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Rotational Velocities for M Dwarfs
We present spectroscopic rotation velocities (v sin i) for 56 M dwarfstars using high-resolution Hobby-Eberly Telescope High ResolutionSpectrograph red spectroscopy. In addition, we have also determinedphotometric effective temperatures, masses, and metallicities ([Fe/H])for some stars observed here and in the literature where we couldacquire accurate parallax measurements and relevant photometry. We haveincreased the number of known v sin i values for mid M stars by around80% and can confirm a weakly increasing rotation velocity withdecreasing effective temperature. Our sample of v sin is peak at lowvelocities (~3 km s-1). We find a change in therotational velocity distribution between early M and late M stars, whichis likely due to the changing field topology between partially and fullyconvective stars. There is also a possible further change in therotational distribution toward the late M dwarfs where dust begins toplay a role in the stellar atmospheres. We also link v sin i to age andshow how it can be used to provide mid-M star age limits. When allliterature velocities for M dwarfs are added to our sample, there are198 with v sin i <= 10 km s-1 and 124 in themid-to-late M star regime (M3.0-M9.5) where measuring precision opticalradial velocities is difficult. In addition, we also search the spectrafor any significant Hα emission or absorption. Forty three percentwere found to exhibit such emission and could represent young, activeobjects with high levels of radial-velocity noise. We acquired twoepochs of spectra for the star GJ1253 spread by almost one month and theHα profile changed from showing no clear signs of emission, toexhibiting a clear emission peak. Four stars in our sample appear to below-mass binaries (GJ1080, GJ3129, Gl802, and LHS3080), with both GJ3129and Gl802 exhibiting double Hα emission features. The tablespresented here will aid any future M star planet search target selectionto extract stars with low v sin i.Based on observations obtained with the Hobby-Eberly Telescope, which isa joint project of the University of Texas at Austin, the PennsylvaniaState University, Stanford University,Ludwig-Maximilians-Universität München, andGeorg-August-Universität Göttingen.
| Evidence for Magnetic Flux Saturation in Rapidly Rotating M Stars
We present magnetic flux measurements in seven rapidly rotating Mdwarfs. Our sample stars have X-ray and Hα emission indicative ofsaturated emission, i.e., emission at a high level, independent ofrotation rate. Our measurements are made using near-infrared FeHmolecular spectra observed with the High Resolution Echelle Spectrometerat Keck. Because of their large convective overturn times, the rotationvelocity of M stars with small Rossby numbers is relatively slow anddoes not hamper the measurement of Zeeman splitting. The Rossby numbersof our sample stars are as small as 0.01. All our sample stars exhibitmagnetic flux of kG strength. We find that the magnetic flux saturatesin the same regime as saturation of coronal and chromospheric emission,at a critical Rossby number of around 0.1. The filling factors of bothfield and emission are near unity by then. We conclude that the strengthof surface magnetic fields remains independent of rotation rate belowthat; making the Rossby number yet smaller by a factor of 10 has littleeffect. These saturated M-star dynamos generate an integrated magneticflux of roughly 3 kG, with a scatter of about 1 kG. The relation betweenemission and flux also has substantial scatter.
| M dwarfs: effective temperatures, radii and metallicities
We empirically determine effective temperatures and bolometricluminosities for a large sample of nearby M dwarfs, for which highaccuracy optical and infrared photometry is available. We introduce anew technique which exploits the flux ratio in different bands as aproxy of both effective temperature and metallicity. Our temperaturescale for late-type dwarfs extends well below 3000K (almost to the browndwarf limit) and is supported by interferometric angular diametermeasurements above 3000K. Our metallicities are in excellent agreement(usually within 0.2dex) with recent determinations via independenttechniques. A subsample of cool M dwarfs with metallicity estimatesbased on hotter Hipparcos common proper motion companions indicates ourmetallicities are also reliable below 3000K, a temperature rangeunexplored until now. The high quality of our data allows us to identifya striking feature in the bolometric luminosity versus temperatureplane, around the transition from K to M dwarfs. We have compared oursample of stars with theoretical models and conclude that thistransition is due to an increase in the radii of the M dwarfs, a featurewhich is not reproduced by theoretical models.
