תוכן
תמונות
הוסף תמונה שלך
DSS Images Other Images
מאמרים קשורים
Potential Members of Stellar Kinematic Groups within 30 pc of the Sun
We analyze the kinematic histories of stars within 30 pc of the Sun, forwhich three-dimensional spatial coordinates and three-dimensionalvelocity vectors are available. From this sample, we extract members ofstellar kinematic groups (SKGs) in the following manner. First, weconsider in the three-dimensional velocity space centered on the localstandard of rest, a sphere with a radius of 8 km s-1centered on the mean velocity vector of a particular SKG. Around eachSKG velocity center, we have found a significant excess of starscompared to background field stars. For each candidate, in thethree-dimensional spatial coordinate space, its trajectory is tracedback in time by the age of the relevant SKG to obtain the estimateddistance from the SKG center at the time of the SKG's birth by theepicyclic approximation and harmonic vertical motion. It often happensthat a star is a candidate member of multiple SKGs. Then we rank thecandidacy to multiple SKGs based on the smallness of distanceseparations. In this manner, we have kinematically selected 238candidates. We further impose at least one of the following qualitativecriteria for being a member: spectral type A or B, variability, or EUVand X-ray emission. We have finally selected 137 candidate members ofSKGs out of a sample of 966 stars.
| Optimizing exoplanet transit searches around low-mass stars with inclination constraints
Aims: We investigate a method to increase the efficiency of atargeted exoplanet search with the transit technique by preselecting asubset of candidates from large catalogs of stars. Assuming spin-orbitalignment, this can be achieved by considering stars that have a higherprobability to be oriented nearly equator-on (inclination close to90°). Methods: We used activity-rotation velocity relationsfor low-mass stars with a convective envelope to study the dependence ofthe position in the activity-vsini diagram on the stellar axisinclination. We composed a catalog of G-, K-, M-type main-sequencesimulated stars using isochrones, an isotropic inclination distributionand empirical relations to obtain their rotation periods and activityindexes. Then the activity-vsini diagram was completed and statisticswere applied to trace the areas containing the higher ratio of starswith inclinations above 80°. A similar statistics was applied tostars from real catalogs with log(R'HK) and vsini data tofind their probability of being oriented equator-on. Results: Wepresent our method to generate the simulated star catalog and thesubsequent statistics to find the highly inclined stars from realcatalogs using the activity-vsini diagram. Several catalogs from theliterature are analyzed and a subsample of stars with the highestprobability of being equator-on is presented. Conclusions:Assuming spin-orbit alignment, the efficiency of an exoplanet transitsearch in the resulting subsample of probably highly inclined stars isestimated to be two to three times higher than with a general searchwithout preselection.Table 4 is only available at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/537/A147
| Observation and modelling of main-sequence star chromospheres - XV. New constraints on the dynamo mechanisms for dM1 stars
With the help of measures of rotation, radius and metallicity for aselected sample of dM1 stars (with Teff= 3460 ± 60 K),we aim to set new constraints on the dynamo mechanisms.We recover 913 high-resolution spectra for 97 different M1 dwarfs fromthe European Southern Observatory and Observatoire de Haute Provencedata bases. We present 660 new measurements of the Ca II resonance linesand 913 new measurements of the H? line for dM1 stars. We alsocompile other measurements available in the literature. In total, weobtain 2216 measures of the Ca II lines for 113 different dM1 stars.This represents the largest compilation of chromospheric linemeasurements at a single spectral type.We cross-correlate these magnetic activity indicators with variousstellar parameters to set new constraints on the dynamo mechanisms andon the properties of the outer atmosphere.We find a correlation of the Ca II line mean equivalent width with theabsolute magnitude and the metallicity. We correct the Ca II linemeasures from the metallicity effect and find that the surface flux inthe Ca II lines grows roughly as the power of 3.6 of the stellar radius.This corrected flux is a direct measure of magnetic activity at thechromospheric level. We find that the total magnetic activity levelgrows roughly as the power of 5.6 of the stellar radius. This trend isconfirmed by the correlation between the H? line and absolutemagnitude and the H? line luminosity and stellar radius: theH? luminosity grows roughly as the volume of the star for lowactivity dM1 stars and as the power of roughly 5/2 of the stellar radiusfor dM1e stars. The advantage