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First High-Contrast Science with an Integral Field Spectrograph: The Substellar Companion to GQ Lupi
We present commissioning data from the OSIRIS integral fieldspectrograph (IFS) on the Keck II 10 m telescope that demonstrate theutility of adaptive optics IFS spectroscopy in studying faint close-insubstellar companions in the halos of bright stars. Our R~2000 J- andH-band spectra of the substellar companion to the 1-10 Myr old GQ Lupcomplement existing K-band spectra and photometry and improve on theoriginal estimate of its spectral type. We find that GQ Lup B issomewhat hotter (M6-L0) than reported in the discovery paper byNeuhäuser and collaborators (M9-L4), mainly due to the surfacegravity sensitivity of the K-band spectral classification indices usedby the discoverers. Spectroscopic features characteristic of low surfacegravity objects, such as lack of alkali absorption and a triangularH-band continuum, are indeed prominent in our spectrum of GQ Lup B. Thepeculiar shape of the H-band continuum and the difference between thetwo spectral type estimates is well explained in the context of thediminishing strength of H2 collision-induced absorption withdecreasing surface gravity, as recently proposed for young ultracooldwarfs by Kirkpatrick and collaborators. Using our updated spectroscopicclassification of GQ Lup B and a reevaluation of the age andheliocentric distance of the primary, we perform a comparative analysisof the available substellar evolutionary models to estimate the mass ofthe companion. We find that the mass of GQ Lup B is 0.010-0.040Msolar. Hence, it is unlikely to be a wide-orbit counterpartto the known radial velocity extrasolar planets, whose masses are<~0.015 Msolar. Instead, GQ Lup A/B is probably a memberof a growing family of very low mass ratio widely separated binariesdiscovered through high-contrast imaging.
| Discovery of Two T Dwarf Companions with the Spitzer Space Telescope
We report the discovery of T dwarf companions to the nearby stars HN Peg(G0 V, 18.4 pc, τ~0.3 Gyr) and HD 3651 (K0 V, 11.1 pc, τ~7 Gyr).During an ongoing survey of 5'×5' fieldssurrounding stars in the solar neighborhood with the Infrared ArrayCamera aboard the Spitzer Space Telescope, we identified thesecompanions as candidate T dwarfs based on their mid-infrared colors.Using near-infrared spectra obtained with SpeX at the NASA InfraredTelescope Facility, we confirm the presence of methane absorption thatcharacterizes T dwarfs and measure spectral types of T2.5+/-0.5 andT7.5+/-0.5 for HN Peg B and HD 3651B, respectively. By comparing ourSpitzer data to images from the Two Micron All Sky Survey obtainedseveral years earlier, we find that the proper motions of HN Peg B andHD 3651B are consistent with those of the primaries, confirming theircompanionship. A comparison of their luminosities to the valuespredicted by theoretical evolutionary models implies masses of0.021+/-0.009 and 0.051+/-0.014 Msolar for HN Peg B and HD3651B, respectively. In addition, the models imply an effectivetemperature for HN Peg B that is significantly lower than the valuesderived for other T dwarfs at similar spectral types, which is the samebehavior reported by Metchev & Hillenbrand for the young late Ldwarf HD 203030B. Thus, the temperature of the L/T transition appears todepend on surface gravity. Meanwhile, HD 3651B is the first substellarcompanion directly imaged around a star that is known to harbor aclose-in planet from radial velocity surveys. The discovery of thiscompanion supports the notion that the high eccentricities of close-inplanets like that near HD 3651 may be the result of perturbations bylow-mass companions at wide separations.
| HD 203030B: An Unusually Cool Young Substellar Companion near the L/T Transition
We present the discovery of a brown dwarf companion to the star HD203030: a G8 V Solar analog with an estimated age between 130 and 400Myr old G8 V. Separated by 11.9" (487 AU in projection) from its hoststar, HD 203030B has an estimated mass of0.023+0.008-0.011 Msolar. The K-bandspectral type of L7.5+/-0.5 places HD 203030B near the critical L/Ttransition in brown dwarfs, which is characterized by the rapiddisappearance of dust in substellar photospheres. From a comparativeanalysis with well-characterized field L/T transition dwarfs, we findthat, despite its young age, HD 203030B has a bolometric luminositysimilar to the >1 Gyr old field dwarfs. Adopting a radius fromcurrent models of substellar evolution, we hence obtain that theeffective temperature of HD 203030B is only1206+74-116 K, markedly lower than the ~1440 Keffective temperatures of field L/T transition dwarfs. The temperaturediscrepancy can be resolved if either (1) the ages of field brown dwarfshave been overestimated by a factor of ~1.5, leading to underestimatedradii, or (2) the lower effective temperature of HD 203030B is relatedto its young age, implying that the effective temperature at the L/Ttransition is gravity dependent.
