claude Bertout, Bernhard which belongs to the places with the highest percentage of Wolf, Joachim Krautter, Reinhard Mundt, Carlos Chavar- clear sky in Norway. As the Skibotn telescope did not have ria, and others. We found signs for mass accretion in the spectroscopic equipment, we brought a fiber-coupled spec- spectra of most classical T Tau stars and redward dis- trometer with a two-stage image tube from Heidelberg. placed absorption at many different spectral lines. The observations were carried out jointly by students and Q: You were among the first to explore the ultraviolet spec- staff from Tromsø and Heidelberg. As you mentioned, the trum of young stars using the newly launched IUE satel- main target was the YY Ori star RW Aur, which could lite. What did you learn? be observed, with minor interruptions, for about 12 days. Our results disagreed with most of the mechanisms which A: In addition to a chromospheric line spectrum, proto- had been suggested for the irregular spectral variations of stars were predicted to emit a strong UV flux originating RW Aur, but they were consistent with the assumption of in the accretion shocks. Indications that this was actu- variable mass accretion being the main cause of the vari- ally observed, were the UV excess at the U band, and the ations. increase of the flux between the U band and the atmo- spheric cutoff, which was seen on spectrograms observed Q: In 1983, you and David Dearborn used models of vari- by Merle Walker with a Lallemand camera.