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Spectroscopic parameters for a sample of metal-rich solar-type stars
Aims.To date, metallicity is the only parameter of a star that appearsto clearly correlate with the presence of planets and their properties.To check for new correlations between stars and the existence of anorbiting planet, we determine accurate stellar parameters for severalmetal-rich solar-type stars. The purpose is to fill the gap of thecomparison sample presented in previous works in the high metal-contentregime. Methods: .The stellar parameters were determined using anLTE analysis based on equivalent widths (EW) of iron lines and byimposing excitation and ionization equilibrium. We also present a firststep in determining these stellar parameters in an automatic manner byusing the code DAOSPEC for the EW determination. Results:.Accurate stellar parameters and metallicities are obtained for oursample composed of 64 high metal-content stars not known to harbor anyplanet. This sample will in the future give us the possibility of betterexploring the existence of differences in the chemical abundancesbetween planet-host stars and stars without known planets in themetal-rich domain. We also report stellar parameters for some recentlydiscovered planet-host stars. Finally, we present an empiricalcalibration for DAOSPEC based on the comparison between its EWmeasurements and the standard "hand made" measurements for the FEROSsample presented in this paper.
| Astrometric proof of companionship for the L dwarf companion candidate GJ1048B
\citet[][ AJ, 121, 2185]{gizis} reported a companion candidate ofspectral type L1 near the K2 dwarf GJ1048 using the Two Micron All-SkySurvey (2MASS). At that time it was not possible to verify companionshipastrometrically using the 2MASS data alone due to the small propermotion of GJ1048. We now show that both objects share the same propermotion by using data from the UK Schmidt Telescope Near-infrared (IVN)Southern Survey as the first epoch and data from 2MASS as the secondepoch. Our technique of subtracting the PSF of the primary from theSuperCOSMOS I scans of the Southern Survey enables the astrometry of thecompanion candidate to be measured directly.
| 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.
| K dwarfs and the chemical evolution of the solar cylinder
K dwarfs have lifetimes older than the present age of the Galactic disc,and are thus ideal stars for investigating the chemical evolution of thedisc. We have developed several photometric metallicity indicators for Kdwarfs, based on a sample of accurate spectroscopic metallicities for 34disc and halo G and K dwarfs. The photometric metallicities lead us todevelop a metallicity index for K dwarfs based only on their position inthe colour-absolute-magnitude diagram. Metallicities have beendetermined for 431 single K dwarfs drawn from the Hipparcos catalogue,selecting the stars by absolute magnitude and removing multiple systems.The sample is essentially a complete reckoning of the metal content innearby K dwarfs. We use stellar isochrones to mark the stars by mass,and select a subset of 220 of the stars, which is complete within anarrow mass interval. We fit the data with a model of the chemicalevolution of the solar cylinder. We find that only a modest cosmicscatter is required to fit our age-metallicity relation. The modelassumes two main infall episodes for the formation of the halo-thickdisc and thin disc, respectively. The new data confirm that the solarneighbourhood formed on a long time-scale of the order of 7 Gyr.
| Astrometry and Photometry for Cool Dwarfs and Brown Dwarfs
Trigonometric parallax determinations are presented for 28 late-typedwarfs and brown dwarfs, including eight M dwarfs with spectral typesbetween M7 and M9.5, 17 L dwarfs with spectral types between L0 and L8,and three T dwarfs. Broadband photometry at CCD wavelengths (VRIz*)and/or near-IR wavelengths (JHK) is presented for these objects and for24 additional late-type dwarfs. Supplemented with astrometry andphotometry from the literature, including 10 L and two T dwarfs withparallaxes established by association with bright, usually Hipparcosprimaries, this material forms the basis for studying variouscolor-color and color-absolute magnitude relations. The I-J color is agood predictor of absolute magnitude for late M and L dwarfs.MJ becomes monotonically fainter with I-J color and withspectral type through late L dwarfs, then brightens for early T dwarfs.The combination of z*JK colors alone can be used to classify late M,early L, and T dwarfs accurately, as well as to predict their absolutemagnitudes, but is less effective at untangling the scatter among mid-and late L dwarfs. The mean tangential velocity of these objects isfound to be slightly less than that for dM stars in the solarneighborhood, consistent with a sample with a mean age of several Gyr.Using colors to estimate bolometric corrections and models to estimatestellar radii, effective temperatures are derived. The latest L dwarfsare found to have Teff~1360 K.
