J/A+A/647/A13 Evolutionary models for main-sequence phase (Graefener, 2021)
Physics and evolution of the most massive stars in 30 Doradus.
Mass loss, envelope inflation, and a variable upper stellar mass limit.
Graefener G.
<Astron. Astrophys. 647, A13 (2021)>
=2021A&A...647A..13G 2021A&A...647A..13G (SIMBAD/NED BibCode)
ADC_Keywords: Models, evolutionary ; Stars, early-type
Keywords: stars: evolution - stars: early-type - stars: winds, outflows -
stars: massive - stars: mass-loss - stars: Wolf-Rayet
Abstract:
The identification of stellar-mass black-hole mergers with up to
80M☉ as powerful sources of gravitational wave radiation led to
increased interest in the physics of the most massive stars. The
largest sample of possible progenitors of such objects, very massive
stars (VMS) with masses up to 300M☉, have been identified in the
30 Dor star-forming region in the Large Magellanic Cloud (LMC). In
this young starburst analogue, VMS were found to dominate stellar
feedback. Despite their importance, the physics and evolution of VMS
is highly uncertain, mainly due to their proximity to the Eddington
limit.
In this work, we investigate the two most important effects that are
thought to occur near the Eddington limit: enhanced mass loss through
optically thick winds and the formation of radially inflated stellar
envelopes.
We compute evolutionary models for VMS at LMC metallicity and perform
a population synthesis of the young stellar population in 30 Dor. We
adjust the input physics of our models to match the empirical
properties of the single-star population in 30 Dor as derived in the
framework of the VLT-Flames Tarantula Survey (VFTS).
Enhanced mass loss and envelope inflation near the Eddington limit
have a dominant effect on the evolution of the most massive stars.
While the observed mass-loss properties and the associated surface
He-enrichment are well described by our new models, the observed
O-star mass-loss rates are found to cover a much larger range than
theoretically predicted, with particularly low mass-loss rates for the
youngest objects. Also, the (rotational) surface enrichment in the
O-star regime appears to not be well understood. The positions of the
most massive stars in the Hertzsprung-Russell diagram (HRD) are
affected by mass loss and envelope inflation. For instance, the
majority of luminous B supergiants in 30 Dor, and the lack thereof at
the highest luminosities, can be explained through the combination of
envelope inflation and mass loss. Finally, we find that the upper
limit for the inferred initial stellar masses in the greater 30 Dor
region is significantly lower than in its central cluster, R 136,
implying a variable upper limit for the masses of stars.
The implementation of mass-loss and envelope physics in stellar
evolution models turns out to be essential for the modelling of the
observable properties of young stellar populations. While the
properties of the most massive stars (≳100M☉) are well
described by our new models, the slightly less massive O stars
investigated in this work show a much more diverse behaviour than
previously thought, which has potential implications for rotational
mixing and angular momentum transport. While the present models are a
big step forward in the understanding of stellar evolution in the
upper HRD, more work is needed to understand the mechanisms that
regulate the mass-loss rates of OB stars and the physics of
fast-rotating stars.
Description:
We use the Modules for Experiments in Stellar Astrophysics (MESA)
version 11701 (Paxton et al. 2011ApJS..192....3P 2011ApJS..192....3P, 2013ApJS..208....4P 2013ApJS..208....4P,
2015ApJS..220...15P 2015ApJS..220...15P, 2018ApJS..234...34P 2018ApJS..234...34P, 2019ApJS..243...10P 2019ApJS..243...10P) to
compute single-star evolutionary models covering the main-sequence
phase from zero to 99% hydrogen exhaustion in the stellar core.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
list.dat 28 198 List of all evolutionary sequence files
data/* . 198 Evolutionary sequences
--------------------------------------------------------------------------------
Byte-by-byte Description of file: list.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
2- 4 I3 Msun Mass [9/500] Initial mass
7- 10 F4.2 --- Omega [0.0/0.9] Initial fraction of critical rotation
13- 28 A16 --- FileName Name of the file with evolutionary sequence,
in subdirectory data
--------------------------------------------------------------------------------
Byte-by-byte Description of file (#): data/*
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 18 E18.9 yr Age Star age (star_age)
19- 34 F16.9 Msun Mass Star mass (star_mass)
35- 50 F16.5 km/s Vrot Rotational velocity (Vrot)
51- 66 F16.9 [Lsun] logL Luminosity (log_L)
67- 80 F14.3 K Teff Effective temperature (Teff)
81- 96 F16.9 [Rsun] logR Radius (log_R)
97-110 F14.6 [Msun/yr] logMdot Wind mass-loss rate (log_Mdot)
111-125 F15.9 --- H1c Center mass fraction H1 (center_h1)
126-140 F15.9 --- He4c Center mass fraction He4 (center_he4)
141-155 F15.9 --- H1s Surface mass fraction H1 (surface_h1)
156-170 F15.9 --- He4s Surface mass fraction He4 (surface_he4)
171-188 E18.9 --- C12s Surface mass fraction C12 (surface_c12)
189-206 E18.9 --- N14s Surface mass fraction N14 (surface_n14)
207-224 E18.9 --- O16s Surface mass fraction O16 (surface_o16)
--------------------------------------------------------------------------------
Acknowledgements:
Goetz Graefener, goetz(at)astro.uni-bonn.de
(End) Patricia Vannier [CDS] 20-Jan-2021