Ýçindekiler
Görüntüler
Resim Yükleyin
DSS Images Other Images
Ýlgili Makaleler
Statistical Constraints for Astrometric Binaries with Nonlinear Motion
Useful constraints on the orbits and mass ratios of astrometric binariesin the Hipparcos catalog are derived from the measured proper motiondifferences of Hipparcos and Tycho-2 (Δμ), accelerations ofproper motions (μ˙), and second derivatives of proper motions(μ̈). It is shown how, in some cases, statistical bounds can beestimated for the masses of the secondary components. Two catalogs ofastrometric binaries are generated, one of binaries with significantproper motion differences and the other of binaries with significantaccelerations of their proper motions. Mathematical relations betweenthe astrometric observables Δμ, μ˙, and μ̈ andthe orbital elements are derived in the appendices. We find a remarkabledifference between the distribution of spectral types of stars withlarge accelerations but small proper motion differences and that ofstars with large proper motion differences but insignificantaccelerations. The spectral type distribution for the former sample ofbinaries is the same as the general distribution of all stars in theHipparcos catalog, whereas the latter sample is clearly dominated bysolar-type stars, with an obvious dearth of blue stars. We point outthat the latter set includes mostly binaries with long periods (longerthan about 6 yr).
| 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.
| Disentangling the composite continuum of symbiotic binaries. I. S-type systems
We describe a method of disentangling the composite, 0.12-5 μmcontinuum of symbiotic binaries. The observed SED is determined by theIUE/HST archival spectra and flux-points corresponding to the opticalUBVRI and infrared JHKLM photometric measurements. The modeled SED isgiven by superposition of fluxes from the cool giant, hot stellar sourceand nebula including the effect of the Rayleigh scattering process andconsidering influence of the iron curtain absorptions. We applied thismethod to 21 S-type symbiotic stars during quiescence, activity andeclipses. We isolated four main components of radiation and determinedtheir properties. (i) Stellar radiation from the giant corresponds to aunique luminosity class - normal giants. Characteristic luminosities are1600 ± 200 and 290 ± 30 Lȯ for red andyellow giants, respectively in our sample of objects. (ii) Hot objectradiation during quiescence consists of the nebular and stellarcomponent. The former radiates at a mean electron temperature of 19 000K and its amount of emission suggests a mass-loss rate from giants viathe wind at dot MW = a few × 10-7Mȯ yr-1. Radiation of the latter conformswell with that of a black-body photosphere at a characteristictemperature of 105 000 K. The corresponding effective radii are a factorof 10 larger than those of white dwarfs, which thus precludes observingthe accretor's surface. Extreme cases of AX Per and V443 Her, for whichthe hot star temperature from the fit is not capable of producing thenebular emission, signal a disk-like structure of the hot stellar sourceeven during quiescence. (iii) Hot object radiation during activityconsists of three components - the stellar and the low- andhigh-temperature nebular radiation. The stellar radiation satisfies thatof a black-body photosphere at a low characteristic temperature of 22000 K (we call it the 1st type of outbursts) or at a very highcharacteristic temperature of ≈165 000 K (2nd type of outbursts). Allthe active objects with a high orbital inclination show features of the1st-type of outbursts (here Z And, AE Ara, CD-43circ14304, TXCVn, BF Cyg, CH Cyg, CI Cyg, AR Pav, AX Per), while AG Dra representsthe 2nd-type. The presence of a two-temperature type of UV spectrum andan enlargement of effective radii of the stellar source by a factor of 10 with respect to the quiescent values during the 1st-type of outburstsuggest an expansion of an optically thick medium at the orbital planein the form of a disk. The low-temperature nebula radiates at a meanelectron temperature of 14 000 K and is subject to eclipses, while thehigh-temperature nebula, which is seen during eclipses as the onlycomponent, is characterized by Te > 30 000 K. Radiativeand geometric properties of the main sources of radiation allowed us toreconstruct a basic structure of the hot object during the 1st-type ofoutburst. There is an edge-on disk around the accretor. Its outer flaredrim represents a warm pseudophotosphere of the hot stellar source, whoseradiation is Rayleigh attenuated and affected by the iron curtainabsorptions in the neutral gas concentrated at the orbital plane. Thelow-temperature nebula is placed just above/below the disk with aconcentration at its edge as to be subject to eclipses and to“see” well the central ionizing source. High above/below theorbital plane, there is a hot nebular emitting region.
| Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data. Revisiting the concept of superclusters
The availability of the Hipparcos Catalogue has triggered many kinematicand dynamical studies of the solar neighbourhood. Nevertheless, thosestudies generally lacked the third component of the space velocities,i.e., the radial velocities. This work presents the kinematic analysisof 5952 K and 739 M giants in the solar neighbourhood which includes forthe first time radial velocity data from a large survey performed withthe CORAVEL spectrovelocimeter. It also uses proper motions from theTycho-2 catalogue, which are expected to be more accurate than theHipparcos ones. An important by-product of this study is the observedfraction of only 5.7% of spectroscopic binaries among M giants ascompared to 13.7% for K giants. After excluding the binaries for whichno center-of-mass velocity could be estimated, 5311 K and 719 M giantsremain in the final sample. The UV-plane constructed from these datafor the stars with precise parallaxes (σπ/π≤20%) reveals a rich small-scale structure, with several clumpscorresponding to the Hercules stream, the Sirius moving group, and theHyades and Pleiades superclusters. A maximum-likelihood method, based ona Bayesian approach, has been applied to the data, in order to make fulluse of all the available stars (not only those with precise parallaxes)and to derive the kinematic properties of these subgroups. Isochrones inthe Hertzsprung-Russell diagram reveal a very wide range of ages forstars belonging to these groups. These groups are most probably relatedto the dynamical perturbation by transient spiral waves (as recentlymodelled by De Simone et al. \cite{Simone2004}) rather than to clusterremnants. A possible explanation for the presence of younggroup/clusters in the same area of the UV-plane is that they have beenput there by the spiral wave associated with their formation, while thekinematics of the older stars of our sample has also been disturbed bythe same wave. The emerging picture is thus one of dynamical streamspervading the solar neighbourhood and travelling in the Galaxy withsimilar space velocities. The term dynamical stream is more appropriatethan the traditional term supercluster since it involves stars ofdifferent ages, not born at the same place nor at the same time. Theposition of those streams in the UV-plane is responsible for the vertexdeviation of 16.2o ± 5.6o for the wholesample. Our study suggests that the vertex deviation for youngerpopulations could have the same dynamical origin. The underlyingvelocity ellipsoid, extracted by the maximum-likelihood method afterremoval of the streams, is not centered on the value commonly acceptedfor the radial antisolar motion: it is centered on < U > =-2.78±1.07 km s-1. However, the full data set(including the various streams) does yield the usual value for theradial solar motion, when properly accounting for the biases inherent tothis kind of analysis (namely, < U > = -10.25±0.15 kms-1). This discrepancy clearly raises the essential questionof how to derive the solar motion in the presence of dynamicalperturbations altering the kinematics of the solar neighbourhood: doesthere exist in the solar neighbourhood a subset of stars having no netradial motion which can be used as a reference against which to measurethe solar motion?Based on observations performed at the Swiss 1m-telescope at OHP,France, and on data from the ESA Hipparcos astrometry satellite.Full Table \ref{taba1} is only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/430/165}
| The CHARA Catalog of Orbital Elements of Spectroscopic Binary Stars
Optical interferometry is entering a new age, with several ground-basedlong-baseline observatories now making observations of unprecedentedresolution. Interferometers bring a new level of resolution to bear onspectroscopic binaries, enabling the full extraction of the physicalparameters for the component stars with high accuracy. In the case ofdouble-lined systems, a geometrically determined orbital parallaxbecomes available as well. The first step in preparing to observespectroscopic binaries is to list them, which has not been done sincethe 1989 publication of the Eighth Catalogue of the Orbital Elements ofSpectroscopic Binaries by Batten et al. We present a new catalog withroughly half again as many listings as the Eighth Catalogue. Angularseparation predictions are made for each catalog entry. The numbers ofspectroscopic binaries available for study as a function of severalimportant observational parameters are explored, and in particular, thenumber of spectroscopic binaries as a function of expected separation isdiscussed.
