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Публикации по объекту
Random forest automated supervised classification of Hipparcos periodic variable stars
We present an evaluation of the performance of an automatedclassification of the Hipparcos periodic variable stars into 26 types.The sub-sample with the most reliable variability types available in theliterature is used to train supervised algorithms to characterize thetype dependencies on a number of attributes. The most useful attributesevaluated with the random forest methodology include, in decreasingorder of importance, the period, the amplitude, the V-I colour index,the absolute magnitude, the residual around the folded light-curvemodel, the magnitude distribution skewness and the amplitude of thesecond harmonic of the Fourier series model relative to that of thefundamental frequency. Random forests and a multi-stage scheme involvingBayesian network and Gaussian mixture methods lead to statisticallyequivalent results. In standard 10-fold cross-validation (CV)experiments, the rate of correct classification is between 90 and 100per cent, depending on the variability type. The main mis-classificationcases, up to a rate of about 10 per cent, arise due to confusion betweenSPB and ACV blue variables and between eclipsing binaries, ellipsoidalvariables and other variability types. Our training set and thepredicted types for the other Hipparcos periodic stars are availableonline.
| A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun
Traditionally, runaway stars are O- and B-type stars with large peculiarvelocities. We would like to extend this definition to young stars (upto ?50 Myr) of any spectral type and to identify those present in theHipparcos catalogue by applying different selection criteria, such aspeculiar space velocities or peculiar one-dimensional velocities.Runaway stars are important for studying the evolution of multiple starsystems or star clusters, as well as for identifying the origins ofneutron stars. We compile the distances, proper motions, spectral types,luminosity classes, V magnitudes and B-V colours, and we utilizeevolutionary models from different authors to obtain star ages. We studya sample of 7663 young Hipparcos stars within 3 kpc from the Sun. Theradial velocities are obtained from the literature. We investigate thedistributions of the peculiar spatial velocity and the peculiar radialvelocity as well as the peculiar tangential velocity and itsone-dimensional components and we obtain runaway star probabilities foreach star in the sample. In addition, we look for stars that aresituated outside any OB association or OB cluster and the Galactic planeas well as stars for which the velocity vector points away from themedian velocity vector of neighbouring stars or the surrounding local OBassociation/cluster (although the absolute velocity might be small). Wefind a total of 2547 runaway star candidates (with a contamination ofnormal Population I stars of 20 per cent at most). Thus, aftersubtracting these 20 per cent, the runaway frequency among young starsis about 27 per cent. We compile a catalogue of runaway stars, which isavailable via VizieR.
| Spin angular momentum evolution of the long-period Algols
We consider the spin angular momentum evolution of the accretingcomponents of Algol-type binary stars. In wider Algols the accretion isthrough a disc so that the accreted material can transfer enough angularmomentum to the gainer that material at its equator should be spinningat breakup. We demonstrate that even a small amount of mass transfer,much less than required to produce today's mass ratios, transfers enoughangular momentum to spin the gainer up to this critical rotationvelocity. However the accretors in these systems have spins typicallybetween 10 and 40per cent of the critical rate. So some mechanism forangular momentum loss from the gainers is required. Unlike solar-typechromospherically active stars, with enhanced magnetic activity whichleads to angular momentum and mass loss, the gainers in classical Algolshave radiative envelopes. We further find that normal radiative tidesare far too weak to account for the necessary angular momentum loss.Thus enhanced mass loss in a stellar wind seems to be required tospin-down the gainers in classical Algol systems. We consider generationof magnetic fields in the radiative atmospheres in a differentiallyrotating star and the possibility of angular momentum loss driven bystrong stellar winds in the intermediate-mass stars, such as theprimaries of the Algols. Differential rotation, induced by the accretionitself, may produce such winds which carry away enough angular momentumto reduce their rotational velocities to the today's observed values. Weapply this model to two systems with initial periods of 5d, one withinitial masses 5 and and the other with 3.2 and . Our calculations showthat, if the mass outflow rate in the stellar wind is about 10per centof the accretion rate and the dipole magnetic field is stronger thanabout 1kG, the spin rate of the gainer is reduced to below breakupvelocity even in the fast phase of mass transfer. Larger mass loss isneeded for smaller magnetic fields. The slow rotation of the gainers inthe classical Algol systems is explained by a balance between thespin-up by mass accretion and spin-down by a stellar wind linked to amagnetic field.
