419 research outputs found
A new LMC K-band distance from precision measurements of nearby red clump stars
High-precision (sigma < 0.01) new JHK observations of 226 of the brightest
and nearest red clump stars in the solar neighbourhood are used to determine
distance moduli for the LMC. The resulting K- and H-band values of 18.47\pm0.02
and 18.49\pm0.06 imply that any correction to the K-band Cepheid PL relation
due to metallicity differences between Cepheids in the LMC and in the solar
neighborhood must be quite small.Comment: 7 pages, 4 figure
Photometry of two unusual A supergiant systems in the Small Magellanic Cloud
We present multiwavelength broadband photometry and V, I time resolved
photometry for two variable bright stars in the SMC, OGLE004336.91-732637.7
(SMC-SC3) and OGLE004633.76-731204.3 (SMC-SC4). The light curves span 12 years
and show long-term periodicities (SMC-SC3) and modulated eclipses (SMC-SC4)
that are discussed in terms of wide-orbit intermediate mass interacting
binaries and associated envelopes. SMC-SC3 shows a primary period of 238.1 days
along with a complicated waveform suggesting ellipsoidal variablity influenced
by an eccentric orbit. This star also shows a secondary variability with an
unstable periodicity that has a mean value of 15.3 days. We suggest this could
be associated with nonradial pulsations.Comment: To be published in Publications of the Astronomical Society of the
Pacific (PASP)
A Catalogue of Be Stars in the Direction of the Galactic Bulge
Detailed studies of Be stars in environments with different metallicities
like the Magellanic Clouds or the Galactic bulge are necessary to understand
the formation and evolution mechanisms of the circumstellar disks. However, a
detailed study of Be stars in the direction of the bulge of our own galaxy has
not been performed until now. We report the first systematic search for Be star
candidates in the direction of the Galactic Bulge. We present the catalogue,
give a brief description of the stellar variability seen, and show some light
curve examples. We searched for stars matching specific criteria of magnitude,
color and variability in the I band. Our search was conducted on the 48 OGLE II
fields of the Galactic Bulge.This search has resulted in 29053 Be star
candidates, 198 of them showing periodic light variations. Nearly 1500 stars in
this final sample are almost certainly Be stars, providing an ideal sample for
spectroscopic multiobject follow-up studies.Comment: Accepted for publication in A &
Photometric standard stars in the BVI system in a wide field centered on the spiral galaxy NGC 300
Based on 13 nights of observations of four fields in NGC 300, we have set up
an extensive sequence of stars with accurate BVI photometry covering a
relatively large (25 x 25 arcmin) region centered on this galaxy. This sequence
of standard stars is very useful for calibrating the photometry of variable
stars and other objects in NGC 300 and other galaxies obtained from wide field
mosaic images. Our standard star list contains B, V and I measurements for 390
stars. The accuracy of the zero points in the V filter and B-V color is better
than 0.02 mag, and about 0.03 mag for the V-I color. We found very good
agreement between our measurements and those previously obtained by Walker for
26 stars near NGC 300.Comment: 12 pages, Latex, 1 Figure in gif format, 1 Table as postscript file.
P.A.S.P. in pres
Binary Cepheids from optical interferometry
Classical Cepheid stars have been considered since more than a century as
reliable tools to estimate distances in the universe thanks to their
Period-Luminosity (P-L) relationship. Moreover, they are also powerful
astrophysical laboratories, providing fundamental clues for studying the
pulsation and evolution of intermediate-mass stars. When in binary systems, we
can investigate the age and evolution of the Cepheid, estimate the mass and
distance, and constrain theoretical models. However, most of the companions are
located too close to the Cepheid (1-40 mas) to be spatially resolved with a
10-meter class telescope. The only way to spatially resolve such systems is to
use long-baseline interferometry. Recently, we have started a unique and
long-term interferometric program that aims at detecting and characterizing
physical parameters of the Cepheid companions, with as main objectives the
determination of accurate masses and geometric distances.Comment: 8 pages, Proceeding of the conference "Setting a new standard in the
analysis of binary stars", September 2013, Leuven, Belgiu
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