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Parameters of Herbig Ae/Be and Vega-type stars
Context: This work presents the characterization of 27 young early-typestars, most of them in the age range 1-10 Myr, and three suspected hotcompanions of post-T Tauri stars belonging to the Lindroos binarysample. Most of these objects show IR excesses in their spectral energydistributions, which are indicative of the presence of disks. The workis relevant in the fields of stellar physics, physics of disks andformation of planetary systems. Aims: The aim of the work is thedetermination of the effective temperature, gravity, metallicity, mass,luminosity and age of these stars. An accurate modelling of their disksrequires the knowledge of most of these parameters, since they willdetermine the energy input received by the disk and hence, its geometryand global properties. Methods: Spectral energy distributions andmid-resolution spectra were used to estimate T_eff, the effectivetemperature. The comparison of the profiles of the Balmer lines withsynthetic profiles provides the value of the stellar gravity, g_*.High-resolution optical observations and synthetic spectra are used toestimate the metallicity, [M/H]. Once Teff, g* and[M/H] are known for each star, evolutionary tracks and isochronesprovide estimations of the mass, luminosity, age and distances (or upperlimits in some cases). The method is original in the sense that it isdistance-independent, i.e. the estimation of the stellar parameters doesnot require the knowledge of the distance to the object. Results:Stellar parameters (effective temperature, gravity, metallicity, mass,luminosity, age and distances - or upper limits) are obtained for thesample of stars mentioned above. A detailed discussion of someindividual objects, in particular VV Ser, RR Tau, 49 Cet and the threesuspected hot companions of post-T Tauris, is presented. Conclusions:These results, apart from their intrinsic interest, would be extremelyvaluable to model the disks surrounding the stars. The paper also showsthe difficulty posed by the morphology and behaviour of the systemstar+disk in the computation of the stellar parameters.Based on observations collected at the German-Spanish AstronomicalCentre, Calar Alto, jointly operated by the Max-Planck Institut fürAstronomie and the Instituto de Astrofísica de Andalucía(CSIC), and on observations made with the WHT telescope operated on theisland of La Palma by the Isaac Newton Group in the Spanish Observatoriodel Roque de los Muchachos of the Instituto de Astrofísica deCanarias.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| 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
| Absolute proper motions of open clusters. I. Observational data
Mean proper motions and parallaxes of 205 open clusters were determinedfrom their member stars found in the Hipparcos Catalogue. 360 clusterswere searched for possible members, excluding nearby clusters withdistances D < 200 pc. Members were selected using ground basedinformation (photometry, radial velocity, proper motion, distance fromthe cluster centre) and information provided by Hipparcos (propermotion, parallax). Altogether 630 certain and 100 possible members werefound. A comparison of the Hipparcos parallaxes with photometricdistances of open clusters shows good agreement. The Hipparcos dataconfirm or reject the membership of several Cepheids in the studiedclusters. Tables 1 and 2 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
| Open clusters with Hipparcos. I. Mean astrometric parameters
New memberships, mean parallaxes and proper motions of all 9 openclusters closer than 300 pc (except the Hyades) and 9rich clusters between 300 and 500 pc have been computed using Hipparcosdata. Precisions, ranging from 0.2 to 0.5 mas for parallaxes and 0.1 to0.5 mas/yr for proper motions, are of great interest for calibratingphotometric parallaxes as well as for kinematical studies. Carefulinvestigations of possible biases have been performed and no evidence ofsignificant systematic errors on the mean cluster parallaxes has beenfound. The distances and proper motions of 32 more distant clusters,which may be used statistically, are also indicated. Based onobservations made with the ESA Hipparcos astrometry satellite