of the H? line is that its formationin not dependent on metallicity.In contrast to the Ca II line, we find no correlation betweenLX and the absolute magnitude. We find that LXroughly correlates with the Ca II luminosity although the correlation isnot very good. This correlation shows that LX grows as thepower of 3/2 of the Ca II luminosity, i.e. the coronal emission growsfaster than the chromospheric emission.We find a correlation between the corrected Ca II line equivalent widthand P/sin i, i.e. the Ca II surface flux grows as the power of -1.5 ofthe rotation period. We also find a correlation between FX,the X-ray surface flux, and P/sin i: FX? (P/sini)-3.7. In other words, the coronal emission is much moredependent on the rotation period than the chromospheric emission.We find that the level of magnetic activity in dM1 stars is moredependent on the stellar radius than on rotation at the chromosphericlevel. We discuss the implications of these results on the models ofstellar dynamos. Based on observations available at Observatoire deHaute Provence and the European Southern Observatory data bases and onHipparcos parallax measurements.
| 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.
| Observation and modelling of main-sequence star chromospheres - XIV. Rotation of dM1 stars
We have measured v sin i for a selected sample of dM1-typestars. We give 114 measurements of v sin i for 88 different stars, andsix upper detection limits. These are the first measurements of v sin ifor most of the stars studied here. This represents the largest sampleof v sin i measurements for M dwarfs at a given spectral type. For thesemeasurements, we used four different spectrographs: HARPS (ESO), SOPHIE(OHP), ÉLODIE (OHP) and UVES (ESO). Two of these spectrographs(HARPS and SOPHIE) are particularly stable in wavelength since they weredesigned for exoplanet searches.We measured v sin i down to an accuracy of 0.3kms-1 for thehighest resolution spectrographs and a detection limit of about1kms-1. We show that this unprecedented accuracy for M dwarfsin our data set is possible because all the targets have the samespectral type. This is an advantage and it facilitates the determinationof the narrowest line profiles for v sin i ~ 0. Although it is possibleto derive the zero-point profiles using several spectral types at atime. These values were combined with other measurements taken from theliterature. The total sample represents detected rotation for 100 stars(10 dM1e and 90 dM1 stars). We confirm our finding of Paper VII that thedistribution of the projected rotation period is bimodal for dM1 starswith a much larger sample, i.e. there are two groups of stars: the fastrotators with P/sin i ~ 4.5d and the slow rotators with P/sin i ~ 14.4d.There is a gap between these two groups. We find that the distributionof stars as a function of P/sin i has two very abrupt cuts, below 10dand above 18d. There are very few stars observed out of this range10-18d. We also observe that the distribution increases slightly from 18to 10d.We find that the M1 subdwarfs (very low metallicity dwarfs) rotate withan average period of P/sin i ~ 7.2d, which is about twice faster as themain group of normal M1 dwarfs. We also find a correlation for P/sin ito decrease with stellar radius among dM1e stars. Such a trend is alsoobserved in dM1 stars.We also derive metallicity and radius for all our target stars using thesame method as in Paper VII. We notably found that 11 of our targetstars are subdwarfs with metallicities below -0.5dex.Based on observations available at Observatoire de Haute Provence andthe European Southern Observatory data bases and on Hipparcos parallaxmeasurements.E-mail: eric_houdebine@yahoo.fr
| Potential Members of Stellar Kinematical Groups within 20 pc of the Sun
We analyze the kinematical histories of stars within 20 pc of the Sun,for which three-dimensional spatial coordinates and three-dimensionalvelocity vectors are available. From this sample, we extract members ofstellar kinematical groups (SKGs) in the following manner. First, in thethree-dimensional velocity space centered on the local standard of rest,we consider a sphere with a radius of 8 km s-1 centeredon the mean velocity vector of a particular SKG. Around each SKGvelocity center, we have found a significant excess of stars compared tobackground stars. For each candidate, in the three-dimensional spatialcoordinate space, its trajectory is traced back in time by the age ofthe relevant SKG, to estimate the distance from the SKG center at thetime of the SKG's birth by the epicycle approximation and verticalharmonic motion. It often happens that a star is a candidate member ofmultiple SKGs. Then we rank the candidacy to multiple SKGs based on thesmallness of distance separations. In this manner, we have kinematicallyselected 74 candidate members of SKGs out of a sample of 383 stars. Ifwe take into account stellar properties, the number is reduced to 68.