| 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
| Further observations of Hipparcos red stars and standards for UBV(RI)C photometry
We present homogeneous and standardized UBV(RI)C JHKphotometry for over 100 M stars selected from an earlier paper on thebasis of apparent photometric constancy. L photometry has been obtainedfor stars brighter than about L = 6. Most of the stars have asubstantial number of UBV(RI)C observations and, it is hoped,will prove useful as red supplementary standards. Additionally, we listJHK photometry for nearly 300 Hipparcos red stars not selected asstandards, as well as L photometry for the brightest stars.
| The First Direct Measurements of Surface Magnetic Fields on Very Low Mass Stars
We present the first direct magnetic field measurements on M dwarfscooler than spectral class M4.5. Utilizing a new method based on the FeHband near 1 μm, we categorize the integrated surface magnetic flux aslow (well under 1 kG), intermediate (between 1 and about 2.5 kG), orstrong (greater than about 3 kG) for a set of more than 20 stars rangingfrom M2 down to M9. Along with the field, we also measure the rotationalbroadening (vsini) and Hα emission strength. Our goal is toadvance the understanding of how dynamo field production varies withstellar parameters for very low mass stars, how the field and emissionactivity are related, and whether there is a connection between therotation and magnetic flux. We find that fields are produced throughoutthe M dwarfs. In the mid-M stars, there is a clear connection betweenslow rotation and weak fields. In the late-M stars, rotation is alwaysmeasurable, and the strongest fields are associated with with the mostrapid rotators. Interestingly, these very cool rapid rotators appear tohave the largest magnetic flux in the whole sample (greater than in theclassical dMe stars). Hα emission is found to be a good proxy formagnetic fields, although the relation between the fractional emissionand the magnetic flux varies with effective temperature. The drop-off inthis fractional emission near the bottom of the main sequence is notaccompanied by a drop-off in magnetic flux. It is clear that themethodology we have developed can be further applied to discover moreabout the behavior of magnetic dynamos and activity in cool and fullyconvective objects.
| 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.
| Exploring the selection of galaxy clusters and groups: an optical survey for X-ray dark clusters
Data from a new, wide-field, coincident optical and X-ray survey, theX-ray Dark Cluster Survey (XDCS), are presented. This survey comprisessimultaneous and independent searches for clusters of galaxies in theoptical and X-ray passbands. Optical cluster detection algorithmsimplemented on the data are detailed. Two distinct optically selectedcatalogues are constructed, one based on I-band overdensity, the otheron overdensities of colour-selected galaxies. The superior accuracy ofthe colour-selection technique over that of the single-passband methodis demonstrated, via internal consistency checks and comparison withexternal spectroscopic redshift information. This is compared with anX-ray-selected cluster catalogue. In terms of gross numbers, the surveyyields 185 I-band-selected, 290 colour-selected and 15 X-ray-selectedsystems, residing in ~11 deg2 of optical + X-ray imaging.The relationship between optical richness/luminosity and X-rayluminosity is examined, by measuring X-ray luminosities at the positionsof our 290 colour-selected systems. Power-law correlations between theoptical richness/luminosity and X-ray luminosity are fitted, bothexhibiting approximately 0.2 dex of intrinsic scatter. Interestingoutliers in these correlations are discussed in greater detail.Spectroscopic follow-up of a subsample of X-ray underluminous systemsconfirms their reality.
| 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
| The radii and spectra of the nearest stars
We discuss direct measurements of the radii of 36 stars located closerthan 25 parsecs to the Sun. We present the data on 307 radii and 326spectral types and luminosity classes for the nearest stars locatedinside the sphere with a radius of 10 parsecs.
| 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.
| UBV(RI)C photometry of Hipparcos red stars
We present homogeneous and standardized UBV(RI)C photometryfor nearly 550 M stars selected from the Hipparcos satellite data baseusing the following selection criteria: lack of obvious variability (noHipparcos variability flag); δ<+10°(V-I)>1.7 and Vmagnitude fainter than about 7.6. Comparisons are made between thecurrent photometry, other ground-based data sets and Hipparcosphotometry. We use linear discriminant analysis to determine aluminosity segregation criterion for late-type stars, and principalcomponent analysis to study the statistical structure of the colourindices and to calibrate absolute magnitude in terms of (V-I) for thedwarf stars. Various methods are used to determine the mean absolutemagnitude of the giant stars. We find 10 dwarf stars, apparentlypreviously unrecognized (prior to Hipparcos) as being within 25pc,including five within 20pc.
| 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.
| 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.
