Massive pre-main sequence stars in M17

• Published in: arXiv.org
• Main Authors: Ramírez-Tannus, María Claudia, Kaper, Lex, de Koter, Alex, Tramper, Frank, Bik, Arjan, Ellerbroek, Lucas E, Ochsendorf, Bram B, Ramírez-Agudelo, Oscar H, Sana, Hugues
• Format: Paper Journal Article
• Language: English
• Published: Ithaca Cornell University Library, arXiv.org 26.04.2017
• Subjects: Accretion disks; Angular momentum; B stars; European Southern Observatory; Homology; Infrared spectra; Massive stars; Near infrared radiation; O stars; Photosphere; Physics - Astrophysics of Galaxies; Physics - Solar and Stellar Astrophysics; Pre-main sequence stars; Protostars; Star formation; Stellar evolution; Velocity distribution; Very Large Telescope
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1704.08216

The formation process of massive stars is still poorly understood. Massive young stellar objects (mYSOs) are deeply embedded in their parental clouds, they are rare and thus typically distant, and their reddened spectra usually preclude the determination of their photospheric parameters. M17 is one of the best studied HII regions in the sky, is relatively nearby, and hosts a young stellar population. With X-shooter on the ESO Very Large Telescope we have obtained optical to near-infrared spectra of candidate mYSOs, identified by Hanson et al. (1997), and a few OB stars in this region. The large wavelength coverage enables a detailed spectroscopic analysis of their photospheres and circumstellar disks. We confirm the pre-main sequence (PMS) nature of six of the stars and characterise the O stars. The PMS stars have radii consistent with being contracting towards the main sequence and are surrounded by a remnant accretion disk. The observed infrared excess and the (double-peaked) emission lines provide the opportunity to measure structured velocity profiles in the disks. We compare the observed properties of this unique sample of young massive stars with evolutionary tracks of massive protostars by Hosokawa & Omukai (2009), and propose that these mYSOs near the western edge of the HII region are on their way to become main-sequence stars (\(\sim 6 - 20\) \(M_{\odot}\)) after having undergone high mass-accretion rates (\({\dot{M}_{\rm acc}} \sim 10^{-4} - 10^{-3}\) \(M_{\odot}\) \(\rm yr^{-1}\)). Their spin distribution upon arrival at the zero age main sequence (ZAMS) is consistent with that observed for young B stars, assuming conservation of angular momentum and homologous contraction.