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A Period Study of the Eclipsing Binary U Sagittae
The O-C curve of the eclipsing binary U Sagittae was analyzed using theKalimeris method. A period decrease was indicated by this curve. Theobserved period P(E) and its rate of change dP/dE as a function of timewere calculated. To reveal any cyclic period variations, the P(E)function was subjected to Fourier analysis. A cyclic period change of9.5 yr duration with amplitude ΔP=6.385×10-6 dayswas obtained. The mass transfer rate for the system was calculated, andthese results have been used to discuss period variability.
| Gamma-ray constraints on the infrared background excess
Motivated by the idea that the recently detected near-infrared (1.2 4μm) excess over the contribution of known galaxies is due toredshifted light from the first cosmic stars [MNRAS 339 (2003) 973], wehave used the effect caused by photon photon absorption on gamma-rayspectra of blazars to put constraints on extragalactic background light(EBL) from the optical to the far-IR bands. Our analysis is mainly basedon the blazar H 1426+428, for which we assume a power-law unabsorbedspectrum. We find that an EBL model with no excess over known galaxiesin the near-infrared background (NIRB) is in agreement with all theconsidered blazars; however, it implies a very peculiar intrinsicspectrum for H 1426+428. Additional data on the blazars 1ES1101-232, H2356-309 and PKS 2155-304 exclude the existence of a strong NIRB excessconsistent with Kelsall’s model of zodiacal light subtraction(ZL); the COBE/DIRBE measurements, after Wright’s model ZLsubtraction, represent a firm NIRB upper limit. The constraints on theoptical EBL are weaker, due to the fact that predictions from differentoptical EBL models are often comparable to the experimental errors. Inthe mid-infrared the SPITZER measurement of νIν = 2.7nW m‑2 sr‑1 at 24 μm gives a goodfit for all the considered blazars.
| 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.
| Automatic classification of eclipsing binaries light curves using neural networks
In this work we present a system for the automatic classification of thelight curves of eclipsing binaries. This system is based on aclassification scheme that aims to separate eclipsing binary systemsaccording to their geometrical configuration in a modified version ofthe traditional classification scheme. The classification is performedby a Bayesian ensemble of neural networks trained with Hipparcos data ofseven different categories including eccentric binary systems and twotypes of pulsating light curve morphologies.
| Astrometric orbits of SB^9 stars
Hipparcos Intermediate Astrometric Data (IAD) have been used to deriveastrometric orbital elements for spectroscopic binaries from the newlyreleased Ninth Catalogue of Spectroscopic Binary Orbits(SB^9). This endeavour is justified by the fact that (i) theastrometric orbital motion is often difficult to detect without theprior knowledge of the spectroscopic orbital elements, and (ii) suchknowledge was not available at the time of the construction of theHipparcos Catalogue for the spectroscopic binaries which were recentlyadded to the SB^9 catalogue. Among the 1374 binaries fromSB^9 which have an HIP entry (excluding binaries with visualcompanions, or DMSA/C in the Double and Multiple Stars Annex), 282 havedetectable orbital astrometric motion (at the 5% significance level).Among those, only 70 have astrometric orbital elements that are reliablydetermined (according to specific statistical tests), and for the firsttime for 20 systems. This represents a 8.5% increase of the number ofastrometric systems with known orbital elements (The Double and MultipleSystems Annex contains 235 of those DMSA/O systems). The detection ofthe astrometric orbital motion when the Hipparcos IAD are supplementedby the spectroscopic orbital elements is close to 100% for binaries withonly one visible component, provided that the period is in the 50-1000 drange and the parallax is >5 mas. This result is an interestingtestbed to guide the choice of algorithms and statistical tests to beused in the search for astrometric binaries during the forthcoming ESAGaia mission. Finally, orbital inclinations provided by the presentanalysis have been used to derive several astrophysical quantities. Forinstance, 29 among the 70 systems with reliable astrometric orbitalelements involve main sequence stars for which the companion mass couldbe derived. Some interesting conclusions may be drawn from this new setof stellar masses, like the enigmatic nature of the companion to theHyades F dwarf HIP 20935. This system has a mass ratio of 0.98 but thecompanion remains elusive.
