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The Sloan Digital Sky Survey Data Release 7 Spectroscopic M Dwarf Catalog. II. Statistical Parallax Analysis
We present a statistical parallax analysis of low-mass dwarfs from theSloan Digital Sky Survey. We calculate absolute r-band magnitudes(Mr ) as a function of color and spectral type andinvestigate changes in Mr with location in the Milky Way. Wefind that magnetically active M dwarfs are intrinsically brighter inMr than their inactive counterparts at the same color orspectral type. Metallicity, as traced by the proxy ?, also affectsMr , with metal-poor stars having fainter absolute magnitudesthan higher metallicity M dwarfs at the same color or spectral type.Additionally, we measure the velocity ellipsoid and solar reflex motionfor each subsample of M dwarfs. We find good agreement between ourmeasured solar peculiar motion and previous results for similarpopulations, as well as some evidence for differing motions of early andlate M-type populations in U and W velocities that cannot be attributedto asymmetric drift. The reflex solar motion and the velocitydispersions both show that younger populations, as traced by magneticactivity and location near the Galactic plane, have experienced lessdynamical heating. We introduce a new parameter, the independentposition altitude (IPA), to investigate populations as a function ofvertical height from the Galactic plane. M dwarfs at all types exhibitan increase in velocity dispersion when analyzed in comparable IPAsubgroups.
| Bayesian inference of stellar parameters and interstellar extinction using parallaxes and multiband photometry
Astrometric surveys provide the opportunity to measure the absolutemagnitudes of large numbers of stars, but only if the individualline-of-sight extinctions are known. Unfortunately, extinction is highlydegenerate with stellar effective temperature when estimated frombroad-band optical/infrared photometry. To address this problem, Iintroduce a Bayesian method for estimating the intrinsic parameters of astar and its line-of-sight extinction. It uses both photometry andparallaxes in a self-consistent manner in order to provide anon-parametric posterior probability distribution over the parameters.The method makes explicit use of domain knowledge by employing theHertzsprung-Russell Diagram (HRD) to constrain solutions and to ensurethat they respect stellar physics. I first demonstrate this method byusing it to estimate effective temperature and extinction from BVJHKdata for a set of artificially reddened Hipparcos stars, for whichaccurate effective temperatures have been estimated from high-resolutionspectroscopy. Using just the four colours, we see the expected strongdegeneracy (positive correlation) between the temperature andextinction. Introducing the parallax, apparent magnitude and the HRDreduces this degeneracy and improves both the precision (reduces theerror bars) and the accuracy of the parameter estimates, the latter byabout 35 per cent. The resulting accuracy is about 200 K in temperatureand 0.2 mag in extinction. I then apply the method to estimate theseparameters and absolute magnitudes for some 47 000 F, G, K Hipparcosstars which have been cross-matched with Two-Micron All-Sky Survey(2MASS). The method can easily be extended to incorporate the estimationof other parameters, in particular metallicity and surface gravity,making it particularly suitable for the analysis of the 109stars from Gaia.
| Chromospheric Activity and Jitter Measurements for 2630 Stars on the California Planet Search
We present time series measurements of chromospheric activity for morethan 2600 main-sequence and subgiant stars on the California PlanetSearch (CPS) program with spectral types ranging from about F5V to M4Vfor main-sequence stars and from G0IV to about K5IV for subgiants. Thelarge data set of more than 44,000 spectra allows us to identify anempirical baseline floor for chromospheric activity as a function ofcolor and height above the main sequence. We define ?S as anexcess in emission in the Ca II H and K lines above the baselineactivity floor and define radial velocity jitter as a function of?S and B - V for main-sequence and subgiant stars. Although thejitter for any individual star can always exceed the baseline level, wefind that K dwarfs have the lowest level of jitter. The lack ofcorrelation between observed jitter and chromospheric activity in Kdwarfs suggests that the observed jitter is dominated by instrumental oranalysis errors and not astrophysical noise sources. Thus, given thelong-term precision for the CPS program, radial velocities are notcorrelated with astrophysical noise for chromospherically quiet K dwarfstars, making these stars particularly well suited for the highestprecision Doppler surveys. Chromospherically quiet F and G dwarfs andsubgiants exhibit higher baseline levels of astrophysical jitter than Kdwarfs. Despite the fact that the rms in Doppler velocities iscorrelated with the mean chromospheric activity, it is rare to seeone-to-one correlations between the individual time series activity andDoppler measurements, diminishing the prospects for correctingactivity-induced velocity variations in F and G dwarfs.Based on observations obtained at the Keck Observatory and LickObservatory, which are operated by the University of California.
