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GSC 3377-0296 is a New Short-Period Eclipsing RS CVn Variable
GSC 3377-0296 is a new eclipsing RS CVn variable, which has beendiscovered in the ROTSE1 database. A very short period of 0.4224672 dayshas been determined from the available ROTSE1 data and our BVRphotometry in 2006 and 2007. Large changes in the light curve occur ontimescales of a few weeks.
| Radial Velocity Studies of Close Binary Stars. XII.
Radial velocity measurements and sine-curve fits to the orbital radialvelocity variations are presented for 10 close binary systems: OO Aql,CC Com, V345 Gem, XY Leo, AM Leo, V1010 Oph, V2612 Oph, XX Sex, W UMa,and XY UMa. Most of these binaries have been observed spectroscopicallybefore, but our data are of higher quality and consistency than in theprevious studies. While most of the studied eclipsing pairs are contactbinaries, V1010 Oph is probably a detached or semidetached double-linedbinary, and XY UMa is a detached, chromospherically active system whosebroadening functions clearly show well-defined and localized dark spotson the primary component. A particularly interesting case is XY Leo,which is a member of visually unresolved quadruple system composed of acontact binary and a detached, noneclipsing, active binary with an 0.805day orbital period. V345 Gem and AM Leo are known members of visualbinaries. We found faint visual companions at about 2"-3" from XX Sexand XY UMa.Based on data obtained at the David Dunlap Observatory, University ofToronto.
| Aus den IBVS 5721, 5722, 5723, 5724, 5726, 5728, 5729, 5731, 5732 und 5735.
Not Available
| Detection of a Large Flare in the RS CVn Star WY Cnc
We report detection of an optical flare in the RS CVn spotted star WYCnc. The flare duration is 64 min, the amplitude is 0.134 mag and theenergy is 1 * 10^35 erg in the B band. The WY Cnc spot activity beforeand during the flare is analyzed.
| Variation in the orbital period of W UMa-type contact systems
The secular variation in the orbital period Porb is studiedas a function of the mass ratio q of the components in a sample of 73contact systems of class W UMa constructed from a survey of current(1991–2003) published photometric and spectroscopic data. Almostall the W UMa-systems (>93% of this sample) are found to have avariation in their orbital periods Porb which alternates insign independently of their division into A-and Wsubclasses. Astatistical study of this sample in terms of the observedcharacteristics dPorb/dt and q showed that on the average thenumbers of increases (35 systems) and decreases (33 systems) in theperiods are the same, which indicates the existence of flows directedalternately from one component to the other and illustrates the cyclicalcharacter of the thermal oscillations. An analysis of the behavior ofdPorb/dt as a function of the mass interval of the primarycomponent yields a more accurate value for the mass ratio, q ≈ 0.4÷ 0.45 at which contact binaries are separated into A-andW-subclasses. No correlations were observed between the fill-out factorfor the outer contact configuration, the total mass of the contactsystem, and the mass ratio of the components, on one hand, and the signof the secular variation in the period. The physical properties andevolutionary features of these systems are discussed.
| Evolutionary Status of Late-Type Contact Binaries
The old model of an unevolved, cool contact binary, in which thesecondary component is strongly oversized due to energy transfer fromthe primary, and the whole system is out of thermal equilibrium,encounters serious problems.I present a new scenario for evolution of contact binaries, which solvesthe problem of thermal nonequilibrium by assuming that contact binariesare past mass exchange with a mass ratio reversal. The scenario isdivided into three phases. In PhaseI loss of angular momentum (AM) dueto magnetized wind of a detached binary is followed until the primarycomponent fills its critical Roche lobe. In Phase II mass transfer takesplace until mass ratio reversal. Arguments are given in favor of such aprocess in pre-contact binaries. In PhaseIII an approximate evolutionarypath of the contact binary is followed until a possible coalescence. AMloss, evolutionary effects of the components and mass transfer to theprimary are taken into account.It is concluded that WUMa type binaries are old objects with secondariesin an advanced evolutionary stage, possibly with small helium cores.Both components fulfill the mass-radius relation for contact binarieswhile being in thermal equilibrium.
| New CCD Times of Minima of Eclipsing Binary Systems
We present a total of 208 CCD timings for 103 eclipsing binaries.
