1 research outputs found
The Physical Properties and Effective Temperature Scale of O-type Stars as a Function of Metallicity. III. More Results from the Magellanic Clouds
In order to better determine the physical properties of hot, massive stars as
a function of metallicity, we obtained very high SNR optical spectra of 26 O
and early B stars in the Magellanic Clouds. These allow accurate modeling even
in cases where the He I 4471 line has an equivalent width of only a few tens of
mA. The spectra were modeled with FASTWIND, with good fits obtained for 18
stars; the remainder show signatures of being binaries. We include stars in
common to recent studies to investigate possible systematic differences. The
"automatic" FASTWIND modeling method of Mokiem and collaborators produced
temperatures 1100 K hotter on the average, presumably due to the different
emphasis given to various temperature-sensitive lines. More significant,
however, is that the automatic method always produced some "best" answer, even
for stars we identify as composite (binaries). The temperatures found by the
TLUSTY/CMFGEN modeling of Bouret, Heap, and collaborators yielded temperatures
1000 K cooler than ours, on average. Significant outliers were due either to
real differences in the data (some of the Bouret/Heap data were contaminated by
moonlight continua) or the fact we could detect the HeI line needed to better
constrain the temperature. Our new data agrees well with the effective
temperature scale we presented previously. We confirm that the "Of"
emission-lines do not track luminosity classes in the exact same manner as in
Milky Way stars. We revisit the the issue of the "mass discrepancy", finding
that some of the stars in our sample do have spectroscopic masses that are
significantly smaller than those derived from stellar evolutionary models. We
do not find that the size of the mass discrepancy is simply related to either
effective temperature or surface gravity.Comment: ApJ, in pres