2012A&A...537A..79R


C.D.S. - SIMBAD4 rel 1.7 - 2020.02.23CET09:22:54

2012A&A...537A..79R - Astronomy and Astrophysics, volume 537A, 79-79 (2012/1-1)

Nitrogen line spectroscopy of O-stars. II. Surface nitrogen abundances for O-stars in the Large Magellanic Cloud.

RIVERO GONZALEZ J.G., PULS J., NAJARRO F. and BROTT I.

Abstract (from CDS):

Nitrogen is a key element for testing the impact of rotational mixing on evolutionary models of massive stars. Recent studies of the nitrogen surface abundance in B-type stars within the VLT-FLAMES survey of massive stars have challenged part of the corresponding predictions. To obtain a more complete picture of massive star evolution, and to allow for additional constraints, these studies need to be extended to O-stars. This is the second paper in a series aiming at the analysis of nitrogen abundances in O-type stars, to establish tighter constraints on the early evolution of massive stars. In this paper, we investigate the Nivλ4058 emission line formation, provide nitrogen abundances for a substantial O-star sample in the Large Magellanic Cloud, and compare our (preliminary) findings with recent predictions from stellar evolutionary models. Stellar and wind parameters of our sample stars were determined by line profile fitting of hydrogen, helium and nitrogen lines, exploiting the corresponding ionization equilibria. Synthetic spectra were calculated by means of the NLTE atmosphere/spectrum synthesis code fastwind, using a new nitrogen model atom. We derived nitrogen abundances for 20 O- and 5 B-stars by analyzing all nitrogen lines (from different ionization stages) present in the available optical spectra. The dominating process responsible for emission at Nivλ4058 in O-stars is the strong depopulation of the lower level of the transition, which increases as a function of dM/dt. Unlike the Niii triplet emission, resonance lines do not play a role for typical mass-loss rates and below. We find (almost) no problem in fitting the nitrogen lines, in particular the ``f'' features. Only for some objects, where lines from Niii/Niv/Nv are visible in parallel, we need to opt for a compromise solution. For five objects in the early B-/late O-star domain that have been previously analyzed by different methods and model atmospheres, we derive consistent nitrogen abundances. The bulk of our sample O-stars seems to be strongly nitrogen-enriched, and a clear correlation of nitrogen and helium enrichment is found. By comparing the nitrogen abundances as a function of vsin i (``Hunter-plot'') with tailored evolutionary calculations, we identify a considerable number of highly enriched objects at low rotation. Our findings seem to support the basic outcome of previous B-star studies within the VLT-FLAMES survey. Owing to the low initial abundance, the detection of strong nitrogen enrichment in the bulk of O-stars indicates that efficient mixing takes place already during the very early phases of stellar evolution of LMC O-stars. For tighter constraints, however, upcoming results from the VLT-FLAMES Tarantula survey need to be waited for, which will comprise a much higher number of O-stars that will be analyzed based on similar methods as presented here.

Abstract Copyright:

Journal keyword(s): stars: abundances - stars: winds, outflows - stars: early-type - stars: atmospheres - line: formation