| Mass loss and orbital period decrease in detached chromospherically active binaries
The secular evolution of the orbital angular momentum (OAM), thesystemic mass (M=M1+M2) and the orbital period of114 chromospherically active binaries (CABs) were investigated afterdetermining the kinematical ages of the subsamples which were setaccording to OAM bins. OAMs, systemic masses and orbital periods wereshown to be decreasing by the kinematical ages. The first-orderdecreasing rates of OAM, systemic mass and orbital period have beendetermined as per systemic OAM, per systemic mass and per orbitalperiod, respectively, from the kinematical ages. The ratio of d logJ/dlogM= 2.68, which were derived from the kinematics of the presentsample, implies that there must be a mechanism which amplifies theangular momentum loss (AML) times in comparison to isotropic AML ofhypothetical isotropic wind from the components. It has been shown thatsimple isotropic mass loss from the surface of a component or bothcomponents would increase the orbital period.
| Photoelectric Minima of Some Eclipsing Binary Stars
Not Available
| A catalogue of eclipsing variables
A new catalogue of 6330 eclipsing variable stars is presented. Thecatalogue was developed from the General Catalogue of Variable Stars(GCVS) and its textual remarks by including recently publishedinformation about classification of 843 systems and making correspondingcorrections of GCVS data. The catalogue1 represents thelargest list of eclipsing binaries classified from observations.
| The analysis of indexed astronomical time series - X. Significance testing of O-C data
It is assumed that O-C (`observed minus calculated') values of periodicvariable stars are determined by three processes, namely measurementerrors, random cycle-to-cycle jitter in the period, and possiblylong-term changes in the mean period. By modelling the latter as arandom walk, the covariances of all O-C values can be calculated. Thecovariances can then be used to estimate unknown model parameters, andto choose between alternative models. Pseudo-residuals which could beused in model fit assessment are also defined. The theory is illustratedby four applications to spotted stars in eclipsing binaries.
| CCD Minima for Selected Eclipsing Binaries in 2005
Not Available
| GSC 2038.0293 is a new short-period eclipsing RS CVn variable.
Not Available
| New Minima of Selected Eclipsing Close Binaries
We present 180 CCD and photoelectric times of minima of selected closeeclipsing binaries.
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| Catalogue of the orbital elements, masses, and luminosities for short-periodic RS CVn-type eclipsing systems
New data on the orbital elements, masses, and luminosities werecollected for 31 pre-contact binary systems of short-periodic {RS}{CVn}-type. We treat the catalogued data statistically in order toaccurately define the properties and evolutionary status of each classsystem. The ages of pre-contact systems were estimated by the isochronemethod. Numerous comments and bibliographic references to the catalogueare also included.
| Photoelectric Minima of Some Eclipsing Binary Stars
Not Available
| X-ray astronomy of stellar coronae
X-ray emission from stars in the cool half of the Hertzsprung-Russelldiagram is generally attributed to the presence of a magnetic coronathat contains plasma at temperatures exceeding 1 million K. Coronae areubiquitous among these stars, yet many fundamental mechanisms operatingin their magnetic fields still elude an interpretation through adetailed physical description. Stellar X-ray astronomy is thereforecontributing toward a deeper understanding of the generation of magneticfields in magnetohydrodynamic dynamos, the release of energy in tenuousastrophysical plasmas through various plasma-physical processes, and theinteractions of high-energy radiation with the stellar environment.Stellar X-ray emission also provides important diagnostics to study thestructure and evolution of stellar magnetic fields from the first daysof a protostellar life to the latest stages of stellar evolution amonggiants and supergiants. The discipline of stellar coronal X-rayastronomy has now reached a level of sophistication that makes tests ofadvanced theories in stellar physics possible. This development is basedon the rapidly advancing instrumental possibilities that today allow usto obtain images with sub-arcsecond resolution and spectra withresolving powers exceeding 1000. High-resolution X-ray spectroscopy has,in fact, opened new windows into astrophysical sources, and has played afundamental role in coronal research.
