Eclipsing binaries in the MOST satellite fields

Sixteen new eclipsing binaries have been discovered by the MOST satellite among guide stars used to point its telescope in various fields. Several previously known eclipsing binaries were also observed by MOST with unprecedented quality. Among the objects we discuss in more detail are short‐period eclipsing binaries with eccentric orbits in young open clusters: V578 Mon in NGC 2244 and HD 47934 in NGC 2264. Long nearly‐continuous photometric runs made it possible to discover three long‐period eclipsing binaries with orbits seen almost edge‐on: HD 45972 with P = 28.1 days and two systems (GSC 154 1247 and GSC 2141 526) with P > 25 days. The high precision of the satellite data led to discoveries of binaries with very shallow eclipses (e.g., HD 46180 with A = 0.016 mag, and HD 47934 with A = 0.025 mag). Ground‐based spectroscopy to support the space‐based photometry was used to refine the models of several of the systems (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Automated Analysis of Light Curves of OGLE LMC Binaries: The Period distribution

We present a new algorithm, the Eclipsing Binary Automated Solver (EBAS) to analyse lightcurves of eclipsing binaries. To replace human visual assessment, we introduce a new ‘alarm’ goodness-of-fit statistic that takes into account correlation between neighbouring residuals. We apply the new algorithm to the whole sample of 2580 binaries found in the OGLE photometric survey of the LMC and derive the photometric 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 days.     

3-D Structure of the Galactic Interstellar Matter: A Contribution from GAIA

We investigate the possibilities for tracing interstellar extinction with the ESA's astrometric space mission GAIA. The analysis is based on detailed simulations of the GAIA photometry, which are used to derive the distribution of interstellar matter in a modelled Galaxy. We find that `small' diffuse clouds (diameter D = 4 pc, E <sub>B-V</sub> = 0.06) will be easily traced with GAIA up to the distances of ∼ 800 pc. `Large' diffuse interstellar clouds (D = 10 pc, E _B-V = 0.13) will be located up to the distances of ∼ 2.5 kpc. This holds for the reddening tracers of spectral types O – K2 brighter than V = 17. Inmost cases, due to their low spatial density, the early type stars (O– A2) cannot provide reliable information about the distribution of interstellar matter. None of the reddening tracers measured by GAIA will provide reliable identification of the individual interstellar clouds beyond the distances of ∼ 3 kpc. Therefore, we conclude that the information available from photometric observations will be not sufficient for the detailed reconstruction of the 3-D distribution of Galactic interstellar matter. It is therefore extremely important to define the new strategies which would allow to combine all the available information, including the earlier space- and/or ground-based investigations, together with the information which will be provided by GAIA itself (parallaxes, E _B-V etc.). This revised version was published online in July 2006 with corrections to the Cover Date.     

Photometric Mass Ratios of Eclipsing Binary Stars

Following a brief history of measurement of eclipsing binary mass ratios from light curves, we show that photometric mass ratios for overcontact and semi-detached binaries are reliable because the relative stellar radii, R/a, are accurately measured and not, as commonly claimed, because of information in the light variation outside eclipse. We explore the accuracy of photometric mass ratios by solving synthetic data of typical precisions for a semi-detached and an overcontact binary for orbital inclinations from 89^∘ down into the partial eclipse range.     

The stellar content of the young open cluster Trumpler 37

With an apparent cluster diameter of 1.5° and an age of 4 Myr, Trumpler 37 is an ideal target for photometric monitoring of young stars as well as for the search of planetary transits, eclipsing binaries and other sources of variability. The YETI consortium has monitored Trumpler 37 throughout 2010 and 2011 to obtain a comprehensive view of variable phenomena in this region. In this first paper we present the cluster properties and membership determination as derived from an extensive investigation of the literature. We also compared the coordinate list to some YETI images. For 1872 stars we found literature data. Among them 774 have high probability of being member and 125 a medium probability. Based on infrared data we re‐calculate a cluster extinction of 0.9–1.2 mag. We can confirm the age and distance to be 3–5 Myr and870 pc. Stellar masses are determined from theoretical models and the mass function is fitted with a power‐law index of α = 1.90 (0.1–0.4 M_⊙) and α = 1.12 (1–10 M_⊙). (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Vilnius Photometry of Red Giant Stars in the Open Cluster NGC 7789

