# 2005ApJ...627..477M

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 Query : 2005ApJ...627..477M

2005ApJ...627..477M - Astrophys. J., 627, 477-519 (2005/July-1)

The physical properties and effective temperature scale of O-type stars as a function of metallicity. II. Analysis of 20 more Magellanic cloud stars and results from the complete sample.

MASSEY P., PULS J., PAULDRACH A.W.A., BRESOLIN F., KUDRITZKI R.P. and SIMON T.

Abstract (from CDS):

In order to determine the physical properties of the hottest and most luminous stars and understand how these properties change as a function of metallicity, we have analyzed HST/UV and high-S/N optical spectra of an additional 20 Magellanic Cloud stars, doubling the sample presented in the first paper in this series. Our analysis uses non-LTE line-blanketed models that include spherical extension and the hydrodynamics of the stellar wind. In addition, our data set includes FUSE observations of O VI and HST near-UV He I and He II lines to test for consistency of our derived stellar properties for a few stars. The results from the complete sample are as follows: (1) We present an effective temperature scale for O stars as a function of metallicity. We find that the SMC O3-7 dwarfs are 4000 K hotter than Galactic stars of the same spectral type. The difference is in the sense expected due to the decreased significance of line blanketing and wind blanketing at the lower metallicities that characterize the SMC. The temperature difference between the SMC and Milky Way O dwarfs decreases with decreasing temperature, becoming negligible by spectral type B0, in accord with the decreased effects of stellar winds at lower temperatures and luminosities. The temperatures of the LMC stars appear to be intermediate between that of the Milky Way and SMC, as expected based on their metallicities. Supergiants show a similar effect but are roughly 3000-4000 K cooler than dwarfs for early O stars, also with a negligible difference by B0. The giants appear to have the same effective temperature scale as dwarfs, consistent with there being little difference in the surface gravities. When we compare our scale to other recent modeling efforts, we find good agreement with some CMFGEN results, while other CMFGEN studies are discordant, although there are few individual stars in common. WM-BASIC modeling by others has resulted in significantly cooler effective temperatures than what we find, as does the recent TLUSTY/CMFGEN study of stars in the NGC 346 cluster, but our results lead to a far more coeval placement of stars in the H-R diagram for this cluster. (2) We find that the wind momentum of these stars scales with luminosity and metallicity in the ways predicted by radiatively driven wind theory, supporting the use of photospheric analyses of hot luminous stars as a distance indicator for galaxies with resolved massive star populations. (3) A comparison of the spectroscopic masses with those derived from stellar evolutionary theory shows relatively good agreement for stars with effective temperatures below 45,000 K; however, stars with higher temperatures all show a significant mass discrepancy, with the spectroscopic masses a factor of 2 or more smaller than the evolutionary masses. This problem may in part be due to unrecognized binaries in our sample, but the result suggests a possible systematic problem with the surface gravities or stellar radii derived from our models. (4) Our sample contains a large number of stars of the earliest O types, including those of the newly proposed O2 subtype. We provide the first quantitative descriptions of their defining spectral characteristics and investigate whether the new types are a legitimate extension of the effective temperature sequence. We find that the N III/N IV emission line ratio used to define the new classes does not, by itself, serve as an effective temperature indicator within a given luminosity class: there are O3.5 V stars that are as hot or hotter than O2 V stars. However, the He I/He II ratio does not fair much better for stars this hot, as we find that He I λ4471/He II λ4542, usually taken primarily as a temperature indicator, becomes sensitive to both the mass-loss rate and surface gravities for the hottest stars. This emphasizes the need to rely on all of the spectroscopic diagnostic lines, and not simply N III/N IV or even He I/He II, for these extreme objects. (5) The two stars with the most discordant radial velocities in our sample happen to be O3 field stars'', i.e., found far from the nearest OB associations. This provides the first compelling observational evidence as to the origin of the field O stars in the Magellanic Clouds, i.e., that these are classic runaway OB stars, ejected from their birthplaces.

Journal keyword(s): Stars: Atmospheres - Stars: Early-Type - Stars: Fundamental Parameters - Stars: Mass Loss