| The ROSAT International X-ray/Optical Survey (RIXOS): source catalogue
We describe the ROSAT International X-ray/Optical Survey (RIXOS), amedium-sensitivity survey and optical identification of X-ray sourcesdiscovered in ROSAT high Galactic latitude fields (|b|>28 deg) andobserved with the Position Sensitive Proportional Counter (PSPC)detector. The survey made use of the central 17arcmin of each ROSATfield. A flux limit of3x10-14ergcm-2s-1 (0.5-2keV) wasadopted for the survey, and a minimum exposure time of 8000s wasrequired for qualifying ROSAT observations. X-ray sources in the surveyare therefore substantially above the detection threshold of each fieldused, and many contain enough counts to allow the X-ray spectral slopeto be estimated. Spectroscopic observations of potential counterpartswere obtained of all sources down to the survey limit in 64 fields,totalling a sky area of 15.77deg2. Positive opticalidentifications are made for 94per cent of the 296 sources thusexamined. A further 18 fields (4.44deg2), containing 105sources above the 3x10-14ergcm-2s-1survey limit, are completely optically identified to a higher flux of8x10-14ergcm-2s-1 (0.5-2keV). Opticalspectroscopic data are supplemented by deep CCD imaging of many sourcesto reveal the morphology of the optical counterparts, and objects toofaint to register on Sky Survey plates. The faintest opticalcounterparts have R~22. This paper describes the survey method, andpresents a catalogue of the RIXOS sources and their opticalidentifications. Finding charts based on Sky Survey data are given foreach source, supplemented by CCD imaging where necessary.
| A systematic analysis of X-ray variability of dM stars
We have systematically analyzed X-ray variability of dM stars. Our database is the sample of all dM stars listed in the CNS3 (Gliese &Jahreiss 1991) catalog which have been observed with the ROSAT PSPC. Ourdata sample includes 86 pointed observations of 55 distinct stars ormultiple systems. A large fraction of stars shows significantvariations, regardless of their quiescent flux. Variability is detectedon all observable time scales. The amplitudes of these variations areindependent of both stellar X-ray and visual luminosity. Compared tosolar X-ray variability properties our results suggest that theamplitude distribution of X-ray variability in dM stars is consistentwith the analogous distribution for solar flares. We discuss the effectof variability on the spread observed in the X-ray luminosity functionof M stars. The comparison of our data with those obtained with EinsteinIPC shows that variations on time scales shorter than a few month aremore common than long term variations comparable to, e.g., the 11 yearssolar cycle.
| Rotation and chromospheric activity in field M dwarfs
We have obtained high resolution spectra for a volume-limited sample of118 field M dwarfs. From these observations we derive projectedrotational velocities and fluxes in the H_alpha and H_beta lines. 8stars are double-lined spectroscopic binaries with measured or probableperiods short enough for rotation to be tidally synchronized with theorbit, and another 11 are visual binaries where we cannot yet separatethe lines of the two stars. Of the remaining 99 stars, 24 haverotational velocities above our detection limit of ~ 2 km.s(-1) , andsome are quite fast rotators, including two with v sin i\ =~ 30 km.s(-1)and one with v sin i\ =~ 50 km.s(-1) . Given the small radii of Mdwarfs, these moderate rotational velocities correspond to rather shortmaximum rotational periods, of only 7-8 hours. These three stars aregood candidates for Doppler imaging. We find that rotation is stronglycorrelated with both spectral type and kinematic population: all starswith measurable rotation are later than M3.5, and all but one havekinematic properties typical of the young disk, or intermediate betweenthe young disk and the the old disk. We interpret this correlation asevidence for a spin-down timescale that increases with decreasing mass.At the age of the old disk or halo, all stars earlier than M5-M6(0.1-0.15Msun) have spun-down to below our detection limit,while at the age of the young disk this has only happened for starsearlier than M3.5. The one star with measurable rotation and akinematics intermediate between old disk and population II has spectraltype M6. It is probably an old star whose mass is low enough that it hasretained significant rotation up to present, still consistently withlonger spin-down times for lower mass stars. We observe, on the otherhand, no conspicuous change in the v sin i\ distribution or activitypattern at the mass (M ~ 0.35 Msun) below which stars remainfully convective down to the main sequence. These new data areconsistent with a saturated correlation between rotation and activity,similar to the one observed for younger or more massive stars:L_X/Lbol and L_{H_alpha }/Lbol both correlate withv sin i\ for v sin i\ -5km.s^{-1} and then saturate at respectively10^{-2.5} and 10^{-3.5}$. Based on observations made at the Observatoirede Haute-Provence (CNRS), France Tables 2 and 4 are also available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html.
| 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
| Distribution and Corrlation of Age, Abundance, and Motion of Lower Main Sequence Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....111..466E&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 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
| Radio continuum emission from stars: a catalogue update.