| X-ray observations of 4 Draconis: symbiotic binary or cataclysmic triple?
We present the first X-ray observations of the 4 Draconis system,consisting of an M3 III giant with a hot ultraviolet companion. It hasbeen claimed that the companion is itself an AM Her-type binary system,an identification that places strong constraints on the evolution ofcataclysmic variables. We find that the X-ray properties of 4 Draconisare consistent with the presence of an accreting white dwarf, but notconsistent with the presence of an AM Her system. We conclude that 4Draconis is therefore most likely a symbiotic binary containing a whitedwarf accreting material from the wind of the red giant.The X-ray spectrum of 4 Draconis is sometimes dominated by partiallyionized photoelectric absorption, presumably due to the wind of the redgiant. We note that X-ray monitoring of such systems would provide apowerful probe of the wind and mass-loss rate of the giant, and wouldallow a detailed test of wind accretion models.
| Technetium and the third dredge up in AGB stars. I. Field stars
We searched for Tc in a sample of long period variables selected bystellar luminosity derived from Hipparcos parallaxes. Tc, as an unstables-process element, is a good indicator for the evolutionary status ofstars on the asymptotic giant branch (AGB). In this paper we study theoccurrence of Tc as a function of luminosity to provide constraints onthe minimum luminosity for the third dredge up as estimated from recentstellar evolution models.A large number of AGB stars above the estimated theoretical limit forthe third dredge up are found not to show Tc. We confirm previousfindings that only a small fraction of the semiregular variables show Tclines in their spectra. Contrary to earlier results by Little et al.(\cite{llmb87}) we find also a significant number of Miras without Tc.The presence and absence of Tc is discussed in relation to the massdistribution of AGB stars. We find that a large fraction of the stars ofour sample must have current masses of less than 1.5 Msun .Combining our findings with stellar evolution scenarios we conclude thatthe fraction of time a star is observed as a SRV or a Mira is dependenton its mass.Partly based on observations collected at the European SouthernObservatory, Paranal, Chile (ESO-Programme 65.L-0317(A)).
| Hipparcos red stars in the HpV_T2 and V I_C systems
For Hipparcos M, S, and C spectral type stars, we provide calibratedinstantaneous (epoch) Cousins V - I color indices using newly derivedHpV_T2 photometry. Three new sets of ground-based Cousins V I data havebeen obtained for more than 170 carbon and red M giants. These datasetsin combination with the published sources of V I photometry served toobtain the calibration curves linking Hipparcos/Tycho Hp-V_T2 with theCousins V - I index. In total, 321 carbon stars and 4464 M- and S-typestars have new V - I indices. The standard error of the mean V - I isabout 0.1 mag or better down to Hp~9 although it deteriorates rapidly atfainter magnitudes. These V - I indices can be used to verify thepublished Hipparcos V - I color indices. Thus, we have identified ahandful of new cases where, instead of the real target, a random fieldstar has been observed. A considerable fraction of the DMSA/C and DMSA/Vsolutions for red stars appear not to be warranted. Most likely suchspurious solutions may originate from usage of a heavily biased color inthe astrometric processing.Based on observations from the Hipparcos astrometric satellite operatedby the European Space Agency (ESA 1997).}\fnmsep\thanks{Table 7 is onlyavailable 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/qcat?J/A+A/397/997
| Do red giant stars pulsate in high overtones?
