D. Szczygiel

Eclipsing binaries in the All Sky Automated Survey catalogue

ASAS is a long term project to monitor bright variable stars over the whole sky. It has discovered 50,122 variables brighter than V < 14 mag south of declination +28 degrees, and among them 11,099 eclipsing binaries. We present a preliminary analysis of 5,384 contact, 2,957 semi-detached, and 2,758 detached systems. The statistics of the distribution provides a qualitative confirmation of decades old idea of Flannery and Lucy that W UMa type binaries evolve through a series of relaxation oscillations: ASAS finds comparable number of contact and semidetached systems. The most surprising result is a very small number of detached eclipsing binaries with periods P < 1 day, the systems believed to be the progenitors of W UMa stars. As many (perhaps all) contact binaries have companions, there is a possibility that some were formed in a Kozai cycle, as suggested by Eggleton and his associates.

Multiperiodic Galactic field RR Lyrae stars in the ASAS catalogue

The All Sky Automated Survey (ASAS) monitors bright stars (8 < V < 14 mag) south of declination +28 ◦ . The ASAS Catalogue of Variable Stars (ACVS) presently contains 50 099 objects; among them are 2212 objects classified as RR Lyrae pulsating variables. We use ASAS photometric V-band data to search for multiperiodicity in those stars. We find that 73 of 1435 RRab stars and 49 of 756 RRc stars exhibit the Blazhko effect. We observe a deficiency of RRab Blazhko variables with main pulsation periods greater than 0.65 d. The Blazhko periods of RRc stars exhibit a strongly bimodal distribution. During our study we discovered the Blazhko effect with multiple periods in object ASAS 050747−3351.9 = SU Col. Blazhko periods of 89.3 and 65.8 d and a candidate of 29.5 d were identified with periodogram peaks near the first three harmonics of the main pulsation. These observations may inspire new models of the Blazhko effect, which has eluded a consistent theory since its discovery about one hundred years ago. Long-term light curve changes were found in 29 stars. We also found 19 Galactic double mode pulsators (RRd), of which four are new discoveries, raising the number of ASAS discoveries of such objects to 16, out of 27 known in the field of our Galaxy.

A model of AW UMa

The contact binary AW UMa has an extreme mass ratio, with the more-massive component (the current primary) close to the main sequence, while the low-mass star at q ≈ 0.1 (the current secondary) has a much larger radius than a main-sequence star of a comparable mass. We propose that the current secondary has almost exhausted hydrogen in its centre and is much

Galactic Fundamental Mode RR Lyrae Stars: Period‐Amplitude Diagram, Metallicities and Distribution

We have analysed 1455 fundamental mode RR Lyrae stars of the Galactic field, using the All Sky Automated Survey (ASAS) data. The sample covers 75% of the sky and contains objects in the close neighbourhood of the Sun, within 4 kpc distance. Unlike in the previous analysis of the close field RRab, we see a clear manifestation of the Oosterhoff groups on the period - amplitude diagram. The relation for Oosterhoff I type variables becomes strongly flattened at large V amplitudes, which was not observed for globular cluster RR Lyrae. We calculate photometric metallicities using two available methods: one of Jurcsik & Kovacs (1996) and the other of Sandage (2004). We find significant discrepancies between results from both methods. Comparison with spectroscopic metallicities undoubtedly favors the method of Jurcsik & Kovacs (1996). In addition, we notice that RRab of Oosterhoff II type might follow a different metallicity-period-phase relation than Oosterhoff I type variables. The spatial distribution of Galactic field RRab does not show any metallicity gradients with distance from the Galactic Center in either of the Oosterhoff groups. However, both the older, metal poor Oosterhoff II variables and the metal rich Oosterhoff I RRab become more concentrated to the Galactic plane with increasing metal content.

Search for GRB optical counterparts with “Pi of the Sky” apparatus

“Pi of the Sky” is a detector designed to search for optical flashes of the cosmic origin in the sky. Its primary goal is to look for optical afterglows associated with the gamma ray bursts (GRB), but it is capable to detect also other optical transients of extragalactic origin. The apparatus consists of two arrays of 16 cameras each, which allow for simultaneous observation of the whole sky. Due to on‐line data analysis in the real time, it has self‐triggering capability and can react to external triggers with negative time delay. The prototype with two cameras has been installed at Las Campanas (Chile) and is operational from July 2004.

Apparatus to search for optical flashes of extragalactic origin

An apparatus is described to search for optical, point-like flashes in the sky at the time scale of seconds. Such flashes are expected to accompany gamma ray bursts (GRB) observed routinely by satellites and proven to be of extragalactic origin. So far only one such flash has been recorded shortly after the GRB, because standard methods of observational astronomy are not suitable for the time scale of seconds. In this paper, a novel approach is proposed based on experience from particle physics experiments. An apparatus is described which monitors the sky continuously. The large data stream is analysed on-line and potentially interesting events are selected by a multilevel trigger system. In the first phase of the project the apparatus consists of two CCD cameras, especially designed for this project and a robotic mount used to scan interesting regions of the sky. In the second phase the experiment will consist of two sets of 16 cameras on fixed mounts, covering almost all visible sky.