Massive pre-main-sequence stars in M17: 1st1^{\rm st} and 2nd2^{\rm nd} overtone CO bandhead emission and the thermal infrared

Recently much progress has been made in probing the embedded stages of massive star formation, pointing to formation scenarios akin to a scaled up version of low-mass star formation. However, the latest stages of massive star formation have rarely been observed. Using 1st and 2nd overtone CO bandhead emission and near- to mid-infrared photometry we aim to characterize the remnant formation disks around 5 unique pre-main-sequence (PMS) stars with masses $6-12~\rm M_{\odot}$, that have constrained stellar parameters thanks to their detectable photospheres. We seek to understand this emission and the disks it originates from in the context of the evolutionary stage of the studied sources. We use an analytic LTE disk model to fit the CO bandhead and the dust emission, found to originate in different disk regions. For the first time we modeled the 2nd overtone emission. Furthermore, we fit continuum normalized bandheads and show the importance of this in constraining the emission region. We also include $^{13}\rm CO$ in our models as an additional probe of the young nature of the studied objects. We find that the CO emission originates in a narrow region close to the star (<1 AU) and under very similar disk conditions (temperatures and densities) for the different objects. This is consistent with previous modeling of this emission in a diverse range of young stellar objects. We discuss these results in the context of the positions of these PMS stars in the Hertzsprung-Russel diagram and the CO emission's association with early age and high accretion rates in (massive) young stellar objects. We conclude that, considering their mass range and for the fact that their photospheres are detected, the M17 PMS stars are observed in a relatively early formation stage. They are therefore excellent candidates for longer wavelength studies to further constrain the end stages of massive star formation.Comment: 21 pages, 12 figure

Spectroscopic variability of massive pre-main-sequence stars in M17

It is a challenge to study the formation process of massive stars: their formation time is short, they are few, often deeply embedded, and at relatively large distances. Our strategy is to study the outcome of the star formation process and to look for signatures remnant of the formation. We have access to a unique sample of (massive) pre-main-sequence (PMS) stars in the giant HII region M17, showing a photosphere and circumstellar disk. The aim is to determine the variability properties of the hot gaseous disks to understand the physical origin of the emission lines and identify dominant physical processes in these disks. We have obtained multiple-epoch (4-5 epochs) VLT/X-shooter spectra of six young stars in M17 covering about a decade. Using stacked spectra we update the spectral classification and identify circumstellar features. With the temporal variance method (TVS) we determine the extent and amplitude of the spectral line variations. The double-peaked emission lines in the PMS stars with gaseous disks are used to determine peak-to-peak velocities, V/R-ratios and the radial velocity of the systems. We identify many disk features, under which a new detection of CO bandhead and CI emission. In three of the stars we detect spectral variability, mainly in lines originating in the circumstellar disk, in a velocity range up to 320 km/s. In two PMS stars the ratio between the blue and red peaks shows a correlation with the peak-to-peak velocity, possibly explained by a spiral-arm structure in the disk. The PMS stars with variability are at similar positions in the HRD but show significant differences in disk lines and variability. The extent and timescale of the variability differs for each star and per line (sets). We find indications for an accretion flow, slow disk winds and/or disk structures in the hot gaseous inner disk as the cause of the variability in these PMS stars.Comment: 27 pages, 24 figures, accepted for publication in Astronomy and Astrophysics, abstract abbreviate

Bringing Stellar Evolution & Feedback Together: Summary of proposals from the Lorentz Center Workshop, 2022

Stars strongly impact their environment, and shape structures on all scales throughout the universe, in a process known as ``feedback''. Due to the complexity of both stellar evolution and the physics of larger astrophysical structures, there remain many unanswered questions about how feedback operates, and what we can learn about stars by studying their imprint on the wider universe. In this white paper, we summarize discussions from the Lorentz Center meeting `Bringing Stellar Evolution and Feedback Together' in April 2022, and identify key areas where further dialogue can bring about radical changes in how we view the relationship between stars and the universe they live in.Comment: Accepted to the Publications of the Astronomical Society of the Pacifi

Physics and Chemistry of Planet-Forming Disks in Extreme Radiation Environments

Our knowledge about the formation history of planetary systems is obtained by comparing the demographics of proto-planetary disks with the exoplanetary system population. Most of the disks that we have been able to characterize to date are located in nearby low-mass star forming regions. However, it is well known that most stars form in denser environments and therefore, it is questionable that the well studied population of planet forming disks is representative of those in which most exoplanets were assembled. Due to their large distances and high densities, so far it has been impossible to study the physical and chemical properties of proto-planetary disks in massive star-forming regions. We will exploit the unique resolution and sensitivity of JWST/MIRI to explore for the first time the impact of disk evaporation on the disk structure, warm disk chemistry, and dust mineralogy, all of which are important for planet formation models and exoplanet atmosphere composition. The derived physical and chemical properties will be compared to similar data of low-mass star forming regions of JWST GTO programmes

Massive pre-main-sequence stars in M17

Context. The young massive-star-forming region M17 contains optically visible massive pre-main-sequence stars that are surrounded by circumstellar disks. Such disks are expected to disappear when these stars enter the main sequence. The physical and dynamical structure of these remnant disks are poorly constrained, especially the inner regions where accretion, photo-evaporation, and companion formation and migration may be ongoing. Aims. We aim to constrain the physical properties of the inner parts of the circumstellar disks of massive young stellar objects B243 (6 M⊙) and B331 (12 M⊙), two systems for which the central star has been detected and characterized previously despite strong dust extinction. Methods. Two-dimensional radiation thermo-chemical modelling with PR

Bringing Stellar Evolution and Feedback Together:Summary of Proposals from the Lorentz Center Workshop

Stars strongly impact their environment, and shape structures on all scales throughout the universe, in a process known as “feedback.” Due to the complexity of both stellar evolution and the physics of larger astrophysical structures, there remain many unanswered questions about how feedback operates and what we can learn about stars by studying their imprint on the wider universe. In this white paper, we summarize discussions from the Lorentz Center meeting “Bringing Stellar Evolution and Feedback Together” in 2022 April and identify key areas where further dialog can bring about radical changes in how we view the relationship between stars and the universe they live in.</p

Bringing stellar evolution and feedback together: summary of proposals from the Lorentz Center workshop

Stars strongly impact their environment, and shape structures on all scales throughout the universe, in a process known as "feedback." Due to the complexity of both stellar evolution and the physics of larger astrophysical structures, there remain many unanswered questions about how feedback operates and what we can learn about stars by studying their imprint on the wider universe. In this white paper, we summarize discussions from the Lorentz Center meeting "Bringing Stellar Evolution and Feedback Together" in 2022 April and identify key areas where further dialog can bring about radical changes in how we view the relationship between stars and the universe they live in