Оглавление
Изображения
Загрузить ваше изображение
DSS Images Other Images
Публикации по объекту
A spectroscopy study of nearby late-type stars, possible members of stellar kinematic groups
Context. Nearby late-type stars are excellent targets for seeking youngobjects in stellar associations and moving groups. The origin of thesestructures is still misunderstood, and lists of moving group membersoften change with time and also from author to author. Most members ofthese groups have been identified by means of kinematic criteria,leading to an important contamination of previous lists by old fieldstars. Aims: We attempt to identify unambiguous moving groupmembers among a sample of nearby-late type stars by studying theirkinematics, lithium abundance, chromospheric activity, and otherage-related properties. Methods: High-resolution echelle spectra(R ~ 57 000) of a sample of nearby late-type stars are used to deriveaccurate radial velocities that are combined with the precise Hipparcosparallaxes and proper motions to compute galactic-spatial velocitycomponents. Stars are classified as possible members of the classicalmoving groups according to their kinematics. The spectra are also usedto study several age-related properties for young late-type stars, i.e.,the equivalent width of the lithium Li i 6707.8 Å line or theR'HK index. Additional information like X-ray fluxes from theROSAT All-Sky Survey or the presence of debris discs is also taken intoaccount. The different age estimators are compared and the moving groupmembership of the kinematically selected candidates are discussed. Results: From a total list of 405 nearby stars, 102 have beenclassified as moving group candidates according to their kinematics.i.e., only ~25.2% of the sample. The number reduces when age estimatesare considered, and only 26 moving group candidates (25.5% of the 102candidates) have ages in agreement with the star having the same age asan MG member.Based on observations collected at the Centro Astronómico HispanoAlemán (CAHA) at Calar Alto, operated jointly by the Max-PlanckInstitut für Astronomie and the Instituto de Astrofísica deAndalucía (CSIC) and observations made with the ItalianTelescopio Nazionale Galileo (TNG) operated on the island of La Palma bythe Fundación Galileo Galilei of the INAF (Istituto Nazionale diAstrofisica) at the Spanish Observatorio del Roque de los Muchachos ofthe Instituto de Astrofísica de Canarias.Appendices and Tables 1,5-15 are available in electronic form at http://www.aanda.orgTable 1 is alsoavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/521/A12
| Chromospheric activity and rotation of FGK stars in the solar vicinity. An estimation of the radial velocity jitter
Context. Chromospheric activity produces both photometric andspectroscopic variations that can be mistaken as planets. Large spotscrossing the stellar disc can produce planet-like periodic variations inthe light curve of a star. These spots clearly affect the spectral lineprofiles, and their perturbations alter the line centroids creating aradial velocity jitter that might “contaminate” thevariations induced by a planet. Precise chromospheric activitymeasurements are needed to estimate the activity-induced noise thatshould be expected for a given star. Aims: We obtain precisechromospheric activity measurements and projected rotational velocitiesfor nearby (d ? 25 pc) cool (spectral types F to K) stars, toestimate their expected activity-related jitter. As a complementaryobjective, we attempt to obtain relationships between fluxes indifferent activity indicator lines, that permit a transformation oftraditional activity indicators, i.e., Ca ii H & K lines, to othersthat hold noteworthy advantages. Methods: We used high resolution(~50 000) echelle optical spectra. Standard data reduction was performedusing the IRAF echelle package. To determine the chromospheric emissionof the stars in the sample, we used the spectral subtraction technique.We measured the equivalent widths of the chromospheric emission lines inthe subtracted spectrum and transformed them into fluxes by applyingempirical equivalent width and flux relationships. Rotational velocitieswere determined using the cross-correlation technique. To inferactivity-related radial velocity (RV) jitter, we used empiricalrelationships between this jitter and the R'_HK index. Results:We measured chromospheric activity, as given by different indicatorsthroughout the optical spectra, and projected rotational velocities for371 nearby cool stars. We have built empirical relationships among themost important chromospheric emission lines. Finally, we used themeasured chromospheric activity to estimate the expected RV jitter forthe active stars in the sample.Based on observations made with the 2.2 m telescope at the CentroAstronómico Hispano Alemán (CAHA) at Calar Alto (Spain)and the Telescopio Nazionale Galileo (TNG) operated on the island of LaPalma by the Istituto Nazionale de Astrofisica Italiano (INAF), in theSpanish Observatorio del Roque de los Muchachos. This research has beensupported by the Programa de Acceso a InfraestructurasCientíficas y Tecnológicas Singulares (ICTS).Tables A1 toA4 are only available in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/520/A79
