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Публикации по объекту
H? Activity of Old M Dwarfs: Stellar Cycles and Mean Activity Levels for 93 Low-mass Stars in the Solar Neighborhood
Through the McDonald Observatory M Dwarf Planet Search, we have acquirednearly 3000 high-resolution spectra of 93 late-type (K5-M5) stars overmore than a decade using the High Resolution Spectrograph on theHobby-Eberly Telescope. This sample provides a unique opportunity toinvestigate the occurrence of long-term stellar activity cycles forlow-mass stars. In this paper, we examine the stellar activity of ourtargets as reflected in the H? feature. We have identifiedperiodic signals for six stars, with periods ranging from days to morethan 10 years, and find long-term trends for seven others. Stellarcycles with P >= 1 year are present for at least 5% of our targets.Additionally, we present an analysis of the time-averaged activitylevels of our sample, and search for correlations with other stellarproperties. In particular, we find that more massive, earlier type(M0-M2) stars tend to be more active than later type dwarfs.Furthermore, high-metallicity stars tend to be more active at a givenstellar mass. We also evaluate H? variability as a tracer ofactivity-induced radial velocity (RV) variation. For the M dwarf GJ1170, H? variation reveals stellar activity patterns matchingthose seen in the RVs, mimicking the signal of a giant planet, and wefind evidence that the previously identified stellar activity cycle ofGJ 581 may be responsible for the recently retracted planet f in thatsystem. In general, though, we find that H? is not frequentlycorrelated with RV at the precision (typically 6-7 ms-1) of our measurements.
| Observation and modelling of main-sequence star chromospheres - XIX. FIES and FEROS observations of dM1 stars
We present 187 high-resolution spectra for 62 different M1 dwarfs fromobservations obtained with the FIbre-fed Echelle Spectrograph (FIES) onthe Nordic Optical Telescope (NOT) and from observations with theFibre-fed Extended Range Echelle Spectrograph (FEROS) from the EuropeanSouthern Observatory (ESO) data base. We also compiled othermeasurements available in the literature.We observed two stars, Gl 745A and Gl 745B, with no Ca II line coreemission and H? line equivalent widths (EWs) of only 0.171 and0.188 Å, respectively. We also observed another very low activityM1 dwarf, Gl 63, with an H? line EW of only 0.199 Å. Theseare the lowest activity M dwarfs ever observed and are of particularinterest for the non-local thermodynamic equilibrium radiative transfermodelling of M1 dwarfs.Thanks to the high signal-to-noise ratio of most of our spectra, we wereable to measure the Ca II H&K full width at half-maximum (FWHM) formost of our stars. We find good correlations between the FWHM values andthe mean Ca II line EW for dM1 stars. Then the FWHM seems to saturatefor dM1e stars. Our previous models of M1 dwarfs can reproduce the FWHMfor dM1e stars and the most active dM1 stars, but fail to reproduce theobservations of lower activity M1 dwarfs. We believe this is due to aneffect of metallicity. We also investigate the dependence of theH? line FWHM as a function of its EW. We find that the modelsglobally agree with the observations including subwarfs, but tend toproduce too narrow profiles for dM1e stars.We re-investigate the correlation between the Ca II line mean EW and theabsolute magnitude. With our new data that notably include several M1subdwarfs, we find a slightly different and better correlation with aslope of -0.779 instead of -0.909. We also re-investigatethe variations of the H? line EW as a function of radius and findthat the EW increases continuously with increasing radius. This confirmsour previous finding that the level of magnetic activity in M1 dwarfsincreases with the radius.For the first time, we investigate the Wilson-Bappu correlation for agiven spectral type. We find a rather linear correlation for stars ofabsolute magnitude greater than 9.6, but below this value the FWHM seemsto saturate. In fact, we show that these Wilson-Bappu type correlationsare activity-FWHM correlations and are due to the diminishing columnmass of the transition region with decreasing activity level. Based onobservations available at the European Southern Observatory data basesand on Hipparcos parallax measurements.
| 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
| The Local Leo Cold Cloud and New Limits on a Local Hot Bubble
We present a multi-wavelength study of the local Leo cold cloud (LLCC),a very nearby, very cold cloud in the interstellar medium (ISM). Throughstellar absorption studies we find that the LLCC is between 11.3 pc and24.3 pc away, making it the closest known cold neutral medium cloud andwell within the boundaries of the local cavity. Observations of thecloud in the 21 cm H I line reveal that the LLCC is very cold, withtemperatures ranging from 15 K to 30 K, and is best fit with a modelcomposed of two colliding components. The cloud has associated 100 μmthermal dust emission, pointing to a somewhat low dust-to-gas ratio of48 ×10-22 MJy sr-1 cm2. We findthat the LLCC is too far away to be generated by the collision among thenearby complex of local interstellar clouds but that the small relativevelocities indicate that the LLCC is somehow related to these clouds. Weuse the LLCC to conduct a shadowing experiment in 1/4 keV X-rays,allowing us to differentiate between different possible origins for theobserved soft X-ray background (SXRB). We find that a local hot bubblemodel alone cannot account for the low-latitude SXRB, but that isotropicemission from solar wind charge exchange (SWCX) does reproduce our data.In a combined local hot bubble and SWCX scenario, we rule out emissionfrom a local hot bubble with an 1/4 keV emissivity greater than 1.1Snowdens pc-1 at 3σ, four times lower than previousestimates. This result dramatically changes our perspective on our localISM.
