Corrections for Hydrostatic Atmospheric Models: Radii and Effective Temperatures of Wolf Rayet Stars

Loore, C. De; Hellings, P.; Lamers, H. J. G. L. M.

doi:10.1007/978-94-009-7910-9_6

Cited by 10 publications

(2 citation statements)

References 3 publications

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“…11 and 12 of Kippenhahn et al (2013) for thorough reviews. When the optical depth of the wind is appreciable, for instance when the star is a WR, the τ = 2/3 surface moves outwards in comparison with the optically-thin case (De Loore et al 1982). To correct for this effect, the Geneva code uses a simple scheme that takes into account both electron-scattering and line opacities.…”

Section: Combining the Geneva Code And Cmfgen Solutionsmentioning

confidence: 99%

The evolution of massive stars and their spectra

Groh

Meynet

Ekström

et al. 2014

A&A

162

189

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For the first time, the interior and spectroscopic evolution of a massive star is analyzed from the zero-age main sequence (ZAMS) to the pre-supernova (SN) stage. For this purpose, we combined stellar evolution models using the Geneva code and stellar atmospheric/wind models using CMFGEN. With our approach, we were able to produce observables, such as a synthetic high-resolution spectrum and photometry, thereby aiding the comparison between evolution models and observed data. Here we analyze the evolution of a nonrotating 60 M star and its spectrum throughout its lifetime. Interestingly, the star has a supergiant appearance (luminosity class I) even at the ZAMS. We find the following evolutionary sequence of spectral types: O3 I (at the ZAMS), O4 I (middle of the H-core burning phase), B supergiant (BSG), B hypergiant (BHG), hot luminous blue variable (LBV; end of H-core burning), cool LBV (H-shell burning through the beginning of the He-core burning phase), rapid evolution through late WN and early WN, early WC (middle of He-core burning), and WO (end of He-core burning until core collapse). We find the following spectroscopic phase lifetimes: 3.22 × 10 6 yr for the O-type, 0.34 × 10 5 yr (BSG), 0.79 × 10 5 yr (BHG), 2.35 × 10 5 yr (LBV), 1.05 × 10 5 yr (WN), 2.57 × 10 5 yr (WC), and 3.80 × 10 4 yr (WO). Compared to previous studies, we find a much longer (shorter) duration for the early WN (late WN) phase, as well as a long-lived LBV phase. We show that LBVs arise naturally in single-star evolution models at the end of the MS when the mass-loss rate increases as a consequence of crossing the bistability limit. We discuss the evolution of the spectra, magnitudes, colors, and ionizing flux across the star's lifetime, and the way they are related to the evolution of the interior. We find that the absolute magnitude of the star typically changes by ∼6 mag in optical filters across the evolution, with the star becoming significantly fainter in optical filters at the end of the evolution, when it becomes a WO just a few 10 4 years before the SN explosion. We also discuss the origin of the different spectroscopic phases (i.e., O-type, LBV, WR) and how they are related to evolutionary phases (H-core burning, H-shell burning, He-core burning).

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Section: Combining the Geneva Code And Cmfgen Solutionsmentioning

confidence: 99%

The evolution of massive stars and their spectra

Groh

Meynet

Ekström

et al. 2014

A&A

162

189

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“…If we conservatively assume that the uncertainty in R is of the same order of magnitude as the wind extension, we can use the relations by de Loore et al (1982) as an estimate. It turns out that for all objects in Table 3 the estimated wind extension is rather high, with R ph ∼ 2...3 R .…”

Section: Rotational Velocitiesmentioning

confidence: 99%

Rotating Wolf-Rayet stars in a post RSG/LBV phase

Gräfener

Harries

Langer

2012

A&A

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Context. Wolf-Rayet (WR) stars with fast rotating cores are thought to be the direct progenitors of long-duration gamma-ray bursts (LGRBs). A well accepted evolutionary channel towards LGRBs is chemically-homogeneous evolution at low metallicities, which completely avoids a red supergiant (RSG), or luminous blue variable (LBV) phase. On the other hand, strong absorption features with velocities of several hundred km s −1 have been found in some LGRB afterglow spectra (GRB 020813 and GRB 021004), which have been attributed to dense circumstellar (CS) material that has been ejected in a previous RSG or LBV phase, and is interacting with a fast WR-type stellar wind. Aims. Here we investigate the properties of Galactic WR stars and their environment to identify similar evolutionary channels that may lead to the formation of LGRBs. Methods. We compile available information on the spectropolarimetric properties of 29 WR stars, the presence of CS ejecta for 172 WR stars, and the CS velocities in the environment of 34 WR stars in the Galaxy. We use linear line-depolarization as an indicator of rotation, nebular morphology as an indicator of stellar ejecta, and velocity patterns in UV absorption features as an indicator of increased velocities in the CS environment. Results. Based on previous nebular classifications, we determine an incidence rate of ∼23% of WR stars with "possible ejecta nebulae" in the Galaxy. We find that this group of objects dominates the population of WR stars with spectropolarimetric signatures of rotation, while WR stars without such nebulae only rarely show indications of rotation. This confirms the correlation between rotation and CS ejecta from our previous work. The corresponding objects are most likely in an early stage after a preceding RSG or LBV phase, and have not yet lost their angular momenta due to the strong mass-loss in the WR phase. From their photometric periods we estimate rotation parameters in the range ω = rot / crit = 0.04...0.25, corresponding to moderate rotation speeds of 36...120 km s −1 . These values are very uncertain, but comply with the specific surface angular momentum requirement for LGRB progenitors. From UV absorption profiles we only find weak evidence for a correlation between rotation and increased CS velocities. In particular, the CS velocities of Galactic WR stars are much lower than what is observed for GRB 020813 and GRB 021004. Conclusions. Our results indicate that, in the Galaxy, "young" WR stars shortly after a RSG/LBV phase, show spectropolarimetric signatures of rotation. Their rotation rates are likely to be enhanced with respect to the majority of Galactic WR stars. According to their estimated specific surface angular momenta, a subgroup of stars exploding in this phase may represent an evolutionary channel towards LGRBs at high metallicities, comparable to the Galaxy. Although the UV absorption features in our sample turn out to be different from those observed in GRB 020813 and GRB 021004, it is interesting that for three WR stars with s...

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Advancements in the Stellar Evolution Theory: The Role of Convective Overshooting All Across the HR Diagram

Chiosi

1986

Spectral Evolution of Galaxies

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Corrections for Hydrostatic Atmospheric Models: Radii and Effective Temperatures of Wolf Rayet Stars

Cited by 10 publications

References 3 publications

The evolution of massive stars and their spectra

The evolution of massive stars and their spectra

Rotating Wolf-Rayet stars in a post RSG/LBV phase

Advancements in the Stellar Evolution Theory: The Role of Convective Overshooting All Across the HR Diagram

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