| The PASTEL catalogue of stellar parameters
Aims: The PASTEL catalogue is an update of the [Fe/H] catalogue,published in 1997 and 2001. It is a bibliographical compilation ofstellar atmospheric parameters providing (T_eff, log g, [Fe/H])determinations obtained from the analysis of high resolution, highsignal-to-noise spectra, carried out with model atmospheres. PASTEL alsoprovides determinations of the one parameter T_eff based on variousmethods. It is aimed in the future to provide also homogenizedatmospheric parameters and elemental abundances, radial and rotationalvelocities. A web interface has been created to query the catalogue onelaborated criteria. PASTEL is also distributed through the CDS databaseand VizieR. Methods: To make it as complete as possible, the mainjournals have been surveyed, as well as the CDS database, to findrelevant publications. The catalogue is regularly updated with newdeterminations found in the literature. Results: As of Febuary2010, PASTEL includes 30151 determinations of either T_eff or (T_eff,log g, [Fe/H]) for 16 649 different stars corresponding to 865bibliographical references. Nearly 6000 stars have a determination ofthe three parameters (T_eff, log g, [Fe/H]) with a high qualityspectroscopic metallicity.The catalogue can be queried through a dedicated web interface at http://pastel.obs.u-bordeaux1.fr/.It is also available in electronic form at the Centre de DonnéesStellaires in Strasbourg (http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=B/pastel),at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) orvia http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/515/A111
| Reaching the boundary between stellar kinematic groups and very wide binaries. The Washington double stars with the widest angular separations
Aims: I look for and characterise very wide binaries and multiplesystems with projected physical separations larger than s = 0.1 pc,which is generally believed to be a sharp upper limit to thedistribution of wide binary semimajor axes. Methods: Iinvestigated in detail 30 Washington double stars with angularseparations of ? > 1000 arcsec. I discarded 23 of them asprobably unbound systems based on discordant astrometry, photometry,spectral types, and radial velocities. The remaining seven systems weresubject to a comprehensive data compilation and derivation(multi-wavelength photometry, heliocentric distance, multiplicity, age,mass, metallicity, membership in a young kinematic group). Results: Of the seven very wide systems, six have projected physicalseparations greater than the hypothetical cutoff at s = 0.1 pc and fourhave separations s > 0.2 pc. Although there are two systems in youngkinematic groups (namely HD 136654 and BD+32 2572 in the HyadesSupercluster, and AU Mic and AT Mic AB in the ? Pictoris movinggroup), there is no clear prevalence of young systems (? < 1 Ga)among these very wide binaries. Finally, I compare the binding energiesof the seven systems with those of other weakly bound systems in thefield.Appendix A is only available in electronic form at http://www.aanda.org
| The main sequence from F to K stars of the solar neighbourhood in SDSS colours
For an understanding of Galactic stellar populations in the SDSS filtersystem well defined stellar samples are needed. The nearby stars providea complete stellar sample representative for the thin disc population.We compare the filter transformations of different authors applied tothe main sequence stars from F to K dwarfs to SDSS filter system anddiscuss the properties of the main sequence. The location of the meanmain sequence in colour-magnitude diagrams is very sensitive tosystematic differences in the filter transformation. A comparison withfiducial sequences of star clusters observed in g', r', and i' show goodagreement. Theoretical isochrones from Padua and from Dartmouth havestill some problems, especially in the (r-i) colours.