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| Period Changes of AO Camelopardalis and AM Leonis and Their Implications for the Presence of Tertiary Components and the Evolutionary States of the Two Overcontact Binary Systems
AO Cam and AM Leo are two short-period overcontact binary systems whosephysical properties are nearly the same. In the present paper, three CCDtimes of minimum light for AO Cam and two photoelectric eclipse timesfor AM Leo are presented. Combining the new determined eclipse timeswith others compiled from the literature, the behavior of their O-Cvariations were investigated. For AO Cam, its orbital period is revised,and it is found that the period shows a cyclic variation with a periodof 20.1 yr and an amplitude of 0.0047 days. In AM Leo, a new periodincrease has occurred recently. Two possibilities of period variations,sudden and continuous changes, are discussed. The period changes of bothsystems cannot be explained by apsidal motion, since both the primaryand the secondary eclipse times vary in the same O-C trend. Of the threemechanisms of magnetic activity cycles, internal mass motions, and thepresence of a third body, we think that the last is more plausible.Assuming that the period changes are due to third bodies revolvingaround the eclipsing pairs, the parameters of the third-component starsare determined. If it exists, the third body in AO Cam is revolving in acircular orbit, whereas that in AM Leo is revolving in an eccentricorbit (e'=0.58). No secular period changes were discovered ineither overcontact binary star, which is in agreement with the recentstatistical relation of Qian. This may suggest that AO Cam and AM Leoare in transition between the angular momentum loss-controlled and thethermal relaxation oscillation-controlled stages of the evolutionaryscheme recently proposed by Qian.
| Possible connection between period change and magnetic activity of the very short-period binary VZ Piscium
New times of light minimum of the short-period (P=0d.26)close binary system, VZ Psc, are presented. A period investigation ofthe binary star, by combining the three new eclipse times with theothers collected from the literatures, shows that the variation of theperiod might be in an alternate way. Under the hypothesis that thevariation of the orbital period is cyclic, a period of 25 years and anamplitude of 0.d0030 for the cyclic change are determined. Ifthis periodic variation is caused by the presence of a third body, themass of the third body (m3) should be no less than 0.081Mȯ. Since both components of VZ Psc are strongchromospherically active and the level of activity of the secondarycomponent is higher than that of the primary one, the period may be moreplausibly explained by cyclic magnetic activity of the less massivecomponent.
| Observational study of interacting binary stars
We present a progress report on the results obtained from photometricand spectroscopic observations of the interacting binary stars SW Cyg,RR Dra, Y Leo, and SW Lyn in our Galaxy. Analogous studies could beeventually carried out for interacting binaries in the Local Groupgalaxies. From this study we note the significant Hα line profilevariations in spectra of SW Cyg taken at two different orbital phases.
| Catalogue of Algol type binary stars
A catalogue of (411) Algol-type (semi-detached) binary stars ispresented in the form of five separate tables of information. Thecatalogue has developed from an earlier version by including more recentinformation and an improved layout. A sixth table lists (1872) candidateAlgols, about which fewer details are known at present. Some issuesrelating to the classification and interpretation of Algol-like binariesare also discussed.Catalogue is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/417/263
| Doppler tomography of Algols
The technique of Doppler tomography has been influential in the study ofmass transfer in Algol-type interacting binaries. The Algols contain ahot blue dwarf star with a magnetically-active late-type companion. Inthe close Algols, the gas stream flows directly into the photosphere ofthe blue mass-gaining star because it does not have enough room to avoidimpact with that star. Doppler tomograms of the Algols have beenproduced from over 2500 time-resolved spectra at wavelengthscorresponding to Hα, Hβ, He I (6678 Å), Si II (6371Å) and Si IV (1394 Å). These tomograms display images ofaccretion structures that include a gas stream, accretion annulus,accretion disk, stream-star impact region, and occasionally a source ofchromospheric emission associated with the cool, mass-losing companion.Some Algol systems alternate between stream-like and disk-like states,and provide direct evidence of active mass transfer within the Algols.This work produced the very first images of the gas stream for theentire class of interacting binaries, and demonstrated that the Algolsare far more active than formerly believed, with variability on timescales of weeks to months.
