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Photometric monitoring of the ROSAT selected late type stars
We monitored the light variations of 16 solar-type stars recentlydiscovered in the X-ray wave-length range during the ROSAT all-skysurvey. We find that 9 out of 16 stars showed appreciable lightvariability with amplitudes of a few hundredths of a magnitude. They areall proved to be in periodic variations. Using the methods of the phasedispersion minimization (PDM) and Fourier Analysis (PERIOD04), we derivethe photometric periods for these stars. The rotational periods arefound range from 0.471 to 17.31 days and the period of stars most (of 7stars) being shorter than 3 days. Apart from binaries system, theresults give further evidence for the spin up of solar-type stars aspredicted by models of angular momentum evolution of pre-main sequencestars.
| Photoelectric Minima of Some Eclipsing Binary Stars
We present 119 minima times of 47 eclipsing binaries.
| New Times of Minima of Eclipsing Binary Systems
We present 82 photoelectric minima observations of 34 eclipsingbinaries.
| New Times of Minima of Some Eclipsing Binary Stars
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| Die BAV-Zusammenarbeit zwischen Fachastronomen und Amateuren.
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| The Case for Third Bodies as the Cause of Period Changes in Selected Algol Systems
Many eclipsing binary star systems show long-term variations in theirorbital periods, evident in their O-C (observed minus calculated period)diagrams. With data from the Robotic Optical Transient Search Experiment(ROTSE-I) compiled in the SkyDOT database, New Mexico State University 1m data, and recent American Association of Variable Star Observers(AAVSO) data, we revisit Borkovits and Hegedüs's best-casecandidates for third-body effects in eclipsing binaries: AB And, TV Cas,XX Cep, and AK Her. We also examine the possibility of a third bodyorbiting Y Cam. Our new data support their suggestion that a third bodyis present in all systems except AK Her, as is revealed by thesinusoidal variations of the O-C residuals. Our new data suggest that athird body alone cannot explain the variations seen in the O-C residualsof AK Her. We also provide a table of 143 eclipsing binary systems thathave historical AAVSO O-C data with new values computed from the SkyDOTdatabase.
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
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| 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.
| Contact Binaries with Additional Components. I. The Extant Data
We have attempted to establish observational evidence for the presenceof distant companions that may have acquired and/or absorbed angularmomentum during the evolution of multiple systems, thus facilitating orenabling the formation of contact binaries. In this preliminaryinvestigation we use several techniques (some of themdistance-independent) and mostly disregard the detection biases ofindividual techniques in an attempt to establish a lower limit to thefrequency of triple systems. While the whole sample of 151 contactbinary stars brighter than Vmax=10 mag gives a firm lowerlimit of 42%+/-5%, the corresponding number for the much better observednorthern-sky subsample is 59%+/-8%. These estimates indicate that mostcontact binary stars exist in multiple systems.
| 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.
| Bericht über die 2. Veraenderlichen-Beobachtungswoche an der VdS-Sternwarte Kirchheim 2005.
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| Beobachtungsergebnisse Bundesdeutsche Arbeitsgemeinschaft fur Veranderliche Sterne e.V.
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| An Orbital Period Study of the W UMa-Type Binary RZ Comae Berenicis
New photoelectric and CCD photometry observations of a short-period WUMa-type binary system, RZ Com, are presented. The light curves ofBroglia (1960, Contr. Milano-Merate, 165) were symmetric in V band,while the present light curve shows a typical O'Connell effect, withMaximum I brighter than Maximum II by 0.015mag. It is found that thelight curve of the binary star has changed from W-subtype to A-subtypeaccording to Binnendijk's classification. This variation may be causedby the activity of dark spot on the primary component. Combining fournewly determined times of the light minimum with others published in theliterature, the orbital period change of the system was investigated. Asmall-amplitude oscillation (A = 0.0058 d), with a period of 44.8yr hasbeen discovered to be superimposed on a long-term period increase with arate of dP/dt = +4.12 × 10-8 d yr-1. Theperiod oscillation can be explained either by the light-time effect viathe presence of an unseen third body or by magnetic-activity cycles ofthe components. The mass ratio of RZ Com is q = 0.43. The secular periodvariation is in agreement with the conclusions of Qian (2001, MNRAS,328, 914; 2003, MNRAS, 342, 1260). This indicates that it is on theTRO-controlled stage of the evolutionary scheme proposed by Qian.
| New Minima of Selected Eclipsing Close Binaries
We present 180 CCD and photoelectric times of minima of selected closeeclipsing binaries.
| New Times of Minima of Some Eclipsing Binary Stars
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| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
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| Indirect evidence for short period magnetic cycles in W UMa stars. Period analysis of five overcontact systems.
Complex period variations of five W UMa type binaries (ABAnd, OO Aql, DK Cyg,V566 Oph, U Peg) were investigatedby analyzing their O-C diagrams, and several common features were found.Four of the five systems show secular period variations at a constantrate on the order of |dot{P}sec/P|10-7yr-1. In the case of AB And, OOAql, and U Peg a high-amplitude, nearlyone-century long quasi-sinusoidal pattern was also found. It might beexplained as light-time effect, or by some magnetic phenomena, althoughthe mathematical, and consequently the physical, parameters of thesefits are very problematic, as the obtained periods are very close to thelength of the total data range. The most interesting feature of thestudied O-C diagrams is a low amplitude ( 2-4×10-3 d)modulation with a period around 18-20 yr in four of the five cases. Thisphenomenon might be indirect evidence of some magnetic cycle inlate-type overcontact binaries as an analog to the observed activitycycles in RS CVn systems.
| Photoelectric Minima of Some Eclipsing Binary Stars
We present 70 minima times of 35 eclipsing binaries.
