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Post Info TOPIC: Romano's Star
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RE: Romano's Star
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Title: The half-century history of studies of Romano's star
Author: Maryeva Olga

Luminous blue variables (LBVs) are rare objects of very high luminosity and mass loss rates, low wind velocities, exhibiting strong irregular photometric and spectral variability. They are generally believed to be a relatively short evolutionary stage in the life of a massive star, marking the transition from the Main Sequence toward Wolf-Rayet (WR) stars. However, recent studies indicate that progenitors of several supernovae underwent LBV-like eruptions. These studies support the view that at least some LBV stars are the end point of the evolution but not a transition phase. LBVs are rare objects, observations of whose in the Galaxy are inevitably connected with difficulties in determination of the distance and interstellar extinction. Hence, studying these rare objects in nearby galaxies is potentially more prospective. Therefore, investigation of the extragalactic star Romano's star (V532 or GR290) which is now classified as LBV/post-LBV star and shows late-WN spectrum, is very important for our understanding of evolution of massive stars in general.

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ATel 5846: New deep minimum of Romano's Star in M33

 



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Title: Modelling the optical spectrum of Romano's star
Authors: Olga Maryeva, Pavel Abolmasov

We consider the Luminous Blue Variable (LBV) star V532 in M33, also known as Romano's star, in two different spectral states: in the optical minimum of 2007/2008 and during a local brightening in 2005. Optical spectra of low and moderate resolution are modelled using the non-LTE model atmosphere code CMFGEN. All the observed properties of the object in the minimum are well described by a late WN star model with a relatively high hydrogen abundance (H/He=1.9), while the spectrum during the outburst corresponds to the spectral class WN11 and is similar to the spectrum of P Cyg. The atmosphere is enriched in nitrogen by about a factor of 6 in both states. Most of the heavy element abundances are consistent with the chemical composition of M33. Bolometric luminosity is shown to vary between the two states by a factor of ~1.5. This makes V532 one more example of a luminous blue variable that shows variations of its bolometric luminosity during an outburst.

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Title: The Extreme LBV Star GR290 (Romano's Star) in M33. Optical Spectrophotometric Monitoring
Authors: V. F. Polcaro, R. F. Viotti, C. Rossi, S. Galleti, R. Gualandi, L. Norci

We study the long term, S Dor-type variability and the present hot phase of the LBV star GR290 (Romano's Star) in M33 in order to investigate possible links between the LBV and WNL stages of very massive stars. We use intermediate resolution spectra, obtained with WHT in December 2008, when GR290 was at minimum (V = 18.6), as well as new low resolution spectra and B V R I photometry obtained with the Loiano and Cima Ekar telescopes during 2007-2010. We identify more than 80 emission lines in the 3100-10000 A range, belonging to different species and to forbidden transitions. Many lines, especially the HeI triplets, show a P Cygni profile with an a-e radial velocity difference from -300 to -500 km/s. The shape of the 4630-4713 A emission blend and of other emission lines resembles that of WN9 stars; the blend deconvolution shows that the HeII 4686 A has a strong broad component with FWHM \simeq 1700 km/s. During 2003-2010 the star underwent large spectral variations, best seen in the 4630-4686 A emission feature. Using the late-WN spectral types of Crowther & Smith (1997), GR290 apparently varied between the WN11 and WN8-9 spectral types, the hotter being the star the fainter its visual magnitude. This spectrum-visual luminosity anticorrelation of GR290 is reminiscent of the behaviour of the best studied LBVs. During the 2008 minimum we find a significant decrease in bolometric luminosity, which could be attributed to absorption by newly formed circumstellar matter. We suggest that, presently, the broad 4686 A line and the optical continuum are formed in a central WR region, while the narrow emission line spectrum originate in an extended, slowly expanding envelope, that is composed by matter ejected during previous high luminosity phases, and ionised by the central nucleus. GR290 could have just entered in a phase preceding the transition from the LBV state to late WN type.

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