Home     Getting Started     To Survive in the Universe    
Inhabited Sky
    News@Sky     Astro Photo     The Collection     Forum     Blog New!     FAQ     Press     Login  

α Equ (Kitalpha)



Upload your image

DSS Images   Other Images

Related articles

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).

Orientations of Orbital Planes of Binaries
Orientations of orbital planes of binaries are analysed by using acomplete sample of known orbital systems. The use of a so large sampleis possible due to the application of a new procedure enabling toinclude the binaries for which the ascending nodes do not certain. It isconcluded that, generally, the distribution of observed orientations ofthe orbital planes does not differ from simulated random orientations.In both cases the same star positions are retained.

Composite spectra Paper 13: 93 Leonis, a chromospherically-active binary
We isolate the spectrum of the secondary component of thecomposite-binary system 93 Leonis by spectrum subtraction, classify it,and measure the mass ratio of the system. An accurate visual orbit and awell-determined parallax provide reliable measurements of orbitalinclination and distance, enabling us to determine precisely theindividual masses and other stellar parameters. The primary star is oftype ~G7 III, and the secondary is a rapidly rotating star of type A7IV. Our photographic spectra at 10 Å mm-1 areinvaluable for accurate spectral classification in such cases.By combining 23 measurements of the secondary's velocity with 102 of theprimary's and deriving a double-lined orbit, we determine the mass ratio(q=M1/M2) of 93 Leo to be 1.09 +/- 0.04. The samevalue is derived by cross-correlating high-dispersion spectra of 93 LeoB extracted from opposite nodal phases. That value of q is consonantwith previous research, but its precision is considerably improved. Weshow that random errors arising from the cross-correlation of broad,weak features constitute a natural limit to that precision.The derived masses of M1= 2.2 Msolar,M2= 2.0 Msolar for the giant and dwarf,respectively, constrain the choice of models for fitting evolutionarytracks in the (logTeff, logL) plane. The giant is almostcertainly on its first ascent of the red giant branch, and the dwarf hasevolved significantly from the main sequence. The stars fit an isochronefor log(age) = 8.95, about 0.9 Gyr. Metallicity near to solar issuggested by the close correspondence between the component spectra andthose of the respective solar-abundance standards.The primary in 93 Leo displays a marked level of chromospheric activity.By combining our high-dispersion spectra we are able to isolate emissionin the Ca II K line. The chromospheric material has a small infallvelocity, giving rise to a disc-averaged redshift of about 4 kms-1, and an unchanging velocity profile which can beattributed to a large number of small, active events like prominencesacross the surface. While we can say that there was no perceptiblechange in the emission strength over an interval of 4 months, we havenot made systematic observations to monitor its long-term stability.We contrast the components of 93 Leo with those of α Equ, whoseanalysis was the subject of Paper 11 in this series. The primarycomponents are very similar, but the two secondary components areextremely different in nature: whereas 93 Leo B is a broad-lined,apparently normal A star, the secondary of α Equ is a sharp-linedAm star of type ~kA3hA4mA9. We question why that should be, andrecommend that a greater emphasis be placed on extracting accuratestellar parameters from the components of spectroscopic binaries as ameans towards a better understanding of the vagaries of stellarevolution.93 Leo has a 9-mag visual companion which appears to be a physicalmember of the system and to be a single-lined spectroscopic binary witha period of the order of a century.

