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