| Spectroscopic investigation of stars on the lower main sequence
Aims. The aim of this paper is to provide fundamental parameters andabundances with a high accuracy for a large sample of cool main sequencestars. This study is part of wider project, in which the metallicitydistribution of the local thin disc is investigated from a completesample of G and K dwarfs within 25 pc. Methods: The stars were observedat high resolution and a high signal-to-noise ratio with the ELODIEechelle spectrograph. The V sin i were obtained with a calibration ofthe cross-correlation function. Effective temperatures were estimated bythe line depth ratio method. Surface gravities (log g) were determinedby two methods: parallaxes and ionization balance of iron. The Mg and Naabundances were derived using a non-LTE approximation. Abundances ofother elements were obtained by measuring equivalent widths. Results:Rotational velocities, atmospheric parameters (T_eff, log g, [Fe/H],V_t), and Li, O, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Co, Ni, and Znabundances are provided for 131 stars. Among them, more than 30 starsare active stars with a fraction of BY Dra and RS CVn type stars forwhich spectral peculiarities were investigated. We find the meanabundances of the majority of elements in active and nonactive stars tobe similar, except for Li, and possibly for Zn and Co. The lithium isreliably detected in 54% of active stars but only in 20% of nonactivestars. No correlation is found between Li abundances and rotationalvelocities. A possible anticorrelation of log A(Li) with the index ofchromospheric activity GrandS is observed. Conclusions: Active andnonactive cool dwarfs show similar dependencies of most elemental ratiosvs. [Fe/H]. This allows us to use such abundance ratios to study thechemical and dynamical evolution of the Galaxy. Among active stars, noclear correlation has been found between different indicators ofactivity for our sample stars.Based on spectra collected with the ELODIE spectrograph at the 1.93-mtelescope of the Observatoire de Haute Provence (France). Tables A.1-A3are only available 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/489/923
| Vertical distribution of Galactic disk stars. IV. AMR and AVR from clump giants
We present the parameters of 891 stars, mostly clump giants, includingatmospheric parameters, distances, absolute magnitudes, spatialvelocities, galactic orbits and ages. One part of this sample consistsof local giants, within 100 pc, with atmospheric parameters eitherestimated from our spectroscopic observations at high resolution andhigh signal-to-noise ratio, or retrieved from the literature. The otherpart of the sample includes 523 distant stars, spanning distances up to1 kpc in the direction of the North Galactic Pole, for which we haveestimated atmospheric parameters from high resolution but lowsignal-to-noise Echelle spectra. This new sample is kinematicallyunbiased, with well-defined boundaries in magnitude and colours. Werevisit the basic properties of the Galactic thin disk as traced byclump giants. We find the metallicity distribution to be different fromthat of dwarfs, with fewer metal-rich stars. We find evidence for avertical metallicity gradient of -0.31 dex kpc-1 and for atransition at ~4-5 Gyr in both the metallicity and velocities. Theage-metallicity relation (AMR), which exhibits a very low dispersion,increases smoothly from 10 to 4 Gyr, with a steeper increase for youngerstars. The age-velocity relation (AVR) is characterized by thesaturation of the V and W dispersions at 5 Gyr, and continuous heatingin U.
