arXiv subjects

Slavek M. Rucinski

Publications and source records attributed to Slavek M. Rucinski.

At least 73 records · Page 4Linked to original sources

arXiv2003

Radial Velocity Studies of Close Binary Stars. IX

Radial-velocity measurements and sine-curve fits to the orbital velocity variations are presented for the eighth set of ten close binary systems: AB And, V402 Aur, V445 Cep, V2082 Cyg, BX Dra, V918 Her, V502 Oph, V1363 Ori, KP Peg, V335 Peg. Half of the systems (V445 Cep, V2082 Cyg, V918 Her, V1363 Ori, V335 Peg) were discovered photometrically by the Hipparcos mission and all systems are double-lined (SB2) contact binaries. The broadening function method permitted improvement of the orbital elements for AB And and V502 Oph. The other systems have been observed for radial velocity variations for the first time; in this group are five bright (V<7.5) binaries: V445 Cep, V2082 Cyg, V918 Her, KP Peg and V335 Peg. Several of the studied systems are prime candidates for combined light and radial-velocity synthesis solutions.

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arXiv2003

Contact binary stars of the W UMa type as distance tracers

Contact binaries can be used for distance determinations of stellar systems. They are easy to discover and identify and are very abundant among solar-type stars, particularly for M_V > +3. The period - luminosity - colour (PLC) relations have similar properties to those for pulsating stars and can currently predict individual values of M_V to about +/-0.25 mag.

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arXiv2002

The 7.5 Magnitude Limit Sample of Bright Short-Period Binary Stars. I. How Many Contact Binaries Are There?

A sample of bright contact binary stars (W UMa-type or EW, and related: with beta Lyr light curves, EB, and ellipsoidal, ELL - in effect, all but the detached, EA), to the limit of Vmax = 7.5 magnitude is deemed to include all discoverable short-period (P<1 days) binaries with photometric variation larger than about 0.05 magnitude. Of the 32 systems in the final sample, 11 systems have been discovered by the Hipparcos satellite. The combined spatial density is evaluated at (1.02+/-0.24)x10^-5 pc^-3. The Relative Frequency of Occurrence (RFO), defined in relation to the Main Sequence stars, depends on the luminosity. An assumption of RFO~1/500 for MV>+1.5 is consistent with the data, although the number statistics is poor with the resulting uncertainty in the spatial density and the RFO by a factor of about two. The RFO rapidly decreases for brighter binaries to a level of 1/5,000 for MV<+1.5 and to 1/30,000 for MV<+0.5. The high RFO of 1/130, previously determined from the deep OGLE-I sample of Disk Population W UMa-type systems towards Baade's Window, is inconsistent with and unconfirmed by the new results. Possible reasons for the large discrepancy are discussed. They include several observational effects, but also a possibility of a genuine increase in the contact-binary density in the central parts of the Galaxy.

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arXiv2001

The photometric-amplitude and mass-ratio distributions of contact binary stars

The distribution of the light-variation amplitudes, A(a), in addition to determining the number of undiscovered contact binary systems falling below photometric detection thresholds and thus lost to statistics, can serve as a tool in determination of the mass-ratio distribution, Q(q), which is very important for understanding of the evolution of contact binaries. Calculations of the expected A(a) show that it tends to converge to a mass-ratio dependent constant value for a->0. Strong dependence of A(a) on Q(q) can be used to determine the latter distribution, but the technique is limited by the presence of unresolved visual companions and by blending in crowded areas of the sky. The bright-star sample to 7.5 magnitude is too small for an application of the technique while the the Baade's Window sample from the OGLE project may suffer stronger blending; thus the present results are preliminary and illustrative only. Estimates based on the Baade's Window data from the OGLE project, for amplitudes a>0.3 mag. where the statistics appear to be complete allowing determination of Q(q) over 0.12 0. The mass-ratio distribution can be approximated by a power law, either Q(q)~(1-q)^a1 with a1=6+/-2 or Q(q)~q^b1, with b1=-2+/-0.5, with a slight preference for the former form. Both forms must be modified by the theoretically expected cut-off caused by a tidal instability at about q_min 0.07-0.1. An expected maximum in Q(q), is expected to be mapped into a local maximum in A(a) around 0.2-0.25 mag.

