Searching for Space Debris Elements with the “Pi of the Sky” System

The main purpose of the “Pi of the Sky” system is to investigate short timescale astrophysical phenomena (particularly gamma-ray bursts, optical transients and variable stars). Wide field, short exposures and full automation of the system, together with effective algorithms, give good prospects for effective identification of space debris elements. These objects can be a great danger for current and future space missions, and should be continuously monitored and cataloged. Algorithms for identifying optical transients (OT), designed for the “Pi of the Sky” experiment enable moving objects like planes, satellites and space debris elements to be identified. The algorithm verifies each OT candidate against a database of known satellites and is also able to automatically self-identify moving objects not present in this database. The data collected by the prototype in the Las Campanas Observatory enabled us to obtain a large sample of observations of moving objects. Some of these objects were identified as high-orbit geostationary (GEO) satellites, which shows that it is possible to observe even distant satellites with small aperture photo lenses. The analysis of the sample is still going on. The preliminary results and algorithms for automatic identification of moving objects will be described here

The catalog of short periods stars from the ''Pi of the Sky'' data

Based on the data from the ''Pi of the Sky'' project we made a catalog of the variable stars with periods from 0.1 to 10 days. We used data collected during a period of two years (2004 and 2005) and classified 725 variable stars. Most of the stars in our catalog are eclipsing binaries - 464 (about 64%), while the number of pulsating stars is 125 (about 17%). Our classification is based on the shape of the light curve, as in the GCVS catalog. However, some stars in our catalog were classified as of different type than in the GCVS catalog. We have found periods for 15 stars present in the GCVS catalog with previously unknown period.Comment: New Astronomy in prin

Theoretical UBVRI colors of iron core white dwarfs

We explore photometric properties of hypothetical iron core white dwarfs and compute their expected colors in UBVRI Johnson broadband system. Atmospheres of iron core WDs in this paper consist of pure iron covered by a pure hydrogen layer of an arbitrary column mass. LTE model atmospheres and theoretical spectra are calculated on the basis of Los Alamos TOPS opacities and the equation of state from the OPAL project, suitable for nonideal Fe and H gases. We have also computed UBVRI colors of the models and determined an area on the B-V vs. U-B and U-B vs. V-I planes, occupied by both pure Fe, and pure H model atmospheres of WD stars. Finally, we search for iron core white dwarf candidates in the available literature.Comment: 13 pages, 12 figures, Astronomy & Astrophysics (2003) in prin

A catalogue of isolated massive white dwarfs

We present in this paper a catalogue of 112 massive isolated white dwarfs, with masses $M > 0.8~ M_{\odot}$. Mass determinations and other parameters of white dwarfs were compiled from the available literature. For each star we present averaged values of mass, effective temperature, logarithm of surface gravity $\log g$, radius, distance, and the surface magnetic field for magnetic white dwarfs. The mass distribution of our sample is a slowly decreasing continuum function for masses larger than $0.9 ~M_{\odot}$, with an overlapping secondary maximum at $1.04 ~M_{\odot}$. We conclude that the mass distribution of known massive magnetic white dwarfs is flat, whereas nonmagnetic WDs exhibit a steeper mass distribution towards the highest masses. The secondary maximum at $1.04 ~M_{\odot}$ is caused exclusively by nonmagnetic white dwarfs. We note that the 4 most massive stars with masses $M \ge 1.3 ~M_{\odot}$ are magnetic white dwarfs. Our results show also, that the occurrence of magnetism in massive white dwarfs does not depend on the cooling age (above ${T_{\rm eff}}= 5000$ K).