Photoelectric Vilnius seven-color photometry is presented and analyzed for a sample of 24 red giant branch and clump stars in the open cluster NGC 7789. For each star we have determined photometric spectral type, absolute magnitude, interstellar reddening, effective temperature, metallicity, and surface gravity. From averages over the stars in the sample we find the mean reddening to the cluster E _Y−V = 0.21± 0.02 (s.d.), or E _B−V = 0.25, and the apparent distance modulus (m−M) _V = 12.21± 0.10 (s.d.), which yield a distance of 1840 pc. The mean overall metallicity is found to be [Fe/H] = −0.18± 0.09 (s.d.). The clump stars, on average, appear to be slightly more metal-rich than the other red giants, which is most probably caused by evolutionary changes of carbon and nitrogen molecular bands falling in the photometric passbands. A difference in mass between the two groups of stars has also been detected, which suggests that the clump stars might have undergone extra mass loss before reaching their core He-burning phase of evolution.     

A two-color CCD survey of the North Celestial Cap: I. The method

We describe technical aspects of an astrometric and photometric survey of the North Celestial Cap (NCC), from the Pole (δ=90°) to δ=80°, in support of the TAUVEX mission. This region, at galactic latitudes from ∼17° to ∼37°, has poor coverage in modern CCD-based surveys. The observations are performed with the Wise Observatory one-meter reflector and with a new mosaic CCD camera (LAIWO) that images in the Johnson–Cousins R and I bands a one-square-degree field with sub-arcsec pixels. The images are treated using IRAF and SExtractor to produce a final catalogue of sources. The astrometry, based on the USNO-A2.0 catalogue, is good to ∼1 arcsec and the photometry is good to ∼0.1 mag for point sources brighter than R=20.0 or I=19.1 mag. The limiting magnitudes of the survey, defined at photometric errors smaller than 0.15 mag, are 20.6 mag (R) and 19.6 (I). We separate stars from non-stellar objects based on the object shapes in the R and I bands, attempting to reproduce the SDSS star/galaxy dichotomy. The completeness test indicates that the catalogue is complete to the limiting magnitudes.     

NGC 1624 (OCl 403, Cr 53) – A very young open cluster

We present the first CCD photometric UBVRI observations of the not-so-well-studied open cluster NGC 1624 (OCl 403, Cr 53; α₂₀₀₀ = 04 h 40 m 36 s; δ₂₀₀₀ = + 50^˚ 27^′ 42″ Trumpler class = I 2 p N). This cluster was observed on 01 February 2004 with the 2 m Himalayan Chandra Telescope at Hanle using a LN2 cooled 2k × 2k CCD. The cluster presents differential reddening with E(B-V) values ranging from 0.70 to 0.90 mag, which could be attributed to the presence of the HII region wherein the cluster is embedded. It is found to be at a distance of 6.025 ± 0.5 kpc and the age of this cluster is estimated to be ∼3.98 × 10⁶ years. In view of these parameters, it can be considered as a young enough cluster located in the direction of the Perseus constellation with the galactic coordinates of l = 155^˚.35 and b = + 02 ^˚.58. Thus it could also be used as a suitable candidate for tracing the Outer Perseus spiral arm of our Galaxy. The initial mass function slope is derived as 1.65 ± 0.25 by applying the corrections for field star contamination and data incompleteness. This is in good agreement with the Salpeter value within the limits of errors.     

Monitoring Possible Light-Time Effect in the Orbital Period of Some Eclipsing Binaries at the Ankara University Observatory

A significant number of close binaries are known to be members of physically bound triple or multiple star systems. The O – C analysis technique which is based on the minima times of an eclipsing binary can reveal the light-time effect due to the presence of gravitationally bound and generally unseen close component(s) in the system. In this study we present shortly the O – C analysis results based on the light-time effect possibilities for two of the eclipsing binaries observationally followed by our group; TZ Boo and CF Tau.     

O'Connell effect in early‐type contact binaries: DU Boo and AG Vir

The paper presents new photoelectric observations of the eclipsing binary systems DU Boo and AG Vir. The systems are somewhat similar – both are A‐type contact binaries with the maximum following the primary minimum being the brighter one. This light curve asymmetry is extremely temporally stable. The phase dependence of the color indices is unexpectedly small for the observed amplitude of the O'Connell effect, amounting to about 0.1 mag in the optical wavelength range which indicates a very large heated area with a temperature contrast of ΔT ≈ 1000–1500 K. The broadening functions (BFs) of the systems do not show any dark solar‐type photospheric spots. On the other hand, there are significant differences of BFs between the quadratures (surprisingly similar in both systems) indicative of stream of matter or bright region causing additional emission seen between the components around the phase 0.25. Absolute parameters of the components slightly depend on the adopted model. Long orbital period of both contact binaries combined with late spectral type indicate that the primary components of either of the systems (but particularly in case of DU Boo) already evolved off the main sequence (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Detached eclipsing binaries: analysis of BD–00° 3357