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
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| Radial Velocity Studies of Close Binary Stars. X.
Radial velocity measurements and sine-curve fits to orbital velocityvariations are presented for the ninth set of 10 close binary systems:V395 And, HS Aqr, V449 Aur, FP Boo, SW Lac, KS Peg, IW Per, V592 Per, TUUMi, and FO Vir. The first three are very close, possibly detached,early-type binaries, and all three require further investigation.Particularly interesting is V395 And, whose spectral type is as early asB7/8 for a 0.685 day orbit binary. KS Peg and IW Per are single-linebinaries, with the former probably hosting a very low mass star. We havedetected a low-mass secondary in an important semidetached system, FOVir, at q=0.125+/-0.005. The contact binary FP Boo is also a very smallmass ratio system, q=0.106+/-0.005. The other contact binaries in thisgroup are V592 Per, TU UMi, and the well-known SW Lac. V592 Per and TUUMi have bright tertiary companions; for these binaries, and for V395And, we used a novel technique of arranging the broadening functionsinto a two-dimensional image in phase. The case of TU UMi turned out tobe intractable even using this approach, and we have not been able toderive a firm radial velocity orbit for this binary. Three systems ofthis group were observed spectroscopically before: HS Aqr, SW Lac, andKS Peg.Based on the data obtained at the David Dunlap Observatory, Universityof Toronto.
| CCD Observations of Times of Minima of Eclipsing Binaries
120 minima timings are reported for 39 E. B. systems observed from 2002to 2005 with the Rigel telescope at Winer Observatory. The timings weredetermined using a folded light curve analysis of light curves derivedfrom CCD images. Typical timing uncertainties were 30-60 sec.
| Photoelectric Minima of Eclipsing Binaries
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| Physical Parameters of Components in Close Binary Systems: IV
The paper presents new geometric, photometric and absolute parameters,derived from combined spectroscopic and photometric solutions, for tencontact binary systems. The analysis shows that three systems (EF Boo,GM Dra and SW Lac) are of W-type with shallow to moderate contact. Sevensystems (V417 Aql, AH Aur, YY CrB, UX Eri, DZ Psc, GR Vir and NN Vir)are of A-type in a deep contact configuration. For six systems (V417Aql, YY CrB, GM Dra, UX Eri, SW Lac and GR Vir) a spot model isintroduced to explain the O'Connell effect in their light curves. Thephotometric and geometric elements of the systems are combined with thespectroscopic data taken at David Dunlap Observatory to yield theabsolute parameters of the components.
| Kinematics of W Ursae Majoris type binaries and evidence of the two types of formation
We study the kinematics of 129 W UMa binaries and we discuss itsimplications on the contact binary evolution. The sample is found to beheterogeneous in the velocity space. That is, kinematically younger andolder contact binaries exist in the sample. A kinematically young (0.5Gyr) subsample (moving group) is formed by selecting the systems thatsatisfy the kinematical criteria of moving groups. After removing thepossible moving group members and the systems that are known to bemembers of open clusters, the rest of the sample is called the fieldcontact binary (FCB) group. The FCB group is further divided into fourgroups according to the orbital period ranges. Then, a correlation isfound in the sense that shorter-period less-massive systems have largervelocity dispersions than the longer-period more-massive systems.Dispersions in the velocity space indicate a 5.47-Gyr kinematical agefor the FCB group. Compared with the field chromospherically activebinaries (CABs), presumably detached binary progenitors of the contactsystems, the FCB group appears to be 1.61 Gyr older. Assuming anequilibrium in the formation and destruction of CAB and W UMa systems inthe Galaxy, this age difference is treated as an empirically deducedlifetime of the contact stage. Because the kinematical ages (3.21, 3.51,7.14 and 8.89 Gyr) of the four subgroups of the FCB group are muchlonger than the 1.61-Gyr lifetime of the contact stage, the pre-contactstages of the FCB group must dominantly be producing the largedispersions. The kinematically young (0.5 Gyr) moving group covers thesame total mass, period and spectral ranges as the FCB group. However,the very young age of this group does not leave enough room forpre-contact stages, and thus it is most likely that these systems wereformed in the beginning of the main sequence or during thepre-main-sequence contraction phase, either by a fission process or mostprobably by fast spiralling in of two components in a common envelope.
| Photoelectric Minima of Some Eclipsing Binary Stars
Not Available
| Photoelectric Minima of Some Eclipsing Binary Stars
We present 24 minima times of 18 eclipsing binaries.
| Sektion Bedeckungsveraenderliche: Lichtkurven in allen Phasen.
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| Was uns (B-R)-Diagramme ueber Bedeckungsveraenderliche sagen.
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| Bericht uber die Veranderlichen-Beobachtungswoche an der VdS-Sternwarte in Kirchheim.
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| Beobachtungssergebnisse Bundesdeutsche Arbeitsgemeinschaft fuer Veraenderliche Sterne e.V.
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