Journal Article

Modelling the optical spectrum of Romano’s star

O. Maryeva and P. Abolmasov

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 419, issue 2, pages 1455-1464
Published in print January 2012 | ISSN: 0035-8711
Published online December 2011 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2011.19802.x
Modelling the optical spectrum of Romano’s star

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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-local thermodynamic equilibrium model atmosphere code cmfgen. All the observed properties of the object in the minimum are well described by a late WN (nitrogen-sequence Wolf-Rayet) 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 another example of an LBV that shows variations in its bolometric luminosity during an outburst.

Keywords: stars: individual: Romano’s star (M33); supergiants; stars: Wolf–Rayet; galaxies: individual: M33

Journal Article.  5214 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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