Detached eclipsing binaries constitute potential accurate distance tracers. They are also useful as the test bench of stellar evolution. In BD–00° 3357 eclipses are partial and its orbital period is 1.^d4. Our combined spectroscopic and photometric solution yields secure parameters of this system. The model of the star was obtained using the Wilson‐Devinney method. As result we obtained a semi major axis of 7.65 R_⊙ and a mass ratio of 0.78. The derived masses and radii are M ₁ = 1.73 M_⊙,M ₂ = 1.34 M_⊙R ₁ = 1.78 R_⊙, R ₂ = 1.32 R_⊙, respectively. These values correspond to the slightly evolved F0 and F6.5 components, both slightly less than 1Gyr old. The distance of the star was estimated to be 310 ± 60 pc, and the corresponding photometric parallax is 3.24 ± 0.74 mas. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Combined UBV and uvby photometry of open clusters. I. NGC 1502

For at all 24 stars in the field of the heavity reddened open cluster NGC 1502 we obtained UBV and uvby photometry. 19 of these stars we classified definitely as members. From the photometric results we derived 1·1 × 10⁷ years as the cluster age, 960 pc as its distance, and <E(B—V)> = 0·78 mag as mean reddening of the cluster. From the reddening of the foreground stars we evaluated that the intracluster reddening has to be smaller than 0·2 mag. The value of the colour excess ratio E(b—y)/E(B—V) = 0·770 leads us to the conclusion that in the spectra of the cluster stars a very broadband structure (VBS) with a central depth of about 0·04 mag is present.     

Brown dwarfs and very low‐mass stars: variability in the Pleiades

We present the results of the optical photometric observations of the Pleiades (125 Myr) cluster. The aim of this research is to look for variability, both due to rotation of single stars and the presence of eclipsing binaries. We have used differential photometry and two different methods of statistical analysis of the data.We have found variability in the Pleiades cluster with amplitudes of about 50 mmag and uncertainties of 5 mmag until I=17.9, well within the brown dwarf regime. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Basic Functions of the Light Curve Analysis of Eclipsing Variables in the Frequency Domain

An analytically tractable method of transforming the problem of light curve analysis of eclipsing binaries from the time domain into the frequency domain was introduced by Kopal (1975, 1979, 1990). This method uses a new general formulation of eclipse functions α, the so-called moments A _2m , and their combinations as g _2m = A _2m+2/(A _2m A _2m+4) functions for the basic spherical model. In this paper, I will review the use of these functions in the light curve analysis of eclipsing binaries.     

The CCD photometric study of the newly identified RS CVn binary star V1034 Hercules

This paper presents a new CCD Bessell VR_cI_c light curves and photometric analysis of the newly discovered RS CVn type eclipsing binary star V1034 Her. The light curves were obtained at the Çanakkale Onsekiz Mart University Observatory in 2006. Variations of the orbital period of the system were firstly studied. The (O − C) diagram with a low range of observing time of about 20 years shows an upward parabola, which indicates a secular increase in the orbital period of the system. The light curves are generally those of detached eclipsing binaries; however, there are large asymmetries between maxima. The VR_cI_c light curves were analysed with two different fitting procedures: Wilson–Devinney method supplemented with a Monte Carlo type algorithm and Information Limit Optimization Technique (ILOT). Our general results find V1034 Her. as a well detached system, in which the components are filling 65% of their Roche lobes. Light curve asymmetries of the system are explained in terms of large dark starspots on the primary component. The primary star shows a long-lived spot distribution with active longitudes in the same hemisphere.     

Interstellar extinction in the direction of the Merope dark cloud in pleiades

The dependence of interstellar extinction on distance in the direction of the dark cloud south of Merope is determined using photoelectric photometry of 93 stars in the Vilnius photometric system. The cloud front edge is detected at 120–130 pc from the Sun and the distance of the Pleiades cluster is found to be 127 pc. Mean extinctionA _V in the Merope cloud is of the order of 1.0 mag. There is no evidence of extinction at distances exceeding the Merope cloud distance. Variable extinction method yieldsR=A _V/E_B-V=3.6, while the maximum polarization wavelength method gives the value 3.4. Some Pleiades stars are suspected to be unresolved binaries.     

