Article

Radiation-Hydrodynamic Models of the evolving Circumstellar Medium around Massive Stars

The Astrophysical Journal (Impact Factor: 6.73). 06/2011; 737(2). DOI: 10.1088/0004-637X/737/2/100
Source: arXiv

ABSTRACT We study the evolution of the interstellar and circumstellar media around
massive stars (M > 40M_{\odot}) from the main sequence through to the
Wolf-Rayet stage by means of radiationhydrodynamic simulations. We use publicly
available stellar evolution models to investigate the different possible
structures that can form in the stellar wind bubbles around Wolf-Rayet stars.
We find significant differences between models with and without stellar
rotation, and between models from different authors. More specifically, we find
that the main ingredients in the formation of structures in the Wolf-Rayet wind
bubbles are the duration of the Red Supergiant (or Luminous Blue Variable)
phase, the amount of mass lost, and the wind velocity during this phase, in
agreement with previous authors. Thermal conduction is also included in our
models. We find that main-sequence bubbles with thermal conduction are slightly
smaller, due to extra cooling which reduces the pressure in the hot, shocked
bubble, but that thermal conduction does not appear to significantly influence
the formation of structures in post-main-sequence bubbles. Finally, we study
the predicted X-ray emission from the models and compare our results with
observations of the Wolf-Rayet bubbles S\,308, NGC\,6888, and RCW\,58. We find
that bubbles composed primarily of clumps have reduced X-ray luminosity and
very soft spectra, while bubbles with shells correspond more closely to
observations.

0 Bookmarks
 · 
81 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Aims. Observations show nebulae around some massive stars but not around others. If observed, their chemical composition is far from homogeneous. Our goal is to put these observational features into the context of the evolution of massive stars and their circumstellar medium (CSM) and, more generally, to quantify the role of massive stars for the chemical and dynamical evolution of the ISM. Methods. Using the A-MAZE code, we perform 2d-axisymmetric hydrodynamical simulations of the evolution of the CSM, shaped by stellar winds, for a whole grid of massive stellar models from 15 to 120 Msun and following the stellar evolution from the zero-age main-sequence to the time of supernova explosion. In addition to the usual quantities, we also follow five chemical species: H, He, C, N, and O. Results. We show how various quantities evolve as a function of time: size of the bubble, position of the wind termination shock, chemical composition of the bubble, etc. The chemical composition of the bubble changes considerably compared to the initial composition, particularly during the red-supergiant (RSG) and Wolf-Rayet (WR) phases. In some extreme cases, the inner region of the bubble can be completely depleted in hydrogen and nitrogen, and is mainly composed of carbon, helium and oxygen. We argue why the bubble typically expands at a lower rate than predicted by self-similarity theory. In particular, the size of the bubble is very sensitive to the density of the ISM, decreasing by a factor of around 2.5 for each additional dex in ISM density. The bubble size also decreases with the metallicity of the central star, as low-metallicity stars have weaker winds. Our models qualitatively fit the observations of WR ejecta nebulae.
    Astronomy and Astrophysics 11/2013; 559:69. · 5.08 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We analyze Chandra observations of the Wolf-Rayet (WR) bubble NGC 6888. This WR bubble presents similar spectral and morphological X-ray characteristics to those of S 308, the only other WR bubble also showing X-ray emission. The observed spectrum is soft, peaking at the N VII line emission at 0.5 keV with additional line emission at 0.7 - 0.9 keV and a weak tail of harder emission up to ~1.5 keV. This spectrum can be described by a two-temperature optically thin plasma emission model (T_{1}~1.4x10^{6} K, T_{2}~7.4x10^{6} K). We confirm the results of previous X-ray observations that no noticeable temperature variations are detected in the nebula. The X-ray-emitting plasma is distributed in three apparent morphological components: two caps along the tips of the major axis and an extra contribution toward the northwest blowout not reported in previous analysis of the X-ray emission toward this WR nebula. Using the plasma model fits of the Chandra ACIS spectra for the physical properties of the hot gas and the ROSAT PSPC image to account for the incomplete coverage of Chandra observations, we estimate a luminosity of L_X = (7.7\pm0.1)x10^{33} erg/s for NGC 6888 at a distance of 1.26 kpc. The average rms electron density of the X-ray-emitting gas is >= 0.4 cm^{-3} for a total mass >= 1.2 Msun.
    The Astronomical Journal 10/2013; 147(2). · 4.97 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Stars do not generally form in isolation. Instead, they form in clusters, and in these clustered environments newborn stars can have profound effects on one another and on their parent gas clouds. Feedback from clustered stars is almost certainly responsible for a number of otherwise puzzling facts about star formation: that it is an inefficient process that proceeds slowly when averaged over galactic scales; that most stars disperse from their birth sites and dissolve into the galactic field over timescales $\ll 1$ Gyr; and that newborn stars follow an initial mass function (IMF) with a distinct peak in the range $0.1 - 1$ $M_\odot$, rather than an IMF dominated by brown dwarfs. In this review we summarize current observational constraints and theoretical models for the complex interplay between clustered star formation and feedback.
    01/2014;

Full-text (2 Sources)

View
16 Downloads
Available from
May 15, 2014