Search for Nanosecond Optical Pulses from Nearby Solar-Type Stars
With ``Earth 2000'' technology we could generate a directed laser pulsethat outshines the broadband visible light of the Sun by 4 orders ofmagnitude. This is a conservative lower bound for the technicalcapability of a communicating civilization; optical interstellarcommunication is thus technically plausible. We have built a pair ofsystems to detect nanosecond pulsed optical signals from a target listthat includes some 13,000 Sun-like stars, and we have made some 16,000observations totaling nearly 2400 hr during five years of operation. Abeam splitter-fed pair of hybrid avalanche photodetectors at the 1.5 mWyeth Telescope at the Harvard/Smithsonian Oak Ridge Observatory(Agassiz Station) triggers on a coincident pulse pair, initiatingmeasurement of pulse width and intensity at subnanosecond resolution. Anidentical system at the 0.9 m Cassegrain at Princeton's Fitz-RandolphObservatory performs synchronized observations with 0.1 μs eventtiming, permitting unambiguous identification of even a solitary pulse.Among the 11,600 artifact-free observations at Harvard, the distributionof 274 observed events shows no pattern of repetition, and is consistentwith a model with uniform event rate, independent of target. With onepossible exception (HIP 107395), no valid event has been seensimultaneously at the two observatories. We describe the search andcandidate events and set limits on the prevalence of civilizationstransmitting intense optical pulses.

Astrophysics in 2002
This has been the Year of the Baryon. Some low temperature ones wereseen at high redshift, some high temperature ones were seen at lowredshift, and some cooling ones were (probably) reheated. Astronomerssaw the back of the Sun (which is also made of baryons), a possiblesolution to the problem of ejection of material by Type II supernovae(in which neutrinos push out baryons), the production of R CoronaeBorealis stars (previously-owned baryons), and perhaps found the missingsatellite galaxies (whose failing is that they have no baryons). A fewquestions were left unanswered for next year, and an attempt is made todiscuss these as well.

Observational constraints for lithium depletion before the RGB
Precise Li abundances are determined for 54 giant stars mostly evolvingacross the Hertzsprung gap. We combine these data with rotationalvelocity and with information related to the deepening of the convectivezone of the stars to analyse their link to Li dilution in the referredspectral region. A sudden decline in Li abundance paralleling the onealready established in rotation is quite clear. Following similarresults for other stellar luminosity classes and spectral regions, thereis no linear relation between Li abundance and rotation, in spite of thefact that most of the fast rotators present high Li content. The effectsof convection in driving the Li dilution is also quite clear. Stars withhigh Li content are mostly those with an undeveloped convective zone,whereas stars with a developed convective zone present clear sign of Lidilution.Based on observations collected at ESO, La Silla, Chile, and at theObservatoire de Haute Provence, France, operated by the Centre Nationalde la Recherche Scientifique (CNRS).

Reprocessing the Hipparcos Intermediate Astrometric Data of spectroscopic binaries. II. Systems with a giant component
By reanalyzing the Hipparcos Intermediate Astrometric Data of a largesample of spectroscopic binaries containing a giant, we obtain a sampleof 29 systems fulfilling a carefully derived set of constraints andhence for which we can derive an accurate orbital solution. Of these,one is a double-lined spectroscopic binary and six were not listed inthe DMSA/O section of the catalogue. Using our solutions, we derive themasses of the components in these systems and statistically analyzethem. We also briefly discuss each system individually.Based on observations from the Hipparcos astrometric satellite operatedby the European Space Agency (ESA 1997) and on data collected with theSimbad database.

Composite spectra Paper 11: α Equulei, an astrometric binary with an Am secondary
The spectrum of the secondary component of the bright composite-binarysystem α Equ, whose visual orbit is already known accurately, isisolated by the method of spectrum subtraction and classified accuratelyfor the first time. The primary is a normal giant of type ~G7, while thesecondary is an Am star of type ~kA3hA4mA9. The system's mass ratio, q ,is determined to be from measurements of the relative radial-velocitydisplacements between the components. Random and systematic errors in qare evaluated on the basis of the scatter of results derived from setsof spectra obtained from three different sources, and from testsconducted on independent versions of the secondary's spectrum. Aspectroscopic analysis of a composite system such as α Equ isstrongly challenged by the blending of a great many lines that arecommon to both spectra. Even when the primary spectrum is thought tohave been subtracted adequately, a seemingly unavoidable ghost spectrumof faint residuals can bias wavelength measurements of the secondary'slines. That blending was the principal cause of a history of puzzlingand discrepant measurements of q in α Equ. The derived masses of ,for the giant and dwarf, respectively, constrain the choice of modelsfor fitting evolutionary tracks in the (logT eff , logL )plane; the stellar points fit a single isochrone (for 0.74Gyr). Bothcomponents are found to be slightly over-luminous compared to normal fortheir supposed luminosity classes. The giant appears to be commencingits first ascent of the red-giant branch. The dwarf has started toevolve away from the main sequence; its M V is similar tothat of a sub-giant.

