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The Physical Natures of Class I and Flat-Spectrum Protostellar Photospheres: A Near-Infrared Spectroscopic Study
We present high-resolution (R~=18,000), high signal-to-noise ratio, 2μm spectra of 52 IR-selected Class I and flat-spectrum young stellarobjects in the Taurus-Auriga, ρ Ophiuchi, Serpens, Perseus, andCorona Australis dark clouds. We detect key absorption lines in 41objects and fit synthetic spectra generated from pre-main-sequencemodels to deduce the effective temperatures, surface gravities, near-IRveilings, rotation velocities, and radial velocities of each of these 41sources. We find these objects to span ranges in effective temperature,surface gravity, and stellar luminosity that appear similar to those oflate spectral type Class II sources and classical T Tauri stars.However, because of significant but uncertain corrections for scatteringand extinction, the derived luminosities for the embedded protostellarobjects must be regarded as being highly uncertain. We determine thatthe mean 2 μm veiling of Class I and flat-spectrum objects issignificantly higher than that of Class II objects in the same regionwhere both types of objects are extensively observed (ρ Oph). Wefind that a significant fraction of our protostellar sample alsoexhibits emission lines. Twenty-three objects show H2emission, which is usually indicative of the presence of energeticoutflows. Thirty-four sources show H I Brγ emission, and a numberof these exhibit profile asymmetries consistent with infall. Eightsources show significant Δv=2 CO emission suggestive of emissionfrom a circumstellar disk. Overall, these observations indicate thatClass I and flat-spectrum objects are self-embedded protostarsundergoing significant mass accretion, although the objects appear tospan a broad range of mass accretion activity.Data presented herein were obtained at the W. M. Keck Observatory fromtelescope time allocated to the National Aeronautics and SpaceAdministration through the agency's scientific partnership with theCalifornia Institute of Technology and the University of California. TheObservatory was made possible by the generous financial support of theW. M. Keck Foundation.
| Astrophysics of Young Star Binaries
This paper describes our study of the astrophysics of individualcomponents in close pre-main-sequence binaries. We observed both starsin 17 systems, located in four nearby star-forming regions, usinglow-resolution (R=760) infrared spectroscopy and photometry. For 29components we detected photospheric absorption lines and were able todetermine spectral type, extinction, K-band excess, and luminosity. Theother five objects displayed featureless or pure emission line spectra.In ~50% of the systems, the extinction and K-band excess of the primarystars dominate those of the secondaries. Masses and ages were determinedfor these 29 objects by placing them on the H-R diagram, overlaid withtheoretical pre-main-sequence tracks. Most of the binaries appear to becoeval. The ages span 5×105 to 1×107yr. The derived masses range from the substellar, 0.06Msolar, to 2.5 Msolar, and the mass ratios fromM2/M1=0.04 to 1.0. Fourteen stars show evidence ofcircumstellar disks. The K-band excess is well correlated with the K-Lcolor for stars with circumstellar material.
| 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.
| 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.
| 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.
| Component Masses of the Young Spectroscopic Binary UZ Tau E
We report estimates of the masses of the component stars in thepre-main-sequence spectroscopic binary UZ Tau E. These results come fromthe combination of our measurements of the mass ratio,M2/M1=0.28+/-0.01, obtained using high-resolutionH-band spectroscopy, with the total mass of the system,(1.31+/-0.08)(D/140 pc) Msolar, derived from millimeterobservations of the circumbinary disk (Simon, Dutrey, & Guilloteau).The masses of the primary and secondary are (1.016+/-0.065)(D/140 pc)Msolar and (0.294+/-0.027)(D/140 pc) Msolar,respectively. Using the orbital parameters determined from our sixepochs of observation, we find that the inclination of the binary orbit,59.8d+/-4.4d, is consistent with that determined for the circumbinarydisk from the millimeter observations, indicating that the disk andbinary orbits are probably coplanar.
| The Smallest Mass Ratio Young Star Spectroscopic Binaries
Using high-resolution near-infrared spectroscopy with the KeckTelescope, we have detected the radial velocity signatures of the coolsecondary components in four optically identified pre-main-sequence,single-lined spectroscopic binaries. All are weak-lined T Tauri starswith well-defined center-of-mass velocities. The mass ratio for oneyoung binary, NTTS 160905-1859, isM2/M1=0.18+/-0.01, the smallest yet measureddynamically for a pre-main-sequence spectroscopic binary. These newresults demonstrate the power of infrared spectroscopy for the dynamicalidentification of cool secondaries. Visible-light spectroscopy, to date,has not revealed any pre-main-sequence secondary stars with masses<0.5 Msolar, while two of the young systems reported hereare in that range. We compare our targets with a compilation of thepublished young, double-lined spectroscopic binaries and discuss ourunique contribution to this sample.