| The most plausible explanation of the cyclic period changes in close binaries: the case of the RS CVn-type binary WW Dra
Cyclic period changes are a fairly common phenomenon in close binarysystems and are usually explained as being caused either by the magneticactivity of one or both components or by the light travel time effect(LTTE) of a third body. We searched the orbital period changes in 182EA-type (including the 101 Algol systems used by Hall), 43 EB-type and53 EW-type binaries with known mass ratio and spectral type of thesecondary component. We reproduced and improved the diagram in Hallaccording to the new collected data. Our plots do not support theconclusion derived by Hall that cyclic period changes are restricted tobinaries having a secondary component with spectral type later than F5.The presence of period changes among systems with a secondary componentof early type indicates that magnetic activity is one, but not the only,cause of the period variation. It is discovered that cyclic periodchanges, probably resulting from the presence of a third body, are morefrequent in EW-type binaries among close systems. Therefore, the mostplausible explanation of the cyclic period changes is the LTTE throughthe presence of a third body. Using the century-long historical recordof the times of light minimum, we analysed the cyclic period change inthe Algol binary WW Dra. It is found that the orbital period of thebinary shows a ~112.2-yr cyclic variation with an amplitude of ~0.1977d.The cyclic oscillation can be attributed to the LTTE by means of a thirdbody with a mass no less than 6.43Msolar. However, nospectral lines of the third body were discovered, indicating that it maybe a candidate black hole. The third body is orbiting the binary at adistance closer than 14.4 au and may play an important role in theevolution of this system.
| Masses and luminosities of O- and B-type stars and red supergiants
Massive stars are of interest as progenitors of supernovae, i.e.neutron stars and black holes, which can be sources of gravitationalwaves. Recent population synthesis models can predict neutron star andgravitational wave observations but deal with a fixed supernova rate oran assumed initial mass function for the population of massive stars. Here we investigate those massive stars, which are supernovaprogenitors, i.e. with O- and early B-type stars, and also allsupergiants within 3 kpc. We restrict our sample to those massive starsdetected both in 2MASS and observed by Hipparcos, i.e. only those starswith parallax and precise photometry. To determine the luminositieswe calculated the extinctions from published multi-colour photometry,spectral types, luminosity class, all corrected for multiplicity andrecently revised Hipparcos distances. We use luminosities andtemperatures to estimate the masses and ages of these stars usingdifferent models from different authors. Having estimated theluminosities of all our stars within 3 kpc, in particular for all O- andearly B-type stars, we have determined the median and mean luminositiesfor all spectral types for luminosity classes I, III, and V. Ourluminosity values for supergiants deviate from earlier results: Previouswork generally overestimates distances and luminosities compared to ourdata, this is likely due to Hipparcos parallaxes (generally moreaccurate and larger than previous ground-based data) and the fact thatmany massive stars have recently been resolved into multiples of lowermasses and luminosities. From luminosities and effective temperatureswe derived masses and ages using mass tracks and isochrones fromdifferent authors. From masses and ages we estimated lifetimes andderived a lower limit for the supernova rate of ?20 events/Myraveraged over the next 10 Myr within 600 pc from the sun. These data arethen used to search for areas in the sky with higher likelihood for asupernova or gravitational wave event (like OB associations).
| A systematic study of variability among OB-stars based on HIPPARCOS photometry
Context: Variability is a key factor for understanding the nature of themost massive stars, the OB stars. Such stars lie closest to the unstableupper limit of star formation. Aims: In terms of statistics, thedata from the HIPPARCOS satellite are unique because of time coverageand uniformity. They are ideal to study variability in this large,uniform sample of OB stars. Methods: We used statisticaltechniques to determine an independant threshold of variabilitycorresponding to our sample of OB stars, and then applied an automaticalgorithm to search for periods in the data of stars that are locatedabove this threshold. We separated the sample stars into 4 maincategories of variability: 3 intrinsic and 1 extrinsic. The intrinsiccategories are: OB main sequence stars (~2/3 of the sample), OBe stars(~10%) and OB Supergiant stars (~1/4).The extrinsic category refers toeclipsing binaries. Results: We classified about 30% of the wholesample as variable, although the fraction depends on magnitude level dueto instrumental limitations. OBe stars tend to be much more variable(≈80%) than the average sample star, while OBMS stars are belowaverage and OBSG stars are average. Types of variables include αCyg, β Cep, slowly pulsating stars and other types from the generalcatalog of variable stars. As for eclipsing binaries, there arerelatively more contact than detached systems among the OBMS and OBestars, and about equal numbers among OBSG stars.