About 30 photometrically variable red giant stars have periods less than10d, as determined by the compilers of the Hipparcos Catalogue fromHipparcos photometric measurements. These periods, when combined withestimates of the radii and masses of these stars, and with pulsationtheory, imply that these stars are pulsating in very high overtones. Wepresent several pieces of evidence which suggest that the periods may bespurious, as a result of the particular aliasing properties of theHipparcos photometry. We conclude that the evidence for high-overtonepulsation in red giant stars is equivocal.
| New periodic variables from the Hipparcos epoch photometry
Two selection statistics are used to extract new candidate periodicvariables from the epoch photometry of the Hipparcos catalogue. Theprimary selection criterion is a signal-to-noise ratio. The dependenceof this statistic on the number of observations is calibrated usingabout 30000 randomly permuted Hipparcos data sets. A significance levelof 0.1 per cent is used to extract a first batch of candidate variables.The second criterion requires that the optimal frequency be unaffectedif the data are de-trended by low-order polynomials. We find 2675 newcandidate periodic variables, of which the majority (2082) are from theHipparcos`unsolved' variables. Potential problems with theinterpretation of the data (e.g. aliasing) are discussed.
| Infrared Properties of Cataclysmic Variables in the 2 Micron All-Sky Survey Second Incremental Data Release
Cataclysmic variables (CVs) have ``traditionally'' been observedprimarily at short wavelengths because accretion-generated luminosity,which peaks in the optical-ultraviolet, dominates the radiated energy ofmost systems. Hence, relatively little is known about their infrared(IR) properties. Investigating CVs in the IR will contribute to theunderstanding of key system components that are expected to radiate atthese wavelengths, such as the cool outer disk, accretion stream, andsecondary star. We have compiled the near-IR J, H, and Ksband photometry of all cataclysmic variables contained in the skycoverage of the Second Incremental Data Release of the 2 Micron All SkySurvey (2MASS). This data comprises 251 cataclysmic variables withreliably identified near-IR counterparts and S/N>10 photometry in oneor more of the three near-IR bands. In addition to tables containing the2MASS data, we present a set of near-IR finding charts for selectedsystems. A comparison between the 2MASS photometry and variousliterature sources of near-IR photometry of cataclysmic variables showsgood agreement after allowing for differences in photometric systems andthe intrinsic variability of cataclysmic variables. The bulk of ouranalysis consists of an exploration of near-IR color-color diagrams ofthe main cataclysmic variable classes. Results from this analysisinclude: (1) dwarf novae in outburst and quiescence occupy distinctregions of their color-color diagram; (2) nova-like CVs (and dwarf novaein outburst) have colors similar to F-K main-sequence stars, althoughthis does not imply that they have F-K type secondary stars; (3) polarsand intermediate polars also occupy distinct regions in theircolor-color diagram, with most polars having colors essentiallyindistinguishable from late (M0+) main-sequence stars; (4) there is nostrong correlation between age and color for novae, except that many oldnovae (>75 yr since outburst) have colors similar to F-K main-sequencestars; and (5) there are unusual and unexplained loci of data points inall the color-color diagrams that warrant further investigation in theIR. Except in the case of the polars, near-IR photometry of cataclysmicvariables does not isolate the luminosity contribution of theirsecondary stars. In general, the near-IR colors of cataclysmic variablesare significantly and systematically offset blueward of the spectraltype of secondary star expected at their orbital periods. This bluecontamination of the near-IR light almost certainly originates from theaccretion process. For a few systems, their near-IR color is redder thanthe secondary star expected at their orbital period. One effect that canexplain some, but not all, of the red-excess cataclysmic variables isthe presence of an evolved secondary star. We suggest that this can alsobe caused by the luminosity contribution of the cool outer regions ofprominent accretion disks. There is at least a weak trend of reddercolor in higher inclination systems (in which the disk rim would be mostvisible and most obscure the hot inner region) that supports thishypothesis.
