Contenidos
Imágenes
Subir su imagen
DSS Images Other Images
Artículos relacionados
On the minimum mass ratio of W UMa binaries
Using Eggleton's stellar evolution code, we study the minimum mass ratio(qmin) of W Ursae Majoris (W UMa) binaries that havedifferent primary masses. It is found that the minimum mass ratio of WUMa binaries decreases with increasing mass of the primary if theprimary's mass is less than about 1.3Msolar, while above thismass the ratio is roughly constant. By comparing the theoretical minimummass ratio with observational data, it is found that the existence oflow-q systems can be explained by the different structure of primarieswith different masses. This suggests that the dimensionless gyrationradius (k21) and thus the structure of the primaryis very important in determining the minimum mass ratio. In addition, weinvestigate the mass loss during the merging process of W UMa systemsand calculate the rotation velocities of the single stars formed bymergers of W UMa binaries due to tidal instability. It is found that inthe case of conservation of mass and angular momentum, the merged singlestars rotate with an equatorial velocity of about~588-819kms-1, which is much larger than their break-upvelocities (vb). This suggests that the merged stars shouldextend to a very large radius (~3.7-5.3 times the radii of theprimaries) or else W UMa systems should lose a large amount of mass(~21-33 per cent of the total mass) during the merging process. If theeffect of magnetic braking is considered, the mass loss decreases to~12-18 per cent of the total mass. This implies that significant angularmomentum and mass might be lost from W UMa systems in the course of themerging process, and this kind of mass and angular momentum loss mightbe driven by the release of orbital energy of the secondaries, similarlyto common-envelope evolution.
| XID II: Statistical Cross-Association of ROSAT Bright Source Catalog X-ray Sources with 2MASS Point Source Catalog Near-Infrared Sources
The 18,806 ROSAT All Sky Survey Bright Source Catalog (RASS/BSC) X-raysources are quantitatively cross-associated with near-infrared (NIR)sources from the Two Micron All Sky Survey Point Source Catalog(2MASS/PSC). An association catalog is presented, listing the mostlikely counterpart for each RASS/BSC source, the probability Pid that the NIR source and X-ray source are uniquelyassociated, and the probability P no-id that none of the2MASS/PSC sources are associated with the X-ray source. The catalogincludes 3853 high quality (P id>0.98) X-ray-NIR matches,2280 medium quality (0.98 >= P id>0.9) matches, and4153 low quality (0.9 >= P id>0.5) matches. Of the highquality matches, 1418 are associations that are not listed in the SIMBADdatabase, and for which no high quality match with a USNO-A2 opticalsource was presented for the RASS/BSC source in previous work. Thepresent work offers a significant number of new associations withRASS/BSC objects that will require optical/NIR spectroscopy forclassification. For example, of the 6133 P id>0.92MASS/PSC counterparts presented in the association catalog, 2411 haveno classification listed in the SIMBAD database. These 2MASS/PSC sourceswill likely include scientifically useful examples of known sourceclasses of X-ray emitters (white dwarfs, coronally active stars, activegalactic nuclei), but may also contain previously unknown sourceclasses. It is determined that all coronally active stars in theRASS/BSC should have a counterpart in the 2MASS/PSC, and that the uniqueassociation of these RASS/BSC sources with their NIR counterparts thusis confusion limited.
| Angular momentum and mass evolution of contact binaries
Various scenarios of contact binary evolution have been proposed in thepast, giving hints of (sometimes contradictory) evolutionary sequencesconnecting A- and W-type systems. As the components of close detachedbinaries approach each other and contact binaries are formed, followingevolutionary paths transforms them into systems of two categories:A-type and W-type. The systems evolve in a similar way but underslightly different circumstances. The mass/energy transfer rate isdifferent, leading to quite different evolutionary results. Analternative scenario of evolution in contact is presented and discussed,based on the observational data of over one hundred low-temperaturecontact binaries. It results from the observed correlations amongcontact binary physical and orbital parameters. Theoretical tracks arecomputed assuming angular momentum loss from a system via stellar wind,accompanied by mass transfer from an advanced evolutionary secondary tothe main-sequence primary. A good agreement is seen between the tracksand the observed graphs. Independently of details of the evolution incontact and a relation between A- and W-type systems, the ultimate fateof contact binaries involves the coalescence of both components into asingle fast rotating star.