| New Interpretation of Superhumps
Observational evidence is presented for periodically variableirradiation of secondary components. This results in strongly modulatedmass outflow. Superhumps are then due to enhanced dissipation of thekinetic energy of the stream. Qualitative interpretation ofsuperhump periods and their variations is also presented.
| BAV-Results of observations - Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating 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.
| 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.
| Updated Elements for Southern Eclipsing Binaries
Analysis of ASAS-3 data for 442 southern eclipsing binaries yielded 131stars with incorrect periods listed in the GCVS catalog
| Up-to-Date Linear Elements of Eclipsing Binaries
About 1800 O-C diagrams of eclipsing binaries were analyzed and up-todate linear elements were computed. The regularly updated ephemerides(as a continuation of SAC) are available only in electronic form at theInternet address: http://www.as.ap.krakow.pl/ephem/.
| 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
| Evolution of Wolf-Rayet Stars in Binary Systems: An Analysis of the Mass and Orbital-Eccentricity Distributions
We have undertaken a statistical study of the component mass ratios andthe orbital eccentricities of WR + O close binary, detachedmain-sequence (DMS), contact early-type (CE), and semidetached (SD)systems. A comparison of the characteristics of WR + O systems and ofDMS, CE, and SD systems has enabled us to draw certain conclusions aboutthe evolutionary paths of WR + O binaries and to demonstrate that up to90% of all known WR + O binaries formed as a result of mass transfer inmassive close O + O binary systems. Since there is a clear correlationbetween the component masses in SD systems with subgiants, the absenceof an anticorrelation between the masses of the WR stars and O stars inWR + O binaries cannot be considered evidence against the formation ofWR + O binaries via mass transfer. The spectroscopic transitionalorbital period P tr sp corresponding to the transition from nearlycircular orbits (e sp<0.1) to elliptical orbits (e sp≥0.1) is14d for WR + O systems and 2d 3d for OB + OB systems. Theperiod range in which all WR + O orbits are circular &$(1mathop dlimits_. 6 ≤slant P ≤slant 14(d) ); is close to the range for SD systems with subgiants, &0mathop dlimits_. 7 ≤slant P ≤slant 15(d); . The large difference between the P tr sp values for WR + O and OB +OB systems suggests that a mechanism of orbit circularization additionalto that for OB + OB systems at the DMS stage (tidal dissipation of theorbital energy due to radiative damping of the dynamical tides) acts inWR + O binaries. It is natural to suggest mass transfer in the parent O+ O binaries as this supplementary orbit-circularization mechanism.Since the transitional period between circular and elliptical orbits forclose binaries with convective envelopes and ages of 5×109 yearsis &P_{tr} = 12mathop dlimits_. 4$; , the orbits of most known SD systems with subgiants had enough timeto circularize during the DMS stage, prior to the mass transfer. Thus,for most SD systems, mass transfer plays a secondary role incircularization of their orbits. In many cases, the initial orbitaleccentricities of the O + O binary progenitors of WR + O systems arepreserved, due to the low viscosity of the O-star envelopes and theshort timescale for their nuclear evolution until the primary O starfills its Roche lobe and the mass transfer begins. The mass transfer inthe parent O + O systems is short-lived, and the number of orbitalcycles during the early mass-transfer stage is relatively low (lowerthan for the progenitors of SD systems by three or four orders ofmagnitude). The continued transfer of mass from the less massive to themore massive star after the component masses have become equal leads tothe formation of a WR + O system, and the orbit's residual eccentricityincreases to the observed value. The increase of the orbitaleccentricity is also facilitated by variable radial mass loss via thewind from the WR star in the WR + O system during its motion in theelliptical orbit. The result is that WR + O binaries can haveconsiderable orbital eccentricities, despite their intense masstransfer. For this reason, the presence of appreciable eccentricitiesamong WR + O binaries with large orbital periods cannot be consideredfirm evidence against mass transfer in the parent O + O binary systems.Only for the WR + O binaries with the longest orbital periods (4 of 35known systems, or 11 %) can the evolution of the parent O + O binariesoccur without filling of the Roche lobe by the primary O star, beinggoverned by radial outflow in the form of the stellar wind and possiblyby the LBV phenomenon, as in the case of HD 5980.