| 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
Not Available
| Archive of Photometric Plates Obtained at Cluj Astronomical Observatory
The archive of photometric plates obtained at the AstronomicalObservatory of Cluj in the period 1952-1974 is presented. The plateinventory is made within the framework of the Wide-Field Plate Databaseproject. The plates were taken in the regions around 110 variable stars(eclipsing variables and RR Lyrae-type stars), as well as in somecomparison stars regions.
| Interior structura variations in the secondary components of two Algol-type eclipsing binary systems: SW Cygni and RR Draconis
SW Cyg and DD Dra are two Algol-type eclipsing binary systems. Bothcontain an A2-type main-sequence primary and a K0-type secondarycomponent with a rather deep primary light minimum in their light curves(2fm 6 and 3fm 8, respectively). In the present paper, orbital periodchanges of these stars are studied based on the analyses of theircentury-long times of light minimum. Several period jumps are found tosuperimpose on a rapid secular increase (dP/dt=+4.71x10-6 and+4.24x10-6 days/year, respectively). Since the periodincreases are rather rapid, the mass exchange between the componentswould be dynamical. SW Cyg is a low-mass ratio system (q=0.20) and it isexpected that the mass ratio of RR Dra may also be very low because ofthe rather deep primary eclipse minimum. The rapid period increasessuggest that a rapid mass transfer also occurs in a low-mass ratioAlogl-type close binary which is opposite to the theoreticallyevolutionary scheme of the binary star. The period jumps superimposed onthe long-term increases are caused by the structura variation of thecool mass-loser via instabilities in the convective outer layer (COL) orvia cyclic magnetic activity of the K0-type components. As the periodjumps do not occur in a short-term alternating way, the structura changecaused by instabilities in the COL via a dynamical mass loss from thecool subgiant may be more plausible.
| Orbital period study of the Algol-type eclipsing binary system TW Draconis
The century-long times of light minimum of the Algol-type eclipsingbinary star, TW Dra (BD/+64°1077, SpA5V+K2III), are investigated byconsidering a new pattern of period change. Two sudden period increasesand two successive period decreases are discovered to superimpose on arapid secular increase (dP/dt=+4.43×10-6days/year). Thesecular increase may be caused by a dynamical mass transfer from thesecondary to the primary component(dm/dt=6.81×10-7Msolar/year) that is inagreement with the semi-detached configuration of the system and withthe existence of a hot spot and a gaseous stream in the binary system.The irregular period jumps superimposed on the secular increase can beexplained by the structure variation of the K2-type giant viainstabilities of the outer convective layer or via magnetic activitycycles.
| Starspots and photometric noise on observed minus calculated (O-C) diagrams
The effects of starspots on the O-C diagrams of eclipsing binaries areinvestigated, with a special emphasis on contact binaries. It is shownthat starspots modulate the O-C differences in a fundamentally differentway than real orbital period variations. Migrating starspots can onlyintroduce high frequency, low amplitude disturbances (generally lessthan 0.01 d), whose characteristics are numerically specified fortypical contact binaries. It becomes evident that the observedsystematic short timescale variations of the O-C diagrams of activecontact binaries (even those like VW Cep) cannot be attributed tostarspots. Furthermore, the basic property of non-linear modulation ofO-C differences is emphasised. This non-linearity has seriousconsequences for the widespread traditional method of O-C diagramanalysis. This traditional method is found inappropriate even on afundamental level, and its mathematical and physical inconsistencies arereviewed.
| Survey of Hα Mass Transfer Structures in Classical Algol-Type Binaries
Five years of Hα survey data for 37 ``classical'' Algol-typebinaries are presented. All these systems have primaries with a spectraltype of A or B, have a period of less than 5 days, and are visible inthe Northern Hemisphere. Data were collected with the 1.02 m reflectorat the US Naval Observatory, Flagstaff Station. The survey consists ofover 460 system spectra. Each system was observed at least once duringthe 5 years, with many systems observed several times over severalepochs. Difference profiles are calculated for most spectra by modelingand subtracting the spectrum of the photospheres of the stellarcomponents. We examined each spectrum for the presence of mass transfer,stream-star and stream-disk interaction, a disk or circumstellar bulge,and chromospheric emission. We present information on the prevalence ofmass transfer activity, disk presence, and system states associated withparticular mass transfer structures. We show that no currently publishedstudy, including this one, has enough data for a rigorous statisticalidentification of system states.
| Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521
| Stars with the Largest Hipparcos Photometric Amplitudes
A list of the 2027 stars that have the largest photometric amplitudes inHipparcos Photometry shows that most variable stars are all Miras. Thepercentage of variable types change as a function of amplitude. Thiscompilation should also be of value to photometrists looking forrelatively unstudied, but large amplitude stars.
| Hα Spectroscopy of RW Monocerotis
Five years of sparse full-orbit Hα spectroscopy are presented forthe short-period Algol RW Monocerotis. A spectroscopic mass ratio isderived that confirms the published photometric mass ratio. Of the twopublished rotation rates of the primary star, 66 and 260 kms-1, the slower best fits our observations. Hα emissionwas not seen during any of five eclipses, indicating that the secondaryis notstrongly chromospherically active. At every epoch an emissionfeature between the two stars was found, confirming that there iscontinuous mass transfer. However, an accompanying accretion disk wasseen in only two of six observing runs, using out-of-eclipsespectroscopy. Comparing with models, we show how a single out-of-eclipseHα observation can provide information on the mass transferpresence at that epoch. Finally, we see redshifted absorption justbefore and after primary eclipse, consistent with the location andvelocity of a mass transfer stream. However, the Hα absorptionequivalent width (with respect to the out-of-eclipse continuum) fallsproportionally with the primary's visibility between first and secondcontact. This indicates that the stream is projected against the entireface of the primary, a much larger area than predicted by theory.
| Morphologies of Hα Accretion Regions in Algol Binaries
We have investigated a group of 18 Algol-type binaries to determine thegeneral morphologies and physical properties of the accretion regions inthese systems. The systems studied were V505 Sgr, RZ Cas, AI Dra, TVCas, TW Cas, delta Lib, RW Tau, TW Dra, beta Per, TX UMa, U Sge, S Equ,U CrB, RS Vul, SW Cyg, CX Dra, TT Hya, and AU Mon, in order ofincreasing orbital period P=1.18-11.11 days. In addition, the RSCVn-type binary HR 1099 (V711 Tau) was observed to illustrate theappearance of chromospheric Hα emission. Nearly 2200 time-resolvedHα spectra were collected from 1992 March to 1994 December withthe McMath-Pierce Solar Telescope at NSO and mostly with theCoudé Feed Telescope at KPNO. The spectra were obtained at phasesaround the entire orbit of each binary and were closely spaced to permitthe detection of transitions in the profiles. Moreover, the spectra wereobtained typically within three orbital cycles to reduce the influenceof secular variations. Difference profiles were calculated bysubtracting a composite theoretical photospheric spectrum from theobserved spectrum. The analysis of the Hα difference profilesdemonstrates that the accretion structures in Algol binaries have fourbasic morphological types: (1) double-peaked emission systems in whichthe accretion structure is a transient or classical accretion disk; (2)single-peaked emission systems in which the accreted gas was found alongthe trajectory of the gas stream and also between the two stars in anaccretion annulus; (3) alternating single- and double-peaked emissionsystems, which can change between a single-peaked and a double-peakedtype within an orbital cycle; and (4) weak spectrum systems in whichthere was little evidence of any accretion structure since thedifference spectra are weak at all phases. The first two types are thedominant morphologies. The first type can be interpreted physically as adisklike distribution, while the second is a gas stream-likedistribution. The most common type in short-period Algols with 2.7days6 days)were found to have slightly variable but permanent accretion disks atall epochs (i.e., CX Dra, TT Hya, and AU Mon), similar to those found incataclysmic variables. SW Cyg (P=4.57 days) was found to be anintermediate case between the shorter period systems with P<4.5 daysand the longer period group with P>6 days. Two systems, U Sge and UCrB, displayed alternating single- and double-peaked emission atdifferent epochs (Type 3), and changes from one type to another weredetected within a 12 hour time interval. Observations at multiple epochssuggest that four members of the single-peaked emission group, namely RWTau, TX UMa, S Equ, and RS Vul, may actually belong to the alternatinggroup. So, the complete group of alternating systems covers periods of2.7 days
| Is asynchronism in semidetached binary systems real?
