High Proper Motion Stars. IV. Radial Velocities of 166 Luyten Half-Second Stars
We present 178 radial velocity measurements for 166 late-type starsselected from the Luyten half-second (LHS) proper motion catalog. Spacevelocities are given for all but two of them. Most of the stars liewithin 25 pc of the Sun, but the list includes a handful ofhigh-velocity transients from the halo population. None of the derivedspace velocities is high enough, however, to provide any constraint onthe escape speed at the solar circle. Twenty-six stars are discussed insomewhat more detail, and evidence is adduced that several of them maybe velocity variables.
|
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.
|
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
|
Revised Coordinates and Proper Motions of the Stars in the Luyten Half-Second Catalog
We present refined coordinates and proper-motion data for the highproper-motion (HPM) stars in the Luyten Half-Second (LHS) catalog. Thepositional uncertainty in the original Luyten catalog is typicallygreater than 10" and is often greater than 30". We have used the digitalscans of the POSS I and POSS II plates to derive more accurate positionsand proper motions of the objects. Out of the 4470 candidates in the LHScatalog, 4323 objects were manually reidentified in the POSS I and POSSII scans. A small fraction of the stars were not found because of thelack of finder charts and digitized POSS II scans. The uncertainties inthe revised positions are typically ~2" but can be as high as ~8" in afew cases, which is a large improvement over the original data.Cross-correlation with the Tycho-2 and Hipparcos catalogs yielded 819candidates (with mR<~12). For these brighter sources, theposition and proper-motion data were replaced with the more accurateTycho-2/Hipparcos data. In total, we have revised proper-motionmeasurements and coordinates for 4040 stars and revised coordinates for4330 stars. The electronic version of the paper5 contains the updated information on all 4470stars in the LHS catalog.
|
Resolved Near-Infrared Spectroscopy of the Mysterious Pre-Main-Sequence Binary System T Tauri S
We obtained new near-infrared images of the prototypicalpre-main-sequence triple system T Tau, as well as the first resolvedmedium-resolution spectra of the close pair T Tau S. At the time of ourobservations, the tight binary had a 13 AU projected separation andshowed significant motion since its discovery 3 yr before. The orbitcannot be strongly constrained yet, but the observed motion of T Tau Sbwith respect to T Tau Sa suggests that the system is at least as massiveas T Tau N itself. This may indicate that T Tau N is not the mostmassive star in the system. The spectrum of T Tau Sa, which is totallyfeatureless except for a strong Brγ emission line, identifies thiscomponent with the ``infrared companion,'' whose exact nature remainsobscure but may be the consequence of its being the most massivecomponent of the system. Contrasting sharply with T Tau Sa, the spectrumof T Tau Sb shows numerous photospheric features consistent with anearly-M spectral type. The presence of a strong Brγ emission lineand of a significant veiling continuum classifies this object as adeeply embedded T Tauri star. From these observations, we conclude thatboth components of T Tau S are embedded in their own dense circumstellarcocoons of material, which are probably fed by a much more extendedstructure.
|
The Palomar/MSU Nearby Star Spectroscopic Survey. III. Chromospheric Activity, M Dwarf Ages, and the Local Star Formation History
We present high-resolution echelle spectroscopy of 676 nearby M dwarfs.Our measurements include radial velocities, equivalent widths ofimportant chromospheric emission lines, and rotational velocities forrapidly rotating stars. We identify several distinct groups by theirHα properties and investigate variations in chromospheric activityamong early (M0-M2.5) and mid (M3-M6) dwarfs. Using a volume-limitedsample together with a relationship between age and chromosphericactivity, we show that the rate of star formation in the immediate solarneighborhood has been relatively constant over the last 4 Gyr. Inparticular, our results are inconsistent with recent large bursts ofstar formation. We use the correlation between Hα activity and ageas a function of color to set constraints on the properties of L and Tdwarf secondary components in binary systems. We also identify a numberof interesting stars, including rapid rotators, radial velocityvariables, and spectroscopic binaries. Observations were made at the 60inch telescope at Palomar Mountain, which is jointly owned by theCalifornia Institute of Technology and the Carnegie Institution ofWashington.
