In the context of long and continuous time-series photometry and after the MOST, CoRoT, KEPLER space missions and large geographic longitude ground-based networks, a new method is offered by the polar location helping to cope with the problem associated with the Earth's day-night cycle. We present the first long time-series photometry from Dome Charlie in the heart of Antarctica and analyze ~4400 photometric measurements of RR Lyrae star S Arae obtained in July and August 2007.
The light curves of the first overtone Pop. I Cepheids (s-Cepheids) show a discontinuity in their {phi}_21_ vs. P diagram, near P=3.2day. This feature, commonly attributed to the 2:1 resonance between the first and the fourth overtones ({omega}_4_~2{omega}_1_), is not reproduced by the hydrodynamical models. With the goal of reexamining the resonance hypothesis, we have obtained new CORAVEL radial velocity curves for 14 overtone Cepheids. Together with 10 objects of Krzyt et al. (1999, in prep.), the combined sample covers the whole range of overtone Cepheid periods. The velocity Fourier parameters display a strong characteristic resonant behavior. In striking contrast to photometric ones, they vary smoothly with the pulsation period and show no jump at 3.2day. The existing radiative hydrodynamical models match the velocity parameters very well. The center of the {omega}_4_=2{omega}_1_ resonance is estimated to occur at Pr=4.58+/-0.04day, i.e. at a period considerably longer than previously assumed (3.2day). We identify two new members of the s-Cepheid group: MY Pup and V440 Per.
Low-resolution spectroscopy obtained with FORS2 at the Very Large Telescope (VLT) has been used for the measurement of individual metal abundances ([Fe/H]) for 110 variable stars, including 107 RR Lyrae stars and one anomalous Cepheid, and to trace the metal distribution of the oldest stellar component in the Sculptor dwarf spheroidal galaxy. The RR Lyrae stars are spread over a 15x15arcmin^2^ area around the galaxy centre.
The goal in writing this paper is five fold: (1) to summarize the scientific achievements in the 20th century on S Dor variables (or LBVs); (2) to present an inventory of these variables in the Galaxy and the Magellanic Clouds with a description of their physical state and instability properties; (3) to emphasize the photometric achievements of the various types of instabilities. Generally this seems to be a neglected item resulting in a number of misunderstandings continuously wandering through literature; (4) to investigate the structure of the S Dor-area on the HR-diagram; (5) to estimate the total numbers of S Dor variables in the three stellar systems.
The US Naval Observatory 0.2m Flagstaff Astrometric Scanning Transit Telescope (FASTT) was used to obtain astrometric information in 16 equatorial fields in support of the Sloan Digital Sky Survey (SDSS). Each field is approximately 7.6{deg}x3.2{deg} in size and was scanned ~10 times with overlapping CCD strip scans; star positions accurate to +/-50mas in each coordinate and magnitudes good to +/-0.011mag were determined. As an ancillary project, this database was searched for new variables, and the results of that search are presented here. Approximately 1500 new variables have been discovered, and accurate coordinates for ~100 previously identified variables and suspected variables are given.
The Sloan Digital Sky Survey (SDSS, Stoughton et al., 2002AJ....123..485S) has scanned the entire region containing the Draco dwarf spheroidal galaxy to 23mag in g*. We present a catalog of stars found in a 453 arcmin^2^, elliptical region centered on the Draco dwarf spheroidal galaxy. Objects in the catalog are matched with five previously published catalogs. The catalog contains SDSS photometry for 5634 individual objects, and also the photometry from matches to any of the other catalogs. A comparison of the photometry between catalogs allows us to identify 142 candidate variable objects. One hundred and twelve of the suspected variables have colors consistent with RR Lyrae variables.
We describe a standard star catalog constructed using multiple SDSS photometric observations (at least four per band, with a median of 10) in the ugriz system. The catalog includes 1.01 million nonvariable unresolved objects from the equatorial stripe 82 (|{delta}_J2000.0_|<1.266{deg}) in the right ascension range 20^h^34^m^-4^h^00^m^ and with the corresponding r-band (approximately Johnson V-band) magnitudes in the range 14-22. The distributions of measurements for individual sources demonstrate that the photometric pipeline correctly estimates random photometric errors, which are below 0.01mag for stars brighter than 19.5, 20.5, 20.5, 20, and 18.5 in ugriz, respectively (about twice as good as for individual SDSS runs). Several independent tests of the internal consistency suggest that the spatial variation of photometric zero points is not larger than ~0.01mag (rms). In addition to being the largest available data set with optical photometry internally consistent at the ~1% level, this catalog provides a practical definition of the SDSS photometric system. Using this catalog, we show that photometric zero points for SDSS observing runs can be calibrated within a nominal uncertainty of 2% even for data obtained through 1mag thick clouds, and we demonstrate the existence of He and H white dwarf sequences using photometric data alone. Based on the properties of this catalog, we conclude that upcoming large-scale optical surveys such as the Large Synoptic Survey Telescope will be capable of delivering robust 1% photometry for billions of sources.
Four Be stars, HR 1960, HR 2968, HR 3237 and HR 3642, selected according to their periodic variations in Hipparcos and Geneva photometries, have been monitored from 1998 until 2001 with the Coralie spectrograph. HR 1960 and HR 3237 are two new spectroscopic binaries, HR 3642 is a new lambda Eri star, and HR 2968 is stable.
We searched the CCD/Transit Instrument (CTI) survey databases for RR Lyrae variable stars. The CTI images a strip of the sky with a narrow spread of declination over all right ascensions. The resulting survey area covers a large range of both Galactic latitude and longitude, amounting to approximately 50deg^2. We detected a total of 42 RR Lyrae stars to a faint limiting magnitude of V=19. Thirty-four of these RR Lyae stars are newly discovered.
We present the second Galaxy Evolution Explorer (GALEX) Ultraviolet Variability (GUVV-2) Catalog, which contains information on 410 newly discovered time-variable sources gained through simultaneous near UV (NUV 1750-2750{AA}) and far-UV (FUV 1350-1750{AA}) photometric observations. Source variability was determined by comparing the NUV and/or FUV fluxes derived from orbital exposures recorded during a series of multiple observational visits to 169 GALEX fields on the sky.
