S316p.126 — Uncovering the monster stars in W49: the most luminous star-forming region in the Milky Way

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Aug 10th at 6:00 PM until 7:30 PM

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Author(s): Shiwei Wu2, Arjan Bik3, Thomas Henning2, Anna Pasquali4, Wolfgang Brandner2, Andrea Stolte1

Institution(s): 1. Argelander Institut fuer Astronomie, 2. Max-Planck-Institute for Astronomy, 3. Stockholm University, 4. Zentrum fuer Astronomie der Universitat Heidelberg

As a part of the LOBSTAR project (Luci OBservations of STARburst regions), which aims at understanding the stellar content of some of the most massive star-forming regions, we present our result on the high-mass stellar content of W49. K-band spectra of the candidate massive stars from VLT/ISAAC and LBT/LUCI provide us with reliable spectral types of dozens of massive stars in this HII region.
The first results show that this region hosts several of the most massive stars in our galaxy. Two most brightest stars, one in the core of the central cluster and one in W49 South, were identified as very massive stars (M > 100 M). Their K-band spectra exhibit strong stellar wind features, and they are classified as O2-3.5If* supergiant stars. After comparison to the Geneva evolutionary models, the mass range of W49nr1 was estimated to be between 100 M and 180 M. Additionally we find 12 O stars with spectral types between O7V and O3V and masses from 25 M to 125 M⊙, respectively.
These results allow us to derive the fundamental parameters of the cluster (mass, age) as well as the total energy output in the form of ionising photons. This will enable us to study the feedback effects of this extreme star forming region in great detail. To our surprise, two young stellar objects with infrared excess feature showing CO emission lines in their spectra are identified. This suggests that circumstellar disks can survive even in this extreme environment. Finally the spatial distribution of the massive stars is analysed to discuss the star formation history and identify potential runaway stars. The extreme properties of this region makes it a good template for more extreme star formation outside our galaxy.

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