| Velocity Observations of Multiple-Mode Asymptotic Giant Branch Variable Stars
Numerous infrared spectroscopic observations were obtained of nineasymptotic giant branch (AGB) field M giants that have multiple periodsof light variability. Each star has a short period of several months,which is typical of low amplitude pulsation for stars on the AGB, aswell as a long period of 1-3 yr, which is significantly longer than thepredicted fundamental-mode pulsations for these stars. The location ofthese stars in the AGB period-luminosity relation is discussed. For sixof the nine giants we found radial-velocity periods that confirm thelong-period light variability. Although we considered the possibilitythat the velocity variations result from orbital motion, we concludethat the long-period velocity changes in most, if not all of the samplestars, likely result from a currently unknown type of pulsation ratherthan duplicity.
| A Catalog and Atlas of Cataclysmic Variables: The Living Edition
The Catalog and Atlas of Cataclysmic Variables (Edition 1: Downes &Shara; Edition 2: Downes, Webbink, & Shara) has been a valuablesource of information for the cataclysmic variable community. However,the goal of having a central location for all objects is slowly beinglost as each new edition is generated. There can also be a long timedelay between new information becoming available on an object and itspublication in the catalog. To eliminate these concerns, as well as tomake the catalog more accessible, we have created a Web site which willcontain a ``living'' edition of the catalog. We have also added orbitalperiod information, as well as finding charts for novae, to thecatalog.
| Long period variable stars: galactic populations and infrared luminosity calibrations
In this paper HIPPARCOS astrometric and kinematic data are used tocalibrate both infrared luminosities and kinematical parameters of LongPeriod Variable stars (LPVs). Individual absolute K and IRAS 12 and 25luminosities of 800 LPVs are determined and made available in electronicform. The estimated mean kinematics is analyzed in terms of galacticpopulations. LPVs are found to belong to galactic populations rangingfrom the thin disk to the extended disk. An age range and a lower limitof the initial mass is given for stars of each population. A differenceof 1.3 mag in K for the upper limit of the Asymptotic Giant Branch isfound between the disk and old disk galactic populations, confirming itsdependence on the mass in the main sequence. LPVs with a thin envelopeare distinguished using the estimated mean IRAS luminosities. The levelof attraction (in the classification sense) of each group for the usualclassifying parameters of LPVs (variability and spectral types) isexamined. Table only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/374/968 or via ASTRIDdatabase (http://astrid.graal.univ-montp2.fr).
| Dynamical Stability of Triple Stars
The dynamical stability of 38 observed hierarchical triple stars withknown orbital elements of the internal and external binary subsystemsand component masses is considered. Four different criteria of dynamicalstability are used. The observed stability parameters and their criticalvalues are calculated by taking into account errors in the orbitalelements and component masses. Most triple systems are stable. Accordingto some criteria, several triple stars (ADS440, xi Tau, lambda Tau,ADS3358, VV Ori, ADS10157, HZ Her, Gliese 795, ADS15971, and ADS16138)may be dynamically unstable. This result is probably associated withunreliability of the empirical stability criteria and/or with errors inthe observed quantities.
| Cataclysmic variables as sources of gravitational waves
General relativity predicts that binary systems of stars producegravitational waves of significant intensity. Here we are particularlyinterested in the cataclysmic variable binaries (CVs). These systemsemit low frequency gravitational waves, f < 10-3 Hz. Wepresent here a catalog of CVs and argue that part of them are capable ofbeing detected by the Laser Interferometer Space Antenna (LISA).