| Obscured clusters. I. GLIMPSE 30 - A young Milky Way star cluster hosting Wolf-Rayet stars
Context: Young massive clusters are usually deeply embedded in dust andgas. They represent excellent astrophysical laboratories for the studyof massive stars. Clusters with Wolf-Rayet (WR) stars are of specialimportance, since this enables us to study a coeval WR population at auniform metallicity and known age. Aims: We started a long-term projectto search the inner Milky Way for hidden star clusters and to study themin detail. GLIMPSE 30 (G30) is one of these clusters. It is situatednear the Galactic plane (l=298.756°, b=-0.408°) and we determineits physical parameters and investigate its high-mass stellar contentespecially WR stars. Methods: Our analysis is based on SOFI/NTTJ_SHKS imaging and low resolution (R˜2000) spectroscopyof the brightest cluster members in the K atmospheric window. For theage determination we applied isochrone fits for MS and Pre-MS stars. Wederived stellar parameters of the WR stars candidates using a fullnonLTE modeling of the observed spectra. Results: Using a variety oftechniques we found that G30 is very young cluster, with age t ≈ 4Myr. The cluster is located in the Carina spiral arm, it is deeplyembedded in dust and suffers reddening of AV ˜10.5± 1.1 mag. The distance to the object is d=7.2±0.9kpc. The mass of the cluster members down to 2.35 M_ȯ is 1600M_ȯ. The cluster's MF for the mass range of 5.6 to 31.6 {M_ȯ}shows a slope of Γ=-1.01± 0.03. The total mass of thecluster obtained by this MF down to 1 M_ȯ is about 3 ×103 M_ȯ. The spectral analysis and the models allow usto conclude that at least one Ofpe/WN and two WR stars can be found inG30. The WR stars are of the WN6-7 hydrogen rich type with progenitormasses of more than 60 M_ȯ. Conclusions: G30 is a new member ofthe family of young Galactic clusters hosting WR stars. It is a factorof two to three less massive than some of the youngest super-massivestar clusters like Arches, Quintuplet and the Central cluster and istheir smaller analog.Based on observations collected with the New Technology Telescope of theESO within observing program 77.D-0089.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| A Catalog of Northern Stars with Annual Proper Motions Larger than 0.15" (LSPM-NORTH Catalog)
The LSPM catalog is a comprehensive list of 61,977 stars north of theJ2000 celestial equator that have proper motions larger than 0.15"yr-1 (local-background-stars frame). The catalog has beengenerated primarily as a result of our systematic search for high propermotion stars in the Digitized Sky Surveys using our SUPERBLINK software.At brighter magnitudes, the catalog incorporates stars and data from theTycho-2 Catalogue and also, to a lesser extent, from the All-SkyCompiled Catalogue of 2.5 million stars. The LSPM catalog considerablyexpands over the old Luyten (Luyten Half-Second [LHS] and New LuytenTwo-Tenths [NLTT]) catalogs, superseding them for northern declinations.Positions are given with an accuracy of <~100 mas at the 2000.0epoch, and absolute proper motions are given with an accuracy of ~8 masyr-1. Corrections to the local-background-stars propermotions have been calculated, and absolute proper motions in theextragalactic frame are given. Whenever available, we also give opticalBT and VT magnitudes (from Tycho-2, ASCC-2.5),photographic BJ, RF, and IN magnitudes(from USNO-B1 catalog), and infrared J, H, and Ks magnitudes(from 2MASS). We also provide an estimated V magnitude and V-J color fornearly all catalog entries, useful for initial classification of thestars. The catalog is estimated to be over 99% complete at high Galacticlatitudes (|b|>15deg) and over 90% complete at lowGalactic latitudes (|b|>15deg), down to a magnitudeV=19.0, and has a limiting magnitude V=21.0. All the northern starslisted in the LHS and NLTT catalogs have been reidentified, and theirpositions, proper motions, and magnitudes reevaluated. The catalog alsolists a large number of completely new objects, which promise to expandvery significantly the census of red dwarfs, subdwarfs, and white dwarfsin the vicinity of the Sun.Based on data mining of the Digitized Sky Surveys (DSSs), developed andoperated by the Catalogs and Surveys Branch of the Space TelescopeScience Institute (STScI), Baltimore.Developed with support from the National Science Foundation (NSF), aspart of the NASA/NSF NStars program.
| Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 Parsecs: The Northern Sample. I.
We have embarked on a project, under the aegis of the Nearby Stars(NStars)/Space Interferometry Mission Preparatory Science Program, toobtain spectra, spectral types, and, where feasible, basic physicalparameters for the 3600 dwarf and giant stars earlier than M0 within 40pc of the Sun. In this paper, we report on the results of this projectfor the first 664 stars in the northern hemisphere. These resultsinclude precise, homogeneous spectral types, basic physical parameters(including the effective temperature, surface gravity, and overallmetallicity [M/H]), and measures of the chromospheric activity of ourprogram stars. Observed and derived data presented in this paper arealso available on the project's Web site.