|
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
|
Accretion-induced Lithium Line Enhancements in Classical T Tauri Stars: RW Aurigae
It is widely accepted that much of the stochastic variability of T Tauristars is due to accretion by a circumstellar disk. The emission-linespectrum as well as the excess continuum emission are common probes ofthis process. In this communication, we present additional probes of thecircumstellar environment in the form of resonance lines of lowionization potential elements. Using a set of 14 high-resolution echelleobservations of the classical T Tauri star (CTTS) RW Aur, taken between1986 and 1996, we carefully measure the continuum veiling at each epochby comparing more than 500 absorption lines with those of an appropriatetemplate. This allows us to accurately subtract out the continuumemission and to recover the underlying photospheric spectrum. In doingso, we find that selected photospheric lines are enhanced by theaccretion process, namely, the resonance lines of Li I and K I. Aresonance line of Ti I and a low excitation potential line of Ca I alsoshow weak enhancements. Simple slab models and computed line bisectorslead us to propose that these line enhancements are markers of cool gasat the beginning of the accretion flow which provides an additionalsource of line opacity. These results suggest that published values ofsurface lithium abundances of classical T Tauri stars are likely to beoverestimated. This would account for the various reports of surfacelithium abundances in excess of meteoritic values among the extremeCTTSs. Computing LTE lithium abundances of RW Aur in a low and then highaccretion state yields abundances which vary by 1 order of magnitude.The low accretion state lithium abundance is consistent with theoreticalpredictions for a star of this age and mass, while the high accretionstate spectrum yields a supermeteoritic lithium abundance.
|
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.
|
The Abundance of CN. Calcium and Heavy Elements in High Velocity Stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....114..825E&db_key=AST
|
Spectral analysis of M dwarfs
We compare 1.16-1.22 μm spectra of cool low-mass dwarfs withsynthetic spectra calculated with a stellar atmosphere code. Thesynthetic spectra give a representation of the overall spectral featureswhich has not been possible in previous comparisons with cool low-massdwarf spectra, although the interpretation of the observed spectra isseverely hampered by the quality of atomic and molecular input data. Theobserved spectral region is rich in absorption features of which thestrongest are K, Fe, Mg and FeH. Each observed spectrum is compared witha grid of synthetic spectra extending well outside the expectedparameter space for M dwarfs. The effective temperatures, metallicitiesand gravities derived are compared with expectations based on previouswork. For the cooler objects the parameters show broad agreement;however, for the hotter objects the poor fit of Fe lines leads to bestfits to models with low gravity and metallicity. All features show astrong sensitivity to temperature, especially the K and FeH. Metallicityand gravity effects are relatively smaller. For the hotter stars, Mg andFe absorption lines are the most useful discriminators between gravityand metallicity. For the cooler objects the complicated dependence ofmodelled equivalent widths on metallicity and gravity makes it awkwardto separate effects due to a single model parameter. The comparisonssuggest a similar spread in metallicities to that anticipated, althoughfor our sample neither kinematic motion nor membership of a particularphotometric class is, on its own, a reliable indicator of metallicity.Comparison of the observed strong K lines in GD 165B with syntheticspectra indicate that it is relatively metal rich. This result togetherwith an improved measurements of its distance means that within the bestavailable constraints it is likely to be a brown dwarf.
|
The Palomar/MSU Nearby Star Spectroscopic Survey.II.The Southern M Dwarfs and Investigation of Magnetic Activity
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....112.2799H&db_key=AST
|
Photometry of Stars with Large Proper Motion
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....112.2300W&db_key=AST
|
Star Streams and Galactic Structure
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....112.1595E&db_key=AST
|
Medium-Resolution Near-Infrared (2.15-2.35 micron) Spectroscopy of Late-Type Main-Sequence Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....110.2415A&db_key=AST
|
The Palomar/MSU Nearby-Star Spectroscopic Survey. I. The Northern M Dwarfs -Bandstrengths and Kinematics
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....110.1838R&db_key=AST
|
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 MSSSO near-infrared photometric system
The JHKL photometric system currently used at the Mount Stromlo andSiding Spring Observatories (MSSSO) is described via an extensive listof standard-star values and filter transmission curves. At JHK thissystem is identical to the Mount Stromlo Observatory (MSO) systemdefined by Jones and Hyland (1982), except for small zero-pointdifferences which we impose here. Transformations are given between theMSSSO system and several near-infrared photometric systems in use inother observatories and the homogenized JHKL system proposed by Besselland Brett (1988).
|
Photometry of dwarf K and M stars
An observational program using UBVRI photometry is presented for 688stars from among the dwarf K and M stars already found spectroscopicallyby Vyssotsky (1958). Of these, 211 have not been observedphotometrically. These observations were obtained over a period ofseveral years at the Kitt Peak National Observatory using a GaAsphotomultiplier with an 0.9 m reflector. Based on night-to-nightvariations in the measures of individual stars, the internal errors maybe estimated to be roughly 0.01 mag for the colors and 0.015 for the Vmagnitudes. The photometric parallaxes reported for each star werecomputed in the manner discussed by Weis (1986).
|
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.
