  Understanding the nature of the instabilities of LBVs is important to
understand the late evolutionary stages of very massive stars.
  We investigate the long term, S Dor-type variability of the luminous blue
variable GR290 (Romano's star) in M33, and its 2006 minimum phase.
  New spectroscopic and photometric data taken in November and December 2006
were employed in conjunction with already published data on GR290 to derive the
physical structure of GR290 in different phases and the time scale of the
variability.
  We find that by the end of 2006, GR 290 had reached the deepest visual
minimum so far recorded. Its present spectrum resembles closely that of the
Of/WN9 stars, and is the hottest so far recorded in this star (and in any LBV
as well), while its visual brightness decreased by about 1.4 mag.
  This first spectroscopic record of GR290 during a minimum phase confirms
that, similarly to AG Car and other LBVs, the star is subject to ample S
Dor-type variations, being hotter at minimum, suggesting that the variations
take place at constant bolometric luminosity.

Astrophysics