| Characterization of variable stars by robust wave variograms: an application to HIPPARCOS mission
Variogram analysis is applied to time series of variable stars. Thismethod allows to characterize time-scales of varying signals. It is wellsuited for periodic and pseudo-periodic signals. The aspects ofrobustness, bin positions and bin widths for the variogram estimator areassessed, evaluated with the help of simulations and adapted to theHipparcos photometry. For instance variogram methodology is successfullyapplied for the detection of spurious periods, the estimation ofmeasurement noise and the analysis of the pseudo-period of some typicalHipparcos variable stars.
| JHK photometry of symbiotic stars
We present the results of multi-epoch JHK photometry of a sample of 30known or suspected symbiotics and related objects. These are the firstresults of an ongoing programme of near-IR monitoring of symbiotic starsfrom the Mt. Abu IR Observatory of Physical Research Laboratory (PRL).
| Stellar radii of M giants
We determine the stellar radii of the M giant stars in the Hipparcoscatalogue that have a parallax measured to better than 20% accuracy.This is done with the help of a relation between a visual surfacebrightness parameter and the Cousins (V - I) colour index, which wecalibrate with M giants with published angular diameters.The radii of(non-Mira) M giants increase from a median value of 50 R_Sun at spectraltype M0 III to 170 R_Sun at M7/8 III. Typical intermediate giant radiiare 65 R_Sun for M1/M2, 90 R_Sun for M3, 100 R_Sun for M4, 120 R_Sun forM5 and 150 R_Sun for M6. There is a large intrinsic spread for a givenspectral type. This variance in stellar radius increases with latertypes but in relative terms, it remains constant.We determineluminosities and, from evolutionary tracks, stellar masses for oursample stars. The M giants in the solar neighbourhood have masses in therange 0.8-4 M_Sun. For a given spectral type, there is a close relationbetween stellar radius and stellar mass. We also find a linear relationbetween the mass and radius of non-variable M giants. With increasingamplitude of variability we have larger stellar radii for a given mass.
| The Infrared Spectral Classification of Oxygen-rich Dust Shells
This paper presents infrared spectral classifications for a flux-limitedsample of 635 optically identified oxygen-rich variables includingsupergiants and sources on the asymptotic giant branch (AGB). Severalclasses of spectra from oxygen-rich dust exist, and these can bearranged in a smoothly varying sequence of spectral shapes known as thesilicate dust sequence. Classification based on this sequence revealsseveral dependencies of the dust emission on the properties of thecentral star. Nearly all S stars show broad emission features fromalumina dust, while most of the supergiants exhibit classic featuresfrom amorphous silicate dust. Mira variables with symmetric light curvesgenerally show broad alumina emission, while those with more asymmetriclight curves show classic silicate emission. These differences may arisefrom differences in the photospheric C/O ratio.
| Catalogue of cataclysmic binaries, low-mass X-ray binaries and related objects (Sixth edition)
The catalogue lists coordinates, apparent magnitudes, orbitalparameters, stellar parameters of the components and other characteristcproperties of 318 cataclysmic binaries, 47 low-mass X-ray binaries and49 related objects with known or suspected orbital periods together witha comprehensive selection of the relevant recent literature. In additionthe catalogue contains a list of references to published finding chartsfor 394 of the 414 objects. A cross-reference list of alias objectdesignations concludes the catalogue. Literature published before 30June 1997 has, as far as possible, been taken into account. Thecatalogue is available in electronic form only via the CDS at ftp130.79.128.5 or http://cdsweb.u-strasbg.fr/Abstract.html
| The ROSAT all-sky survey catalogue of optically bright late-type giants and supergiants
We present X-ray data for all late-type (A, F, G, K, M) giants andsupergiants (luminosity classes I to III-IV) listed in the Bright StarCatalogue that have been detected in the ROSAT all-sky survey.Altogether, our catalogue contains 450 entries of X-ray emitting evolvedlate-type stars, which corresponds to an average detection rate of about11.7 percent. The selection of the sample stars, the data analysis, thecriteria for an accepted match between star and X-ray source, and thedetermination of X-ray fluxes are described. Catalogue only available atCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| On the X-ray emission from M-type giants