| Improved Astrometry and Photometry for the Luyten Catalog. II. Faint Stars and the Revised Catalog
We complete construction of a catalog containing improved astrometry andnew optical/infrared photometry for the vast majority of NLTT starslying in the overlap of regions covered by POSS I and by the secondincremental Two Micron All Sky Survey (2MASS) release, approximately 44%of the sky. The epoch 2000 positions are typically accurate to 130 mas,the proper motions to 5.5 mas yr-1, and the V-J colors to0.25 mag. Relative proper motions of binary components are measured to 3mas yr-1. The false-identification rate is ~1% for11<~V<~18 and substantially less at brighter magnitudes. Theseimprovements permit the construction of a reduced proper-motion diagramthat, for the first time, allows one to classify NLTT stars intomain-sequence (MS) stars, subdwarfs (SDs), and white dwarfs (WDs). We inturn use this diagram to analyze the properties of both our catalog andthe NLTT catalog on which it is based. In sharp contrast to popularbelief, we find that NLTT incompleteness in the plane is almostcompletely concentrated in MS stars, and that SDs and WDs are detectedalmost uniformly over the sky δ>-33deg. Our catalogwill therefore provide a powerful tool to probe these populationsstatistically, as well as to reliably identify individual SDs and WDs.
| Multiplicity among solar-type stars. III. Statistical properties of the F7-K binaries with periods up to 10 years
Two CORAVEL radial velocity surveys - one among stars in the solarneighbourhood, the other in the Pleiades and in Praesepe - are merged toderive the statistical properties of main-sequence binaries withspectral types F7 to K and with periods up to 10 years. A sample of 89spectroscopic orbits was finally obtained. Among them, 52 relate to afree-of-bias selection of 405 stars (240 field stars and 165 clusterstars). The statistics corrected for selection effects yield thefollowing results: (1) No discrepancy is found between the binariesamong field stars and the binaries in open cluster. The distributions ofmass ratios, of periods, the period-eccentricity diagram and the binaryfrequencies are all within the same error intervals. (2) Thedistribution of mass ratios presents two maxima: a broad peak from q ~0.2 to q ~ 0.7, and a sharp peak for q > 0.8 (twins). Both arepresent among the early-type as well as among the late-type part of thesample, indicating a scale-free formation process. The peak for q >0.8 gradually decreases when long-period binaries are considered.Whatever their periods, the twins have eccentricities significantlylower than the other binaries, confirming a difference in the formationprocesses. Twins could be generated by in situ formation followed byaccretion from a gaseous envelope, whereas binaries with intermediatemass ratios could be formed at wide separations, but they are madecloser by migration led by interactions with a circumbinary disk. (3)The frequency of binaries with P<10 years is about 14%. (4) About0.3% of binaries are expected to appear as false positives in a planetsearch. Therefore, the frequency of planetary systems among stars ispresently 7+4-2%. The extension of thedistribution of mass ratios in the planetary range would result in avery sharp and very high peak, well separated from the binary stars withlow mass ratios. Based on photoelectric radial-velocity measurementscollected at Haute-Provence observatory and on observations made withthe ESA Hipparcos astrometry satellite.
| 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
| Photometric Measurements of the Fields of More than 700 Nearby Stars
In preparation for optical/IR interferometric searches for substellarcompanions of nearby stars, we undertook to characterize the fields ofall nearby stars visible from the Northern Hemisphere to determinesuitable companions for interferometric phase referencing. Because theKeck Interferometer in particular will be able to phase-reference oncompanions within the isoplanatic patch (30") to about 17th magnitude atK, we took images at V, r, and i that were deep enough to determine iffield stars were present to this magnitude around nearby stars using aspot-coated CCD. We report on 733 fields containing 10,629 measurementsin up to three filters (Gunn i, r and Johnson V) of nearby stars down toabout 13th magnitude at V.
| 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.