|
Far infrared properties of late type dwarfs. Infrared fluxes of K & M dwarfs
IRAS fluxes/upper limits are presented for a large sample of K and Mdwarfs. Good agreement is found between the 12 micrometer fluxes andthose derived from the photospheric models of Mould (1976).Relationships between the optical and infrared colors are derived. Theactive dMe/dKe stars appear systematically brighter in the infraredcompared with the less active dM/dK stars, which could be attributed tomore efficient nonradiative heating in their atmosphere. Any systematicdifferences found in our results when compared with those obtained fromprevious studies are attributed to the different analysis packages used.
|
Infrared colors of low-mass stars
A total of 322 red dwarf stars are studied in a review of IR IJHKphotometry to discern chromospheric activity and kinematic dataregarding metallicity effects in the IR color:color diagrams. Themetallicity variations are employed to assess changes in the H(-)continuum opacity and water-vapor characterizations. The stars areclassified in terms of metal-richness with five categories includingyoung disk, old disk, and halo types with attention given to the inverserelationship between metallicity and water-band absorption strength. Theresults include IR photometric parallax relations for each metallicitygroup and absolute magnitudes for single stars as well as temperatures,intrinsic colors, and spectral types. The body of data is useful forconstraining models of the interiors and atmospheres of this class ofstars.
|
The frequency of low-mass companions to K and M stars in the solar neighbourhood
The measurements of radial velocities of 200 stars from the Gliesecatalog during 5 years with an accuracy of 0.5 km/s indicate the absenceof substellar mass companions with periods less than 3000 d. Theprobability of companion detection is determined by numerical modeling.New data on spectroscopic orbits of late-type dwarfs are used toestimate the distribution of companion masses by the maximum likelihoodmethod. The statistical properties of low-mass binaries are differentfrom those of more massive main-sequence and giant systems: thefrequency of spectroscopic binaries is less (10 +/- 2 percent) while atleast half of them have a mass ratio exceeding 0.5. Evidence is foundfor a nonmonotonic distribution of the masses of secondary componentswith a deficit in the 0.2-0.3 solar mass range.
|
Speckle-interferometric observations of stars from the Gliese catalog
Speckle-interferometric observations of dwarf stars with variable orsuspected variable radial velocities were carried out with the 6-mtelescope with the aim of resolving them directly. Of the 21 starsobserved, only Gliese 600 = BD + 11 deg 2874 was resolved for the firsttime. The observations led to the discovery of a new interferometricbinary, Gl 600, and showed the lack of resolvable components for anumber of nearby dwarfs with variable velocities, which imposesrestrictions on the luminosity difference of their satellites.
|
CA II H and K measurements made at Mount Wilson Observatory, 1966-1983
Summaries are presented of the photoelectric measurements of stellar CaII H and K line intensity made at Mount Wilson Observatory during theyears 1966-1983. These results are derived from 65,263 individualobservations of 1296 stars. For each star, for each observing season,the maximum, minimum, mean, and variation of the instrumental H and Kindex 'S' are given, as well as a measurement of the accuracy ofobservation. A total of 3110 seasonal summaries are reported. Factorswhich affect the ability to detect stellar activity variations andaccurately measure their amplitudes, such as the accuracy of the H and Kmeasurements and scattered light contamination, are discussed. Relationsare given which facilitate intercomparison of 'S' values with residualintensities derived from ordinary spectrophotometry, and for convertingmeasurements to absolute fluxes.
|
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.
|
K- and M-type dwarf stars within 25 parsecs of the sun. I - The age-chromospheric activity relations from H-alpha equivalent widths
The available equivalent-width measurements of H-alpha in dwarf K and Mstars within 25 pc of the sun indicate that, as a chromosphericdiagnostic, the H-alpha decay rate is about t exp 0.5. The decay rate ofline emission in Mg II h and k (Ca II H and K) is about t exp 0.3. Thedecay rates are derived from observations of members of a few stellarsuperclusters and groups, for which the consistency of results arguesstrongly for the importance of more data. The only major inconsistencyencountered is for the unique HR 1614 group which, in theage/chromospheric-activity progression, gives different results from MgII h and k and from WH-alpha.
|
Photographic astrometry of binary and proper-motion stars.
In the study of dwarf star distances and of binary-star masses at the61-cm Swarthmore refractor, parallaxes of 69 stars and systems wereobtained by processing some 5000 astrometric plates from April 1988 toJuly 1989. These results are listed along with 11 binary-star massratios and three unresolved pairs.
|
BVRI photometry of the Gliese Catalogue stars
Photoelectri BVRI photometry on the Cousins (Kron-Cape) system has beenobtained for many of the southern faint stars in the Gliese Catalog(1969). This extends the work of Cousins (1980) and provides a uniformset of data for the nearby stars. Several red dwarfs are noted, whichwere used to define the red end of the Cousins system.
|
UBV (RI)c photometry of faint nearby stars.
Not Available
|
INHABITED SKY