| A high-resolution spectroscopic survey of late-type stars: chromospheric activity, rotation, kinematics, and age
Aims: We present a compilation of spectroscopic data from asurvey of 144 chromospherically active young stars in the solarneighborhood, which may be used to investigate different aspects of itsformation and evolution in terms of kinematics and stellar formationhistory. The data have already been used by us in several studies. Withthis paper, we make all these data accessible to the scientificcommunity for future studies on different topics. Methods: Weperformed spectroscopic observations with echelle spectrographs to coverthe entirety of the optical spectral range simultaneously. Standard datareduction was performed with the IRAF echelle package. We applied thespectral subtraction technique to reveal chromospheric emission in thestars of the sample. The equivalent width of chromospheric emissionlines was measured in the subtracted spectra and then converted tofluxes using equivalent width-flux relationships. Radial and rotationalvelocities were determined by the cross-correlation technique.Kinematics, equivalent widths of the lithium line ?6707.8 Åand spectral types were also determined. Results: A catalog ofspectroscopic data is compiled: radial and rotational velocities, spacemotion, equivalent widths of optical chromospheric activity indicatorsfrom Ca II H & K to the calcium infrared triplet and the lithiumline in ?6708 Å. Fluxes in the chromospheric emission linesand R'_HK are also determined for each observation of a star in thesample. We used these data to investigate the emission levels of ourstars. The study of the H? emission line revealed two differentpopulations of chromospheric emitters in the sample, clearly separatedin the logFH?/Fbol - (V-J) diagram. Thedichotomy may be associated with the age of the stars.Based on observations made with the 2.2 m telescope of theGerman-Spanish Astronomical Centre, Calar Alto (Almería, Spain),operated jointly by the Max-Planck-Institute for Astronomy, Heidelberg,and the Spanish National Commission for Astronomy; the Nordic OpticalTelescope (NOT), operated on the island of La Palma jointly by Denmark,Finland, Iceland, Norway and Sweden, in the Spanish Observatorio delRoque de Los Muchachos of the Instituto de Astrofísica deCanarias; the Isaac Newton Telescope (INT) operated on the island of LaPalma by the Isaac Newton Group in the Spanish Observatorio del Roque deLos Muchachos of the Instituto de Astrofísica de Canarias; withthe Italian Telescopio Nazionale Galileo (TNG) operated on the island ofLa Palma by the Centro Galileo Galilei of the INAF (Istituto Nazionaledi Astrofisica) at the Spanish Observatorio del Roque de Los Muchachosof the Instituto de Astrofísica de Canarias; and with theHobby-Eberly Telescope (HET) operated by McDonald Observatory on behalfof The University of Texas at Austin, the Pennsylvania State University,Stanford University, Ludwig-Maximilians-Universität München,and Georg-August-Universität Göttingen. This research has madeuse of the SIMBAD database and VizieR catalog access tool, operated atCDS, Strasbourg, France.Tables A.1-A.4 and reduced spectra are alsoavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/514/A97
| Search for cold debris disks around M-dwarfs. II
Although 70% of the stars in the Galaxy are M-dwarfs, thermal emissionsearches for cold debris disks have been conducted mostly for A-type andsolar-type stars. We report on new ?