| The evolutionary status of W Ursae Majoris-type systems
Well-determined physical parameters of 130 W Ursae Majoris (W UMa)systems were collected from the literature. Based on these data, theevolutionary status and dynamical evolution of W UMa systems areinvestigated. It is found that there is no evolutionary differencebetween W- and A-type systems in the M-J diagram, which is consistentwith the results derived from the analysis of observed spectral type andof M-R and M-L diagrams of W UMa systems. M-R and M-L diagrams of W- andA-type systems indicate that a large amount of energy should betransferred from the more massive to the less massive component, so thatthey are not in thermal equilibrium and undergo thermal relaxationoscillation. Moreover, the distribution of angular momentum, togetherwith the distribution of the mass ratio, suggests that the mass ratio ofthe observed W UMa systems decreases with decreasing total mass. Thiscould be the result of the dynamical evolution of W UMa systems, whichsuffer angular momentum loss and mass loss as a result of the magneticstellar wind. Consequently, the tidal instability forces these systemstowards lower q values and finally to rapidly rotating single stars.
| Times of Minima for Neglected Eclipsing Binaries 2006-2007
CCD minima observations of eclipsing binaries during 2006-2007 for anumber of neglected eclipsing binaries are presented.
| Formation and Evolution of W Ursae Majoris Contact Binaries
The origin and evolution of W UMa systems are discussed based on All SkyAutomated Survey (ASAS) data and the mean kinematic ages of foursubgroups of 97 field contact binaries (FCBs). The period distributionof eclipsing binaries discovered by ASAS suggests that a period limit totidal locking for the close binaries is about 2.24 days, so that most WUMa systems might be formed from detached binaries with periodsP<~2.24 days, and a maximum advanced time from a detached system to aW UMa is about 3.23 Gyr. Moreover, the secular evolution of the angularmomentum (AM), the system mass, and the orbital period of 97 FCBs wereinvestigated according to the mean kinematic ages, which were setaccording to AM bins. AMs, systemic masses, and orbital periods wereshown to be decreasing with kinematic age. Their first-order decreasingrates have been determined as J˙/J=1.86×10-10yr-1, M˙/M=0.95×10-10 yr-1,and P˙/P=1.24×10-10 yr-1, and theaverage amplification (A¯=dlnJ/dlnM) is derived to be 1.96. Theseare lower than those derived from detached chromospherically activebinaries (CABs). This suggests that the magnetic activity level of FCBsis indeed weaker than that of CABs. Meanwhile, the decreasing rate of AMof FCBs is found to be equal to an average value in a cycle of a cyclicmodel of contact binaries. This might suggest that the evolution of FCBsundergoes thermal relaxation oscillation (TRO) and that the coalescenceof W UMa systems is a very long process, which is also indicated by thedynamical evolution of FCBs.
| CCD Minima for Selected Eclipsing Binaries in 2007
Not Available
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| Contact Binaries with Additional Components. II. A Spectroscopic Search for Faint Tertiaries
It is unclear how very close binary stars form, given that during thepre-main-sequence phase the component stars would have been inside eachother. One hypothesis is that they formed farther apart but were broughtin closer after formation by gravitational interaction with a thirdmember of the system. If so, all close binaries should be members oftriple (or higher order) systems. As a test of this prediction, wepresent a search for the signature of third components in archivalspectra of close binaries. In our sample of 75 objects, 23 show evidencefor the presence of a third component, down to a detection limit oftertiary flux contributions of about 0.8% at 5200 Å (consideringonly contact and semidetached binaries, we find 20 out of 66). In ahomogeneous subset of 59 contact binaries, we are fairly confident thatthe 15 tertiaries we have detected are all tertiaries present with massratios 0.28<~M3/M12<~0.75 and implied outerperiods P<~106 days. We find that if the frequency oftertiaries were the same as that of binary companions to solar-typestars, one would expect to detect about 12 tertiaries. In contrast, ifall contact binaries were in triple systems, one would expect about 20.Thus, our results are not conclusive but are sufficiently suggestive towarrant further studies.
| 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.
| CCD Minima for Selected Eclipsing Binaries in 2005
Not Available
| Physical Parameters of Components in Close Binary Systems. V
The paper presents combined spectroscopic and photometric orbitalsolutions for ten close binary systems: CN And, V776 Cas, FU Dra, UVLyn, BB Peg, V592 Per, OU Ser, EQ Tau, HN UMa and HT Vir. Thephotometric data consist of new multicolor light curves, while thespectroscopy has been recently obtained within the radial velocityprogram at the David Dunlap Observatory (DDO). Absolute parameters ofthe components for these binary systems are derived. Our results confirmthat CN And is not a contact system. Its configuration is semi-detachedwith the secondary component filling its Roche lobe. The configurationof nine other systems is contact. Three systems (V776 Cas, V592 Per andOU Ser) have high (44-77%) and six (FU Dra, UV Lyn, BB Peg, EQ Tau, HNUMa and HT Vir) low or intermediate (8-32%) fill-out factors. Theabsolute physical parameters are derived.