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arXiv2000

Eclipsing Binaries in the OGLE Variable Star Catalogs.V. Long-Period Beta Lyrae-type Systems in the Small Magellanic Cloud and the PLC-beta Relation

Thirty eight long-period (P>10 days), apparently contact binary stars discovered by the OGLE-II project in the SMC appear to be Beta Lyrae-type systems with ellipsoidal variations of the cool components dominating over eclipse effects in the systemic light variations and in the total luminosity. A new period-luminosity- color (PLC) relation has been established for these systems; we call it the PLC-beta relation, to distinguish it from the Cepheid relation. Two versions of the PLC-beta relation - based on the (B-V)0 or (V-I)0 color indices - have been calibrated for 33 systems with (V-I)0>0.25 spanning the orbital period range of 11 to 181 days. The relations can provide maximum-light, absolute-magnitude estimates accurate to epsilon-M_V~0.35 mag. within the approximate range -3<M_V<+1. In terms of their number in the SMC, the long-period Beta Lyrae-type binaries are about 50 times less common than the Cepheids. Nevertheless, their large luminosities coupled with continuous light variations make these binaries very easy to spot in nearby galaxies, so that the PLC-beta relation can offer an auxiliary and entirely independent method of distance determination to nearby stellar systems rich in massive stars. The sample of the long-period Beta Lyrae systems in the SMC analyzed in this paper is currently the best defined and uniform known sequence of such binaries.

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arXiv2000

Radial Velocity Studies of Close Binary Stars.III

Radial velocity measurements and simple sine-curve fits to the orbital velocity variations are presented for the third set of ten contact binary systems: CN And, HV Aqr, AO Cam, YY CrB, FU Dra, RZ Dra, UX Eri, RT LMi, V753 Mon, OU Ser. All systems but two are contact, double-line spectroscopic binaries with four of them (YY CrB, FU Dra, V753 Mon, OU Ser) being the recent discoveries of the Hipparcos satellite project. The most interesting object is V753 Mon with the mass-ratio closest to unity among all contact systems (q = 0.970 pm 0.003) and large total mass ((M1+M2)sin^3i = 2.93 pm 0.06). Several of the studied systems are prime candidates for combined light and radial-velocity synthesis solutions.

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arXiv2000

W UMa-type Binary Stars in Globular Clusters

A sample of 86 contact binary systems in 14 globular clusters with available color index data in (B-V) or in (V-I) has been analyzed. At least one third of all systems are numerous foreground Galactic Disk projections over long lines of sight to the clusters. Since the selection of the cluster members has been based on the MV(logP, color) calibrations, the matter of a metallicity-correction required particular attention with the result that such a correction is apparently not needed at the present level of accuracy. Analysis of the color-magnitude and period-color relations shows that globular cluster members are under-luminous relative to the Galactic Disk contact systems mainly because of the smaller sizes and, consequently, shorter orbital periods; the color-index effect of the diminished blanketing is less important, especially for (V-I). The variability amplitudes for the Blue Straggler systems show a significantly different distribution from that for systems below the Turn Off Point (TOP): The BS systems show only small amplitudes while the distribution for the systems below the TOP is peculiar in containing only large amplitude systems. This difference is linked to an observational selection effect so that efforts at determining the frequency of occurrence of the contact systems below the TOP have been judged to be premature; the frequency among the BS stars could be at about 45+-10 BS stars per one contact BS binary.

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arXiv1999

Early-type contact systems in the LMC MACHO database

Two sub-samples of blue, luminous contact systems from among 86 systems discovered in LMC by the MACHO project and classified as EB3 have been analyzed: a sub-sample of 29 extremely-blue systems (XB) with the observed colours V-R_C<-0.1 and a sub-sample of 36 moderately-blue (MB) systems with -0.1<V-R_C<0. To be so blue, the XB systems must be intrinsically very hot and almost unreddened so that lack of information on reddening is unimportant for them; their properties offer us a first-time insight into the absolute-magnitude calibration for massive contact binaries. It has been found that the LMC systems are apparently not limited by the blue, short-period envelope in the colour-period diagram which had been established on the basis of systems observed in the solar neighborhood, in galactic open clusters and in the sample of Old Disk systems in the direction of the Galactic Bulge. The period - magnitude correlation for the XB systems has a similar slope to those established in the absolute-magnitude, B-V and V-I_C based, calibrations for W~UMa-type systems.

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arXiv1999

W Crv: The shortest-period Algol with non-degenerate components?