| Rotation and Magnetic Activity in a Sample of M-Dwarfs
We have analyzed the rotational broadening and chromospheric activity ina sample of 123 M-dwarfs, using spectra taken at the W.M. KeckObservatory as part of the California Planet Search program. We findthat only seven of these stars are rotating more rapidly than ourdetection threshold of v sin i ? 2.5 km s-1.Rotation appears to be more common in stars later than M3 than in theM0-M2.5 mass range: we estimate that less than 10% of early-M stars aredetectably rotating, whereas roughly a third of those later than M4 showsigns of rotation. These findings lend support to the view thatrotational braking becomes less effective in fully convective stars. Bymeasuring the equivalent widths of the Ca II H and K lines for the starsin our sample, and converting these to approximate L Ca/Lbol measurements, we also provide constraints on theconnection between rotation and magnetic activity. Measurable rotationis a sufficient, but not necessary condition for activity in our sample:all the detectable rotators show strong Ca II emission, but so too do asmall number of non-rotating stars, which we presume may lie at highinclination angles relative to our line of sight. Our data areconsistent with a "saturation-type" rotation-activity relationship, withactivity roughly independent of rotation above a threshold velocity ofless than 6 km s-1. We also find weak evidence for a"gap" in L Ca/L bol between a highly activepopulation of stars, which typically are detected as rotators, andanother much less active group.
| Tracers of Chromospheric Structure. I. Observations of Ca II K and Hα in M Dwarfs
We report on our observing program4This paper is based onobservations obtained with the Apache Point Observatory 3.5 m telescope,which is owned and operated by the Astrophysical Research Consortium.Some of the data presented herein were obtained at the W. M. KeckObservatory, which is operated as a scientific partnership among theCalifornia Institute of Technology, the University of California and theNational Aeronautics and Space Administration. The Observatory was madepossible by the generous financial support of the W. M. Keck Foundation.to capture simultaneous spectra of Ca II and Balmer lines in a sample ofnearby M3 dwarfs. Our goal is to investigate the chromospherictemperature structure required to produce these lines at the observedlevels. We find a strong positive correlation between instantaneousmeasurements of Ca II K and the Balmer lines in active stars, althoughthese lines may not be positively correlated in time-resolvedmeasurements. The relationship between Hα and Ca II K remainsambiguous for weak and intermediate activity stars, with Hαabsorption corresponding to a range of Ca II K emission. A similarrelationship is also observed between Ca II K and the higher-orderBalmer lines. As our sample consists of a single spectral type,correlations between these important chromospheric tracers cannot beascribed to continuum effects, as suggested by other authors. These dataconfirm prior nonsimultaneous observations of the Hα line behaviorwith increasing activity, showing an initial increase in the Hαabsorption with increasing Ca II K emission, prior to Hα fillingin and eventually becoming a pure emission line in the most activestars. We also compare our optical measurements with archival UV andX-ray measurements, finding a positive correlation between thechromospheric and coronal emission for both high and intermediateactivity stars. We compare our results with previous determinations ofthe active fraction of low-mass stars, and discuss them in the contextof surface inhomogeneity. Lastly, we discuss the application of thesedata as empirical constraints on new static models of quiescent M dwarfatmospheres.