| Photoelectric Minima of Eclipsing Binaries
Not Available
| 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.
| Times of Minima for Neglected Eclipsing Binaries in 2004
Times of minima obtained during 2004 for a number of neglected eclipsingbinaries are presented.
| Photoelectric Minima of Some Eclipsing Binary Stars
Not Available
| SB9: The ninth catalogue of spectroscopic binary orbits
The Ninth Catalogue of Spectroscopic Binary Orbits(http://sb9.astro.ulb.ac.be) continues the series of compilations ofspectroscopic orbits carried out over the past 35 years by Batten andcollaborators. As of 2004 May 1st, the new Catalogue holds orbits for2386 systems. Some essential differences between this catalogue and itspredecessors are outlined and three straightforward applications arepresented: (1) completeness assessment: period distribution of SB1s andSB2s; (2) shortest periods across the H-R diagram; (3)period-eccentricity relation.
| Key parameters of W UMa-type contact binaries discovered by HIPPARCOS
A sample of W UMa-type binaries which were discovered by the HIPPARCOSsatellite was constructed with the aid of well defined selectioncriteria described in this work. The selection process showed up thatseveral systems of which the variability types have been assigned as EBin HIPPARCOS catalogue are genuine contact binaries of W UMa-type. Thelight curves of the 64 selected systems based on HIPPARCOS photometrywere analyzed with the aid of light curve synthesis method by Rucinskiand their geometric elements (namely mass ratio q, degree of contact f,and orbital inclination i) were determined. The solutions were obtainedfor the first time for many of the systems in the sample and would be agood source for their future light curve analyses based on more precisefollow-up observations.Based on observations made with the ESA HIPPARCOSastrometry satellite.
| 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.
| Radial Velocity Studies of Close Binary Stars. VIII.
Radial velocity measurements and sine-curve fits to the orbital velocityvariations are presented for the seventh set of 10 close binary systems:V410 Aur, V523 Cas, QW Gem, V921 Her, V2357 Oph, V1130 Tau, HN UMa, HXUMa, HD 93917, and NSV 223. All systems but three (V523 Cas, HD 93917,NSV 223) were discovered photometrically by the Hipparcos mission. Allsystems are double-lined (SB2) binaries, and all but the detached, veryclose system V1130 Tau are contact binaries. The broadening functionpermitted improvement of the orbital elements for V523 Cas, which wasthe only system observed before for radial velocity variations.Spectroscopic/visual companions were detected for V410 Aur and HX UMa.Several of the studied systems are prime candidates for combined lightand radial velocity synthesis solutions.Based on data obtained at the David Dunlap Observatory, University ofToronto.
| Catalogue of the field contact binary stars
A catalogue of 361 galactic contact binaries is presented. Listedcontact binaries are divided into five groups according to the type andquality of the available observations and parameters. For all systemsthe ephemeris for the primary minimum, minimum and maximum visualbrightness and equatorial coordinates are given. If available,photometric elements, (m1+m2)sin3i,spectral type, parallax and magnitude of the O'Connell effect are alsogiven. Photometric data for several systems are augmented by newobservations. The quality of the available data is assessed and systemsrequiring modern light-curve solutions are selected. Selectedstatistical properties of the collected data are discussed.
| The 74th Special Name-list of Variable Stars
We present the Name-list introducing GCVS names for 3153 variable starsdiscovered by the Hipparcos mission.
|
Enviar un nuevo artículo
Enlaces relacionados
- - No se han encontrado enlaces -
En viar un nuevo enlace
Miembro de los siguientes grupos:
|
Datos observacionales y astrométricos
| Constelación: | Osa Mayor |
| Ascensión Recta: | 11h15m56.38s |
| Declinación: | +37°38'35.3" |
| Magnitud Aparente: | 9.841 |
| Movimiento Propio en Ascensión Recta: | 54 |
| Movimiento Propio en Declinación: | -36.9 |
| B-T magnitude: | 10.433 |
| V-T magnitude: | 9.89 |
Catálogos y designaciones:
|