Simbad objects: 36

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Number of rows : 36

N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2020
#notes
1 NAME SMC G 00 52 38.0 -72 48 01   2.79 2.2     ~ 9230 1
2 NGC 346 Cl* 00 59 05.090 -72 10 33.24           ~ 443 0
3 SK -66 15 * 04 55 22.3467574781 -66 28 19.098729637 11.888 12.660 12.894   12.759 B0.5Ia 15 0
4 SK -66 16 * 04 55 29.4149795029 -66 23 12.244972977 11.605 12.361 12.461   11.908 O9.7Ib 12 0
5 [ELS2006] N11 072 * 04 55 51.6265905319 -66 21 57.852345464 13.563 14.435 14.565   14.841 B0.2V 12 0
6 [ELS2006] N11 058 * 04 55 52.3580778754 -66 34 13.578379045 13.090 13.953 14.197   14.422 O5.5V((f)) 8 0
7 [ELS2006] N11 029 * 04 55 56.3300648375 -66 29 04.281485315   13.51 13.63     OC9.7Ib 10 0
8 SK -66 18 * 04 55 59.8223175692 -65 58 29.733466248 12.394 13.294 13.467   13.725 O6V((f)) 15 0
9 [ELS2006] N11 068 * 04 56 04.6017531938 -66 23 58.016984839 13.496 14.377 14.545   14.657 O7V((f)) 9 0
10 [L72] LH 9-89 * 04 56 11.0181680111 -66 28 24.362661410 12.580 13.531 13.645   13.837 B0IIIn 10 0
11 PGMW 1017 * 04 56 15.5466559821 -66 27 21.279164707   13.7 13.93     B0III 11 0
12 [L72] LH 9-79 * 04 56 19.3232502450 -66 27 01.963315207   14.16 14.40     O6.5V((f)) 11 0
13 [ELS2006] N11 051 * 04 56 29.6991219110 -66 21 38.865891354 12.909 13.812 13.990   14.173 O5Vn((f)) 9 0
14 NGC 1761 As* 04 56 39 -66 29.0     9.94     ~ 96 0
15 PGMW 3042 * 04 56 39.176 -66 24 49.94 13.590 14.514 14.461   14.708 O9.5Vn 11 0
16 PGMW 3058 * 04 56 42.146 -66 24 54.61 12.901 14.092 14.089   13.991 O3V((f*)) 16 0
17 [L72] LH 10-3061 * 04 56 42.460 -66 25 18.09 12.699 13.595 13.491   13.405 ON2III(f*) 25 0
18 PGMW 3100 * 04 56 45.2038993380 -66 25 10.779707928 13.007 13.736 13.648   13.547 O5III(f+) 12 0
19 [L72] LH 9-25 * 04 56 50.5121532801 -66 28 23.631866606 14.324 15.094 15.392   15.602 O9.5V 8 0
20 LHA 120-N 11 HII 04 56 51.4 -66 24 24           ~ 231 0
21 NGC 1763 As* 04 56 51.5 -66 24 25     9.40     ~ 154 3
22 [ELS2006] N11 026 * 04 56 52.5285896229 -66 19 56.232359011 12.646 13.405 13.580     O2.5III(f*) 14 0
23 PGMW 3168 * 04 56 54.4601951589 -66 24 15.871362997   13.57 13.68     O7II(f) 16 0
24 [ELS2006] N11 066 * 04 56 57.5053052609 -66 35 21.667466092 13.286 14.211 14.362   14.618 O7V((f)) 8 0
25 [ELS2006] N11 045 * 04 56 58.3150366846 -66 31 33.332893037   13.82 13.97     O9-9.5III 8 0
26 PGMW 3204 * 04 56 58.7897 -66 24 40.710   13.85 14.02     O6.5V((f)) 15 0
27 [ELS2006] N11 061 * 04 57 25.7198813633 -66 21 05.742989591 13.418 14.233 14.231   14.208 O9V 8 0
28 [ELS2006] N11 036 * 04 57 41.0087860813 -66 29 56.643348574 12.877 13.577 13.803   13.845 B0.5Ib 14 0
29 SK -70 69 * 05 05 18.6719268373 -70 25 49.876064190 12.586 13.616 13.854   14.074 O3V(f) 38 0
30 NAME LMC G 05 23 34.6 -69 45 22     0.4     ~ 14544 1
31 SK -66 100 * 05 27 45.4472881165 -66 55 15.296369854 12.227 12.976 13.204   13.501 O6II(f) 43 0
32 W61 16-8 * 05 28 46.9223603487 -68 47 47.799613299 12.283 13.444 13.666   13.854 ON2III(f*) 18 0
33 HD 269698 s*b 05 31 44.2083142709 -67 38 01.378514813 9.520 12.00 12.22 12.47 11.167 O4Ia 108 0
34 BI 237 * 05 36 14.6329670483 -67 39 19.168530216 12.865 13.790 13.830   13.948 O2V(f*) 32 0
35 BI 253 * 05 37 34.4596743399 -69 01 10.179743278 12.765 13.650 13.669   13.742 O2V(f*) 40 0
36 Schulte 22 ** 20 33 08.799 +41 13 18.21 14.33 13.59 11.55     O3If*+O6V((f)) 63 0

    Equat.    Gal    SGal    Ecl

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2020.02.23-09:22:54

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