GR 290 (Romano's Star): 2. Light history and evolutionary state

Abstract

We have built the historical light curve of the luminous variable GR 290 back to 1901, from old observations of the star found in several archival plates of M 33. These old recordings together with published and new data show that for at least half a century the star was in a low luminosity state, with B ~18. After 1960, five large variability cycles of visual luminosity were recorded. The amplitude of the oscillations was seen increasing towards the 1992-1994 maximum, then decreasing during the last maxima. The recent light curve indicates that the photometric variations have been quite similar in all the bands, and that the B-V color index has been constant within +/-0.1 m despite the 1.5m change of the visual luminosity. The spectrum of GR 290 at the large maximum of 1992-94, was equivalent to late-B type, while, during 2002-2014, it has varied between WN10h-11h near the visual maxima to WN8h-9h at the luminosity minima. We have detected, during this same period, a clear anti-correlation between the visual luminosity, the strength of the HeII 4686 A emission line, the strength of the 4600-4700 A lines blend and the spectral type. From a model analysis of the spectra collected during the whole 2002-2014 period we find that the Rosseland radius R_{2/3}, changed between the minimum and maximum luminosity phases by a factor of 3, while T_eff varied between about 33,000 K and 23,000 K. The bolometric luminosity of the star was not constant, but increased by a factor of ~1.5 between minimum and maximum luminosity, in phase with the apparent luminosity variations. In the light of current evolutionary models of very massive stars, we find that GR 290 has evolved from a ~60 M_Sun progenitor star and should have an age of about 4 million years. We argue that it has left the LBV stage and is moving to a Wolf-Rayet stage of late nitrogen spectral type.

arXiv commentAccepted on The Astronomical Journal, 10 figures. Replaced because the previous uploaded file was that without the final small corrections requested by the referee

References in corpus (19)

• Maps of Dust IR Emission for Use in Estimation of Reddening and CMBR Foregrounds
• The Wolf-Rayet stars in the Large Magellanic Cloud: A comprehensive analysis of the WN class
• A Survey of Local Group Galaxies Currently Forming Stars: III. A Search for Luminous Blue Variables and Other H-alpha Emission-Lined Stars
• Fundamental properties of core-collapse Supernova and GRB progenitors: predicting the look of massive stars before death
• The evolution of massive stars and their spectra I. A non-rotating 60 Msun star from the zero-age main sequence to the pre-supernova stage
• On the nature of the prototype LBV AG Carinae I. Fundamental parameters during visual minimum phases and changes in the bolometric luminosity during the S-Dor cycle
• Metal production in M33: space and time variations
• The distance of M33 and the stellar population in its outskirts
• The spiral galaxy M33 mapped in the FIR by ISOPHOT: A spatially resolved study of the warm and cold dust
• Bona-fide, strong-variable galactic Luminous Blue Variable stars are fast rotators: detection of a high rotational velocity in HR Carinae
• Luminous and Variable Stars in M31 and M33. II. Luminous Blue Variables, Candidate LBVs, Fe II Emission Line Stars, and Other Supergiants
• The Long Term Optical Variability of the BL Lac object S5 0716+714: Evidence for a Precessing Jet
• On the nature of candidate luminous blue variables in M33
• Crowded field 3D spectroscopy of LBV candidates in M33
• A Three-Decade Outburst of the LMC Luminous Blue Variable R127 Draws to a Close
• The Wolf-Rayet stars in M31: I. Analysis of the late-type WN stars
• Modelling the optical spectrum of Romano's star
• Pulsations as a Driver for LBV Variability
• The 2006 hot phase of Romano's star (GR 290) in M33

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• How long can LBVs sleep? A long-term photometric vaiability and spectral study of the Galactic candidate luminous blue variable MN112
• On variability of DDO68-V1, a unique extremely metal-poor LBV
• A search for OB stars in the field of the galactic OB association Bochum 7
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