| 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.
| 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.
| 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
| Accurate Coordinates and 2MASS Cross Identifications for (Almost) All Gliese Catalog Star
We provide precise J2000, epoch 2000 coordinates, andcross-identifications to sources in the 2MASS Point Source Catalog fornearly all stars in the Gliese, Gliese-Jahreiss, and Woolley catalogs ofnearby stars. The only Gliese objects where we were not successful aretwo Gliese sources that are actually QSOs; two proposed companions tobrighter stars, which we believe do not exist; four stars included inone of the catalogs but identified there as only optical companions; oneprobable plate flaw; and two stars that simply remain unrecovered. Forthe 4251 recovered stars, 2693 have coordinates based on Hipparcospositions, 1549 have coordinates based on 2MASS data, and 9 havepositions from other astrometric sources. All positions have beencalculated at epoch 2000 using proper motions from the literature, whichare also given here.
| UBV(RI)C JHK observations of Hipparcos-selected nearby stars
We present homogeneous, standardized UBV(RI)C photometry forover 700 nearby stars selected on the basis of Hipparcos parallaxes.Additionally, we list JHK photometry for about half of these stars, aswell as L photometry for 86 of the brightest. A number of stars withpeculiar colours or anomalous locations in various colour-magnitudediagrams are discussed.
| 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.
| 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
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| Exploring the Frequency of Close-in Jovian Planets around M Dwarfs
We discuss our high-precision radial velocity results of a sample of 90M dwarfs observed with the Hobby-Eberly Telescope and the Harlan J.Smith 2.7 m Telescope at McDonald Observatory, as well as the ESO VLTand the Keck I telescopes, within the context of the overall frequencyof Jupiter-mass planetary companions to main-sequence stars. None of thestars in our sample show variability indicative of a giant planet in ashort-period orbit, with a<=1 AU. We estimate an upper limit of thefrequency f of close-in Jovian planets around M dwarfs as <1.27% (atthe 1 σ confidence level). Furthermore, we determine that theefficiency of our survey in noticing planets in circular orbits is 98%for companions with msini>3.8MJ and a<=0.7 AU. Foreccentric orbits (e=0.6) the survey completeness is 95% for all planetswith msini>3.5MJ and a<=0.7 AU. Our results pointtoward a generally lower frequency of close-in Jovian planets for Mdwarfs as compared to FGK-type stars. This is an important piece ofinformation for our understanding of the process of planet formation asa function of stellar mass.Based on data collected with the Hobby-Eberly Telescope, which isoperated by McDonald Observatory on behalf of the University of Texas atAustin, Pennsylvania State University, Stanford University,Ludwig-Maximilians-Universität München, andGeorg-August-Universität Göttingen. Also based on observationscollected at the European Southern Observatory, Chile (ESO programs65.L-0428, 66.C-0446, 267.C-5700, 68.C-0415, 69.C-0722, 70.C-0044,71.C-0498, 072.C-0495, 173.C-0606). Additional data were obtained at theW. M. Keck Observatory, which is operated as a scientific partnershipamong the California Institute of Technology, the University ofCalifornia, and the National Aeronautics and Space Administration(NASA), and with the McDonald Observatory Harlan J. Smith 2.7 mtelescope.
| 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.
| A Dedicated M Dwarf Planet Search Using The Hobby-Eberly Telescope
We present the first results from our planet-search program using the9.2 m Hobby-Eberly Telescope (HET) at McDonald Observatory to detectplanets around M-type dwarf stars by means of high-precision radialvelocity (RV) measurements. Although more than 100 extrasolar planetshave been found around solar-type stars of spectral type F-K, there isonly a single M dwarf (GJ 876) known to harbor a planetary system. Withthe current incompleteness of Doppler surveys with respect to M dwarfs,it is not yet possible to decide whether this is due to a fundamentaldifference in the formation history and overall frequency of planetarysystems in the low-mass regime of the Hertzsprung-Russell diagram, orsimply an observational bias. Our HET M dwarf survey plans to survey 100M dwarfs in the next 3 to 4 years, with the primary goal being to answerthis question. Here we present the results from the first year of thesurvey, which show that our routine RV precision for M dwarfs is 6 ms-1. We found that GJ 864 and GJ 913 are binary systems withas yet undetermined periods, while five out of 39 M dwarfs reveal a highRV scatter and represent candidates for having short-period planetarycompanions. For one of them, GJ 436 (rms=20.6 m s-1), we havealready obtained follow-up observations, but no periodic signal ispresent in the RV data.Based on data collected with the Hobby-Eberly Telescope, which isoperated by McDonald Observatory on behalf of the University of Texas atAustin, Pennsylvania State University, Stanford University,Ludwig-Maximilians-Universität München, andGeorg-August-Universität Göttingen.