Spectral Classification of the Hot Components of a Large Sample of Stars with Composite Spectra, and Implication for the Absolute Magnitudes of the Cool Supergiant Components.
A sample of 135 stars with composite spectra has been observed in thenear-UV spectral region with the Aurélie spectrograph at theObservatoire de Haute-Provence. Using the spectral classifications ofthe cool components previously determined with near infrared spectra, weobtained reliable spectral types of the hot components of the samplesystems. The hot components were isolated by the subtraction methodusing MK standards as surrogates of the cool components. We also derivedthe visual magnitude differences between the components usingWillstrop's normalized stellar flux ratios. We propose a photometricmodel for each of these systems on the basis of our spectroscopic dataand the Hipparcos data. We bring to light a discrepancy for the Gsupergiant primaries between the visual absolute magnitudes deduced fromHipparcos parallaxes and those tabulated by Schmidt-Kaler for the GIbstars: we propose a scale of Mv-values for these stars incomposite systems. By way of statistics, about 75% of the hot componentsare dwarf or subgiant stars, and 25% should be giants. The distributionin spectral types is as follows: 41% of B-type components, 57% of typeA, and 2% of type F; 68% of the hot components have a spectral type inthe range B7 to A2. The distribution of the ΔMv-valuesshows a maximum near 0.75 mag.

The Rate of Visual Binaries among the Brightest X-Ray Stars
Using the Tycho Double Star Catalogue and the Hipparcos Catalogue, Icompare the rates of occurrence of resolved visual doubles among thebrightest X-ray stars from the ROSAT All-Sky Survey Bright SourceCatalog (RASS-BSC) and generally in these two catalogs. A strongcorrelation between visual binarity and brightness in X-rays is found.The rate of binarity, quantified as the fraction of resolved components,is 7 times higher for the RASS-BSC stars than generally for all Tycho-2stars. In order to eliminate the distance bias in the sample, I comparethe rates in a distance-limited sample of Hipparcos stars within 50 pc.The comparison has shown that the fraction of visual and unresolvedorbiting binaries among stars with counterparts in the RASS-BSC, hencebright in X-rays, is 2.4 times higher than among fainter X-ray stars,i.e., the ones whose X-ray brightness is below the limit of theRASS-BSC. This difference is not caused by the enhancement of theobserved flux due to the combined component's radiation. Previouslyfound in the nearby open clusters, the correlation between binarity andX-ray luminosity exists for nearby field stars as well. Possibleimplications of the discrepancy are discussed, including thebinarity-age and binarity-rotation velocity relations. The H-R diagramof components of nearby visual binaries indicates that the red clumpgiants luminous in X-rays may be unresolved binaries.

Composite Spectra. XII. μ Leonis: An Evolving Am Binary
It is shown by techniques of spectrum disentangling that both componentsof the composite-spectrum binary ο Leo (V=3.52 mag) have Amcharacteristics, even though the primary is an evolving giant(logg=3.25) with Teff~6100 K. This is believed to be thefirst isolation of such a cool Am star, and the finding challenges thetheories of diffusion, which are widely accepted as the cause ofmetallicism. The primary component of ο Leo appears to bedeficient in Ca and Sc, as are classical Am stars-though the δ Delstars which are described as evolved Am stars are not-and thereforeseems to be in a class on its own. It is suggested that the unusualstate of the primary component is attributable either to its currentstate of rapid evolution or to regular Am-star evolution that isdifficult to recognize spectroscopically. This paper describes thetechnical problems that have hitherto prevented the identification ofsuch unexpected properties in this easily observed binary, determinesthe physical parameters of the component stars, examines theirevolutionary states, and debates the possible classification of thegiant component. Future directions for this work will include detailedchemical composition analyses and an observing program designed tosearch for other cases of substantially evolved Am stars.

