Detalles de publicación

PP 010038

Multiple Major Outbursts from a Restless Luminous Blue Variable in NGC 3432

A. Pastorello (1), M. T. Botticella (1), C. Trundle (1), S. Taubenberger (2), S. Mattila (3,4), E. Kankare (5,3), N. Elias-Rosa (6), S. Benetti (7), G. Duszanowicz (8), L. Hermansson (9), J. E. Beckman (10,11), F. Bufano (7), M. Fraser (1), A. Harutyunyan (12), H. Navasardyan (7), S. J. Smartt (1), S. D. van Dyk (6), J. S. Vink (13), R. M. Wagner (14)
((1)Queen's University Belfast, (2) Max-Planck-Institut fuer Astrophysik, (3) University of Turku, (4) Stockholm University, (5) Nordic Optical Telescope, (6) Spitzer Science Center, (7) INAF Osservatorio Astronomico di Padova, (8) Moonbase Observatory, (9) Sandvretens Observatory, (10) Instituto de Astrofisica de Canarias, (11) Consejo Superior de Investigaciones Cienticas of Spain, (12) Fundacion Galileo Galilei - INAF, (13) Armagh Observatory, (14) Large Binocular Telescope Observatory)
We present new photometric and spectroscopic observations of an unusual
luminous blue variable (LBV) in NGC 3432, covering three major outbursts in
October 2008, April 2009 and November 2009. Previously, this star experienced
an outburst also in 2000 (known as SN 2000ch). During outbursts the star
reached an absolute magnitude between -12.1 and -12.8. Its spectrum showed H,
He I and Fe II lines with P-Cygni profiles during and soon after the eruptive
phases, while only intermediate-width lines in pure emission (including He II
4686A were visible during quiescence. The fast-evolving light curve soon after
the outbursts, the quasi-modulated light curve, the peak magnitude and the
overall spectral properties are consistent with multiple episodes of
variability of an extremely active LBV. However, the widths of the spectral
lines indicate unusually high wind velocities (1500-2800 km/s), similar to
those observed in Wolf-Rayet stars. Although modulated light curves are typical
of LBVs during the S-Dor variability phase, the luminous maxima and the high
frequency of outbursts are unexpected in S-Dor variables. Such extreme
variability may be associated with repeated ejection episodes during a giant
eruption of an LBV. Alternatively, it may be indicative of a high level of
instability shortly preceding the core-collapse or due to interaction with a
massive, binary companion. In this context, the variable in NGC 3432 shares
some similarities with the famous stellar system HD 5980 in the Small
Magellanic Cloud, which includes an erupting LBV and an early Wolf-Rayet star.

 
Aceptado para publicación en MNRAS | Enviado el 2010-06-04 | Proyecto P3/86