2012A&A...543A..95R


Query : 2012A&A...543A..95R

2012A&A...543A..95R - Astronomy and Astrophysics, volume 543A, 95-95 (2012/7-1)

Nitrogen line spectroscopy in O-stars. III. The earliest O-stars.

RIVERO GONZALEZ J.G., PULS J., MASSEY P. and NAJARRO F.

Abstract (from CDS):

The classification scheme proposed by Walborn et al. (2002AJ....123.2754W), based primarily on the relative strengths of the NIVλ4058 and NIIIλ4640 emission lines, has been used in a variety of studies to spectroscopically classify early O-type stars. Owing to the lack of a solid theoretical basis, this scheme has not yet been universally accepted though. We provide first theoretical predictions for the NIVλ4058/NIIIλ4640 emission line ratio in dependence of various parameters, and confront these predictions with results from the analysis of a sample of early-type LMC/SMC O-stars. Stellar and wind parameters of our sample stars are determined by line profile fitting of hydrogen, helium and nitrogen lines, exploiting the helium and nitrogen ionization balance. Corresponding synthetic spectra are calculated by means of the NLTE atmosphere/spectrum synthesis code fastwind. Though there is a monotonic relationship between the NIV/NIII emission line ratio and the effective temperature, all other parameters being equal, theoretical predictions indicate additional dependencies on surface gravity, mass-loss, metallicity, and, particularly, nitrogen abundance. For a given line ratio (i.e., spectral type), more enriched objects should be typically hotter. These basic predictions are confirmed by results from the alternative model atmosphere code cmfgen. The effective temperatures for the earliest O-stars, inferred from the nitrogen ionization balance, are partly considerably hotter than indicated by previous studies. Consistent with earlier results, effective temperatures increase from supergiants to dwarfs for all spectral types in the LMC. The relation between observed NIVλ4058/NIIIλ4640 emission line ratio and effective temperature, for a given luminosity class, turned out to be quite monotonic for our sample stars, and to be fairly consistent with our model predictions. The scatter within a spectral sub-type is mainly produced by abundance effects. Our findings suggest that the Walborn et al. (2002AJ....123.2754W) classification scheme is able to provide a meaningful relation between spectral type and effective temperature, as long as it is possible to discriminate for the luminosity class. In terms of spectral morphology, this might be difficult to achieve in low-Z environments such as the SMC, owing to rather low wind-strengths. According to our predictions, the major bias of the classification scheme is due to nitrogen content, and the overall spectral type-Teff relation for low-metallicity (e.g., SMC) O-stars might be non-monotonic around O3.5/O4.

Abstract Copyright:

Journal keyword(s): stars: early-type - stars: fundamental parameters - stars: atmospheres - line: formation

Simbad objects: 26

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Number of rows : 26
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 NAME SMC G 00 52 38.0 -72 48 01   2.79 2.2     ~ 10258 1
2 AzV 177 * 00 56 44.1036082560 -72 03 31.678578504 13.22 14.39 14.62   14.90 O4Vz 24 0
3 Cl* NGC 346 W 3 * 00 59 00.7591806336 -72 10 28.171806492 11.46 12.61 12.80   13.63 O2III(f) 59 0
4 NGC 346 Cl* 00 59 05.090 -72 10 33.24           ~ 460 0
5 AzV 435 * 01 08 17.9083159848 -71 59 54.357974016 12.93 13.98 14.11   13.97 O3V((f*)) 16 0
6 NAME Magellanic Clouds GrG 03 00 -71.0           ~ 6319 1
7 [L72] LH 9-79 * 04 56 19.3227419616 -66 27 01.960411536   14.16 14.40     O6.5V((f)) 11 0
8 PGMW 3058 * 04 56 42.146 -66 24 54.61 12.901 14.092 14.089   13.991 O3V((f*)) 16 0
9 [L72] LH 10-3061 * 04 56 42.5074945536 -66 25 18.217550208 12.699 13.595 13.491   13.405 ON2III(f*) 25 0
10 [ELS2006] N11 026 * 04 56 52.5287243472 -66 19 56.230847832 12.646 13.405 13.580     O2.5III(f*) 14 0
11 Brey 10a WR* 04 57 27.4544617632 -67 39 02.864000880 12.213 13.314 13.496   13.564 O2If*/WN5 54 1
12 SK -65 47 s*b 05 20 54.7193542416 -65 27 17.880205176 11.451 12.270 12.466   12.741 O4If 18 0
13 NAME LMC G 05 23 34.6 -69 45 22     0.4     ~ 16065 1
14 W61 16-8 * 05 28 46.9222348728 -68 47 47.796287748 12.283 13.444 13.666   13.854 ON2III(f*) 18 0
15 W61 28-5 * 05 34 28.4650523832 -69 43 56.833403844 12.795 13.630 13.774   14.063 O4V(f+) 10 0
16 W61 28-23 * 05 34 50.1539297904 -69 46 32.544537024 12.698 13.596 13.702   13.752 O3.5V(f+) 12 0
17 [M2002] LMC 163521 * 05 35 45.2600 -69 11 35.105   14.11 14.3     O3.5III(f+) 10 0
18 BI 237 * 05 36 14.6333257920 -67 39 19.168082640 12.865 13.790 13.830   13.948 O2V(f*) 33 0
19 BI 253 * 05 37 34.4595697440 -69 01 10.178659452 12.765 13.650 13.669   13.742 O2V(f*) 43 0
20 RMC 136 Cl* 05 38 42.396 -69 06 03.36           ~ 1861 1
21 CXOU J053842.4-690601 * 05 38 42.482 -69 06 01.07   14.33 14.49     O2-3.5V 17 0
22 Cl* NGC 2070 MH 859 * 05 38 44.2218 -69 05 56.973   13.67 13.94   13.73 O3III(f+) 23 1
23 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
24 W61 3-24 * 05 39 13.5533958720 -69 30 05.012730900   14.48 14.6     O3.5V(f+) 9 0
25 HD 46223 Y*O 06 32 09.3068103600 +04 49 24.705695568 6.73 7.50 7.28 6.95 6.79 O4V((f)) 367 0
26 HD 64568 * 07 53 38.2051918848 -26 14 02.598056556 8.64 9.50 9.39 9.77 9.204 O3V((f*))z 103 0

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2022.07.02-19:57:21

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