The tidal effects on the lithium abundance of binary systems with giant component
We analyse the behavior of lithium abundance as a function of effectivetemperature, projected rotational velocity, orbital period andeccentricity for a sample of 68 binary systems with giant component andorbital period ranging from about 10 to 6400 days. For these binarysystems the Li abundances show a gradual decrease with temperature,paralleling the well established result for single giants. We have alsoobserved a dependence of lithium content on rotation. Binary systemswith moderate to high rotation present also moderate to high Li content.This study shows also that synchronized binary systems with giantcomponent seem to retain more of their original lithium than theunsynchronized systems. For orbital periods lower than 100 to 250 days,typically the period of synchronization for this kind of binary systems,lithium depleted stars seems to be unusual. The suggestion is made thatthere is an ``inhibited zone" in which synchronized binary systems withgiant component having lithium abundance lower than a threshold levelshould be unusual. Based on observations collected at ESO, La Silla.

Optical Interferometry
The field of optical and infrared (IR) interferometry has seen rapidtechnical and scientific progress over the past few years. A number ofinstruments capable of precise visibility measurements have been built,and closure-phase imaging with multitelescope arrays has beendemonstrated. Astronomical results from these instruments includemeasurements of stellar diameters and their wavelength dependence, limbdarkening, stellar surface structure, and distances of Cepheids and ofNova Cygni 1992. Precise stellar masses have been obtained frominterferometric observations of spectroscopic binaries, andcircumstellar disks and shells have been resolved. Searches forsubstellar companions and extrasolar planets with interferometricastrometry will begin soon. Nulling interferometry will enable studiesof exozodiacal disks from the ground and the detection andcharacterization of terrestrial extrasolar planets from space. Thesedevelopments are reviewed, as well as progress in some key technologicalareas.

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 ( or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521

The proper motions of fundamental stars. I. 1535 stars from the Basic FK5
A direct combination of the positions given in the HIPPARCOS cataloguewith astrometric ground-based catalogues having epochs later than 1939allows us to obtain new proper motions for the 1535 stars of the BasicFK5. The results are presented as the catalogue Proper Motions ofFundamental Stars (PMFS), Part I. The median precision of the propermotions is 0.5 mas/year for mu alpha cos delta and 0.7mas/year for mu delta . The non-linear motions of thephotocentres of a few hundred astrometric binaries are separated intotheir linear and elliptic motions. Since the PMFS proper motions do notinclude the information given by the proper motions from othercatalogues (HIPPARCOS, FK5, FK6, etc.) this catalogue can be used as anindependent source of the proper motions of the fundamental stars.Catalogue (Table 3) is only available at the CDS via anonymous ftp tocdsarc.u-strasbg.fr ( or viahttp://cdsweb.u-strastg.fr/cgi-bin/qcat?J/A+A/365/222

CaII K Emission-Line Asymmetry among Red Giants Detected by the ROSAT Satellite
Spectra of the Ca II H and K lines are reported for a number of fieldgiants from which soft X-ray emission was detected by the ROSATsatellite. Several of these stars are RS CVn systems and exhibit verystrong Ca II emission. The majority of the noninteracting giants in thesample have MV>-2.0, as determined from Hipparcosparallaxes, and spectral types earlier than K3. The Ca II Kemission-line profile for these stars is most often double-peaked andasymmetric, with the short-wavelength peak being stronger than thelongward peak. This asymmetry is in the same sense as for the integrateddisk of the Sun. The X-ray and Ca II K-line data indicate that giants ofspectral types G and early K have coronae and chromospheres seeminglyanalogous to those of the Sun. Four M giants that were detected by ROSATwere also observed. Their Ca II emission spectra show asymmetries inwhich the violet wing is weaker than the red wing, a phenomenon that istypical of M giants in general and indicative of mass outflows in theirchromospheres. The majority of these M giants, but not all, are known tobe in binary systems, so it is possible that the X-ray emission for atleast some of them may come from a companion. Alternatively, some or allof these M giants may be examples of hybrid stars.