We have searched for X-ray emission from M-type giants and supergiantslisted in the Bright Star Catalogue (BSC) in the data of the ROSATall-sky survey (RASS). These stars lie to the far right of the X-raydividing line and are thus not expected to be X-ray sources. Any X-raydetection would therefore violate the common paradigm of X-ray darkM-type giants beyond the X-ray dividing line. We found 11 BSC M-typegiants and supergiants to coincide with RASS X-ray sources. While for 4stars the X-ray emission is very likely related to their cataclysmic orsymbiotic nature or can be attributed to a visual G-type companion, theother 7 stars are candidates for intrinsic X-ray emission. Of theseobjects, 3 have a rather large offset between optical and X-rayposition, so their proper identification with late-type giants is atleast questionable. For the remaining four stars, we obtained opticallow-dispersion spectra in order to search for emission lines indicativeof a possible symbiotic nature. None of these stars shows any brightemission lines, so they are probably quite normal M-type giants. Wediscuss possible origins of X-ray emission in these stars and theimportance of evolutionary aspects. Based on observations by the ROSATand Calar Alto Observatories
| A Catalog and Atlas of Cataclysmic Variables-Second Edition
We present a catalog of all 1020 known cataclysmic variables (CVs). Thispaper is a major update of the first edition of the catalog (Downes andShara 1993, PASP, 105, 127), which contained coordinates (measured inthe reference frame of the Hubble Space Telescope Guide Star Survey forthe non-novae, and obtained from the literature for the novae), thevariability type, the magnitude range, and references to both findingcharts and spectroscopy. Also included in the catalog were findingcharts for all dwarf novae, novalike variables, and objects classifiedonly as cataclysmic variables known as of 1993; a similar catalog andatlas for novae has been published by Duerbeck (1978a). This updatededition includes 195 new objects (172 CVs and 23 non-CVs), revisedidentifications for 57 objects, and revised information (classificationand spectral references) when available. We also now include plateidentification information for the coordinate measurements, a referenceto the classification, proper motion information where appropriate, anda table showing the CVs observed by space-based observatories. Thissecond edition is inclusive of the first edition, although only new orupdated charts are presented. (SECTION: Special Issue on CataclysmicVariable Stars)
| Classification and Identification of IRAS Sources with Low-Resolution Spectra
IRAS low-resolution spectra were extracted for 11,224 IRAS sources.These spectra were classified into astrophysical classes, based on thepresence of emission and absorption features and on the shape of thecontinuum. Counterparts of these IRAS sources in existing optical andinfrared catalogs are identified, and their optical spectral types arelisted if they are known. The correlations between thephotospheric/optical and circumstellar/infrared classification arediscussed.
| CA II K Emission Line Asymmetries Among Red Giants
In the spectra of red giants the chromospheric emission feature found inthe core of the Ca II K line often exhibits an asymmetric profile. Thisasymmetry can be documented by a parameter V/R which is classified as> 1, 1, or < 1 if the violet wing of the emission profile is ofgreater, equal, or lower intensity than the redward wing. A literaturesearch has been conducted to compile a V/R dataset which builds on thelarge survey of bright field giants made by Wilson (1976). Among starsof luminosity classes II-III-IV the majority of those with V/R > 1are found to be bluer than B-V =1.3, while those with V/R < 1 aremostly redder than this colour. Stars with nearly symmetric profiles,V/R≈ 1, are found throughout the colour range 0.8 < B-V < 1.5.There is no sharp transition line separating stars of V/R > 1 and< 1 in the colour-magnitude diagram, but rather a `transition zone'centered at B-V ≈ 1.3. The center of this zone coincides closely witha `coronal dividing line' identified by Haish, Schmitt and Rosso (1991)as the red envelope in the H-R diagram of giants detected in soft x-rayemission by ROSAT. It is suggested that both the transition to a Ca II Kemission asymmetry of V/R < 1 and the drop in soft x-ray activityacross the coronal dividing line are related to changes in the dynamicalstate of the chromospheres of red giants. By contrast, the onset ofphotometric variability due to pulsation occurs among stars of early-Mspectral type, that are redward of the mid-point of the Ca II V/R`transition zone', suggesting that the chromospheric motions whichproduce an asymmetry of V/R < 1 are established prior to the onset ofpulsation.
