Westerlund 1 as a Template for Massive Star Evolution

AbstractWith a dynamical mass Mdyn ~ 1.3×105 M⊙ and a lower limit Mcl > 5 × 104 M⊙ from star counts, Westerlund 1 is the most massive young open cluster known in the Galaxy and thus the perfect laboratory to study massive star evolution. We have developed a comprehensive spectral classification scheme for supergiants based on features in the 6000–9000Å range, which allows us to identify > 30 very luminous supergiants in Westerlund 1 and ~ 100 other less evolved massive stars, which join the large population of Wolf-Rayet stars already known. Though detailed studies of these stars are still pending, preliminary rough estimates suggest that the stars we see are evolving to the red part of the HR diagram at approximately constant luminosity.

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The Evolution of the Precursor of SN 1987 A

International Astronomical Union Colloquium ◽

10.1017/s0252921100094173 ◽

1988 ◽

Vol 108 ◽

pp. 408-409

Author(s):

André Maeder

Keyword(s):

Mass Loss ◽

Massive Star ◽

Essential Property ◽

Solar Mass ◽

Star Evolution ◽

Final Mass ◽

The Galaxy ◽

Age Sequence ◽

Massive Star Evolution ◽

Hr Diagram

SummaryIdeally, the evolutionary models for the precursor of SN 1987 A should account for both the SN properties and the observational constraints for massive stars with relevant mass and composition.Mass loss is an essential property of massive star evolution. Recent parametrisations of mass loss rates for galactic stars cover the whole HR diagram. There are indications that for given L and Teff values, is lower at lower metallicity and therefore is lower in the LMC than in the Galaxy, thus we take with f < 1. Various models of an intitial 20 M⊙ star with f=0.2, 0.4, 0.6 and 1.0 are constructed (cf. Fig. 1) with a metallicity Z=0.006 and a moderate overshooting dover=0.3 Hp. From these models, we suggest an initial mass on the zero age sequence of 17 to 18 M⊙. The pre-SN location in the HR diagram very much depends on the remaining stellar mass, or more precisely on the mass of the remaining H-rich envelope. A final location at log Teff ≃ 4.2 is obtained for a final mass of about 9.0 M⊙ (cf. Fig.1). Scaled to an initial value of 17 M⊙, this corresponds to a final mass of about 8 M⊙ and a remaining H-rich envelope of a few tenths of a solar mass at most. The stellar surface exhibits CNO equilibrium values with C/N ≃ 0.01 and O/N ≃ 0.1 in mass fraction, and an hydrogen content X (surf) = 0.39. The blue progenitor is obtained for f=0.4, i.e. for -values in the LMC equal to 40% of the galactic values.

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A spectroscopic multiplicity survey of Galactic Wolf-Rayet stars

Astronomy and Astrophysics ◽

10.1051/0004-6361/202038446 ◽

2020 ◽

Vol 641 ◽

pp. A26

Author(s):

K. Dsilva ◽

T. Shenar ◽

H. Sana ◽

P. Marchant

Keyword(s):

Massive Star ◽

Massive Stars ◽

Detection Threshold ◽

Significance Level ◽

Multiple Systems ◽

La Palma ◽

Star Evolution ◽

Short Period ◽

The Galaxy ◽

Massive Star Evolution

Context. It is now well established that the majority of massive stars reside in multiple systems. However, the effect of multiplicity is not sufficiently understood, resulting in a plethora of uncertainties about the end stages of massive-star evolution. In order to investigate these uncertainties, it is useful to study massive stars just before their demise. Classical Wolf-Rayet stars represent the final end stages of stars at the upper-mass end. The multiplicity fraction of these stars was reported to be ∼0.4 in the Galaxy but no correction for observational biases has been attempted. Aims. The aim of this study is to conduct a homogeneous radial-velocity survey of a magnitude-limited (V ≤ 12) sample of Galactic Wolf-Rayet stars to derive their bias-corrected multiplicity properties. The present paper focuses on 12 northern Galactic carbon-rich (WC) Wolf-Rayet stars observable with the 1.2 m Mercator telescope on the island of La Palma. Methods. We homogeneously measured relative radial velocities (RVs) for carbon-rich Wolf-Rayet stars using cross-correlation. Variations in the derived RVs were used to flag binary candidates. We investigated probable orbital configurations and provide a first correction of observational biases through Monte-Carlo simulations. Results. Of the 12 northern Galactic WC stars in our sample, seven show peak-to-peak RV variations larger than 10 km s−1, which we adopt as our detection threshold. This results in an observed spectroscopic multiplicity fraction of 0.58 with a binomial error of 0.14. In our campaign, we find a clear lack of short-period (P < ∼100 d), indicating that a large number of Galactic WC binaries likely reside in long-period systems. Finally, our simulations show that at the 10% significance level, the intrinsic multiplicity fraction of the Galactic WC population is at least 0.72.

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Outflowing Envelopes From Stars at Arbitrary Optical Depths a New Approach to the Problem

Highlights of Astronomy ◽

10.1017/s1539299600021316 ◽

1998 ◽

Vol 11 (1) ◽

pp. 381-381

Author(s):

A.V. Dorodnitsyn

Keyword(s):

Differential Equations ◽

Massive Star ◽

System Of Differential Equations ◽

Continuous Transition ◽

Satisfactory Description ◽

Sonic Point ◽

New Approach ◽

Star Evolution ◽

Matter Flux ◽

Massive Star Evolution

We have considered a stationary outflowing envelope accelerated by the radiative force in arbitrary optical depth case. Introduced approximations provide satisfactory description of the behavior of the matter flux with partially separated radiation at arbitrary optical depths. The obtained systemof differential equations provides a continuous transition of the solution between optically thin and optically thick regions. We analytically derivedapproximate representation of the solution at the vicinity of the sonic point. Using this representation we numerically integrate the system of equations from the critical point to the infinity. Matching the boundary conditions we obtain solutions describing the problem system of differential equations. The theoretical approach advanced in this work could be useful for self-consistent simulations of massive star evolution with mass loss.

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