VLT/X-shooter spectroscopy of massive young stellar objects in the 30 Doradus region of the Large Magellanic Cloud

The process of massive star (M ≥ 8 M⊙) formation is still poorly understood. Observations of massive young stellar objects (MYSOs) are challenging due to their rarity, short formation timescale, large distances, and high circumstellar extinction. Here, we present the results of a spectroscopic analysis of a population of MYSOs in the Large Magellanic Cloud. We took advantage of the spectral resolution and wavelength coverage of X-shooter (300−2500 nm), which is mounted on the European Southern Observatory Very Large Telescope, to detect characteristic spectral features in a dozen MYSO candidates near 30 Doradus, the largest starburst region in the Local Group hosting the most massive stars known. The X-shooter spectra are strongly contaminated by nebular emission. We used a scaling method to subtract the nebular contamination from our objects. We detect Hα, β, [O I] 630.0 nm, Ca II, infrared triplet [Fe II] 1643.5 nm, fluorescent Fe II 1687.8 nm, H2 2121.8 nm, Brγ, and CO bandhead emission in the spectra of multiple candidates. This leads to the spectroscopic confirmation of ten candidates as bona fide MYSOs. We compared our observations with photometric observations from the literature and find all MYSOs to have a strong near-infrared excess. We computed lower limits to the brightness and luminosity of the MYSO candidates, confirming the near-infrared excess and the massive nature of the objects. No clear correlation is seen between the Brγ luminosity and metallicity. Combining our sample with other LMC samples results in a combined detection rate of disk features, such as fluorescent Fe II and CO bandheads, which is consistent with the Galactic rate (40%). Most of our MYSOs show outflow features

The outcome of massive star formation

Massive stars play a crucial role in the Universe. They shape their surroundings by injecting large amounts of energy and momentum and they produce new, heavy elements that are the building blocks of new stars, planets, and life. They are usually observed in close binaries. Due to the lack of observations covering the earliest stages of their lives, the formation process of massive (binary) stars is poorly understood. In this thesis we present observational studies of the outcome of massive star formation. We present the first spectroscopically confirmed population of massive pre-main sequence stars in the giant HII region M17, where their temperature, luminosity, radius, and projected radial velocity are measured. We also discuss their multiplicity properties and find that the young stars in M17 show a very low radial velocity dispersion in comparison to somewhat older stellar clusters of similar mass. We propose that massive stars are formed in binaries with wide orbits that shrink in the first few million years of evolution. By studying the young populations in three other Galactic star forming regions we find a possible relation between the age of the clusters and the radial velocity dispersion of their massive stars. The latter supports the hypothesis that massive stars form in wide orbits. We present a study of diffuse interstellar bands (DIBs) towards M17 and find a relation of the DIB strength with the grain size distribution of the interstellar medium. Finally, we present two ongoing projects to test the wide binary hypothesis

X-Shooting ULLYSES: massive stars at low metallicity. I. Project Description

International audienceObservations of individual massive stars, super-luminous supernovae, gamma-ray bursts, and gravitational-wave events involving spectacular black-hole mergers, indicate that the low-metallicity Universe is fundamentally different from our own Galaxy. Many transient phenomena will remain enigmatic until we achieve a firm understanding of the physics and evolution of massive stars at low metallicity (Z). The Hubble Space Telescope has devoted 500 orbits to observe 250 massive stars at low Z in the ultraviolet (UV) with the COS and STIS spectrographs under the ULLYSES program. The complementary ``X-Shooting ULLYSES'' (XShootU) project provides enhanced legacy value with high-quality optical and near-infrared spectra obtained with the wide-wavelength coverage X-shooter spectrograph at ESO's Very Large Telescope. We present an overview of the XShootU project, showing that combining ULLYSES UV and XShootU optical spectra is critical for the uniform determination of stellar parameters such as effective temperature, surface gravity, luminosity, and abundances, as well as wind properties such as mass-loss rates in function of Z. As uncertainties in stellar and wind parameters percolate into many adjacent areas of Astrophysics, the data and modelling of the XShootU project is expected to be a game-changer for our physical understanding of massive stars at low Z. To be able to confidently interpret James Webb Space Telescope (JWST) spectra of the first stellar generations, the individual spectra of low Z stars need to be understood, which is exactly where XShootU can deliver

X-Shooting ULLYSES: massive stars at low metallicity. I. Project Description

International audienceObservations of individual massive stars, super-luminous supernovae, gamma-ray bursts, and gravitational-wave events involving spectacular black-hole mergers, indicate that the low-metallicity Universe is fundamentally different from our own Galaxy. Many transient phenomena will remain enigmatic until we achieve a firm understanding of the physics and evolution of massive stars at low metallicity (Z). The Hubble Space Telescope has devoted 500 orbits to observe 250 massive stars at low Z in the ultraviolet (UV) with the COS and STIS spectrographs under the ULLYSES program. The complementary ``X-Shooting ULLYSES'' (XShootU) project provides enhanced legacy value with high-quality optical and near-infrared spectra obtained with the wide-wavelength coverage X-shooter spectrograph at ESO's Very Large Telescope. We present an overview of the XShootU project, showing that combining ULLYSES UV and XShootU optical spectra is critical for the uniform determination of stellar parameters such as effective temperature, surface gravity, luminosity, and abundances, as well as wind properties such as mass-loss rates in function of Z. As uncertainties in stellar and wind parameters percolate into many adjacent areas of Astrophysics, the data and modelling of the XShootU project is expected to be a game-changer for our physical understanding of massive stars at low Z. To be able to confidently interpret James Webb Space Telescope (JWST) spectra of the first stellar generations, the individual spectra of low Z stars need to be understood, which is exactly where XShootU can deliver