Radial velocity data for both components of W Crv are presented. In spite of providing full radial-velocity information, the new data are not sufficient to establish the configuration of this important system because of large seasonal light-curve variations which prevent a combined light-curve/radial-velocity solution. It is noted that the primary minimum is free of the photometric variations, a property which may help explain their elusive source. Photometrically, the system appears to be a contact binary with poor or absent energy exchange, but such an explanation - in view of the presence of the mass-transfer effects - is no more plausible than any one of the semi-detached configurations with either the more-massive or less-massive components filling their Roche lobes. Lengthening of the orbital period and the size of the less-massive component above its main-sequence value suggest that the system is the shortest-period (0.388 days) known Algol with non-degenerate components.

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arXiv1999

Eclipsing Binaries in the OGLE Variable Star Catalog. IV. The Pre-Contact, Equal-Mass Systems

We used the database of eclipsing binaries detected by the OGLE microlensing project in the pencil-beam search volume toward Baade's Window to define a sample of 74 detached, equal-mass, main-sequence binary stars with short orbital periods in the range 0.19<P<8 days. The logarithmic slope of the period distribution, logN propto (-0.8 pm 0.2) logP, was used to infer the angular-momentum-loss (AML) efficiency for the late, rapidly-rotating members of close binaries. It is very likely that the main cause of the negative slope is a discovery selection bias that progressively increases with the orbital period length. Assuming a power-law dependence for the correction for the bias: bias propto -C logP (with C ge 0), the AML braking-efficiency exponent alpha in dH/dt = P^-alpha can take any value alpha = (-1.1 pm 0.2) + C. Very simple considerations of discovery biases suggest C simeq 4/3, which would give an AML braking law very close to the "saturated" one, with no dependence on the period. However, except for plausibility arguments, we have no firm data to support this estimate of C, so that alpha remains poorly constrained. The results signal the utmost importance of the detection bias evaluation for variable star databases used in analyses similar to the one presented in this study.

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arXiv1999

Radial Velocity Studies of Close Binary Stars.II

Radial velocity measurements and simple sine-curve fits to the orbital velocity variations are presented for the second set of ten contact binary systems. Eight systems are of the A-type: AH Aur, CK Boo, DK Cyg, UZ Leo, XZ Leo, V839 Oph, GR Vir and NN Vir. V842 Her is the only W-type, while SV Equ appears to be a semi-detached system seen at a low orbital inclination rather than a contact binary. Several of the studied system are prime candidates for complete light and radial-velocity synthesis solutions.

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arXiv1999

Radial Velocity Studies of Close Binary Stars.I

Radial velocity data are presented for 10 W UMa-type systems: GZ And, V417 Aql, LS Del, EF Dra, V829 Her, FG Hya, AP Leo, UV Lyn, BB Peg, AQ Psc, together with preliminary, circular-orbit determinations of spectroscopic elements, with the main goal of obtaining mean radial velocities and mass-ratios for these systems. This is the first part of a series which will contain radial velocity data for Northern-hemisphere, short-period eclipsing binaries, accessible to medium-resolution spectroscopic studies with 1.8-meter class telescopes.

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arXiv1998

Contact Binaries of the Galactic Disk: Comparison of the Baade's Window and Open Cluster Samples

The paper integrates the available data for contact binaries of the disk population in a deep galactic field and in old open clusters. The two basic data sets consist of 98 systems in the volume-limited 3 kpc sub-sample of contact binaries detected by the OGLE microlensing project toward Baade's Window (BW3) and of 63 members of 11 old open clusters (CL). Supplementary data on the intrinsically bright, but spatially rare, long-period binaries are provided by 238 systems in the BW sample to the distance of 5 kpc (BW5). The basic BW3 sample and the CL sample are remarkably similar in the period, color, luminosity and variability-amplitude distributions, in spite of very different sample selections. The contact systems are found in the color interval 0.3 < (B-V)0 < 1.2 where the turn-off points (TOP) of the considered clusters are located; however, they are not concentrated at the respective TOP locations but, once the TOP happens to fall in the above color interval, they can appear anywhere within it. The luminosity function for the BW sample appears to be very similar in shape to that for the solar neighborhood main-sequence stars when corrections for the galactic disk structure are applied, implying a flat apparent frequency-of-occurrence distribution. In the interval 2.5 < M_V < 7.5, the frequency relative to MS stars equals about 1/130 for the exponential disk length scale h_R = 2.5 kpc and about 1/100 for h_R = 3.5 kpc. (abridged)

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arXiv1997

Eclipsing Binaries in the OGLE Variable Star Catalog.III. Long-Period Contact Systems