| Spectroscopic and photometric observations of the short-period RS CVn-type star BH Virginis
High-resolution spectroscopic observations around theHα line and BVRI photometry from 1993 to 2003 of theeclipsing short-period RS CVn star BH Vir are presented. Thesimultaneous solution of our radial velocity curves and light curvesyielded the following values for global parameters of the components:M1= 1.173 ± 0.006 Mȯ; M2=1.046 ± 0.005 Mȯ; R1= 1.22 ±0.05 Rȯ; R2= 1.11 ± 0.04Rȯ; i= 87.5° ±0.8°. The measured rotational broadening of the spectrallines corresponds to equatorial velocities V1 = 79.8 kms-1 and V2= 68.4 km s-1. Our datareveal considerable Hα emission excess of the twostellar components. We modelled the photometric data to find the sizeand location of the starspots for each year. The established decreasingtrend of the spot latitudes may indicate a latitudinal cycle of at leasta decade.Based on spectral observations collected at the National AstronomicalObservatory at Rozhen and photometric observations collected at Mt.Laguna Observatory operated by San Diego State University, research wassupported in part by the NATO Linkage grant No. PST.CLG.978810, grantNo. 8/2003 of the Shoumen University, a Cottrell College Science Awardof the Research Corporation, and grants from NASA and the GaposchkinFund administered by the AAS Small Grants Program.Photometric and spectroscopic data are only available in electronic format the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) orvia http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/424/993Figures \ref{Fig2}-\ref{Fig7} and Figs. \ref{Fig9}-\ref{Fig16} are onlyavailable in electronic form at http://www.edpsciences.org
| Kinematics of chromospherically active binaries and evidence of an orbital period decrease in binary evolution
The kinematics of 237 chromospherically active binaries (CABs) werestudied. The sample is heterogeneous with different orbits andphysically different components from F to M spectral-type main-sequencestars to G and K giants and supergiants. The computed U, V, W spacevelocities indicate that the sample is also heterogeneous in velocityspace. That is, both kinematically younger and older systems exist amongthe non-evolved main sequence and the evolved binaries containing giantsand subgiants. The kinematically young (0.95 Gyr) subsample (N= 95),which is formed according to the kinematical criteria of moving groups,was compared with the rest (N= 142) of the sample (3.86 Gyr) toinvestigate any observational clues of binary evolution. Comparing theorbital period histograms between the younger and older subsamples,evidence was found supporting the finding of Demircan that the CABs losemass (and angular momentum) and evolve towards shorter orbital periods.The evidence of mass loss is noticeable on the histograms of the totalmass (Mh+Mc), which is compared between theyounger (only N= 53 systems available) and older subsamples (only N= 66systems available). The orbital period decrease during binary evolutionis found to be clearly indicated by the kinematical ages of 6.69, 5.19and 3.02 Gyr which were found in the subsamples according to the periodranges of logP<= 0.8, 0.8 < logP<= 1.7 and 1.7 < logP<=3, respectively, among the binaries in the older subsample.
| An analysis of the light curves of the overcontact binary system V2388 Ophiuchi
We present four seasons' (2000-2003) ground-based photometry of theshort-period contact binary V2388 Oph. The system is the brightercomponent of visual binary HIP 87655. The magnitude difference betweenthe visual companion and the eclipsing pair was estimated to be 1.19 m,1.09 m and 1.09 m in B, V and R bandpasses, respectively. The lightcurves in BVR are solved by the WD code. Combining the parameters foundby the light curve analysis with those of the radial velocity solutionwe derived the masses and radii of the star components as:M1=1.80(2) Mȯ, M2=0.34(1)Mȯ, R1=2.60(2) Rȯ,R2=1.30(1) Rȯ. The primary component appearsto be more evolved in the mass-radius, mass-luminosity planes and alsoin the HR diagram. It lies near the terminal-age main-sequence, whichagrees well with the position of deeper-contact A-type systems. Thelarge fill-out factor of 0.65 does also support this classification.
| High-resolution Doppler images of the spotted contact binary AE Phe
We present Doppler images of the short period (P= 0.362 d) W UMa binaryAE Phe. In order to obtain the necessary S/N ratio and time resolutionrequired to see individual star-spot features in highly rotationallybroadened profiles, we use least-squares deconvolution, which makes useof the information content of the several thousand lines in a typicalechelle spectrum. This yields a single rotation profile (free ofsidelobes due to blending) per spectrum with a typical S/N ratio ofseveral thousand.We use radial velocity curves, generated from standard profile fittingtechniques, to measure velocity amplitudes and the mass ratio. Failureto model star-spots with this method leads to a biased set of values,and we show that an imaging code is essential if accurate systemparameters are to be derived.Images are reconstructed from four nights of data which revealstar-spots at most latitudes on both components of the common envelopesystem. Our model requires that the primary component be several hundredK cooler than the secondary in order to reproduce the profile depthchanges with phase. In a two-temperature imaging model, we interpretthis as being due to 27 per cent greater - but unresolved - spot fillingon the primary relative to the secondary component. The images revealthat dark spots are present on both stars at various latitudes andlongitudes. Star-spots are also found in the neck region of bothcomponents, which appear to be darker on the side of each star leadingin rotation phase - particularly on the secondary component. Weinvestigate the reproducibility of the images from night to night andconclude that the star-spots evolve significantly on very shorttime-scales, of the order of 1 d. This is significantly faster than theweek time-scales found on active single stars and the Sun.