Spectral Classification of Unresolved Binary Stars with Artificial Neural Networks
An artificial neural network technique has been developed to performtwo-dimensional spectral classification of the components of binarystars. The spectra are based on the 15 Å resolution near-infrared(NIR) spectral classification system described by Torres-Dodgen &Weaver. Using the spectrum with no manual intervention except wavelengthregistration, a single artificial neural network (ANN) can classifythese spectra with Morgan-Keenan types with an average accuracy of about2.5 types (subclasses) in temperature and about 0.45 classes inluminosity for up to 3 mag of difference in luminosity. The error intemperature classification does not increase substantially until thesecondary contributes less than 10% of the light of the system. Byfollowing the coarse-classification ANN with a specialist ANN, the meanabsolute errors are reduced to about 0.5 types in temperature and 0.33classes in luminosity. The resulting ANN network was applied to sevenbinary stars.

Resolved double-lined spectroscopic binaries: A neglected source of hypothesis-free parallaxes and stellar masses
Double-lined spectroscopic binaries, once visually resolved (VB-SB2),provide hypothesis-free orbital parallaxes and masses of bothcomponents. Unlike eclipsing-spectroscopic binaries for which manyaccurate masses are already known (Andersen 1991; Andersen 1997), thenumber of VB-SB2 remains rather small. This paper presents 40 suchsystems for which published visual observations and radial velocitiesallow a simultaneous adjustment of both data sets. The precision of theindividual masses as well as the evolution of that precision withrespect to the published precision is investigated.

Magnitudes absolues des étoiles standards MK des types G à M à partir des parallaxes Hipparcos. The absolute magnitudes of the G to M type MK standards from the Hipparcos parallaxes
We analyse a sample of about 500 MK standards of cool spectral types (Gto M) for to compare the visual absolute magnitudes obtained from bothHipparcos data and Schmidt-Kaler calibrations. Our purpose is tovalidate our spectroscopic work \cite[(Ginestet et al. 1997, 1999)]{G97}on stars with composite spectra with the help of Hipparcos data.Contrary to what is claimed in other papers, the absolute magnitudedomain devoted to the giant stars does not overlap the domain of dwarfs.We find that the discrepancies between absolute magnitudes fromHipparcos data and absolute magnitudes deduced from Schmidt-Kalercalibrations increase with the relative error sigma (pi )/pi on theparallaxes. So, for sigma (pi )/pi <= 0.05 only 3% of the starspresent a discrepancy of one luminosity class, while this percentagereaches 54% for 0.25 < sigma (pi )/pi <= 0.50. Curiously, theluminosity of the giants seems to increase with the distance of thestars, whereas the supergiants of the sample appear underluminous atleast for d < 600 pc! We point out a list of 14 MK standards whoseluminosity classes may be erroneous and need a new spectralclassification, in the near infrared. The case of composite-spectrumbinaries is also discussed. Most of these are too distant for accurateparallaxes even with Hipparcos: only sixteen stars have sigma (pi )/pi<= 0.10; for these, we give new spectral classifications in agreementwith both our classifications in the near infrared of the coolcomponents and Hipparcos data. Finally, for stars having high-precisionparallaxes (sigma (pi )/pi <= 5%) there is no serious problem forSchmidt-Kaler calibrations whith respect to Hipparcos data. The datacorresponding to parallaxes of lower precisions should be used withcaution and only for statistical analyses.