=1.2 mm continuumobservations of thirty M-dwarfs, using the MAMBO-2 bolometer arraycamera at the IRAM 30 m telescope. For a statistical analysis, wecombine these data with our prior SCUBA and MAMBO-2 observations of 20other M-dwarfs. Our sample consists of M-dwarfs in moving groups, withrelatively young ages, and of nearby M-dwarfs with unknown ages. Onlyone cold debris disk (GJ842.2) was detected significantly. We comparethe implied disk abundance constraints with those found in twocomparable submillimeter surveys of 10 to 190 Myr old A- and FGK-typestars. For the 19 youngest (ages less than 200 Myr) M-dwarfs in oursample, we derive a cold disk fraction of5.3+10.5-5.0%, compared to15+11.5-11.5% for FGK-stars and22+33-20% for A-stars. Hence, for this age group,there is an apparent trend of fewer cold disks for later stellar types.Although its statistical significance is marginal, this trend isstrengthened by the deeper observations of our M-dwarf sample. We derivea cold disk fraction of <10% for the older (likely a few Gyr)M-dwarfs in our sample. Finally, although inconclusively related to adebris disk, we present the complex millimeter structure found aroundthe position of the M 1.5 dwarf GJ526 in our sample.
| 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.
| Observation and modelling of main-sequence stellar chromospheres - VII. Rotation and metallicity of dM1 stars
We have measured v sini and metallicity from high-resolutionspectroscopic observations of a selected sample of dM1-type stars.To measure v sini, we first selected three template stars known fortheir slow rotation or their very low activity levels and thencross-correlated their spectra with those of our target stars. Theexcess broadening of the cross-correlation peaks gives v sini. Formetallicity, we compiled all available measurements from the literatureand correlated them with the stellar radius. Provided the parallax isknown, this new method allows us to derive metallicities for all ourtarget stars.We measured v sini to an accuracy of 2 kms-1. These valueswere combined with other measurements taken from the literature. We havedetected rotation in seven dM1e stars and 11 dM1 stars and upper limitsfor 20 other dM1 stars. Our results show that the distribution of therotation period may be bimodal for dM1 stars, i.e. there are two groupsof stars: the fast rotators with Prot ~ 6 d and the slowrotators with Prot ~ 24 d. There is a gap between these twogroups.We obtained a correlation between metallicity and stellar radius whichallows us to derive metallicities for all stars in our sample and moregenerally for all dM1 stars with [M/H] in the range -1.5 to 0.5 dex,with a reasonable accuracy. We compare this correlation to models andfind a significant disagreement in radii. However, the observed shape ofthe correlation is globally reproduced by the models. We derive themetallicity for 87 M1 dwarfs and subdwarfs.Based on observations collected at Observatoire de Haute Provence andthe European Southern Observatory and on Hipparcos parallaxmeasurements.E-mail: eric_houdebine@yahoo.fr
| 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
| The Gemini Deep Planet Survey
We present the results of the Gemini Deep Planet Survey, a near-infraredadaptive optics search for giant planets and brown dwarfs around 85nearby young stars. The observations were obtained with the Altairadaptive optics system at the Gemini North telescope, and angulardifferential imaging was used to suppress the speckle noise of thecentral star. Typically, the observations are sensitive to angularseparations beyond 0.5" with 5 σ contrast sensitivities inmagnitude difference at 1.6 μm of 9.5 at 0.5", 12.9 at 1", 15.0 at2", and 16.5 at 5". These sensitivities are sufficient to detect planetsmore massive than 2 MJ with a projected separation in therange 40-200 AU around a typical target. Second-epoch observations of 48stars with candidates (out of 54) have confirmed that all candidates areunrelated background stars. A detailed statistical analysis of thesurvey results is presented. Assuming a planet mass distributiondn/dm~m-1.2 and a semimajor-axis distributiondn/da~a-1, the 95% credible upper limits on the fraction ofstars with at least one planet of mass 0.5-13 MJ are 0.28 forthe range 10-25 AU, 0.13 for 25-50 AU, and 0.093 for 50-250 AU; thisresult is weakly dependent on the semimajor-axis distribution power-lawindex. The 