An updated version of my catalogue of radio stars is presented. Somestatistics and availability are discussed.
| A volume-limited ROSAT survey of extreme ultraviolet emission from all nondegenerate stars within 10 parsecs
We report the results of a volume-limited ROSAT Wide Field Camera (WFC)survey of all nondegenerate stars within 10 pc. Of the 220 known starsystems within 10 pc, we find that 41 are positive detections in atleast one of the two WFC filter bandpasses (S1 and S2), while weconsider another 14 to be marginal detections. We compute X-rayluminosities for the WFC detections using Einstein Imaging ProportionalCounter (IPC) data, and these IPC luminosities are discussed along withthe WFC luminosities throughout the paper for purposes of comparison.Extreme ultraviolet (EUV) luminosity functions are computed for singlestars of different spectral types using both S1 and S2 luminosities, andthese luminosity functions are compared with X-ray luminosity functionsderived by previous authors using IPC data. We also analyze the S1 andS2 luminosity functions of the binary stars within 10 pc. We find thatmost stars in binary systems do not emit EUV radiation at levelsdifferent from those of single stars, but there may be a fewEUV-luminous multiple-star systems which emit excess EUV radiation dueto some effect of binarity. In general, the ratio of X-ray luminosity toEUV luminosity increases with increasing coronal emission, suggestingthat coronally active stars have higher coronal temperatures. We findthat our S1, S2, and IPC luminosities are well correlated withrotational velocity, and we compare activity-rotation relationsdetermined using these different luminosities. Late M stars are found tobe significantly less luminous in the EUV than other late-type stars.The most natural explanation for this results is the concept of coronalsaturation -- the idea that late-type stars can emit only a limitedfraction of their total luminosity in X-ray and EUV radiation, whichmeans stars with very low bolometric luminosities must have relativelylow X-ray and EUV luminosities as well. The maximum level of coronalemission from stars with earlier spectral types is studied also. Tounderstand the saturation levels for these stars, we have compiled alarge number of IPC luminosities for stars with a wide variety ofspectral types and luminosity classes. We show quantitatively that ifthe Sun were completely covered with X-ray-emitting coronal loops, itwould be near the saturation limit implied by this compilation,supporting the idea that stars near upper limits in coronal activity arecompletely covered with active regions.
| A survey of proper motion stars. 12: an expanded sample
We report new photometry and radial velocities for almost 500 stars fromthe Lowell Proper Motion Catalog. We combine these results with ourprior sample and rederive stellar temperatures based on the photometry,reddening, metallicities (using chi squared matching of our 22,500 lowSignal to Noise (S/N) high resolution echelle spectra with a grid ofsynthetic spectra), distances, space motions, and Galactic orbitalparameters for 1269 (kinematics) and 1261 (metallicity) of the 1464stars in the complete survey. The frequency of spectroscopic binariesfor the metal-poor ((m/H) less than or equal to -1.2) stars with periodsshorter than 3000 days is at least 15%. The spectroscopic binaryfrequency for metal-rich stars ((m/H) greater than -0.5) appears to belower, about 9%, but this may be a selection effect. We also discussspecial classes of stars, including treatment of the double-linedspectroscopic binaries, and identification of subgiants. Four possiblenew members of the class of field blue stragglers are noted. We pointout the detection of three possible new white dwarfs, six broad-lined(binary) systems, and discuss briefly the three already knownnitrogen-rich halo dwarfs. The primary result of this paper will beavailable on CD-ROM, in the form of a much larger table.
| 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.
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Membro dei seguenti gruppi:
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Osservazione e dati astrometrici
| Costellazione: | Pesci |
| Ascensione retta: | 01h43m20.18s |
| Declinazione: | +04°19'17.9" |
| Magnitudine apparente: | 11.173 |
| Distanza: | 11.254 parsec |
| Moto proprio RA: | -423.4 |
| Moto proprio Dec: | -765.2 |
| B-T magnitude: | 12.993 |
| V-T magnitude: | 11.324 |
Cataloghi e designazioni:
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INHABITED SKY
