7 research outputs found
Variability of B and Be stars in the LMC/SMC: binaries and pulsations
To study the variability of the 523 B and Be stars observed in the Magellanic
clouds with the VLT-FLAMES, we cross-matched the stars of our sample with the
photometric database MACHO, which provides for each star an 8 years lightcurve.
We searched for long, medium, and short-term periodicity and found the
eclipsing binaries in our sample. For these stars, combining, spectroscopy and
photometry, we were able to provide information on several systems of stars
(systemic velocities, ratios of masses, etc). We also present the ratios of
B-binaries to B-non binaries in the LMC/SMC in comparison with the MW. Note
that this ratio is also an important issue to understand the mechanism of
star-formation at low metallicity. We also found the first multiperiodic B and
Be stars in the SMC, in particular the first SMC Beta Cep and SPB, while,
according to the models, pulsations were not foreseen in low metallicity
environments, i.e. typically in the SMC. Our results show that the instability
strips are shifted towards higher temperatures in comparison with the Milky
Way' strips of pulsating B-type stars. By the fact that we found more pulsating
Be stars than pulsating B stars in the SMC, it seems that the fast rotation
favours the presence of pulsations. However, the ratio of pulsating B-type
stars to "non"-pulsating B-type stars at low metallicity is lower than at high
metallicity.Comment: poster IAUS25
Be stars and binaries in the field of the SMC open cluster NGC330 with VLT-FLAMES
Observations of hot stars belonging to the young cluster SMC-NGC330 and its
surrounding region were obtained with the VLT-GIRAFFE facilities in MEDUSA
mode. We investigated the B and Be star properties and proportions in this
environment of low metallicity. We also searched for rapid variability in Be
stars using photometric databases. With spectroscopic measurements we
characterized the emission and properties of Be stars. By cross-correlation
with photometric databases such as MACHO and OGLE, we searched for binaries in
our sample of hot stars, as well as for short-term variability in Be stars. We
report on the global characteristics of the Be star sample (131 objects). We
find that the proportion of early Be stars with a large equivalent width of the
Halpha emission line is higher in the SMC than in the LMC and MW. We find a
slight increase in the proportion of Be stars compared to B-type stars with
decreasing metallicity. We also discovered spectroscopic and photometric
binaries, and for the latter we give their orbital period. We identify 13 Be
stars with short-term variability. We determine their period(s) and find that 9
Be stars are multiperiodic.Comment: english not yet corrected, 23 pages, 4th article about the study in
the LMC NGC2004 and SMC NGC33