95% credible interval for the fraction of stars with at leastone brown dwarf companion having a semimajor axis in the range 25-250 AUis 0.019+0.083-0.015, irrespective of anyassumption on the mass and semimajor-axis distributions. Theobservations made as part of this survey have resolved the stars HD14802, HD 166181, and HD 213845 into binaries for the first time.Based on observations obtained at the Gemini Observatory, which isoperated by the Association of Universities for Research in Astronomy,Inc., under a cooperative agreement with the NSF on behalf of the Geminipartnership: the National Science Foundation (United States), theParticle Physics and Astronomy Research Council (United Kingdom), theNational Research Council (Canada), CONICYT (Chile), the AustralianResearch Council (Australia), CNPq (Brazil), and CONICET (Argentina).
| Search for cold debris disks around M-dwarfs
Debris disks are believed to be related to planetesimals left overaround stars after planet formation has ceased. The frequency of debrisdisks around M-dwarfs which account for 70% of the stars in the Galaxyis unknown while constrains have already been found for A- to K-typestars. We have searched for cold debris disks around 32 field M-dwarfsby conducting observations at λ = 850~μm with the SCUBAbolometer array camera at the JCMT and at λ = 1.2 mm with theMAMBO array at the IRAM 30-m telescopes. This is the first survey of alarge sample of M-dwarfs conducted to provide statistical constraints ondebris disks around this type of stars. We have detected a new debrisdisk around the M0.5 dwarf GJ 842.2 at λ = 850~μm, providingevidence for cold dust at large distance from this star (~300 AU). Bycombining the results of our survey with the ones of Liu et al. (2004),we estimate for the first time the detection rate of cold debris disksaround field M-dwarfs with ages between 20 and 200 Myr. This detectionrate is 13+6-8% and is consistent with thedetection rate of cold debris disks (9-23%) around A- to K-type mainsequence stars of the same age. This is an indication that cold disksmay be equally prevalent across stellar spectral types.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| Where Are the M Dwarf Disks Older Than 10 Million Years?
We present 11.7 μm observations of nine late-type dwarfs obtained atthe Keck I 10 m telescope in 2002 December and 2003 April. Our targetswere selected for their youth or apparent IRAS 12 μm excess. For allnine sources, excess infrared emission is not detected. We find thatstellar wind drag can dominate the circumstellar grain removal andplausibly explain the dearth of M dwarf systems older than 10 Myr withcurrently detected infrared excesses. We predict that M dwarfs possessfractional infrared excesses on the order ofLIR/L*~10-6 and that this may bedetectable with future efforts.
| 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.
| Activity and kinematics of members of the TW Hydrae association
We present high-resolution echelle spectroscopy of 20 stars in 16systems catalogued as members of the TW Hydrae association, and 16 starsidentified as possible new members. We have calibrated the range ofcoronal and chromospheric activity expected for such young stars as afunction of spectral type by combining our observations with literaturedata for field and open cluster stars. We also compute space motions forTWA members and candidate members with proper motion measurements, usingtwo techniques to estimate distances to stars lacking directtrigonometric parallax measurements. The mean space motion of the fourTWA members with known parallaxes is (U, V, W: -10.0, -17.8, -4.6) kms-1. 14 of the candidates have properties inconsistent withcluster membership; the remaining two are potential new members,although further observations are required to confirm this possibility.
| 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 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.
