Tartalom
Képek
Kép feltöltése
DSS Images Other Images
Kapcsolódó cikkek
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).
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| 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.
| 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.
| 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 general catalogue of trigonometric [stellar] paralaxes
Not Available
| The kinematics of young disk population supercluster members
A discussion of the total space motions of early-type members of youngdisk population superclusters, derived from distances based on aphotometric calibration of four-color and H-beta photometry, shows anincrease in total velocity with increasing radial distance from the sun,within each supercluster. The rate of increase with distance varies fromsupercluster to supercluster because it results from the interaction oftwo effects - an 'expansion' that involves the total space motion and a'rotation' that involves only the V-velocity because it arises from therequirement that supercluster members have isoperiodic, galactic orbits.The ratio of the velocity in the direction of galactic rotation(V-velocity) to the total space motion determines the size of theresultant effect from the contradictory 'rotation' and 'expansion'terms. The expansion term is 40 to 45 km's/kpc in the superclustersdiscussed, whereas the rotation term is dV/dX = -(b-A) = 26 km/s/kpc,where B and A are the constants of galactic rotation.
| The IC 2391 supercluster
Sixty-three field stars and the sparse cluster IC 2391 have beenidentified as members of the IC 2391 supercluster. The members have atleast 95 percent of their space motion, directed toward (A,D) = (5.82h,- 12.44d). Like members of the very similar Pleiades supercluster, theIC 2391 supercluster contains objects of two ages: t = 8 x 19 exp 7 and2.5 x 10 exp 8 yr. A prototype very active chromosphere star and theenigmatic giant variable TZ For are supercluster members together withtwo A-type stars suspected of possessing particulate disks. Anespecially interesting member is the system of Xi Cep (HR 8417) in whichthe two brightest components are greatly undermassive.
| A photometric search for halo binaries. I - New observatinal data. II - Results
Carney (1982) has reported JHK photometry for 76 Hyades dwarfs. Inconnection with the present investigation, results of similarobservations of field halo stars are provided along with some uvbyphotometry. In addition, older spectrophotometric and photometric dataused previously for temperature determinations have been collected. Theinfrared and uvby data were obtained primarily with the objective ofidentifying binaries with dissimilar components among a sample of fieldhalo dwarfs by comparing metallicity insensitive blue and infraredcolors. Attention is given to 111 spectrophotometric scans of 89 stars,67 uvby measures of 41 stars, 127 UBV measures of 87 stars, 147 (RI)Jmeasures of 127 stars, 8 JHK measures of eight stars in the 'HCO'system, and 212 JHK measures of 137 stars in the 'CIT' system. Themajority of these stars are dwarfs, and most of them are metal poor. Theresults of a search for binaries in 71 halo dwarf stars are alsopresented, taking into account a few other dwarfs of special interest.
| Three-dimensional motion of dwarf stars and RR Lyrae variables
A collection of 220 high-velocity dwarfs, 532 low-velocity dwarfs, and114 RR Lyrae variables is given in tables with calculations ofkinematical quantities in a three-dimensional model of galactic space. Ametal indicator, Delta-S, for RR Lyrae variables is transformed into theultraviolet excess, delta (0.6), which is utilized for a statisticalstudy of kinematics under the same metallicity classification. It isfound that the primordial Galaxy contracted by a factor of at least 20in the radial direction as compared to at least 50 in the Z direction.
|
Új cikk hozzáadása
Kapcsolódó hivatkozások
- - (nincs kapcsolódó hivatkozás) -
Új link hozzáadása
Besorolás csoportokba:
|
Pozíciós és asztrometriai adatok
| Csillagkép: | Cefeusz |
| Rektaszcenzió: | 21h06m56.39s |
| Deklináció: | +69°40'28.5" |
| Vizuális fényesség: | 8.183 |
| Távolság: | 32.841 parszek |
| RA sajátmozgás: | 109.1 |
| Dec sajátmozgás: | 65 |
| B-T magnitude: | 9.132 |
| V-T magnitude: | 8.262 |
Katalógusok és elnevezések:
|
INHABITED SKY
