M. Nalezyty

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 t he 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.

On the Compton scattering redistribution function in plasma

Compton scattering is the dominant opacity source in hot neutron stars, accretion disks around black holes and hot coronae. We collected here a set of numerical expressions of the Compton scattering redistribution functions for unpolarized radiation (RF), which are more exact than the widely used Kompaneets equation. The principal aim of this paper is presentation of the RF by Guilbert (1981) which is corrected for the computational errors in the original paper. This corrected RF was used in the series of papers on model atmosphere computations of hot neutron stars. We have also organized four existing algorithms for the RF computations into a unified form ready to use in radiative transfer and model atmosphere codes. The exact method by Nagirner and Poutanen (1993) was numerically compared to all other algorithms in a very wide spectral range from hard X-rays to radio waves. Sample computations of the Compton scattering redistribution functions in thermal plasma were done for temperatures corresponding to the atmospheres of bursting neutron stars and hot intergalactic medium. Our formulae are also useful to the study Compton scattering of unpolarised microwave background radiation in hot intra-cluster gas and the Sunyaev-Zeldovich effect. We conclude, that the formulae by Guilbert (1981) and the exact quantum mechanical formulae yield practically the same redistribution functions for gas temperatures relevant to the atmospheres of X-ray bursting neutron stars,

Spectral analysis of the burst source 4U 1728-34

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What is new on the second edition of the variable stars catalogue from the Pi of the Sky data

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

We analyse burst of MXB 1728-34 obtained by the RXTE PCA instrument during the observational period from 1995 to 2005. Each spectrum was integrated over 0.25 second and was fitted to the extensive grid of atmospheric models after background subtraction. Theoretical model spectra were calculated by the ATM code for various chemical compositions, effective temperatures from 107 K to 3×107 K and surface gravities from critical gravity up to log g = 15.0 (cgs units). As the result of the fitting procedure we obtained the surface redshift z and the surface gravity log g simultaneously for each trial set of parameters. Therefore, we are able to calculate mass and radius of the neutron star in MXB 1728-34. Many satisfactory fits were obtained for each chemical composition, but for models with iron abundance 100 times greater than the solar value fits were better than others. For this chemical composition we recommend that mass and radius of the neutron star is in the range: M = 0.103 – 1.564 Mʘ and R = 1.745 – 10.620 km.

Physical parameters of the DA white dwarfs from ESO SN Ia Progenitor Survey data

We present current status of the work on the second edition of the variable star catalogue. We used the data from the period from 2006 to 2007. Our catalogue contains about 1000 variable stars of different types. We determined periods for 34 variable stars, which already exists in the GCVS catalogue. For three of them we determined type of variability, previously unknown.

Variable stars classification based on photometric data from the "Pi of the Sky" project

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.

Estimation of space debris detection possibility by Pi of the Sky telescopes

We present determinations of masses, radii and bolometric luminosities for DA white dwarfs observed for the ESO SN Ia Progenitor Survey. Masses and radii of 513 stars were determined from their effective temperatures and surface gravities, obtained by Koester et al. (2009 [6]). We have used a grid of theoretical mass‐radius relations for carbon and oxygen core stars with hydrogen envelopes derived by Panei et al. (2000 [10]).