| The 78th Name-List of Variable Stars
We present the next regular Name-List of variable stars containinginformation on 1706 variable stars recently designated in the system ofthe General Catalogue of Variable Stars.
| Effective temperature scale and bolometric corrections from 2MASS photometry
We present a method to determine effective temperatures, angularsemi-diameters and bolometric corrections for population I and II FGKtype stars based on V and 2MASS IR photometry. Accurate calibration isaccomplished by using a sample of solar analogues, whose averagetemperature is assumed to be equal to the solar effective temperature of5777 K. By taking into account all possible sources of error we estimateassociated uncertainties to better than 1% in effective temperature andin the range 1.0-2.5% in angular semi-diameter for unreddened stars.Comparison of our new temperatures with other determinations extractedfrom the literature indicates, in general, remarkably good agreement.These results suggest that the effective temperaure scale of FGK starsis currently established with an accuracy better than 0.5%-1%. Theapplication of the method to a sample of 10 999 dwarfs in the Hipparcoscatalogue allows us to define temperature and bolometric correction (Kband) calibrations as a function of (V-K), [m/H] and log g. Bolometriccorrections in the V and K bands as a function of T_eff, [m/H] and log gare also given. We provide effective temperatures, angularsemi-diameters, radii and bolometric corrections in the V and K bandsfor the 10 999 FGK stars in our sample with the correspondinguncertainties.
| Evolution of Cold Circumstellar Dust around Solar-type Stars
We present submillimeter (Caltech Submillimeter Observatory 350 μm)and millimeter (Swedish-ESO Submillimetre Telescope [SEST] 1.2 mm, OwensValley Radio Observatory [OVRO] 3 mm) photometry for 127 solar-typestars from the Formation and Evolution of Planetary Systems SpitzerLegacy program that have masses between ~0.5 and 2.0 Msolarand ages from ~3 Myr to 3 Gyr. Continuum emission was detected towardfour stars with a signal-to-noise ratio>=3: the classical T Tauristars RX J1842.9-3532, RX J1852.3-3700, and PDS 66 with SEST, and thedebris-disk system HD 107146 with OVRO. RX J1842.9-3532 and RXJ1852.3-3700 are located in projection near the R CrA molecular cloud,with estimated ages of ~10 Myr (Neuhäuser et al.), whereas PDS 66is a probable member of the ~20 Myr old Lower Centaurus-Crux subgroup ofthe Scorpius-Centaurus OB association (Mamajek et al.). The continuumemission toward these three sources is unresolved at the 24" SESTresolution and likely originates from circumstellar accretion disks,each with estimated dust masses of ~5×10-5Msolar. Analysis of the visibility data toward HD 107146(age~80-200 Myr) indicates that the 3 mm continuum emission is centeredon the star within the astrometric uncertainties and resolved with aGaussian-fit FWHM size of (6.5"+/-1.4")×(4.2"+/-1.3"), or185AU×120 AU. The results from our continuum survey are combinedwith published observations to quantify the evolution of dust mass withtime by comparing the mass distributions for samples with differentstellar ages. The frequency distribution of circumstellar dust massesaround solar-type stars in the Taurus molecular cloud (age~2 Myr) isdistinguished from that around 3-10 Myr and 10-30 Myr old stars at asignificance level of ~1.5 and ~3 σ, respectively. These resultssuggest a decrease in the mass of dust contained in small dust grainsand/or changes in the grain properties by stellar ages of 10-30 Myr,consistent with previous conclusions. Further observations are needed todetermine if the evolution in the amount of cold dust occurs on evenshorter timescales.
| 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.
