2013A&A...555A...1B


Query : 2013A&A...555A...1B

2013A&A...555A...1B - Astronomy and Astrophysics, volume 555A, 1-1 (2013/7-1)

Massive stars at low metallicity. Evolution and surface abundances of O dwarfs in the SMC.

BOURET J.-C., LANZ T., MARTINS F., MARCOLINO W.L.F., HILLIER D.J., DEPAGNE E. and HUBENY I.

Abstract (from CDS):

We aim to study the properties of massive stars at low metallicity, with an emphasis on their evolution, rotation, and surface abundances. We focus on O-type dwarfs in the Small Magellanic Cloud. These stars are expected to have weak winds that do not remove significant amounts of their initial angular momentum. We analyzed the UV and optical spectra of twenty-three objects using the NLTE stellar atmosphere code cmfgen and derived photospheric and wind properties. The observed binary fraction of the sample is ≃26%, which is consistent with more systematic studies if one considers that the actual binary fraction is potentially larger owing to low-luminosity companions and that the sample was biased because it excluded obvious spectroscopic binaries. The location of the fastest rotators in the Hertzsprung-Russell (H-R) diagram built with fast-rotating evolutionary models and isochrones indicates that these could be several Myr old. The offset in the position of these fast rotators compared with the other stars confirms the predictions of evolutionary models that fast-rotating stars tend to evolve more vertically in the H-R diagram. Only one star of luminosity class Vz, expected to best characterize extreme youth, is located on the zero-age main sequence, the other two stars are more evolved. We found that the distribution of O and B stars in the ε(N)-vsini diagram is the same, which suggests that the mechanisms responsible for the chemical enrichment of slowly rotating massive stars depend only weakly on the star's mass. We furthermore confirm that the group of slowly rotating N-rich stars is not reproduced by the evolutionary tracks. Even for more massive stars and faster rotators, our results call for stronger mixing in the models to explain the range of observed N abundances. All stars have an N/C ratio as a function of stellar luminosity that match the predictions of the stellar evolution models well. More massive stars have a higher N/C ratio than the less massive stars. Faster rotators show on average a higher N/C ratio than slower rotators, again consistent with the expected trend of stronger mixing as rotation increases. When comparing the N/O versus N/C ratios with those of stellar evolution models, the same global qualitative agreement is reached. The only discrepant behavior is observed for the youngest two stars of the sample, which both show very strong signs of mixing, which is unexpected for their evolutionary status.

Abstract Copyright:

Journal keyword(s): stars: early-type - stars: fundamental parameters - stars: rotation - stars: abundances - Magellanic Clouds

Simbad objects: 32

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Number of rows : 32
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2024
#notes
1 AzV 80 * 00 50 43.8139294080 -72 47 41.547243120 12.22 13.24 13.376   13.59 O4-6n(f)p 32 0
2 AzV 117 * 00 52 12.3498883656 -73 18 38.761467732   13.87 13.88     A0 3 0
3 NAME SMC G 00 52 38.0 -72 48 01   2.79 2.2     ~ 11227 1
4 AzV 148 * 00 53 42.2323318536 -72 42 35.278898580 12.99 13.97 14.16   14.33 B0 13 0
5 AzV 177 * 00 56 44.1036082560 -72 03 31.678578504 13.22 14.39 14.62   14.90 O4Vz 26 0
6 AzV 189 * 00 57 32.5145162232 -72 28 51.133365372 13.29 14.34 14.47   14.67 B0(IV) 11 0
7 Cl* NGC 346 MPG 12 * 00 58 14.0865065520 -72 10 44.292892764   19.15 17.98   16.72 B0IV(Nstr) 32 0
8 Cl* NGC 346 ELS 28 * 00 58 31.7543622456 -72 10 57.965696544 13.58 14.73 14.94   15.23 OC6Vz 27 0
9 Cl* NGC 346 ELS 50 * 00 58 55.2212724984 -72 09 06.692331348 14.07 15.24 15.49   15.80 O8Vn 12 0
10 Cl* NGC 346 ELS 7 * 00 58 57.3961905528 -72 10 33.660822720 12.68 13.82 14.13   14.28 O4V((f+)) 52 0
11 Cl* NGC 346 W 3 * 00 59 00.7591806336 -72 10 28.171806492 11.46 12.61 12.80   13.63 O2III(f) 62 0
12 Cl* NGC 346 NMC 34 * 00 59 00.9631326096 -72 11 09.278888748 14.11 15.20 15.46   15.57 O6.5V 12 0
13 Cl* NGC 346 NMC 28 * 00 59 01.8187292184 -72 10 31.216864152   13.95 14.18     O5.5V((f+)) 31 0
14 NGC 346 Cl* 00 59 04.4000 -72 10 39.000           ~ 494 0
15 Cl* NGC 346 NMC 17 * 00 59 06.7498587648 -72 10 41.262204828 13.05 14.19 14.33   14.60 O8V 21 0
16 Cl* NGC 346 ELS 51 * 00 59 08.6965433496 -72 10 14.136149136 14.03 15.17 15.40   15.62 O7Vz 15 0
17 Cl* NGC 346 ELS 22 * 00 59 18.6176208672 -72 11 09.887619084   14.65 14.91     O9V 20 0
18 Cl* NGC 346 ELS 46 Y*O 00 59 31.8683861040 -72 13 35.225231592   15.16 15.44     O7Vn 13 0
19 Cl* NGC 346 ELS 31 * 00 59 54.0614692656 -72 04 31.420184880 13.71 14.81 15.05   15.33 O8Vz 19 0
20 SK 84 * 01 00 06.7253852112 -72 47 19.124459916 12.58 13.71 13.91   14.16 O6V 44 0
21 AzV 267 * 01 01 15.6926628168 -72 06 35.367953616   14.58 14.84     O7.5-8V 18 0
22 AzV 326 * 01 03 09.308 -72 25 56.69   13.84 13.92 14.07 14.40 B0(IV) 12 0
23 AzV 388 * 01 05 39.5306276568 -72 29 26.938329540 12.79 13.86 14.12   14.37 O5V 42 0
24 AzV 429 EB* 01 07 59.8335369624 -72 00 53.979262812 13.40 14.49 14.69   14.91 O7Vz 20 0
25 AzV 446 * 01 09 25.4274489696 -73 09 29.906782668 13.37 14.38 14.61   14.91 O6.5Vz 22 0
26 AzV 461 * 01 11 25.5705843312 -72 09 48.802253292 13.22 14.40 14.61   14.94 O8V+neb 20 0
27 AzV 468 * 01 12 05.8755103152 -72 40 56.600864328 13.83 14.86 15.14   15.49 O8.5V 15 0
28 NAME Magellanic Clouds GrG 03 00 -71.0           ~ 7127 0
29 NAME LMC G 05 23 34.6 -69 45 22     0.4     ~ 17552 0
30 RMC 136 Cl* 05 38 42.396 -69 06 03.36   5.81 5.40     ~ 2027 2
31 NGC 2244 OpC 06 32 10.8 +04 54 50           ~ 638 1
32 NAME Mon I MoC 06 35 +10.1           ~ 257 0

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