| The effect of activity on stellar temperatures and radii
Context: Recent analyses of low-mass eclipsing binary stars haveunveiled a significant disagreement between the observations andpredictions of stellar structure models. Results show that theoreticalmodels underestimate the radii and overestimate the effectivetemperatures of low-mass stars but yield luminosities that accord withobservations. A hypothesis based upon the effects of stellar activitywas put forward to explain the discrepancies. Aims: In this paper westudy the existence of the same trend in single active stars and providea consistent scenario to explain systematic differences between activeand inactive stars in the H-R diagram reported earlier. Methods: Theanalysis is done using single field stars of spectral types late-K and Mand computing their bolometric magnitudes and temperatures throughinfrared colours and spectral indices. The properties of the stars insamples of active and inactive stars are compared statistically toreveal systematic differences. Results: After accounting for a numberof possible bias effects, active stars are shown to be cooler thaninactive stars of similar luminosity therefore implying a larger radiusas well, in proportions that are in excellent agreement with those foundfrom eclipsing binaries. Conclusions: The present results generalisethe existence of strong radius and temperature dependences on stellaractivity to the entire population of low-mass stars, regardless of theirmembership in close binary systems.Tables 1 and 2 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/478/507
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| Ca II H and K Chromospheric Emission Lines in Late-K and M Dwarfs
We have measured the profiles of the Ca II H and K chromosphericemission lines in 147 main-sequence stars of spectral type M5-K7 (masses0.30-0.55 Msolar) using multiple high-resolution spectraobtained during 6 years with the HIRES spectrometer on the Keck Itelescope. Remarkably, the average FWHM, equivalent widths, and lineluminosities of Ca II H and K increase by a factor of 3 with increasingstellar mass over this small range of stellar masses. We fit the Ca II Hand K lines with a double-Gaussian model to represent both thechromospheric emission and the non-LTE central absorption. Most of thesample stars display a central absorption that is typically redshiftedby ~0.1 km s-1 relative to the emission. This implies thatthe higher level, lower density chromospheric material has a smalleroutward velocity (or higher inward velocity) by 0.1 km s-1than the lower level material in the chromosphere, but the nature ofthis velocity gradient remains unknown. The FWHM of the Ca II H and Kemission lines increase with stellar luminosity, reminiscent of theWilson-Bappu effect in FGK-type stars. Both the equivalent widths andFWHM exhibit modest temporal variability in individual stars. At a givenvalue of MV, stars exhibit a spread in both the equivalentwidth and FWHM of Ca II H and K, due both to a spread in fundamentalstellar parameters, including rotation rate, age, and possiblymetallicity, and to the spread in stellar mass at a given MV.The K line is consistently wider than the H line, as expected, and itscentral absorption is more redshifted, indicating that the H and K linesform at slightly different heights in the chromosphere where thevelocities are slightly different. The equivalent width of Hαcorrelates with Ca II H and K only for stars having Ca II equivalentwidths above ~2 Å, suggesting the existence of a magneticthreshold above which the lower and upper chromospheres become thermallycoupled.Based on observations obtained at the W. M. Keck Observatory, which isoperated jointly by the University of California and the CaliforniaInstitute of Technology. Keck time has been granted by both NASA and theUniversity of California.
| 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.
| Chromospheric Ca II Emission in Nearby F, G, K, and M Stars
We present chromospheric Ca II H and K activity measurements, rotationperiods, and ages for ~1200 F, G, K, and M type main-sequence stars from~18,000 archival spectra taken at Keck and Lick Observatories as a partof the California and Carnegie Planet Search Project. We have calibratedour chromospheric S-values against the Mount Wilson chromosphericactivity data. From these measurements we have calculated medianactivity levels and derived R'HK, stellar ages,and rotation periods from general parameterizations for 1228 stars,~1000 of which have no previously published S-values. We also presentprecise time series of activity measurements for these stars.Based on observations obtained at Lick Observatory, which is operated bythe University of California, and on observations obtained at the W. M.Keck Observatory, which is operated jointly by the University ofCalifornia and the California Institute of Technology. The KeckObservatory was made possible by the generous financial support of theW. M. Keck Foundation.
| The Brown Dwarf Desert at 75-1200 AU
We present results of a comprehensive infrared coronagraphic search forsubstellar companions to nearby stars. The research consisted of (1) a178-star survey at Steward and Lick observatories, with opticalfollow-up from Keck Observatory, capable of detecting companions withmasses greater than 30 MJ, and semimajor axes between about140 to 1200 AU; (2) a 102-star survey using the Keck Telescope, capableof detecting extrasolar brown dwarfs and planets typically more massivethan 10 MJ, with semimajor axes between about 75 and 300 AU.Only one brown dwarf companion was detected, and no planets. Thefrequency of brown dwarf companions to G, K, and M stars orbitingbetween 75 and 300 AU is measured to be 1%+/-1%, the most precisemeasurement of this quantity to date. The frequency of massive (greaterthan 30 MJ) brown dwarf companions at 120-1200 AU is found tobe f=0.7%+/-0.7%. The frequency of giant planet companions with massesbetween 5 and 10 MJ orbiting between 75 and 300 AU ismeasured here for the first time to be no more than ~3%. Together withother surveys that encompass a wide range of orbital separations, theseresults imply that substellar objects with masses between 12 and 75MJ form only rarely as companions to stars. Theories of starformation that could explain these data are only now beginning toemerge.