Evolution of X-ray activity of 1-3 Msun late-type stars in early post-main-sequence phases
We have investigated the variation of coronal X-ray emission duringearly post-main-sequence phases for a sample of 120 late-type starswithin 100 pc, and with estimated masses in the range 1-3Msun, based on Hipparcos parallaxes and recent evolutionarymodels. These stars were observed with the ROSAT/PSPC, and the dataprocessed with the Palermo-CfA pipeline, including detection andevaluation of X-ray fluxes (or upper limits) by means of a wavelettransform algorithm. We have studied the evolutionary history of X-rayluminosity and surface flux for stars in selected mass ranges, includingstars with inactive A-type progenitors on the main sequence and lowermass solar-type stars. Our stellar sample suggests a trend of increasingX-ray emission level with age for stars with masses M > 1.5Msun, and a decline for lower-mass stars. A similar behaviorholds for the average coronal temperature, which follows a power-lawcorrelation with the X-ray luminosity, independently of their mass andevolutionary state. We have also studied the relationship between X-rayluminosity and surface rotation rate for stars in the same mass ranges,and how this relationships departs from the Lx ~vrot2 law followed by main-sequence stars. Ourresults are interpreted in terms of a magnetic dynamo whose efficiencydepends on the stellar evolutionary state through the mass-dependentchanges of the stellar internal structure, including the properties ofenvelope convection and the internal rotation profile.

Circularization of binary orbits.
Not Available

Catalogs of temperatures and [Fe/H] averages for evolved G and K stars
A catalog of mean values of [Fe/H] for evolved G and K stars isdescribed. The zero point for the catalog entries has been establishedby using differential analyses. Literature sources for those entries areincluded in the catalog. The mean values are given with rms errors andnumbers of degrees of freedom, and a simple example of the use of thesestatistical data is given. For a number of the stars with entries in thecatalog, temperatures have been determined. A separate catalogcontaining those data is briefly described. Catalog only available atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr ( or viahttp://cdsweb.u-strasbg.fr/Abstract.html

Spectral classifications in the near infrared of stars with composite spectra. III. Study of a sample of 137 objects with the Aurelie spectrograph
We provide spectral classifications for a sample of 137 stars mentionedas having composite spectra. The classifications were carried out on 33Angstroms /mm spectra in the region 8370 - 8870 Angstroms. Of these 137objects, 115 correspond in the infrared to cool stars (G, K or M) ofluminosity classes III, II and I; for 22 stars, we find only hot spectraof types B, A, F or Am, so that they do not fulfil our definition ofcomposite spectra. We detect four new Am stars, and one Am star (HD70826) turns out to be a composite spectrum object. As in Paper II, thecool components of composite spectra show a strong concentration in thevicinity of G8III. Based upon observations carried out at Observatoirede Haute-Provence (OHP).

Ultraviolet and Optical Studies of Binaries with Luminous Cool Primaries and Hot Companions. V. The Entire IUE Sample
We have obtained or retrieved IUE spectra for over 100 middle- andlate-type giant and supergiant stars whose spectra indicate the presenceof a hot component earlier than type F2. The hot companions areclassified accurately by temperature class from their far-UV spectra.The interstellar extinction of each system and the relative luminositiesof the components are derived from analysis of the UV and opticalfluxes, using a grid of UV intrinsic colors for hot dwarfs. We find thatthere is fair agreement in general between current UV spectralclassification and ground-based hot component types, in spite of thedifficulties of assigning the latter. There are a few cases in which thecool component optical classifications disagree considerably with thetemperature classes inferred from our analysis of UV and opticalphotometry. The extinction parameter agrees moderately well with otherdeterminations of B-V color excess. Many systems are worthy of furtherstudy especially to establish their spectroscopic orbits. Further workis planned to estimate luminosities of the cool components from the dataherein; in many cases, these luminosities' accuracies should becomparable to or exceed those of the Hipparcos parallaxes.

