V. Laugalys

Large-Scale Errors in CCD Photometry of M 67

Abstract The accuracy of new CCD photometry in the Vilnius system of the M67 cluster is analyzed. The observational material is obtained during six observing runs in 1994-2001 with the 1 meter telescope of the USNO Flagstaff Station. The main task was to establish CCD standards of high accuracy and to eliminate large-scale errors from our CCD photometry. We compare our results with the published CCD photometric data in other photometric systems. The comparison reveals considerable systematic errors in some datasets.

Seven-Color Photometry and Classification of Stars in the Direction of Open Cluster M29 (NGC 6913) in Cygnus

Abstract Magnitudes and color indices in the Vilnius seven-color system were determined for 1752 stars down to V = 19.5 mag in the direction of the open cluster M29 (NGC 6913). The region is centered at RA = 20:24, DEC = +38:30 (J2000) and covers an area of 1.5 sq. deg. The photometric data are used to classify about 70% of stars in spectral and luminosity classes and peculiarity types.

Discovery, Observational Data and the Orbit of the Centaur Asteroid 2012 DS85

Abstract A project for astrometric and photometric observations of asteroids at Mt. Graham Observatory with the VATT telescope is described. One of the most important results is a discovery of the Centaur 2012 DS85. Astrometric and photometric data on the asteroid are presented. The orbit of the asteroid was computed from 67 observations. Combined with its apparent brightness, the orbit gives an absolute magnitude of 9.43. Using a typical albedo value of 0.08 for Centaurs and TNOs (Moullet et al. 2011), we get a diameter of 2012 DS85 at about 61 km.

Flatfielding Errors in Strömvil CCD Photometry

Abstract The importance of determining the error of the flat field in CCD photometry is detailed and our methods of doing this are described. We now have reached a precision of 1-1.5 % in our photometry. Color-magnitude diagrams of the open cluster M67 (ours and Laugalys et al. 2003) are compared.

OVERLAPPING OPEN CLUSTERS NGC 1750 AND NGC 1758 BEHIND THE TAURUS DARK CLOUDS. II. CCD PHOTOMETRY IN THE VILNIUS SYSTEM

Abstract Seven-color photometry in the Vilnius system has been obtained for 420 stars down to V = 16 mag in the area containing the overlapping open clusters NGC 1750 and NGC 1758 in Taurus. Spectral and luminosity classes, color excesses, interstellar extinctions and distances are given for 287 stars. The classification of stars is based on their reddening-free Q-parameters. 18 stars observed photoelectrically were used as standards. The extinction vs. distance diagram exhibits the presence of one dust cloud at a distance of 175 pc which almost coincides with a distance of other dust clouds in the Taurus complex. The clusters NGC 1750 and NGC 1758 are found to be at the same distance of ~760 pc and may penetrate each other. Their interstellar extinction AV is 1.06 mag which corresponds to EB-V = 0.34 mag.

Calibration of the Strömvil Photometric System

Abstract A calibration of color indices of the Strömvil photometric system in terms of physical parameters of stars is presented. The calibration is based on photoelectric photometry of about 1000 stars with known effective temperatures, distances, gravities and metallicities. The observations were accomplished in 2000-2003 with the 1.5 meter telescope of the Steward Observatory. The distances were taken from the Hipparcos catalog, and Te, log g, [Fe/H]) were collected from several literature sources and averaged.