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Published October 11, 2010 | Supplemental Material + Published
Journal Article Open

Multiple major outbursts from a restless luminous blue variable in NGC 3432

Abstract

We present new photometric and spectroscopic observations of an unusual luminous blue variable (LBV) in NGC 3432, covering three major outbursts in 2008 October, 2009 April and 2009 November. 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 iiλ4686) 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^(−1)), 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.

Additional Information

© 2010 The Authors. Journal compilation © 2010 RAS. Accepted 2010 June 4; Received 2010 June 4; in original form 2010 April 30. This paper is based on observations made with the Italian Telescopio Nazionale Galileo (TNG) operated on the island of La Palma by the Fundación Galileo Galilei of the INAF (Istituto Nazionale di Astrofisica); the Liverpool Telescope operated on the island of La Palma at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias; the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway and Sweden, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias; the Hale Telescope, Palomar Observatory, as part of a continuing collaboration between the California Institute of Technology, NASA/JPL and Cornell University; the 2.2-m telescope of the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Max-Planck Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC); and the 1.82-m telescope of INAF-Asiago Observatory. This paper is also based in part on data obtained from the Isaac Newton Group Archive which is maintained as part of the CASU Astronomical Data Centre at the Institute of Astronomy, Cambridge; on data collected at the Kiso observatory (University of Tokyo) and obtained from the SMOKA, which is operated by the Astronomy Data Center, National Astronomical Observatory of Japan and on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute, operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS 5-26555. This manuscript alsomade use of SDSS data. Funding for the SDSS and SDSS-II has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, the U.S. Department of Energy, the National Aeronautics and Space Administration, the Japanese Monbukagakusho, the Max Planck Society and the Higher Education Funding Council for England. The SDSS Web Site is http://www.sdss.org. This manuscript used information contained in the Bright Supernova Web Pages (http://www.RochesterAstronomy.org/snimages, maintained by D. Bishop), as part of the Rochester Academy of Sciences and in the AAVSO International Data Base.We are grateful to the amateur astronomers K. Itagaki, C. Deforeit, T. Tamura, G. Youman, B. Häusler, R. Johnson and E. Prosperi for sharing their images of NGC 3432 with us, to P. Holmström for his help in the observations at the Sandvreten Observatory, and to G. Gräfener for useful discussions. We also thank S. Otero and K. Weis for giving us access to the comparison data of η Car and 2002kg, and C. Inserra and the Padova-Asiago Supernova Group to provide us an unpublished spectrum of 2009ip. SB acknowledges partial financial support from ASI contracts 'COFIS'. ST acknowledges support by the Trans-regional Collaborative Research Centre TRR33 'The Dark Universe' of the German Research Foundation (DFG). SM and EK acknowledge support from the Academy of Finland (project 8120503). This work, conducted as part of the award 'Understanding the lives of massive stars from birth to supernovae' (S. J. Smartt) made under the European Heads of Research Councils and European Science Foundation EURYI (European Young Investigator) Awards scheme (see http://www.esf.org/euryi).

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Published - Pastorello2010p11759Mon_Not_R_Astron_Soc.pdf

Supplemental Material - MNR_17142_sm_tables1and2.zip

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August 22, 2023
Modified:
October 20, 2023