| 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
| An observational study of Algol-type binaries
The primary purpose of this thesis is to obtain more accurate orbitalparameters for a number of Algol-type binaries. In this study, fivesystems were observed in two observing runs in 1994 (La Palma, 7 nights)and 1997 (Mexico, 4 nights). The 1994 run consisted of single slitobservations of U CrB, TU Mon and TX UMa. In 1997, U CrB was repeatedand RS Vul and GU Her were added to the target list; in this case, theobserving was carried out with an Echelle spectrograph. Data reductionwas done using FIGARO and IRAF for the 1994 and 1997 data sets,respectively. The radial velocity curves of these five systems wereanalysed to obtain accurate orbital parameters, in particular to try toobtain radial velocity semi-amplitudes, K1 and K2, for both components.For U CrB, a new pair of K1 and K2 was found which leads us to a muchmore sensible point in the evolutionary sequence of this system. For TXUMa and TU Mon only confirmation of their published K1 values could beachieved because of their low resolution spectra which did not enablethe other component to be resolved. For RS Vul, K1 was confirmed.Because of the inadequate phase coverage at one quadrature, the K2 valuecould not be improved, but a comparison was made with the latestpublished value. GU Her was defined to be a `cool algol' (i.e. bothcomponents are late type sub giants), and the K1 and K2 value of thesystem was found for the first time. Besides radial velocity studies,magnetic activity in Algol-type binaries and its relation to theirevolutionary sequences is also discussed. In this part of study someAlgol--type binaries are categorised into four Groups depending on theevolutionary stage of the system. We claim to find that there is aremarkable correlation between evolutionary status and X--ray activityin the mass losing star of the system. In addition to already observedand categorised systems a list of systems is presented as candidates forthis categorisation.
| Magnetic activity and evolution of Algol-type stars - II
We examine the possibility of probing dynamo action in mass-losingstars, components of Algol-type binaries. Our analysis is based on thecalculation of non-conservative evolution of these systems. We model thesystems USge and betaPer where the more massive companion fills itsRoche lobe at the main sequence (case AB) and where it has a smallhelium core (early case B) respectively. We show that to maintainevolution of these systems at the late stages which are presumablydriven by stellar `magnetic braking', an efficient mechanism forproducing large-scale surface magnetic fields in the donor star isneeded. We discuss the relevance of dynamo operation in the donor starto the accelerated mass transfer during the late stages of evolution ofAlgol-type binaries. We suggest that the observed X-ray activity inAlgol-type systems may be a good indicator of their evolutionary statusand internal structure of the mass-losing stellar components.
| Accurate Position Estimates For Known Variables
Not Available
| Stardial: an Autonomous Astronomical Camera on the World Wide Web
We describe the use of an autonomous astronomical camera, called``Stardial,'' for undergraduate instruction. Stardial delivers images ofthe night sky nearly in real-time to the world wide web(www.astro.uiuc.edu/~stardial/). The world wide web (WWW) interface isrobust, inexpensive, and accommodates many students asynchronously withrespect to the instructor(s). The guiding philosophy is to providestudents with authentic astronomical data so that they may learn aboutscience by doing it themselves. Students respond favorably to theopportunity to learn from their own experiences with authentic data,complete with its irregularities and its surprises. Stardial has beenoperational for one academic year (1996-97) at the University ofIllinois at Urbana-Champaign. In this paper we describe Stardial'sinstrumentation, some of the curriculum based upon Stardial's uniquedata, and the experiences of students who have used Stardial. Weconclude with possible research topics using Stardial data and with abrief look to the future of remote laboratories. (SECTION: AstronomicalInstrumentation)The name ``Stardial'' derives from the fact that like a sundial,Stardial is a stationary device placed outside 24 hours a day, and thatboth depend on and make evident the rotation of the Earth. A sundialoperates with sunlight, while Stardial operates with starlight. Therethe similarity ends.
| R Canis Majoris---Revisited
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJ...458..371S&db_key=AST
| R Canis Majoris: absolute elements and evolutionary status.
