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1

Ultra-Short-Period Binary Systems in the OGLE Fields Toward the Galactic Bulge

Soszyński I., Stępień K., Pilecki B., Mróz P., Udalski A., Szymański M. K., Pietrzyński G., Wyrzykowski Ł., Ulaczyk K., Poleski R., Kozłowski S., Pietrukowicz P., Skowron J., Pawlak M.

Acta Astronomica

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2015

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Vol. 65, No. 1

39--62

EN

We present a sample of 242 ultra-short-period (Porb <0.22 d) eclipsing and ellipsoidal binary stars identified in the OGLE fields toward the Galactic bulge. Based on the light curve morphology, we divide the sample into candidates for contact binaries and non-contact binaries. In the latter group we distinguish binary systems consisting of a cool main-sequence star and a B-type subdwarf (HW Vir stars) and candidates for cataclysmic variables, including five eclipsing dwarf novae. One of the detected eclipsing binary systems - OGLE-BLG-ECL-000066 - with the orbital period below 0.1 d, likely consists of M dwarfs in a nearly contact configuration. If confirmed, this would be the shortest-period M-dwarf binary system currently known. We discuss possible evolutionary mechanisms that could lead to the orbital period below 0.1 d in an M-dwarf binary.

2

The All Sky Automated Survey. The Catalog of Variable Stars in the Kepler Field of View

Pigulski A., Pojmański G., Pilecki B., Szczygieł D. M.

Acta Astronomica

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2009

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Vol. 59, No. 1

33--46

EN

We present the catalog of 947 variable stars located in the field of view of the Kepler satellite. The catalog is a result of the analysis of VI photometry obtained during the first 17-month observations in the ASAS3-North station. The variable stars we present are divided into eleven groups according to the presented variability; the groups are briefly discussed. The catalog is intended to be a source of information for target selection process and follow-up programs.

3

Galactic Fundamental Mode RRLyrae Stars. Period-Amplitude Diagram, Metallicities and Distribution

Szczygieł D. M., Pojmański G., Pilecki B.

Acta Astronomica

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2009

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Vol. 59, No. 2

137--167

EN

We have analyzed 1455 fundamental mode RR Lyr 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 neighborhood of the Sun, within 4 kpc distance. Unlike in the previous analysis of the close field RRab stars, 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 Lyr. We calculate photometric metallicities using two available methods: one of Jurcsik and Kovács (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 and Kovács (1996). In addition, we notice that RRab stars of Oosterhoff II type might follow a different metallicity-period-phase relation than Oosterhoff I type variables. The spatial distribution of Galactic field RRab stars 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 stars become more concentrated to the Galactic plane with increasing metal content.

4

Coronal Activity from the ASAS Eclipsing Binaries

Szczygieł D. M., Socrates A., Paczyński B., Pojmański G., Pilecki B.

Acta Astronomica

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2008

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Vol. 58, No. 4

405--418

EN

We combine the catalog of eclipsing binaries from the All Sky Automated Survey (ASAS) with the ROSAT All Sky Survey (RASS). The combination results in 836 eclipsing binaries that display coronal activity and is the largest sample of active binary stars assembled to date. By using the (V-I) colors of the ASAS eclipsing binary catalog, we are able to determine the distances and thus bolometric luminosities for the majority of eclipsing binaries that display significant stellar activity. A typical value for the ratio of soft X-ray to bolometric luminosity is L_X/L_bol≈ a few ×10^-4, similar to the ratio of soft X-ray to bolometric flux F_X/F in the most active regions of the Sun. Unlike rapidly rotating isolated late-type dwarfs - stars with significant outer convection zones - a tight correlation between Rossby number and activity of eclipsing binaries is absent. We find evidence for the saturation effect and marginal evidence for the so-called ``super-saturation'' phenomena. Our work shows that wide-field stellar variability searches can produce a high yield of binary stars with strong coronal activity.

5

The All Sky Automated Survey. Catalog of Variable Stars. V. Declinations 0° - +28° of the Northern Hemisphere

Pojmański G., Pilecki B., Szczygieł D.

Acta Astronomica

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2005

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Vol. 55, No. 3

275--301

EN

This paper contains the fifth part of the Catalog of Variable Stars created from the V-band photometric data collected by 9°×9° camera of the All Sky Automated Survey. Preliminary list of variable stars found in the fields located between declination 0° and +28° of the northern hemisphere is presented. 11 509 stars brighter than V=15 mag were found to be variable (2 482 eclipsing, 1 397 regularly pulsating, 318 Miras and 7 310 other stars). Automated algorithm taking into account light curve properties (period, Fourier coefficients) and other available data (2MASS colors, IRAS fluxes) was applied to roughly classify the objects. This paper concludes our preliminary efforts to detect variable stars brighter than V≈14 mag over the sky south of declination +28°. A short summary of the current ASAS Catalog of Variable Stars is presented and links to the on-line data are provided. All the photometric data are available over the INTERNET at http://www.astrouw.edu.pl/~gp/asas/asas.html or http://archive.princeton.edu/~asas