Automated analysis of eclipsing binary light curves – II. Statistical analysis of OGLE LMC eclipsing binaries

In the first paper of this series, we presented EBAS – Eclipsing Binary Automated Solver, a new fully automated algorithm to analyse the light curves of eclipsing binaries, based on the ebop code. Here, we apply the new algorithm to the whole sample of 2580 binaries found in the Optical Gravitational Lensing Experiment (OGLE) Large Magellanic Cloud (LMC) photometric survey and derive the orbital elements for 1931 systems. To obtain the statistical properties of the short-period binaries of the LMC, we construct a well-defined subsample of 938 eclipsing binaries with main-sequence B-type primaries. Correcting for observational selection effects, we derive the distributions of the fractional radii of the two components and their sum, the brightness ratios and the periods of the short-period binaries. Somewhat surprisingly, the results are consistent with a flat distribution in log P between 2 and 10 d. We also estimate the total number of binaries in the LMC with the same characteristics, and not only the eclipsing binaries, to be about 5000. This figure leads us to suggest that  (0.7 ± 0.4)  per cent of the main-sequence B-type stars in the LMC are found in binaries with periods shorter than 10 d. This frequency is substantially smaller than the fraction of binaries found by small Galactic radial-velocity surveys of B stars. On the other hand, the binary frequency found by Hubble Space Telescope ( HST ) photometric searches within the late main-sequence stars of 47 Tuc is only slightly higher and still consistent with the frequency we deduced for the B stars in the LMC.     

Numerical simulations of the Hyades dynamics and the nature of the moving Hyades cluster

We present our numerical simulations of the dynamical evolution of the Hyades open cluster. The simulations were performed usinga modified NBODY6 algorithm that included tidal forces and a realistic orbit of the cluster in a gravitational field described by the Miyamoto-Nagai potential. Our goal was to study the nature of movingclu sters. We show that the stars that were earlier cluster members could be later identified within a sphere of 50 pc in diameter around the Sun. The number of such stars for the chosen initial mass and virial radius of the cluster does not exceed ten. The maximum space velocity of these stars relative to the core of the current cluster does not exceed 3 km s^?1. Our numerical simulations confirm the assumption that some of the moving clusters near the Sun could consist of stars that have escaped from open clusters in the course of their dynamical evolution.     

Analysis of the spatial distribution of gamma-ray bursts in their host galaxies

We compare the radial distributions of known localized gamma-ray bursts (GRBs) relative to the centers of their host galaxies with the distributions of known objects in nearby galaxies (supernovae of various types, X-ray binaries), the hypothetical dark-matter profiles, and the distribution of luminous matter in galaxies in the model of an exponential disk. By comparing the moments of empirical distributions, we show that the radial distribution of GRBs in galaxies differs significantly from that of other sources. We suggest a new statistical method for comparing empirical samples that is based on estimating the number of objects within a given radius. The exponential disk profile was found to be in best agreement with the radial distribution of GRBs. The distribution of GRBs relative to the centers of their host galaxies also agrees with the dark matter profile at certain model parameters.     

Role of HD Molecules in the Cooling of the Primordial Gas

This paper examines the effect of HD molecules on the thermochemical evolution of the primordial gas behind the fronts of shock waves that may develop during the epoch of galaxy formation. A critical shock velocity is found at which deuterium efficiently converts to HD molecules and the contribution of HD molecules to cooling is dominant. Above this value of the shock velocity the gas can cool to temperatures close to that of the cosmic background radiation. In this case the Jeans mass will depend only on the red shift and the initial density, with M_J ∝ δ _c ^−0.5 (1 + z)^0.5. For z≳45, HD molecules heat the gas and for large red shifts they generally cease to play a significant role in the thermal evolution of the gas. __________ Translated from Astrofizika, Vol. 48, No. 4, pp. 585–601 (November 2005).     

The unique eclipsing system KH 15D: New photometric data

We present results of photometric observations of the young eclipsing system KH 15D made during two observational seasons, 2002–2004. A comparison of our data with the earlier results of Hamilton et al. and Herbst et al. reveals the existence of a multiyear photometric trend in the brightness: over a period of 5 years the brightness of the system in the I_c band decreased by almost 1 stellar magnitude. It is also shown that the systematic variations in the eclipse parameters reported by Herbst et al. continue to the present. The shape of the light curve has not changed significantly and, as before, it is characterized by a slight brightening in the central portion of the eclipses. These results are discussed in the context of current models for KH 15D.Translated from Astrofizika, Vol. 48, No. 1, pp. 5–14 (February 2005).     

Helium and neon in comet 81P/Wild 2 samples from the NASA Stardust mission

Helium and neon distributions are reported for a variety of Stardust comet 81P/Wild 2 samples, including particle tracks and terminal particles, cell surface and subsurface slices from the comet coma and interstellar particle collection trays, and numerous small aerogel blocks extracted from comet cells C2044 and C2086. Discussions and conclusions in several abstracts published during the course of the investigation are included, along with the relevant data. Measured isotope ratios span a broad range, implying a similar range for noble gas carriers in the Wild 2 coma. The meteoritic phase Q‐²⁰Ne/²²Ne ratio was observed in several samples. Some of these, and others, exhibit ²¹Ne excesses too large for attribution to spallation by galactic cosmic ray irradiation, suggesting exposure to a solar proton flux greatly enhanced above current levels in an early near‐Sun environment. Still others display evidence for a solar wind component, particularly one C2086 block with large abundances of isotopically solar‐like helium and neon. Eighty‐nine small aerogel samples were cut from depths up to several millimeters below the cell C2044 surface and several millimeters away from the axis of major track T41. A fraction of these yielded measurable and variable helium and neon abundances and isotope ratios, although none contained visible tracks or carrier particle fragments and their locations were beyond estimated penetration ranges for small particles or ions incident on the cell surface, or for lateral ejecta from T41. Finding plausible emplacement mechanisms and sources for these gases is a significant challenge raised by this study.     

On the Question of Calculating the Parameters of Vortices in the Near-Surface Atmosphere of Mars

Solar System Research - The paper is dedicated to the study of dust vortices on the Earth and Mars. The hydrodynamic similarity of convective vortices is considered, and the similarity criteria are...