A sample of contact binaries discovered by the OGLE project in Baade's Window, with orbital periods longer than one day and with available color and light-curve data, has been analyzed. It consists of only 32 systems, in contrast to 388 WUMa-type systems with shorter periods which were analyzed before. Most systems are very distant and are probably located close to or in the galactic Bulge. Two groups of contact binaries are seen in the sample: (1) a continuation of the WUMa-type sequence, extending up to the orbital periods of 1.3 - 1.5 day, but rather sharply ending in this period range; (2) an inhomogeneous group of rare systems with long periods up to 26 days, all with red colors and relatively shallow eclipses. While the systems of the first group share most of the characteristics of the typical WUMa-type systems (except that they are on the average brighter and more distant, hence more reddened), the long-period systems do not seem to form an early-type extension of contact binaries, but may consist of a mixture of late-type objects, including tidally distorted red giants with invisible companions.

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arXiv1997

Absolute Magnitude Calibration for the W UMa-type Systems Based on Hipparcos Data

Hipparcos parallax data for 40 contact binary stars of the W UMa-type (with errors in M_V < 0.5) are used to derive a new, (B-V)-based absolute-magnitude calibration of the form M_V = M_V(logP,B-V). The calibration covers the ranges 0.26 < (B-V)_0 < 1.14, 0.24 < P < 1.15 day, and 1.4 < M_V < 6.1; it is based on a solution weighted by relative errors in the parallaxes (2.7% to 24%). Previous calibrations have not been based on such a wide period and color space, and while they have been able to predict M_V with sufficient accuracy for systems closely following the well-known period-color relation, the new calibration should be able to give also good predictions for more exotic "outlying" contact binary systems. The main limitations of this calibration are the inadequate quality of the ground-based photometric data, and the restriction to the (B-V) index, which is more sensitive to metallicity effects than the (V-I) index; metallicities are, however, basically unknown for the local W UMa-type systems.

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arXiv1997

VLA Observations of Radio Variability of ER Vulpeculae in 1995

VLA continuous monitoring of ER Vul during two 11.5 hour sessions in September 1995 in the radio continuum at 3.6 cm (X-band) showed a variation pattern similar to that observed in 1990 and 1991, but at a lower mean flux level. Simultaneous observations with the EUVE satellite in the 70 - 140 A band did not show any significant flaring variability of the star.

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arXiv1997

EUVE Investigation of Three Short-Period Binary Stars

EUVE satellite spectroscopic observations (SW, MW and LW bands covering 80 - 160, 170 - 350 and 450 A with resolutions 0.5, 1 and 2 A) and photometric observations (Deep Sky Survey, broad-band 70 - 140 A) have been obtained for two contact, 44i Boo B and VW Cep, and one detached, ER Vul, close binary stars. All three systems have orbital periods shorter than one day and thus are expected to show "saturated" levels of chromospheric, transition-region and lower-corona emissions. The spectroscopic data were of sufficient quality for an attempt at an emission-measure determination only for 44i Boo B. This determination, based entirely on iron lines, and utilizing Singular Value Decomposition formalism developed by Schmitt et al. (1996) indicates lack of any dominating temperature regime with the emission measure rising from log T about 6 to log T about 7.2. However, strong dependence of the resulting emission-measure curve on the inclusion of individual lines formed at high temperatures casts some doubts about the quality of the solution. A comparison of the line strengths have been made for selected strongest chromospheric, transition-region and lower-coronal emission lines; it included the data for the single, rapidly-rotating star AB Dor which is the only such star with the rotation period shorter than one day which has been observed with the EUVE. If the single-epoch observations are representative, the results indicate that AB Dor is under-active relative to the three binary stars which show similar levels of activity.

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arXiv1997

The shortest-period M-dwarf eclipsing system BW3 V38

The photometric data for a short-period (0.1984 day) eclipsing binary V38 discovered by the OGLE micro-lensing team in Baade's W indow field BW3 have been analyzed. The de-reddened color (V-I_C)_0=2.3 and the light-curve synthesis solution of the I-filter light curve suggest a pair of strongly-distorted M-dwarfs, with parameters between those of YY Gem and CM Dra, revolving on a tightest known orbit among binaries consisting of Main Sequence stars. The primary, more massive and hotter, component maybe filling its Roche lobe. The very small amount of angular momentum in the orbital motion makes the system particularly important for studies of angular momentum loss at the faint end of the Main Sequence. Spectroscopic observations of the orbital radial velocity variations as well as of activity indicators are urgently needed for a better understanding of the angular-momentum and internal-structure evolutionary state of the system.

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