| 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
| Infrared spectroscopy of cataclysmic variables - III. Dwarf novae below the period gap and nova-like variables
We present K-band spectra of the short-period dwarf novae YZ Cnc, LYHya, BK Lyn, T Leo, SW UMa and WZ Sge, the nova-like variables DW UMa,V1315 Aql, RW Tri, VY Scl, UU Aqr and GP Com, and a series of fielddwarf stars with spectral types ranging from K2 to M6. The spectra ofthe dwarf novae are dominated by emission lines of Hi and Hei. The largevelocity and equivalent widths of these lines, in conjunction with thefact that the lines are double-peaked in the highest inclinationsystems, indicate an accretion disc origin. In the case of YZ Cnc and TLeo, for which we obtained time-resolved data covering a completeorbital cycle, the emission lines show modulations in their equivalentwidths that are most probably associated with the bright spot (theregion where the gas stream collides with the accretion disc). There areno clear detections of the secondary star in any of the dwarf novaebelow the period gap, yielding upper limits of 10-30per cent for thecontribution of the secondary star to the observed K-band flux. Inconjunction with the K-band magnitudes of the dwarf novae, we use thederived secondary star contributions to calculate lower limits to thedistances to these systems. The spectra of the nova-like variables aredominated by broad, single-peaked emission lines of Hi and Hei - eventhe eclipsing systems we observed do not show the double-peaked profilespredicted by standard accretion disc theory. With the exception of RWTri, which exhibits Nai, Cai and 12CO absorption featuresconsistent with a M0V secondary contributing 65per cent of the observedK-band flux, we find no evidence for the secondary star in any of thenova-like variables. The implications of this result are discussed.
| 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 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
| Determination of effective temperatures for an extended sample of dwarfs and subdwarfs (F0-K5).
We have applied the InfraRed Flux Method (IRFM) to a sample of 475dwarfs and subdwarfs in order to derive their effective temperatureswith a mean accuracy of about 1.5%. We have used the new homogeneousgrid of theoretical model atmosphere flux distributions developed byKurucz (1991, 1993) for the application of the IRFM. The atmosphericparameters of the stars cover, roughly, the ranges:3500K<=T_eff_<=8000K -3.5<=[Fe/H]<=+0.53.5<=log(g)<=5. The monocromatic infrared fluxes at the continuum,and the bolometric fluxes are derived using recent results, whichsatisfy the accuracy requeriments of the work. Photometric calibrationshave been revised and applied to estimate metallicities, although directspectroscopic determinations were preferred when available. The adoptedinfrared absolute flux calibration, based on direct optical measurementsof angular stellar diameters, sets the effective temperatures determinedusing the IRFM on the same scale than those obtained by direct methods.We derive three temperatures, T_J_, T_H_ and T_K_, for each star usingthe monochromatic fluxes at different infrared wavelengths in thephotometric bands J, H, and K. They show good consistency over 4000 K,and no trend with wavelength may be appreciated. We provide a detaileddescription of the steps followed for the application of the IRFM, aswell as the sources of the errors associated to the different inputs ofthe method, and their transmission into the final temperatures. We alsoprovide comparison with previous works.
| 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.
| Low mass companions to nearby stars: Spectral classification and its relation to the stellar/substellar break
The relationship between mass and spectral class for main-sequence starshas never been obtained for dwarfs cooler than M6; currently, the truenature of objects classified as M7, M8, M9, or later (be they stellar orsubstellar) is not known. In this paper, spectral types for thecomponents in five low mass binary systems are estimated based onpreviously published infrared speckle measurements, red/infraredphotometry, and parallax data, together with newly acquired highsignal-to-noise composite spectra of the systems and revised magnitudedifference relations for M dwarfs. For two of these binaries, thesecondary has a smaller mass (less than 0.09 solar mass) than any objecthaving a dynamically measured mass and a known spectral type, thusextending the spectral class/mass relation to lower masses than haspreviously been possible. Data from the higher mass components (0.09solar mass less than M less than 0.40 solar mass) are consistent withearlier results; the two lowest mass objects -- though having masserrors which could place them on either side of the M dwarf/brown dwarfdividing line (Mass is about 0.08 solar mass) -- are found to havespectral types no cooler than M6.5 V. An extrapolation of the updatedspectral class/mass relation to the hydrogen-burning limit suggests thatobjects of type M7 and later may be substellar. Direct confirmation ofthis awaits the discovery of a close, very late-type binary for whichdynamical masses can be measured.