| Late-type members of young stellar kinematic groups - I. Single stars
This is the first paper of a series aimed at studying the properties oflate-type members of young stellar kinematic groups. We concentrate ourstudy on classical young moving groups such as the Local Association(Pleiades moving group, 20-150Myr), IC 2391 supercluster (35Myr), UrsaMajor group (Sirius supercluster, 300Myr), and Hyades supercluster(600Myr), as well as on recently identified groups such as the Castormoving group (200Myr). In this paper we compile a preliminary list ofsingle late-type possible members of some of these young stellarkinematic groups. Stars are selected from previously established membersof stellar kinematic groups based on photometric and kinematicproperties as well as from candidates based on other criteria such astheir level of chromospheric activity, rotation rate and lithiumabundance. Precise measurements of proper motions and parallaxes takenfrom the Hipparcos Catalogue, as well as from the Tycho-2 Catalogue, andpublished radial velocity measurements are used to calculate theGalactic space motions (U, V, W) and to apply Eggen's kinematic criteriain order to determine the membership of the selected stars to thedifferent groups. Additional criteria using age-dating methods forlate-type stars will be applied in forthcoming papers of this series. Afurther study of the list of stars compiled here could lead to a betterunderstanding of the chromospheric activity and their age evolution, aswell as of the star formation history in the solar neighbourhood. Inaddition, these stars are also potential search targets for directimaging detection of substellar companions.
| Infrared Colors at the Stellar/Substellar Boundary
We present new infrared JHK photometry for 61 halo and disk stars aroundthe stellar/substellar boundary. We also present new L' photometry for21 of these stars and for 40 low-mass stars taken from the Leggettphotometry compilation. These data are combined with available opticalphotometry and astrometric data to produce color-color and absolutemagnitude-color diagrams; the current sample extends the similar workpresented in the 1992 paper into more metal-poor and lower mass regimes.The disk and halo sequences are compared to the predictions of thelatest model atmospheres and structural models. We find good agreementbetween observation and theory except for known problems in the V and Hpassbands, probably due to incomplete molecular data for TiO, metalhydrides, and H_2O. The metal-poor M subdwarfs are well matched by themodels since oxide opacity sources are less important in this case. Theknown extreme M subdwarfs have metallicities about one-hundredth solar,and the coolest subdwarfs have T_eff ~ 3000 K with masses~0.09M/M_ȯ. The grainless models are not able to reproduce the fluxdistributions of disk objects with T_eff < 2500 K; however, apreliminary version of the NextGen-Dusty models that includeshomogeneous formation and extinction by dust grains is able to match thecolors of these very cool objects. The least luminous objects in thissample are GD 165B, three DENIS objects-DBD 0205, DBD 1058, and DBD1228-and Kelu-1. These have T_eff ~ 2000 K and are at or below thestellar limit with masses <=0.075M/M_ȯ. Photometry alone cannotconstrain these parameters further since the age is unknown, butpublished lithium detections for two of these objects (Kelu-1 and DBD1228) imply that they are young (aged about 1 Gyr) and substellar (mass<= 0.06M/M_ȯ).
| 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
| 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
| Pre-Main-Sequence Stars in the Pleiades Supercluster
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....110.1749E&db_key=AST
| The general catalogue of trigonometric [stellar] paralaxes
Not Available
|
הכנס מאמר חדש
לינקים קשורים
הכנס לינק חדש
משמש של הקבוצה הבאה
|
תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | כלבי ציד |
| התרוממות ימנית: | 13h19m40.13s |
| סירוב: | +33°20'47.5" |
| גודל גלוי: | 10.568 |
| מרחק: | 17.385 פארסק |
| תנועה נכונה: | -296.3 |
| תנועה נכונה: | -144.2 |
| B-T magnitude: | 12.533 |
| V-T magnitude: | 10.731 |
קטלוגים וכינוים:
|
INHABITED SKY