| A 2MASS L Dwarf Companion to the Nearby K Dwarf GJ 1048
We report the discovery of a probable L1 companion to the nearby K2dwarf GJ 1048 using the Two Micron All-Sky Survey (2MASS). This source,2MASSI J0235599-233120, or GJ 1048B, has 2MASS near-infrared colors andabsolute magnitudes consistent with an early L dwarf companion with aprojected separation of 250 AU. The L1 spectral type is confirmed byfar-red optical and low-resolution IR spectroscopy. We present evidencethat GJ 1048 is a young (<~1 Gyr) system, and that GJ 1048B may be ahigh-mass brown dwarf below the hydrogen burning limit. Additionalstudies of the GJ 1048 system will help constrain the characteristics ofL dwarfs as a function of age and mass.
| A Search for L Dwarf Binary Systems
We present analysis of Hubble Space Telescope (HST) planetary cameraimages of 20 L dwarfs identified in the course of the Two Micron All SkySurvey. Four of the targets, 2MASSW J0746425+200032, 2MASSsJ0850359+105716, 2MASSW J0920122+351742, and 2MASSW J1146345+223053,have faint red companions at separations between 0.07" and 0.29"(1.6-7.6 AU). Ground-based infrared imaging confirms the last as acommon proper motion companion. The surface density of backgroundsources with comparable colors is extremely low, and we identify allfour as physical binaries. In three cases, the bolometric magnitudes ofthe components differ by less than 0.3 mag. Since the cooling rate forbrown dwarfs is a strong function of mass, similarity in luminositiesimplies comparable masses. The faint component in the 2M0850 system,however, is over 1.3 mag fainter than the primary in the I band and ~0.8mag fainter in Mbol. Indeed, 2M0850B is ~0.8 mag fainter in Ithan the lowest luminosity L dwarf currently known, while the absolutemagnitude we deduce at J is almost identical with MJ for Gl229B. We discuss the implications of these results for the temperaturescale in the L/T transition region. 2M0850 is known to exhibit 6708Å Li I absorption, indicating that the primary has a mass lessthan 0.06 Msolar. Theoretical models predict that themagnitude difference implies a mass ratio of ~0.75. The apparent binaryfraction of the current sample, 20%, is comparable to the results ofprevious surveys of late-type M dwarfs in the field and in the Hyades.However, the mean separation of the L dwarf binaries in the currentsample is smaller than the M dwarf value by a factor of 2, and only onesystem would be detected at the distance of the Hyades. We discuss thelikely binary frequency among L dwarfs in light of these new data.
| The ROSAT all-sky survey catalogue of the nearby stars
We present X-ray data for all entries of the Third Catalogue of NearbyStars \cite[(Gliese & Jahreiss 1991)]{gli91} that have been detectedas X-ray sources in the ROSAT all-sky survey. The catalogue contains1252 entries yielding an average detection rate of 32.9 percent. Inaddition to count rates, source detection parameters, hardness ratios,and X-ray fluxes we also list X-ray luminosities derived from Hipparcosparallaxes. Catalogue also available at CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| The catalogue of nearby stars metallicities.
Not Available
| Nearby Star Data Published 1969-1978
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1979A&AS...38..423G&db_key=AST
| Dwarf K and M stars in the southern hemisphere.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972AJ.....77..486U&db_key=AST
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| Takýmyýldýz: | Balina |
| Sað Açýklýk: | 02h36m00.78s |
| Yükselim: | -23°31'16.8" |
| Görünürdeki Parlaklýk: | 8.343 |
| Uzaklýk: | 21.259 parsek |
| özdevim Sað Açýklýk: | 87.1 |
| özdevim Yükselim: | 15 |
| B-T magnitude: | 9.716 |
| V-T magnitude: | 8.457 |
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