| The low mass Hyades and the evaporation of clusters
The 135 single stars and 85 binary systems, redder than R-I = +0.34 magand brighter than V = 17 mag, between alpha = 3.75 h and 5.0 h and delta= +5 deg and + 25 deg show a luminosity function that differsconsiderably from that of the general field stars within 20 pc of theSun. The ratio of double star components to single cluster membersincreases markedly with decreasing luminosity. Forty-three single starsand 16 binary systems that are members of the Hyades supercluster within20 pc of the Sun show the same luminosity function as the field stars inthat region. Fifty percent of the cluster members and 40 percent of thesupercluster members are components of binary stars. The equivalentwidths of H-alpha appear to support a range of ages (approximately 8 to16 x 108 yr) for the cluster stars and demonstrate that theoldest objects are in the supercluster. A list of cluster members, whichmay include the end of the stable main sequence, but for which accurate(R-I) photometry is not available, is included. The half-dozen knownparallax stars of the faintest luminosity contain at least onesupercluster member, TVLM 868-110639, which is probably beyond thestable, nuclear burning main sequence as a 'transitional' or 'brown'dwarf.
| 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.
| The mass distribution of the secondary components of K and M dwarfs
Three homogeneous samples of late-type single- and double-lined mainsequence spectroscopic binaries (a total of 56 systems) were analyzed bythe maximum likelihood method. The distribution function of the massesof secondary components in each of the three samples exhibits two peaksat 0.1 and 0.5 solar mass and a gap at 0.2 solar mass. The bimodalcharacter of the distribution disappears with orbital periods greaterthan about 150 d. At the lower end of the main sequence the frequency ofspectroscopic binaries is less, and two-thirds of them have mass ratiosgreater than 0.5.
| A standard stellar spectral sequence in the red/near-infrared - Classes K5 to M9
Spectra of 39 K and M dwarf spectroscopic standards, as well as 38secondary standards, are shown from 6300 to 9000 A. This sequence of 77spectra ranges from K5 V to M9 and has been classified on the Boeshaarsystem. Spectra of 14 giant and higher luminosity star are presentedfrom 6900 to 9000 A, along with two miscellaneous spectra. Also given isan extensive list of atomic and molecular features found in the spectraof late K and M stars of all luminosity classes. From the spectralslopes and the strengths of the red/near-infrared spectral features itis possible to distinguish giants from dwarfs and to classify M dwarfsof all spectral subclasses. The library of spectra has been used toconstruct a spectral class versus mass relation which allows massestimates to be made based upon a dwarf's spectral class alone. Therelation is based on eight objects having both well-determined massesand spectral types.
| 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.
| 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
| Magnetic structure in cool stars. XVI - Emissions from the outer atmosphere of M-type dwarfs
Consideration is given to emission from the outer atmospheres of M-typedwarfs in several spectral lines originating from the chromosphere, thetransition-region, and the soft X-ray emission from the corona. It isshown that M-type dwarfs systematically deviate from relations betweenflux densities in soft X-rays and chromospheric and transition-regionemission lines. The quantitative relation between the equivalent widthof H-alpha and the Ca II, H, and K emission index is determined. It issuggested that the emission in the Balmer spectrum may result from backheating by coronal soft X-rays.
| The infrared luminosity function for low-mass stars
IR observational luminosity functions are presented for M dwarfs towardsthe South Galactic Pole and the Hyades cluster. A compilation of VRIJHKdata is given for 200 parallax stars. Two-color NIR/IR diagrams of thedata are used to demonstrate metallicity and gravity effects. It isshown that I-J is the purest temperature color index. The corrections tothe luminosity functions that are necessary to allow for magnitudeerrors (Malmquist effects) are discussed. It is found that there is arise in the luminosity function and the mass function for stars in thesolar neighborhood with masses close to the hydrogen-burning limit.
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