| The general catalogue of trigonometric [stellar] paralaxes
Not Available
| The importance of surface inhomogeneities for K and M dwarf chromospheric fluxes
We present published and archived spectroscopic and spectrophotometricdata of H-alpha, Ca II, Mg II, and X-rays for a large sample of K and Mdwarfs. The data set points to the importance that surfaceinhomogeneities have in the flux luminosity diagrams in these late-typedwarfs, irrespective of whether the Balmer lines are in emission orabsorption. Although supporting the fact that cooler stars exhibitincreasing levels of surface activity, evident through an increasingincidence of Balmer emission, surface inhomogeneities, or variations inthe local temperature and density structure, at the chromospheric level,dominate the total Ca II and Mg II fluxes. We show that the flux-fluxand luminosity-luminosity relations indicate differing extents ofinhomogeneity from the chromosphere through to the corona. A goodcorrelation between Ca II and Mg II fluxes indicates that they areformed in overlapping regions of the chromosphere, so that thecontribution of surface inhomogeneities is not evident from thisparticular flux-flux diagram. In the region of the upper chromospherethrough to the transition and corona, the correlation between Ly-alphaand X-ray fluxes indicates regions with similar levels of arealinhomogeneity. This appears to be uncorrelated with that at thechromospheric level.
| The rotation velocities and metallicities of dwarf stars in the solar neighborhood
The rotation velocities (or upper limits) of 260 dwarfs from the Gliese(1969) catalog are determined using a photoelectric radial velocityscanner. The dependence of the correlation dip equivalent width (thestrength of metal lines) on the color (B-V) and metallicity is examined.Given the color and equivalent width, the method can determine the Fe/Habundance ratio with an accuracy up to 0.2.
| A study of excess H-alpha emission in chromospherically active M dwarf
Spectroscopic observations from three observatories are combined tostudy the properties of the excess H-alpha emission which characterizesthe most chromospherically active subset of the M dwarf stars, known asthe dMe stars. It is demonstrated that the excess H-alpha luminosityfrom these stars is a monotonically decreasing function of their (R-I)color, and evidence is presented which suggests that the product of themean surface brightness and the mean filling factor of the emissiveregions is essentially constant with color. Another significant resultof the study is a linear correlation between the excess luminosity inH-alpha and the coronal X-ray luminosity.
| Space motions of low-mass stars.
Radial-velocity measures are presented for 225 stars, most of which aredwarf K and M stars. The data were obtained with the CfA digitalspeedometer, whose uncertainty is less than 1 km/s. Calibrations ofthree earlier radial-velocity studies and comparisons with three othercontemporary ones lead to the evaluation of the standard error for anindividual star as determined in each investigation. The data from twomasks, matching solar type and M type stars, form a ratio that measuresstellar surface temperature quite closely and appear to be useful indetecting the presence of unseen companions. A few previouslyunrecognized binaries have been detected; those with most certaintyinclude stars nos. 366B, 453, and 46A of the McCormick lists of dwarfstars.
| H-alpha photometry of dwarf K and M stars
Attention is given to the distribution of stars in the N-W, R-I planefor the case of 188 dM and dK stars for which H-alpha photometry hasbeen obtained. Most are found to lie along a single 'main sequence' ofabsorption which slopes up towards 0 EW with increasing R-I. Theabsorption EWs are noted to be large by comparison with photosphericmodel predictions, implying either that the models are in error or thatchromospheres are present in virtually all late-type dwarfs, and areresponsible for the H-alpha distribution feature in both absorption andemission.
| Radial-velocity measures and the existence of astrophysical binaries in late-type dwarf stars
Radial velocities with errors of 1-2 km/s are presented based on CCDscans obtained with the Kitt Peak National Observatory coude feedtelescope between 1982 and 1985 of 48 dK-M stars that lack Balmeremission. Comparison with Gliese's (1969) values shows only two stars tobe spectroscopic binary candidates with small velocity amplitudes. Noevidence for any short period (less than 10 days) binaries is found,supporting the conclusions of Young et al. (1986) that there are noastrophysical binaries among these chromosherically inactive dM stars.