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 ( or viahttp://cdsweb.u-strasbg.fr/Abstract.html

The Tokyo PMC catalog 90-93: Catalog of positions of 6649 stars observed in 1990 through 1993 with Tokyo photoelectric meridian circle
The sixth annual catalog of the Tokyo Photoelectric Meridian Circle(PMC) is presented for 6649 stars which were observed at least two timesin January 1990 through March 1993. The mean positions of the starsobserved are given in the catalog at the corresponding mean epochs ofobservations of individual stars. The coordinates of the catalog arebased on the FK5 system, and referred to the equinox and equator ofJ2000.0. The mean local deviations of the observed positions from theFK5 catalog positions are constructed for the basic FK5 stars to comparewith those of the Tokyo PMC Catalog 89 and preliminary Hipparcos resultsof H30.

A catalogue of [Fe/H] determinations: 1996 edition
A fifth Edition of the Catalogue of [Fe/H] determinations is presentedherewith. It contains 5946 determinations for 3247 stars, including 751stars in 84 associations, clusters or galaxies. The literature iscomplete up to December 1995. The 700 bibliographical referencescorrespond to [Fe/H] determinations obtained from high resolutionspectroscopic observations and detailed analyses, most of them carriedout with the help of model-atmospheres. The Catalogue is made up ofthree formatted files: File 1: field stars, File 2: stars in galacticassociations and clusters, and stars in SMC, LMC, M33, File 3: numberedlist of bibliographical references The three files are only available inelectronic form at the Centre de Donnees Stellaires in Strasbourg, viaanonymous ftp to cdsarc.u-strasbg.fr (, or viahttp://cdsweb.u-strasbg.fr/Abstract.html

Spectral classifications in the near infrared of stars with composite spectra. II. Study of a sample of 180 stars
A sample of 180 supposedly composite-spectrum stars has been studied onthe basis of spectra obtained in the near infrared (8370-8780 Angstroms)at a dispersion of 33 Anstroms/mm. The objective was to study the coolercomponents of the systems. Of our sample, 120 are true compositespectra, 35 are hot spectra of types B, F and 25 are Am stars. We find astrong concentration of the cooler components of the composite spectraaround G8III. In view of the difficulty of classifying compositespectra, because of the super position of an early type dwarf and a latetype giant or supergiant spectrum, we have made several tests to controlthe classification based upon the infrared region. Since all tests gavepositive results, we conclude that our classifications can be consideredas being both reliable and homogeneous. Table \ref{tab1} is alsoavailable electronically at the CDS via anonymous ftp orhttp://cdsweb.u-strasbg.fr/Abstracts.html} Based upon observationscarried out at Observatoire de Haute-Provence (CNRS).

On the link between coronal activity and orbital period in evolved binary stars.
The analysis of the relationship between X-emission flux and orbitalperiod indicates a drop in the X-ray emission of binaries with evolvedcomponents at orbital periods of about 100 days: Intense X-ray emittershave an orbital period lower than 100 days, whereas with an orbitalperiod greater than about 100 days are weak X-ray emitters. Thiscritical period corresponds to the orbital period separating binarysystems with circular orbits from those of eccentric orbits.

Professional-amateur collaboration in variable star research: IV. One possibility for amateur/professional collaboration
Not Available

Submit a new article

Related links

  • - No Links Found -
Submit a new link

Member of following groups:

Observation and Astrometry data

Right ascension:21h15m49.40s
Apparent magnitude:3.92
Distance:57.11 parsecs
Proper motion RA:52.7
Proper motion Dec:-85.8
B-T magnitude:4.552
V-T magnitude:3.993

Catalogs and designations:
Proper NamesKitalpha
Bayerα Equ
Flamsteed8 Equ
HD 1989HD 202447
TYCHO-2 2000TYC 536-2354-1
USNO-A2.0USNO-A2 0900-19486612
BSC 1991HR 8131
HIPHIP 104987

→ Request more catalogs and designations from VizieR