54 research outputs found
The half-century history of studies of Romano's star
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.Comment: 8 pages, 2 figures, to appear in Baltic Astronomy, based on the talk
presented on "Modern stellar astronomy-2014" (Rostov-on-Don
Properties of dwarf stars in Cygnus OB2
We present the results of investigation of five stars, originally classified
as dwarfs, belonging to Cyg OB2 association, their stellar and wind properties.
Using both TLUSTY and CMFGEN codes we derived effective temperatures, surface
gravities, chemical abundances, mass-loss rates and projected rotation
velocities. Due to the fact that distance to the stars is well known, we were
able to estimate their luminosities. Using evolutionary models we estimated the
ages of these sample stars and find that lower mass ones - MT282 and MT343 -
belong to older population of the association. Their ages are greater than 10
Myr. The ages of three other stars - MT317, MT299, MT259 - are between 4-6 Myr.Comment: 16 pages, 10 figures, accepted for publication in PAS
Wind and nebula of the M33 variable GR290 (WR/LBV)
Context: GR290 (M33/V532=Romano's Star) is a suspected post-LBV star located
in M33 galaxy that shows a rare Wolf-Rayet spectrum during its minimum light
phase. In spite of many studies, its atmospheric structure, its circumstellar
environment and its place in the general context of massive stars evolution is
poorly known. Aims: Detailed study of its wind and mass loss, and study of the
circumstellar environment associated to the star. Methods: Long-slit spectra of
GR290 were obtained during its present minimum luminosity phase with the GTC
together with contemporaneous BVRI photometry. The data were compared with
non-LTE model atmosphere synthetic spectra computed with CMFGEN and with CLOUDY
models for ionized interstellar medium regions. Results: The current
mag, is the faintest at which this source has ever been observed. The non-LTE
models indicate effective temperature =27-30 kK at radius
=27-21 Rsun and mass loss rate Msun
yr. The terminal wind speed =620 is faster
than ever before recorded while the current luminosity Lsun is the lowest ever deduced. It is overabundant in He and N and
underabundant in C and O. It is surrounded by an unresolved compact HII region
with dimensions 4 pc, from where H-Balmer, HeI lines and [OIII] and [NII]
are detected. In addition, we find emission from a more extended interstellar
medium (ISM) region which appears to be asymmetric, with a larger extent to the
East (16-40 pc) than to the West. Conclusions: In the present long lasting
visual minimum, GR290 is in a lower bolometric luminosity state with higher
mass loss rate. The nearby nebular emission seems to suggest that the star has
undergone significant mass loss over the past years and is nearing
the end stages of its evolution.Comment: submitted to A&A, 12 pages, 9 figures, 7 table
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