| Evolutionary Oddities in Old Disk Population Clusters
With a luminosity zero point fixed by the kinematics of old disksuperclusters (HR 1614, t = 6 Gyr, [Fe/H] = +0.1 dex) and groups(Arcturus, t = 14 Gyr, [Fe/H] = -0.65 dex), the luminosities and colorsof evolved old disk stars, especially red horizontal branch (RHB), earlyasymptotic branch [AGB(1)], thermally pulsing asymptotic giant branch[AGB(2)], and sdOB stars in old disk clusters (NGC 6791, 47 Tuc, M71,M67, Mel 66, NGC 2420, NGC 2204, and NGC 2443) are discussed. (1) TheRHB stars in the old disk all have M_V = +0.7 +/- 0.1 (M_K = -1.3 +/-0.1) mag. (2) Large-amplitude red variables (LARVs) with quasi-stableperiods and light curves are old disk stars on AGB(2). (3) AGB(1)objects include CH stars and semiregular (SRa) variables. (4) Thepopulous and overabundant cluster NGC 6791 may be the only disk clusterwith sdOB stars, populating the lower portion of the bifurcated extendedhorizontal branch that is usual in most ``blue tailed'' and high-densityhalo clusters. (5) Post-red giant branch (RGB) stars in old diskclusters show a B - V (b - y) defect when compared with RGB stars,possibly because of a change in the character of the atmospheres. (6) Ifthe bulk of the LARVs are pulsating in the fundamental mode, R Vir (P =145 days) is possibly a first-overtone pulsator. (7) The overabundantold disk clusters are within the solar circle, with Liller 1 being atthe Galactic center. (8) Several probable RHB stars at the southGalactic pole are identified. (9) The period-age relation, combined withthe known spatial distribution of Galactic LARVs, leads to a relationbetween age and scale height of distribution that monotonicallyincreases with age, leaving no obvious reason for a bifurcation of thepopulation.
| Spectroscopy of the open cluster Blanco 1 II. H alpha emission as an indicator of relative age
We present the results of H alpha (6562\AA) and Li i (6708\AA)observations of 114 low-mass stars of the young open cluster Blanco 1.We also present observations of 30 stars in Ca ii(K). This work extendsthe first Blanco 1 spectroscopic study of Panagi et al. (1994). From asample of four well-studied clusters, including Blanco 1, we find thatthe fraction of H alpha emission-line stars amongst K dwarfs is a goodindicator of relative age, with a smaller fraction indicative of olderage. Blanco 1 shows a relatively small fraction of emitters,inconsistent with previous age estimates for the cluster. We estimatethe cluster age to to be 90 +/- 25 Myr, slightly older than thePleiades. The method is shown to be more sensitive to age than lithiumand a useful alternative to other age measurement techniques. Thevariation of H alpha with (B-V) is similar to that observed in the oldersolar neighbourhood dwarfs, suggesting that, at least for theabsorption-line stars, the contribution of stellar rotation to theequivalent width is unclear. We combine both spectroscopy and photometryto revise cluster membership and give accurate positions for all thesestars. Tables A1 and A2 are available at the CDS via anonymous ftp130.79.128.5 or http://cdsweb.u-strabg.fr./Abstract.html
| 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.
| SANTIAGO 91, a right ascension catalogue of 3387 stars (equinox J2000).
The positions in right ascension of 3387 stars belonging to the Santiago67 Catalogue, observed with the Repsold Meridian Circle at Cerro Calan,National Astronomical Observatory, during the period 1989 to 1994, aregiven. The average mean square error of a position, for the wholeCatalogue, is +/-0.009 s. The mean epoch of the catalogue is 1991.84.
| The late B-type stars: Refined MK classification, confrontation with stromgren photometry, and the effects of rotation
In the fourth and final of a series of papers on the late B to the earlyF type stars, we refine the Morgan Keenan (MK) spectral classificationsystem for the late B type stars and consider the effect of rotation onboth spectral classification and Stroemgren photometry of these stars.We extend the work of Morgan by establishing self-consistent sequencesof narrow and broadlined standards. We reclassify a number of Bp stars,compare these classifications with Stroemgren photometry and considerthe question of whether all Bp stars are main-sequence objects.