| MSC - a catalogue of physical multiple stars
The MSC catalogue contains data on 612 physical multiple stars ofmultiplicity 3 to 7 which are hierarchical with few exceptions. Orbitalperiods, angular separations and mass ratios are estimated for eachsub-system. Orbital elements are given when available. The catalogue canbe accessed through CDS (Strasbourg). Half of the systems are within 100pc from the Sun. The comparison of the periods of close and widesub-systems reveals that there is no preferred period ratio and allpossible combinations of periods are found. The distribution of thelogarithms of short periods is bimodal, probably due to observationalselection. In 82\% of triple stars the close sub-system is related tothe primary of a wide pair. However, the analysis of mass ratiodistribution gives some support to the idea that component masses areindependently selected from the Salpeter mass function. Orbits of wideand close sub-systems are not always coplanar, although thecorresponding orbital angular momentum vectors do show a weak tendencyof alignment. Some observational programs based on the MSC aresuggested. Tables 2 and 3 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| X-ray sources <1 degree from Seyfert galaxies.
Archived PSPC observations of 26 Seyfert galaxies have been analyzed forbright X-ray sources out to the full extent of the field (< about50'). Of all Seyferts known this represents a sample 88% complete toB_T_=10mag, 74% complete to 11mag and 50% complete to 12mag. Using thesame reduction algorithm, 14 fields centered on stars at high galacticlatitudes have been used as control fields. Excluding the two brightestSeyferts, a subset of 24 Seyferts with corrected apparent magnitudebetween 8.04
| ROSAT Observations of Symbiotic Binaries and Related Objects
Not Available
| Photometry of Symbiotic Stars: an International Campaign 7b. CQ DRA (4Dra), YY Her, V 443 Her, BX Mon, AG Peg, AX Per, V 741 Per, FGG Sge, QW Sge, PU VUL
We present new observations of 10 symbiotic and symbiotic-like stars.The photoelectric UBV(R) observations cover the period 1994.75 to1996.0. The CCD VRI, photographic and visual data also cover earliertimes. The main results can be summarized as follows: (1) CQ Dra: Theexpected sudden brightening in the U color has been observed around JD 2449 700. After then, the star's brightness declined smoothly in allthree colors. (2) YY Her: The steady decline of the star's brightness inthe V and R colors has been observed. (3) V443 Her: Variability with anamplitude of about 0.4 mag in the V color has been detected, whilenothing similar has been found in the R and I. (4) AX Per: Our presentdata cover in part the primary minimum of the star. During the autumn of1995, a small increase in all three colors has been observed. (5) PUVul: A brightness minimum at JD 2 449 953, best pronounced in the Vcolor, has been observed.
|
Yeni bir Makale Öner
Ýlgili Baðlantýlar
Yeni Bir Baðlantý Öner
sonraki gruplarýn üyesi:
|
Gözlemler ve gökölçümü verileri
| Takýmyýldýz: | Ejderha |
| Sað Açýklýk: | 12h30m06.70s |
| Yükselim: | +69°12'04.0" |
| Görünürdeki Parlaklýk: | 4.95 |
| Uzaklýk: | 178.253 parsek |
| özdevim Sað Açýklýk: | -60.3 |
| özdevim Yükselim: | -54.2 |
| B-T magnitude: | 7.084 |
| V-T magnitude: | 5.203 |
Kataloglar ve belirtme:
|
INHABITED SKY