| Dwarf K and M stars of high proper motion found in a hemispheric survey
A recently completed visual/red spectral region objective-prism surveyof more than half the sky found some 2200 dwarf K and M stars ofnegligible proper motion (Stephenson, 1986). The present paper adds the1800-odd spectroscopically identified dwarfs that did prove to havesignificant proper motions. About half of these had previous spectralclassifications of some sort, especially by Vyssotsky (1952, 1956). Forthe great majority, the present coordinates are more accurate thanprevious data. The paper includes about 50 stars with unpublishedparallaxes, likely to have parallaxes of 0.05 arcsec or more. Combiningthe present data with the first paper suggests that the number oflow-proper-motion stars in that paper was not unreasonable.
| New subdwarfs. IV - UBV photometry of 1690 high-proper-motion stars
A photometric list of 1690 stars of known high proper motion is used tosearch for potential high-velocity stars of various metallicity valuesin order to find candidates for trigonometric programs on subdwarfs andto enlarge the sample with which to study the relation between stellarkinematics and metal abundance. A list of 113 stars with tangentialspace velocities of 300 km/s or greater is obtained, the highesttangential velocity relative to the sun being 630 km/s. By using thevariation of the tangential velocity with longitude and adopting thegalactic rotation at the solar circle to be 220 km/s, the rotation ofthe subdwarf system is estimated at 0 + or - 50 km/s from the transversevelocity alone, in agreement with determinations based on other methods.
| G. P. Kuiper's spectral classifications of proper-motion stars
Spectral classifications are listed for over 3200 stars, mainly of largeproper motion, observed and classified by Kuiper during the years1937-1944 at the Yerkes and McDonald Observatories. While Kuiper himselfpublished many of his types, and while improved classifications are nowavailable for many of these stars, much of value remains. For many ofthe objects, no other spectral data exist.
| Predicted infrared brightness of stars within 25 parsecs of the sun
Procedures are given for transforming selected optical data intoinfrared flux densities or irradiances. The results provide R, T(eff)blackbody approximations for about 2000 of the stars in Woolley et al.'sCatalog of Stars (1970) within 25 pc of the sun, and additional whitedwarfs, with infrared flux densities predicted for them at ninewavelengths from 2.2 to 101 microns including the Infrared AstronomySatellite bands.
| Observations of late-type dwarfs of the young and old disk population using DDO photometry
Intermediate-band DDO photometry is presented for 52 dwarf starscovering the spectral range from K2 to M2. All the stars have measuresof the emission intensities of the H and K lines of calcium in theirspectra, and it is suggested that thirty of these stars are young stars,based on their motion and calcium emission intensities. The DDOphotometry clearly defines the locus of the K and early M dwarfs, andshows a small separation between the young and old stars, which isinterpreted as a small difference in surface gravity and a possiblymarginal difference in cyanogen intensity.
| The motions of K and M dwarf stars of different ages
Parallax and proper-motion results are summarized for 145 nearby K and Mdwarfs, and space motions are calculated for most of the sample, whichis not biased toward stars with high velocity. The space motions andtheir U, V, and W components are presented, the mean motion and velocitydispersion of the stars are derived, and the velocity distributions arecompared with previous results. The stars are divided into groupsrepresenting the young-disk, old-disk, and halo populations, and thesizes of the groups are examined along with their kinematicalproperties. The weights of the space motions of the individual starscomprising each group are evaluated by means of a rigorous method basedon the premise that the error in tangential velocity must necessarily bea distance-dependent parameter whereas that in radial velocity is not.The results obtained indicate an outward motion of the young stars withrespect to the old ones and confirm that the kinematical local standardof rest is age-sensitive.
| The luminosity law for late-type main-sequence stars in the solar neighborhood
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1974PASP...86..697E&db_key=AST
|
Добавить новую статью
Внешние ссылки
- - Внешних ссылок не найдено -
Добавить внешнюю ссылку
Группы:
|
Наблюдательные данные и астрометрия
| Созвездие: | Андромеда |
| Прямое восхождение: | 00h43m32.86s |
| Склонение: | +33°50'40.4" |
| Видимая звёздная величина: | 8.761 |
| Расстояние: | 20.764 парсек |
| Собственное движение RA: | -204.4 |
| Собственное движение Dec: | -358.8 |
| B-T magnitude: | 10.176 |
| V-T magnitude: | 8.878 |
Каталоги и обозначения:
|
