J/A+A/625/A104 Stellar parameters of OB stars in SMC wing (Ramachandran+, 2019)
Testing massive star evolution, star formation history, and feedback at low
metallicity: Spectroscopic analysis of OB stars in the SMC Wing
Ramachandran V., Hamann W.-R., Oskinova L.M., Gallagher J.S., Hainich R.,
Shenar T., Sander A.A.C., Todt H., Fulmer L.
<Astron. Astrophys. 625, A104 (2019)>
=2019A&A...625A.104R 2019A&A...625A.104R (SIMBAD/NED BibCode)
ADC_Keywords: Magellanic Clouds ; Stars, OB ; MK spectral classification
Keywords: stars: evolution - stars: massive - stars: mass-loss -
Magellanic Clouds - Hertzsprung-Russell and C-M diagrams -
techniques: spectroscopic
Abstract:
Stars which start their lives with spectral types O and early-B are
the progenitors of core-collapse supernovae, long gamma-ray bursts,
neutron stars, and black holes. These massive stars are the primary
sources of stellar feedback in star-forming galaxies. At low
metallicities, the properties of massive stars and their evolution are
not yet fully explored. Here we report a spectroscopic study of 320
massive stars of spectral types O (23 stars) and B (297 stars) in the
Wing of the Small Magellanic Cloud (SMC). The spectra, which we
obtained with the ESO Very Large Telescope, were analyzed using
state-of-the-art stellar atmosphere models, and the stellar parameters
were determined. We find that the stellar winds of our sample stars
are generally much weaker than theoretically expected. The stellar
rotation rates show broad, tentatively bi-modal distribution. The
upper Hertzsprung-Russell diagram (HRD) is well populated by the stars
of our sample from a specific field in the SMC Wing. A few very
luminous O stars are found close to the main sequence, while all
other, slightly evolved stars obey a strict luminosity limit.
Considering additionally massive stars in evolved stages, with
published parameters and located all over the SMC, essentially
confirms this picture. The comparison with single-star evolutionary
tracks suggest a dichotomy in the fate of massive stars in the SMC.
Only stars with an initial mass below ∼30M☉ seem to evolve from
the main sequence to the cool side of the HRD to become a red
supergiant and to explode as type II-P supernova. In contrast, stars
with initially more than ∼30M☉ol appear to stay always hot and
might evolve quasi chemically homogeneously, finally collapsing to
relatively massive black holes. However, we find no indication that
chemical mixing is correlated with rapid rotation.
We measure the key parameters of stellar feedback and establish the
links between the rates of star formation and supernovae. Our study
demonstrates that in metal-poor environments the stellar feedback is
dominated by core-collapse supernovae in combination with winds and
ionizing radiation supplied by a few of the most massive stars. We
found indications of stochastic mode of massive star-formation, where
the resulting stellar population is fully capable of producing large
scale structures like the supergiant shell SMC-SGS 1 in the Wing. The
low level of feedback in metal-poor stellar populations allows star
formation episodes to persist over long time scales.
Description:
Spectroscopic study of 320 OB stars in the Wing of the Small
Magellanic Cloud is presented here. The full catalog of the survey
targets is given in table B1 with their names, positions, and spectral
types. The stellar and wind parameters of individual OB stars derived
from spectral analysis are given in table B2. The ages and masses
derived based on stellar evolutionary tracks are given in table B4.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tableb1.dat 44 320 Coordinates and spectral types of sample OB stars
tableb2.dat 86 320 Stellar parameters of all OB stars in the
N 206 superbubble
tableb4.dat 14 320 Ages and evolutionary masses of the OB stars
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See also:
J/A+A/609/A7 : Of-type stars in N206 in the LMC (Ramachandran+, 2018)
J/A+A/615/A40 : OB stars in N206 in the LMC (Ramachandran+, 2018)
Byte-by-byte Description of file: tableb1.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- SMCSGS-FS [1/320] Catalog number
5- 17 F13.10 deg RAdeg Right ascension (J2000)
19- 32 F14.10 deg DEdeg Declination (J2000)
34- 44 A11 --- SpType Spectral and luminosity class
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Byte-by-byte Description of file: tableb2.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- SMCSGS-FS [1/320] Catalog number
5- 19 A15 --- SpType Spectral and luminosity class
21- 22 I2 kK Teff Effective temperature
24- 27 F4.2 [Lsun] logL Luminosity
29- 31 F3.1 [cm/s2] logg Gravity
33- 37 F5.1 [Msun/yr] logdM/dt Mass-loss rate
39 A1 --- n_logdM/dt [*] Note on logdM/dt (1)
42- 45 F4.2 mag E(B-V) Color excess
47- 50 F4.1 mag VMAG Absolute visual magnitude
52- 55 F4.1 Rsun R Stellar radius
57- 60 I4 km/s vinf Terminal velocity
62 A1 --- n_vinf [*] Note on vinf (2)
65- 67 I3 km/s vsini Projected rotational velocity
69- 71 I3 km/s RV Radial velocity
73- 74 I2 Msun M Stellar mass
76- 79 F4.1 [s-1] logQ Rate of hydrogen ionizing photons
81- 84 F4.1 [Lsun] logLmec Mechanical luminosity
86 A1 --- n_logLmec [*] Note on logLmec (3)
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Note (1): * indicates logdM/dt values determined from UV P-Cygni profiles.
We derived a relation for these measured logdM/dt and logL and applied for
rest of the stars.
Note (2): * indicates vinf values determined from UV P-Cygni profiles. Other
values are theoretically calculated from escape velocity.
Note (3): * indicates logLmec values calculated for nine stars with UV spectra.
For the rest of the stars we adopted values from the derived relation of
these nine stars.
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Byte-by-byte Description of file: tableb4.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- SMCSGS-FS [1/320] Catalog number
5- 9 F5.1 Myr Age Age of the star
11- 14 F4.1 Msun Mass Evolutionary mass
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Acknowledgements:
Varsha Ramachandran, varsha(at)astro.physik.uni-potsdam.de
(End) Patricia Vannier [CDS] 09-Apr-2019