Photometric study of the active binary star V1430 Aquilae

New BVR light curves and a photometric analysis of the eclipsing binary star V1430 Aql are presented. The light curves were obtained at the Çanakkale Onsekiz Mart University Observatory in 2004. The light curves are generally those of detached eclipsing binaries, but there are large asymmetries between maxima. New BVR light curves were analysed with an ILOT procedure. Light curve asymmetries of the system were explained in terms of large dark starspots on the primary component. The primary star shows a long‐lived and quasi‐poloidal spot distribution with active longitudes in opposite hemispheres. Absolute parameters of the system were derived.We also discuss the evolution of the system: the components are likely to be pre‐main sequence stars, but a post‐main sequence stage cannot be ruled out. More observations are needed to decide this point. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Carbon recombination lines from the Galactic plane at 34.5 & 328 MHz

We present the results of a search for carbon recombination lines in the Galaxy at 34.5 MHz (C575α) made using the dipole array at Gauribidanur near Bangalore. Observations made towards 32 directions resulted in detections of lines, in absorption at nine positions. Followup observations at 328 MHz (C272α) using the Ooty Radio Telescope detected these lines in emission. A VLA D-array observation of one of the positions at 330 MHz yielded no detection implying a lower limit of 10′ for the angular size of the line forming region. The longitude-velocity distribution of the observed carbon lines indicate that the line forming regions are located mainly between 4 kpc and 7 kpc from the Galactic centre. Combining our results with published carbon recombination line data near 76 MHz (Erickson, McConnell & Anantharamaiah 1995), we obtain constraintson the physical parameters of the line forming regions. We find thatif the angular size of the line forming regions is ≥ 4°, then the range of parameters that fit the data are:T _e =20–40 K,n _e ∼ 0.1–0.3 cm⁻³ and pathlengths ∼ 0.07–0.9 pc which may correspond to thin photodissociated regions around molecular clouds. On the other hand, if the line forming regions are ∼ 2° in extent, then warmer gas (T _e ∼ 60–300 K) with lower electron densities (n _e ∼ 0.03–0.05 cm⁻³) extending over several tens of parsecs along the line of sight and possibly associated with atomic HI gas can fit the data. Based on the range of derived parameters, we suggest that the carbon line regions are most likely associated with photo-dissociation regions.     

Eclipsing Binaries in Open Clusters

The study of detached eclipsing binaries in open clusters can provide stringent tests of theoretical stellar evolutionary models, which must simultaneously fit the masses, radii, and luminosities of the eclipsing stars and the radiative properties of every other star in the cluster. We review recent progress in such studies and discuss two unusually interesting objects currently under analysis. GV Carinae is an A0 m + A8 m binary in the Southern open cluster NGC 3532; its eclipse depths have changed by 0.1 mag between 1990 and 2001, suggesting that its orbit is being perturbed by a relatively close third body. DW Carinae is a high-mass unevolved B1 V + B1 V binary in the very young open cluster Collinder 228, and displays double-peaked emission in the centre of the Hα line which is characteristic of Be stars. We conclude by pointing out that the great promise of eclipsing binaries in open clusters can only be satisfied when both the binaries and their parent clusters are well-observed, a situation which is less common than we would like.     

Variable stars in the Bochum Galactic Disk Survey

We present a first overview of variable stars in the Bochum Galactic Disk Survey (GDS) with emphasis on eclipsing binaries (EBs). This ongoing survey is performed by a robotic twin refractor at the Universitätssternwarte Bochum located near Cerro Armazones in Chile. It comprises a mosaic of 268 fields in a stripe of Δb = ±3° along the Galactic plane observed once per month simultaneously in the Sloan r and i filters with a detection limit of r_s ∼ 16 mag and i_s ∼ 15 mag. The data from the first three years until the end of February 2014 yields a total of 41718 variable stars with variability amplitudes between 0.1–6 mag. A cross‐match with SIMBAD identified 11 465 of these variables unambiguously, while 2184 had multiple matches; most of the remaining stars could be matched with 2MASS objects. Among the SIMBAD‐listed objects with single matches, only 1982 turned out as known variables while a further 256 are suspected of variability. That leaves a total of 39480 potentially new variables. The group of known variables comprises 419 stars (21 %) that are classified as EBs while 443 (22%) are of other types; for the remaining 1120 catalogued variables (57 %) the type is unknown. Investigating variability as a function of spectral type, we find that SIMBAD provides spectral types for 2811 (25 %) of the identified stars. Spectral classes B (26 %), A (20 %), and M (25%) contain the most numerous variables, while all other classes contribute less than 10% each. More than half of the B (55 %) and A (56%) stars are designated as EBs, suggesting that hundreds of new B‐ and A‐type EBs may be contained in the GDS archive. In contrast, among the numerous M stars no EBs are known. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)