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Astron. Astrophys. 334, 1007-1015 (1998)


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A spectroscopic analysis of the Luminous Blue Variable candidate WRA 751 *

P. García-Lario 1, A. Riera 2, 3 and A. Manchado 4

1 ISO Science Operations Centre, Estación de Villafranca del Castillo, Apartado de Correos 50727, E-28080 Madrid, Spain
2 Departament de Física i Enginyeria nuclear, Escola Universitària de Vilanova i la Geltrú, Universitat Politécnica de Catalunya,
Av. Víctor Balaguer, s/n, E-08000 Barcelona, Spain
3 Departament d'Astronomia i Meteorologia, Universitat de Barcelona, Av. Diagonal 647, E-08028 Barcelona, Spain
4 Instituto de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, Spain

Received 3 July 1997 / Accepted 5 March 1998

Abstract

We present spectroscopic observations of the LBV candidate WRA 751 taken at different epochs during the period 1989-1995. These observations are used to monitor the temporal evolution of the spectrum over the last few years. In addition, we identify most of the emission and absorption features in the spectral range 4100-9250 Å  and obtain a new determination of the extinction towards this source of E(B-V) = 1.5 based on the relative intensities of the [Ni II] lines.

Our data suggest that the star is an evolved LBV star now in a relative quiescent state. No significant changes are found over the years in the emission line spectrum, although the continuum brightness seems to be globally fading. A high density and dusty circumstellar core is found to be surrounded by a low density nebula characterized by a significant [N/O] overabundance ([FORMULA] [FORMULA]). Using the photoionization-shock code MAPPINGS we estimate an effective temperature for the central star of [FORMULA] = 25000 K. Most of the spectral features observed in the core, like the strong [Ni II] emission and the permitted emission lines of O, Fe, Si and Mg appear to be originated by continuum fluorescence.

The complex profile observed in H [FORMULA] is explained as the result of a strong density discontinuity in the shell which might have been originated as a consequence of a recent episode of enhanced mass loss. From the observed profile we estimate a terminal velocity of the wind of [FORMULA] 175 km s-1, typical of LBVs.

If we assume the previously reported distance of 4-5 kpc, from the apparent size of the nebular emission (22") and the expansion velocity deduced from the double-peaked [N II] lines (24 km s-1) the kinematic age of the nebula is found to be [FORMULA] 10,000 years, consistent with the predicted LBV lifetimes.

Key words: stars: supergiants – stars: emission line, Be – stars: mass loss – stars: individual: WRA 751

* Based on observations collected at the European Southern Observatory (La Silla, Chile)

Send offprint requests to: P. García-Lario

© European Southern Observatory (ESO) 1998

Online publication: June 2, 1998

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