Not Available
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| Photometric elements, absolute dimensions and evolutionary status of the eclipsing binary HU Tauri (HR 1471).
The photometric elements of HU Tauri are derived from an analysis of itsblue and visual light curves using the Wilson & Devinney (1971)light curve synthesis method. The photometric elements suggest that HUTauri is a semidetached system and the primary minimum in its lightcurve is due to an occultation eclipse. Combining the photometricelements and spectroscopic orbital elements the absolute dimensions ofthe system are derived. The masses and radii of the B8 V primary andF8-G2 III-IV type secondary are found to be 4.68Msun_,2.9Rsun_ and 1.26Msun_, 3.34Rsun_respectively. The cool and less massive secondary has filled its Rochelobe and it is over luminous for its mass.
| New rotational velocities for eclipsing binaries, and a comparison of spectroscopic and photometric rotations
Rotational velocities are determined spectroscopically for 38 eclipsingbinaries, including many long-period, nominally semidetached, systems.We note that spectroscopic rotations may differ from rotations derivedfrom light-curve modeling using the Wilson-Devinney program. In'direct-impact' mass-transferring systems, or in most systems withperiods smaller than about 7 days, observations suggest that the tworotations are usually about the same. In cases where the stream missesthe gainer and an accretion disk forms, however, photometric rotationestimates often exceed spectroscopic determinations. The possiblephysical significance of this situation is briefly discussed. Doubt iscast on the likelihood that the rotation of the hot component of U Sgehas changed detectably in the last 30 years.
| Gravitational radiation and spiralling time of close binary systems (V)
Forty-six binary systems with their primary component masses between 2and 3 solar masses have been considered for gravitational radiationstudy. Power output by gravitational radiation (PB) and spiral timetau(0) for all individual systems have been evaluated. A relation hasbeen given between PB and tau(0). The rate of decrease of orbital periodhas also been given for 10 eccentric orbit systems.
| Observations of CNO Processing in Massive Interacting Binary Systems
Not Available
| Period changes of ten eclipsing variable stars
The period variations of 10 eclipsing binary stars (WZ And, RX Cas, SXCas, TW Cas, XX Cep, RX Gem, TT Her, TU Mon, RW Per, and TX UMa) areexamined. A physical interpretation of the combined observational resultis given on the basis of a study of each individual star and in view ofthe Biermann-Hall (1973) model.
| Temperatures from the log G - log M diagram for Algol-type binaries
The behavior of the primary and secondary components in a sample ofdouble-lined Algol-type eclipsing binaries in the log g - log Te diagramis analyzed. Results indicate that the hotter components behave likenormal main-sequence stars while the effect of irradiation may partlyexplain the 'overluminosity' of the cool components.
| The system of RS Sagittari
New photoelectric times of minimum light of RS Sgr are reported. Aperiod study of all available individual times of minimum light gives asmall or negligible variation of the period. Absolute dimensions werederived from recent measures of the lines of the fainter component. RSSgr appears to be a semidetached Algol-like system. Taken for grantedthat the period variation is real, RS Sgr is thought to be apostmass-exchange object probably in the slow phase of evolution.
| A Study of the DM and SD Type Eclipsing Variables by Means of the Cluster Analysis Technique
Not Available
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Наблюдательные данные и астрометрия
| Созвездие: | Единорог |
| Прямое восхождение: | 07h53m19.75s |
| Склонение: | -03°02'31.1" |
| Видимая звёздная величина: | 9.24 |
| Собственное движение RA: | -4.9 |
| Собственное движение Dec: | 3.5 |
| B-T magnitude: | 9.205 |
| V-T magnitude: | 9.238 |
Каталоги и обозначения:
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