Spectral Analysis of the Pre-WN Candidate HD 326823

Details Spectral Analysis of the Pre-WN Candidate HD 326823 Spectral Analysis of the Pre-WN Candidate HD 326823

Feb 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aj....133..489m&link_type=abstract

The Astronomical Journal, Volume 133, Issue 2, pp. 489-495.

Astronomy and Astrophysics

Astronomy

8

Stars: Fundamental Parameters, Stars: Individual: Hd 326823

Scientific paper

We present a spectral analysis of the peculiar emission-line star HD 326823. As has been reported in the literature, this object seems to be a rare, massive star entering the Wolf-Rayet (W-R) phase. In order to confirm its evolutionary status, we used the radiative transfer code CMFGEN to obtain its physical parameters and chemical abundances for the first time. By analyzing ultraviolet to optical observations of HD 326823, we were able to obtain the following parameters: L=2×105 Lsolar, R*=30 Rsolar, T*=22,280 K, M˙=5.2×10-6 Msolar yr-1, and v∞=200 km s-1. In addition, we demonstrated that this star is severely hydrogen-depleted and helium-rich, with XH~3% and XHe~96% (mass fractions), confirming previous qualitative claims of a hydrogen deficiency. From the N II λ5754 transition, we estimated an upper limit for the nitrogen abundance that is compatible with the idea that HD 326823 is a pre-WN star (XN<~1%). Our models indicate that the Fe II lines present in the optical spectrum are not formed in a spherically symmetric wind. We found that the iron ionization structure is dominated by Fe III and Fe IV, and that these ions dominate the UV. By comparing our results with WNE and WNL stars in the H-R diagram, we suggest that HD 326823 is a pre-WN8 star. The use of the transformed radius-temperature diagram also confirms a pre-WNL status. The idea that stars may enter the W-R stage with a very low hydrogen mass fraction is supported by our results.

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