| Fifth fundamental catalogue. Part 2: The FK5 extension - new fundamental stars
The mean positions and proper motions for 3117 new fundamental starsessentially in the magnitude range about 4.5 to 9.5 are given in thisFK5 extension. Mean apparent visual magnitude is 7.2 and is on average2.5 magnitudes fainter then the basic FK5 which has a mean magnitude of4.7. (The basic FK5 gives the mean positions and proper motions for theclassical 1535 fundamental stars). The following are discussed: theobservational material, reduction of observations, star selection, andthe system for the FK5 extension. An explanation and description of thecatalog are given. The catalog of 3117 fundamental stars for the equinoxand epoch J2000.0 and B1950.0 is presented. The parallaxes and radialvelocities for 22 extension stars with large forecasting effects aregiven. Catalogs used in the compilation of the FK5 fundamental catalogare listed.
| UBV and uvby-beta photometry of stars in the region of the Zeta SCULPTORIS cluster
Photoelectric observations of 130 stars in the region of Zeta Sculptorishave been obtained in UBV and uvby-beta. A total of 32 stars areidentified as cluster members, and several other F and G type stars areidentified as probable members. Results indicate an interstellarreddening of E(B-V) = 0.02 mag and that the cluster is slightly metaldeficient.
| Interstellar reddening towards the south galactic pole
B, A and F type stars are observed in an area of about 400 squaredegrees around the galactic south pole (SGP) using theStroemgren-Crawford uvby-beta system at the 60 cm telescope of theBochum station on La Silla, Chile. With calibrations for B and F typestars and the provisional calibration for the stars of Stroemgren's LateGroup-A-stars, intrinsic (b-y)0 colors are derived and then used todescribe the interstellar absorption structure of the SGP. To determinethe galactic extinction perpendicular to the galactic plane, thereddening values of distant stars are averaged in order to include boththe reddened and unreddened areas at the SGP. A mean value E(b-y)SGPequals 0.019 m is derived and is found to agree well with earliervalues, except with that of Knude (1977). Explanations for the deviationare considered, implying that Knude's value is systematically too high.
| Spectral types in the Zeta SCULPTORIS open cluster
The spectral types of 20 stars in the Blanco 1 open cluster (ZetaSculptoris) are reported. Spectral classification in the MK system wasperformed on the basis of 125-A/mm dispersion spectra obtained with a0.9-m telescope and a Cassegrain spectrograph. Of the stars classified,one classical Am star, one peculiar star with a weak K-line and one Apstar with marginal Si II lines enhancement were found, while the starZeta Scl itself is observed to be a main sequence object and thusprobably a foreground star. An H-R diagram of the cluster is alsopresented, and other probable members and nonmembers are indicated.
| Multicolor photometry of the ZET Scl open cluster.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1978PASP...90...81P&db_key=AST
| A finding list of stars of spectral type A7 and earlier in regions at high galactic latitudes. VI. Near South Galactic Pole.
Not Available
| NGC 2516 and the Pleiades Group
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972ApJ...173...63E&db_key=AST
| Radial Velocities and Spectral Classification of A-Type Stars Near the South Galactic Pole
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1971PASP...83..643B&db_key=AST
| A finding list of early-type stars near the south galactic pole.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1971AJ.....76..338S&db_key=AST
| A Very Young Cluster with a Moderate Metal Deficiency
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1970ApJ...161..159E&db_key=AST
| Three-colour photometry of early-type stars near the galactic poles
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1963MNRAS.127...83W&db_key=AST
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לינקים קשורים
הכנס לינק חדש
משמש של הקבוצה הבאה
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | פסל |
| התרוממות ימנית: | 00h06m09.08s |
| סירוב: | -29°09'05.0" |
| גודל גלוי: | 7.889 |
| מרחק: | 227.79 פארסק |
| תנועה נכונה: | 16.9 |
| תנועה נכונה: | 2.1 |
| B-T magnitude: | 7.868 |
| V-T magnitude: | 7.888 |
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