| Spectroscopic and photometric observations of the short-period RS CVn-type star WY Cnc
High-resolution spectroscopic observations around the H\alphaline and BVRI photometry of the eclipsing short-period RS CVn star WYCnc are presented. The solutions of our radial velocity curves and lightcurves yielded the following values for masses and radii of thecomponents: M1=0.84 Mȯ, M2=0.46Mȯ, R1=1.06 Rȯ,R2= 0.65 Rȯ. The measured rotationalbroadenings of the spectral lines correspond to equatorial velocitiesV1=78 km s-1 and V2=49 kms-1. The distortions of our multicolor light curve of WY Cncwere reproduced by two cool spots on the primary star. An increase ofthe out-of-eclipse brightness by 0.1 mag in February 2001 was detected.Our spectra show Hα line in emission from the secondarystar. The chromospheric activity appeared also in the observed emissioncores of the CaII H and K lines as well as the CaI 6494 line.Based on spectral observations collected at the National AstronomicalObservatory at Rozhen, research was supported in part by the NATOLinkage grant No. PST.CLG.978810 and grant No. 1/2002 of the ShoumenUniversity
| CCD Times of Minima of Some Eclipsing Binaries in 2003
We present CCD observations of minima of 31 eclipsing binaries observedby SAVS sky survey in 2003.
| Photoelectric Minima of Selected Eclipsing Binaries
Not Available
| The Hamburg/RASS Catalogue of optical identifications. Northern high-galactic latitude ROSAT Bright Source Catalogue X-ray sources
We present the Hamburg/RASS Catalogue (HRC) of optical identificationsof X-ray sources at high-galactic latitude. The HRC includes all X-raysources from the ROSAT Bright Source Catalogue (RASS-BSC) with galacticlatitude |b| >=30degr and declination delta >=0degr . In thispart of the sky covering ~ 10 000 deg2 the RASS-BSC contains5341 X-ray sources. For the optical identification we used blue Schmidtprism and direct plates taken for the northern hemisphere Hamburg QuasarSurvey (HQS) which are now available in digitized form. The limitingmagnitudes are 18.5 and 20, respectively. For 82% of the selectedRASS-BSC an identification could be given. For the rest either nocounterpart was visible in the error circle or a plausibleidentification was not possible. With ~ 42% AGN represent the largestgroup of X-ray emitters, ~ 31% have a stellar counterpart, whereasgalaxies and cluster of galaxies comprise only ~ 4% and ~ 5%,respectively. In ~ 3% of the RASS-BSC sources no object was visible onour blue direct plates within 40\arcsec around the X-ray sourceposition. The catalogue is used as a source for the selection of(nearly) complete samples of the various classes of X-ray emitters.
| A period investigation of two chromospherically active binary stars: RT Coronae Borealis and PW Herculis
Orbital period variations of two chromospherically active binarysystems, RT CrBand PW Her, arepresented. It is shown that the orbital period of RT CrB undergoes acyclic oscillation with a period of 53.9years. For PW Her, an alternatechange, with a period of 42.7years, is found to superimpose on a rapidsecular increase (dP/dt=+3.53×10-6 days/year). If theperiod oscillations of those two systems are caused by the light-timeeffect of a third body, the analysis for RT CrB indicatesthat the third body would be a low-mass main-sequence star, while, forPW Her, the massof the third body should be no less than 7.8 Msolar. Since nospectral lines of the third body were seen in PW Her from thespectroscopic study by Popper [AJ 100 (1990) 247], if there is a thirdbody in the system, it can only be a black hole. However, as bothcomponents in the two binary stars were showing strong chromosphericactivity, the alternate period variations are more plausibly explainedas the result of magnetic activity cycles. No secular period changes ofRT CrB are found,which is in agreement with the detached evolved configuration of thesystem. The long-term period increase of PW Her may indicatethat it is on an active phase of mass transfer(dm/dt=2.17×10-6 Msolar/year).
| New Times of Minima of Eclipsing Binary Systems
We present 58 photoelectric minima observations of 19 eclipsingbinaries.
| VLA Radio Positions of Stars: 1978-1995
VLA astrometric positions of the radio emission from 52 stars arereported, from observations obtained between 1978 and 1995. Thepositions of these stars have been obtained and reduced in a uniformmanner. Based on our measurements, the offset of the optical (Hipparcos)frame from the radio reference frame is in agreement with the Hipparcosextragalactic link results, within their mean errors. Comparison of theVLA measurements with the Hipparcos optical positions confirms earlierestimates of the accuracy of these positions as 30 mas. Long-termmeasurements of UX Ari have improved its proper motion.
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