| Improved Astrometry and Photometry for the Luyten Catalog. II. Faint Stars and the Revised Catalog
We complete construction of a catalog containing improved astrometry andnew optical/infrared photometry for the vast majority of NLTT starslying in the overlap of regions covered by POSS I and by the secondincremental Two Micron All Sky Survey (2MASS) release, approximately 44%of the sky. The epoch 2000 positions are typically accurate to 130 mas,the proper motions to 5.5 mas yr-1, and the V-J colors to0.25 mag. Relative proper motions of binary components are measured to 3mas yr-1. The false-identification rate is ~1% for11<~V<~18 and substantially less at brighter magnitudes. Theseimprovements permit the construction of a reduced proper-motion diagramthat, for the first time, allows one to classify NLTT stars intomain-sequence (MS) stars, subdwarfs (SDs), and white dwarfs (WDs). We inturn use this diagram to analyze the properties of both our catalog andthe NLTT catalog on which it is based. In sharp contrast to popularbelief, we find that NLTT incompleteness in the plane is almostcompletely concentrated in MS stars, and that SDs and WDs are detectedalmost uniformly over the sky δ>-33deg. Our catalogwill therefore provide a powerful tool to probe these populationsstatistically, as well as to reliably identify individual SDs and WDs.
| Hipparcos red stars in the HpV_T2 and V I_C systems
For Hipparcos M, S, and C spectral type stars, we provide calibratedinstantaneous (epoch) Cousins V - I color indices using newly derivedHpV_T2 photometry. Three new sets of ground-based Cousins V I data havebeen obtained for more than 170 carbon and red M giants. These datasetsin combination with the published sources of V I photometry served toobtain the calibration curves linking Hipparcos/Tycho Hp-V_T2 with theCousins V - I index. In total, 321 carbon stars and 4464 M- and S-typestars have new V - I indices. The standard error of the mean V - I isabout 0.1 mag or better down to Hp~9 although it deteriorates rapidly atfainter magnitudes. These V - I indices can be used to verify thepublished Hipparcos V - I color indices. Thus, we have identified ahandful of new cases where, instead of the real target, a random fieldstar has been observed. A considerable fraction of the DMSA/C and DMSA/Vsolutions for red stars appear not to be warranted. Most likely suchspurious solutions may originate from usage of a heavily biased color inthe astrometric processing.Based on observations from the Hipparcos astrometric satellite operatedby the European Space Agency (ESA 1997).}\fnmsep\thanks{Table 7 is onlyavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/397/997
| Revised Coordinates and Proper Motions of the Stars in the Luyten Half-Second Catalog
We present refined coordinates and proper-motion data for the highproper-motion (HPM) stars in the Luyten Half-Second (LHS) catalog. Thepositional uncertainty in the original Luyten catalog is typicallygreater than 10" and is often greater than 30". We have used the digitalscans of the POSS I and POSS II plates to derive more accurate positionsand proper motions of the objects. Out of the 4470 candidates in the LHScatalog, 4323 objects were manually reidentified in the POSS I and POSSII scans. A small fraction of the stars were not found because of thelack of finder charts and digitized POSS II scans. The uncertainties inthe revised positions are typically ~2" but can be as high as ~8" in afew cases, which is a large improvement over the original data.Cross-correlation with the Tycho-2 and Hipparcos catalogs yielded 819candidates (with mR<~12). For these brighter sources, theposition and proper-motion data were replaced with the more accurateTycho-2/Hipparcos data. In total, we have revised proper-motionmeasurements and coordinates for 4040 stars and revised coordinates for4330 stars. The electronic version of the paper5 contains the updated information on all 4470stars in the LHS catalog.
| 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.
| Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521
| Photometric Measurements of the Fields of More than 700 Nearby Stars
In preparation for optical/IR interferometric searches for substellarcompanions of nearby stars, we undertook to characterize the fields ofall nearby stars visible from the Northern Hemisphere to determinesuitable companions for interferometric phase referencing. Because theKeck Interferometer in particular will be able to phase-reference oncompanions within the isoplanatic patch (30") to about 17th magnitude atK, we took images at V, r, and i that were deep enough to determine iffield stars were present to this magnitude around nearby stars using aspot-coated CCD. We report on 733 fields containing 10,629 measurementsin up to three filters (Gunn i, r and Johnson V) of nearby stars down toabout 13th magnitude at V.
| The Palomar/MSU Nearby Star Spectroscopic Survey.II.The Southern M Dwarfs and Investigation of Magnetic Activity
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....112.2799H&db_key=AST
| Photometry of Stars with Large Proper Motion
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....112.2300W&db_key=AST
| 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.
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Наблюдательные данные и астрометрия
| Созвездие: | Волопас |
| Прямое восхождение: | 14h29m29.71s |
| Склонение: | +15°31'57.5" |
| Видимая звёздная величина: | 10.758 |
| Расстояние: | 14.273 парсек |
| Собственное движение RA: | -1052 |
| Собственное движение Dec: | 1306.3 |
| B-T magnitude: | 12.455 |
| V-T magnitude: | 10.899 |
Каталоги и обозначения:
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