We analyze statistical relationships between the parameters ofAlgol-type binaries with asynchronous rotation of the primary componentsand provide observational evidence for denser, more extended gaseousenvelopes in the eclipsing systems of this group. We conclude thatasynchronism of the primary components in such systems is not real. Thelines that are used to determine the rotational velocities of thesecomponents originate mostly in the part of the atmosphere which acquiresan additional angular momentum during the interaction with the gasstream and produces a transient accretion disk near the equatorialplane.
| Catalogue of H-alpha emission stars in the Northern Milky Way
The ``Catalogue of Stars in the Northern Milky Way Having H-alpha inEmission" appears in Abhandlungen aus der Hamburger Sternwarte, Band XIin the year 1997. It contains 4174 stars, range {32degr <= l() II< 214degr , -10degr < b() II < +10degr } having the Hαline in emission. HBH stars and stars of further 99 lists taken from theliterature till the end of 1994 were included in the catalogue. We givethe cross-identification of stars from all lists used. The catalogue isalso available in the Centre de Données, Strasbourg ftp130.79.128.5 or http://cdsweb.u-strasbg.fr and at the HamburgObservatory via internet.
| On the relation of changes of the period and brightness in the close binaries SW Cygni and U Sagittae
The analysis of the available data allows to conclude that changes ofthe orbital periods in both Algol-type systems, SW Cyg and U Sge, arecorrelated with the brightness variations of the late-type loser. Theepisodes of decrease of the orbital period are accompanied by minimum ofbrightness of the loser in both cases.
| Interaction of Eclipsing Binaries with their Environment
The interaction of eclipsing binary star systems with the mass around(in the form of star, planet, envelope or disk) affects the orbitalperiod of these systems. Thus, the long-term orbital period changes ofeclipsing binaries which can be deduced by using the observed times ofeclipse minima provide a good tool in understanding the interaction ofeclipsing binaries with their environment. In the present contributionmany examples of the orbital period changes of different eclipsingbinaries are presented and interpreted in terms of the interaction withtheir environment.
| Catalogue of stars in the northern Milky Way having H-alpha in emission
Not Available
| Rotation of Algol binaries - a line profile model applied to observations.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996MNRAS.283..613M&db_key=AST
| The cyclic period changes of the close binary VV Ursae Majoris.
An analysis of the set of the minimum timings of the Algol-typeeclipsing binary VV UMa is presented. The period variations are cyclicwith the cycle-length of 22years. They are consistent with the presenceof the third body with the orbital period P_2_=22.28years and minimummass of 0.4Msun_. The apsidal motion must be ruled outbecause VV UMa is a semi-detached system according to the previousanalyses. The stellar magnetic activity (Applegate =1992ApJ...385..621A)of the cold convective secondary may be an alternative cause of theobserved period changes. The cycle-length, the magnitude of the periodchange and other characteristics are consistent with the magneticactivity.
| Doppler Tomography of Accretion Disks in Algol Binaries
Doppler tomography of H alpha spectra of four Algol-type binaries TTHya, SW Cyg, U CrB, and U Sge has revealed quasi-stable accretion disksaround the mass gaining star in each system. In the tomograms, theseaccretion structures are nearly symmetric distributions of gas betweenthe stellar surface and the Roche lobe around the mass gainer. The diskis most stable in TT Hya and SW Cyg, which have orbital periods greaterthan 4.5 days. However, the morphology of the accretion structures inthe shorter period systems, U CrB and U Sge, can change from a disklikedistribution to a streamlike distribution. During a streamlike epoch ofthese systems, the gas stream in the Doppler tomogram closely followsthe predicted free fall path from the inner Lagrangian point toward themass gainer. However, during the disklike stage, the intensity of thedisk is comparable to that of the gas stream. These tomograms displaythe first maps of accretion disks in the Algol-type class of interactingbinaries.
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Dades d'Observació i Astrometria
| Constel·lació: | Cygnus |
| Ascensió Recta: | 20h06m57.93s |
| Declinació: | +46°17'58.2" |
| Magnitud Aparent: | 9.355 |
| Moviment propi RA: | -5.2 |
| Moviment propi Dec: | -6.8 |
| B-T magnitude: | 9.618 |
| V-T magnitude: | 9.377 |
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