Full paper

 Number of rows : 52
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2022
#notes
1 M 31 G 00 42 44.330 +41 16 07.50 4.86 4.36 3.44     ~ 11880 1
2 LIN 78 Em* 00 46 32.6338987968 -73 06 05.564426436 12.53 13.59 13.7   13.85 O3/4V 41 1
3 BBB SMC 266 s*b 00 47 50.0484011088 -73 08 21.054056928   12.35 12.55 12.36   O6I(f) 65 0
4 LIN 156 s*b 00 50 32.4050818488 -72 52 36.441355908 11.553 12.604 12.756   12.89 O5.5I(f) 48 0
5 NAME SMC G 00 52 38.0 -72 48 01   2.79 2.2     ~ 10314 1
6 AzV 177 * 00 56 44.1036082560 -72 03 31.678578504 13.22 14.39 14.62   14.90 O4Vz 24 0
7 Cl* NGC 346 MPG 12 * 00 58 14.0865065520 -72 10 44.292892764   19.15 17.98   16.72 B0IV(Nstr) 31 0
8 AzV 207 * 00 58 33.1896798552 -71 55 46.721984016 12.99 14.13 14.35   14.58 O7Vz((f)) 32 0
9 NGC 346 Cl* 00 59 05.090 -72 10 33.24           ~ 462 0
10 AzV 296 * 01 02 08.6480463408 -72 13 20.012601648 13.01 14.19 14.38   14.62 O7.5V((f)) 17 0
11 AzV 377 * 01 05 07.3821781944 -72 48 18.712907748 13.18 14.34 14.59   14.83 O5V((f)) 17 0
12 AzV 378 * 01 05 09.4353086232 -72 05 34.656190260 12.60 13.64 13.90   14.18 O9.5III 23 0
13 AzV 396 * 01 06 04.2151992024 -72 13 34.156269624 12.92 14.02 14.22   14.54 B0III 9 0
14 AzV 435 * 01 08 17.9083159848 -71 59 54.357974016 12.93 13.98 14.11   13.97 O3V((f*)) 16 0
15 AzV 440 * 01 08 56.0209984488 -71 52 46.695754200 13.42 14.30 14.58   14.76 O7.5III((f)) 20 0
16 AzV 446 * 01 09 25.4274489696 -73 09 29.906782668 13.37 14.38 14.61   14.91 O6.5Vz 19 0
17 SK 148 * 01 12 29.0077488048 -72 29 29.054516928 11.913 13.014 13.176   13.32 O8.5II((f)) 40 0
18 Dachs SMC 3-10 EB* 01 13 42.4497160176 -73 17 29.516706528 12.49 13.54 13.48 13.72 13.54 O2-3V+companion 28 0
19 Brey 10a WR* 04 57 27.4544617632 -67 39 02.864000880 12.213 13.314 13.496   13.564 O2If*/WN5 54 1
20 SK -65 47 s*b 05 20 54.7193542416 -65 27 17.880205176 11.451 12.270 12.466   12.741 O4If 18 0
21 NAME LMC G 05 23 34.6 -69 45 22     0.4     ~ 16153 1
22 [GMP94] 496 * 05 26 44.2108 -68 48 42.116   13.50 13.73     O5V(f) 9 0
23 LH 58 As* 05 26 45 -68 49.9   7.97 7.96     ~ 58 0
24 W61 16-8 * 05 28 46.9222348728 -68 47 47.796287748 12.283 13.444 13.666   13.854 ON2III(f*) 18 0
25 W61 28-5 * 05 34 28.4650523832 -69 43 56.833403844 12.795 13.630 13.774   14.063 O4V(f+) 10 0
26 NGC 2033 As* 05 34 43 -69 44.2   11.53 11.63     ~ 28 0
27 W61 28-23 * 05 34 50.1539297904 -69 46 32.544537024 12.698 13.596 13.702   13.752 O3.5V(f+) 12 0
28 Brey 58 WR* 05 35 42.2160 -69 11 54.240   14.62 14.13     O3If*/WN6 37 0
29 [M2002] LMC 163521 * 05 35 45.2600 -69 11 35.105   14.11 14.3     O3.5III(f+) 10 0
30 NGC 2044 As* 05 36 11 -69 11.8   10.69 10.59     ~ 83 0
31 BI 237 * 05 36 14.6333257920 -67 39 19.168082640 12.865 13.790 13.830   13.948 O2V(f*) 33 0
32 BI 253 * 05 37 34.4595697440 -69 01 10.178659452 12.765 13.650 13.669   13.742 O2V(f*) 43 0
33 Cl* NGC 2070 MH 57 * 05 38 40.2160044288 -69 05 59.915264352   12.97 13.0   12.91 O3If*/WN6-A 36 1
34 Brey 78 WR* 05 38 40.2960 -69 05 59.640           O2.5If*/WN6 36 0
35 [HSH95] 33 * 05 38 42.2113 -69 06 00.983     14.43     O3V 7 0
36 RMC 136 Cl* 05 38 42.396 -69 06 03.36           ~ 1872 1
37 BAT99 110 WR* 05 38 42.47 -69 06 02.0   13.73 13.73     O2If* 37 0
38 CXOU J053842.4-690601 * 05 38 42.482 -69 06 01.07   14.33 14.49     O2-3.5V 17 0
39 Cl* NGC 2070 MH 551 * 05 38 42.52 -69 06 03.8   14.64 14.81     O3V 14 0
40 Cl* NGC 2070 MH 608 * 05 38 42.68 -69 06 02.1   14.49 14.39     ~ 16 0
41 CXOU J053842.7-690601 * 05 38 42.720 -69 06 01.99   14.67 14.63     O3III 15 0
42 Cl* NGC 2070 MH 859 * 05 38 44.2218 -69 05 56.973   13.67 13.94   13.73 O3III(f+) 23 1
43 NGC 2074 As* 05 39 03 -69 29.9           ~ 60 0
44 W61 3-14 * 05 39 05.29 -69 29 23.0   13.26 13.4     O3V+OV 8 0
45 CPD-69 471 * 05 39 11.6284 -69 30 37.417 11.415 12.374 12.273   12.275 O2-3(n)fp 15 0
46 [L72] LH 114-7 * 05 43 13.0005 -67 51 16.007   13.41 13.66     O2III(f*)+OV 14 0
47 HD 93128 SB* 10 43 54.3957741024 -59 32 57.497266716 8.82 8.97 8.77 9.40 8.71 O3.5V((fc))z 94 1
48 HD 93129 ** 10 43 57.462360 -59 32 51.27000 6.26 7.840 7.884 7.839   O2If*+O3.5V((f)) 195 1
49 V* V560 Car SB* 10 44 33.7393258944 -59 44 15.434446956 6.89 7.80 7.75 7.56 7.46 O3.5V((f))+O8V 289 0
50 HD 93250 * 10 44 45.0275085072 -59 33 54.680974848 6.73 8.12 7.50 8.38   O4III(fc) 302 0
51 HD 303308 ** 10 45 05.9147911152 -59 40 05.925360036 7.45 8.30 8.17 7.92 7.75 O4.5V((fc)) 288 0
52 Cl Pismis 24 17 Y*O 17 24 44.7309068928 -34 12 02.698328196 13.61 13.33 11.84 11.35 9.61 O3.5III(f*) 40 0

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2022.08.10-06:31:26