| 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.
| Radial Velocities for 889 Late-Type Stars
We report radial velocities for 844 FGKM-type main-sequence and subgiantstars and 45 K giants, most of which had either low-precision velocitymeasurements or none at all. These velocities differ from the standardstars of Udry et al. by 0.035 km s-1 (rms) for the 26 FGKstandard stars in common. The zero point of our velocities differs fromthat of Udry et al.: =+0.053km s-1. Thus, these new velocities agree with the best knownstandard stars both in precision and zero point, to well within 0.1 kms-1. Nonetheless, both these velocities and the standardssuffer from three sources of systematic error, namely, convectiveblueshift, gravitational redshift, and spectral type mismatch of thereference spectrum. These systematic errors are here forced to be zerofor G2 V stars by using the Sun as reference, with Vesta and day sky asproxies. But for spectral types departing from solar, the systematicerrors reach 0.3 km s-1 in the F and K stars and 0.4 kms-1 in M dwarfs. Multiple spectra were obtained for all 889stars during 4 years, and 782 of them exhibit velocity scatter less than0.1 km s-1. These stars may serve as radial velocitystandards if they remain constant in velocity. We found 11 newspectroscopic binaries and report orbital parameters for them. Based onobservations obtained at the W. M. Keck Observatory, which is operatedjointly by the University of California and the California Institute ofTechnology, and on observations obtained at the Lick Observatory, whichis operated by the University of California.
| 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.
| Meeting the Cool Neighbors. I. Nearby Stars in the NLTT Catalogue: Defining the Sample
We are currently undertaking a program aimed at identifying previouslyunrecognized late-type dwarfs within 20 pc of the Sun. As a first step,we have cross-referenced Luyten's NLTT proper-motion catalog against thesecond incremental release of the Two Micron All Sky Survey (2MASS)Point Source Catalog and use optical/infrared colors, derived bycombining Luyten's mr estimates with 2MASS data, to identifycandidate nearby stars. This paper describes the definition of areference sample of 1245 stars and presents a compilation of literaturedata for more than one-third of the sample. Only 274 stars havetrigonometric parallax measurements, but we have used data for nearbystars with well-determined trigonometric parallaxes to computecolor-magnitude relations in the (MV, V-K), (MV,V-I), and (MI, I-J) planes and use those relations todetermine photometric parallaxes for NLTT stars with optical photometry.Based on the 2MASS JHKs data alone, we have identified afurther 42 ultracool dwarfs (J-Ks>0.99) and useJ-Ks colors to estimate photometric parallaxes. Combiningthese various techniques, we identify 308 stars with formal distances ofless than 20 pc, while a further 46 have distance estimates within 1σ of our survey limit. Of these 354 stars, 75, including 39 of theultracool dwarfs, are new to nearby-star catalogs. Two stars with bothoptical and near-infrared photometry are potential additions to theimmediate solar neighborhood, with formal distance estimates of lessthan 10 pc.
| 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
| 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
| Preliminary Version of the Third Catalogue of Nearby Stars
Not Available
| Photometric parallaxes for selected stars of color class M from the NLTT catalog. III - The declination zone +20 deg to +45 deg
VRI photometry and photometric parallaxes are presented for a sample of787 late-type stars in the NLTT catalog for which no trigonometricparallaxes have been measured. Additional photometry of 108 stars withtrigonometric parallaxes is also presented. For the program stars, 131have pi(ph) of 0.04 arcsec or greater and six of these have pi(ph) of0.10 arcsec or greater. The percentage of subdwarfs among the stars thusfar surveyed is probably less than 3 percent.
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