| The Geneva-Copenhagen survey of the Solar neighbourhood. Ages, metallicities, and kinematic properties of 14 000 F and G dwarfs
We present and discuss new determinations of metallicity, rotation, age,kinematics, and Galactic orbits for a complete, magnitude-limited, andkinematically unbiased sample of 16 682 nearby F and G dwarf stars. Our63 000 new, accurate radial-velocity observations for nearly 13 500stars allow identification of most of the binary stars in the sampleand, together with published uvbyβ photometry, Hipparcosparallaxes, Tycho-2 proper motions, and a few earlier radial velocities,complete the kinematic information for 14 139 stars. These high-qualityvelocity data are supplemented by effective temperatures andmetallicities newly derived from recent and/or revised calibrations. Theremaining stars either lack Hipparcos data or have fast rotation. Amajor effort has been devoted to the determination of new isochrone agesfor all stars for which this is possible. Particular attention has beengiven to a realistic treatment of statistical biases and errorestimates, as standard techniques tend to underestimate these effectsand introduce spurious features in the age distributions. Our ages agreewell with those by Edvardsson et al. (\cite{edv93}), despite severalastrophysical and computational improvements since then. We demonstrate,however, how strong observational and theoretical biases cause thedistribution of the observed ages to be very different from that of thetrue age distribution of the sample. Among the many basic relations ofthe Galactic disk that can be reinvestigated from the data presentedhere, we revisit the metallicity distribution of the G dwarfs and theage-metallicity, age-velocity, and metallicity-velocity relations of theSolar neighbourhood. Our first results confirm the lack of metal-poor Gdwarfs relative to closed-box model predictions (the ``G dwarfproblem''), the existence of radial metallicity gradients in the disk,the small change in mean metallicity of the thin disk since itsformation and the substantial scatter in metallicity at all ages, andthe continuing kinematic heating of the thin disk with an efficiencyconsistent with that expected for a combination of spiral arms and giantmolecular clouds. Distinct features in the distribution of the Vcomponent of the space motion are extended in age and metallicity,corresponding to the effects of stochastic spiral waves rather thanclassical moving groups, and may complicate the identification ofthick-disk stars from kinematic criteria. More advanced analyses of thisrich material will require careful simulations of the selection criteriafor the sample and the distribution of observational errors.Based on observations made with the Danish 1.5-m telescope at ESO, LaSilla, Chile, and with the Swiss 1-m telescope at Observatoire deHaute-Provence, France.Complete Tables 1 and 2 are only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/418/989
| New periodic variables from the Hipparcos epoch photometry
Two selection statistics are used to extract new candidate periodicvariables from the epoch photometry of the Hipparcos catalogue. Theprimary selection criterion is a signal-to-noise ratio. The dependenceof this statistic on the number of observations is calibrated usingabout 30000 randomly permuted Hipparcos data sets. A significance levelof 0.1 per cent is used to extract a first batch of candidate variables.The second criterion requires that the optimal frequency be unaffectedif the data are de-trended by low-order polynomials. We find 2675 newcandidate periodic variables, of which the majority (2082) are from theHipparcos`unsolved' variables. Potential problems with theinterpretation of the data (e.g. aliasing) are discussed.
| 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.
| The Vienna-KPNO search for Doppler-imaging candidate stars. I. A catalog of stellar-activity indicators for 1058 late-type Hipparcos stars
We present the results from a spectroscopic Ca ii H&K survey of 1058late-type stars selected from a color-limited subsample of the Hipparcoscatalog. Out of these 1058 stars, 371 stars were found to showsignificant H&K emission, most of them previously unknown; 23% withstrong emission, 36% with moderate emission, and 41% with weak emission.These spectra are used to determine absolute H&K emission-linefluxes, radial velocities, and equivalent widths of theluminosity-sensitive Sr ii line at 4077 Ä. Red-wavelengthspectroscopic and Strömgren y photometric follow-up observations ofthe 371 stars with H&K emission are used to additionally determinethe absolute Hα -core flux, the lithium abundance from the Li i6708 Å equivalent width, the rotational velocity vsin i, theradial velocity, and the light variations and its periodicity. Thelatter is interpreted as the stellar rotation period due to aninhomogeneous surface brightness distribution. 156 stars were found withphotometric periods between 0.29 and 64 days, 11 additional systemsshowed quasi-periodic variations possibly in excess of ~50 days. Further54 stars had variations but no unique period was found, and four starswere essentially constant. Altogether, 170 new variable stars werediscovered. Additionally, we found 17 new SB1 (plus 16 new candidates)and 19 new SB2 systems, as well as one definite and two possible new SB3systems. Finally, we present a list of 21 stars that we think are mostsuitable candidates for a detailed study with the Doppler-imagingtechnique. Tables A1--A3 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| 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.
| E. W. Fick Observatory stellar radial velocity measurements. I - 1976-1984
Stellar radial velocity observations made with the large vacuumhigh-dispersion photoelectric radial velocity spectrometer at FickObservatory are reported. This includes nearly 2000 late-type starsobserved during 585 nights. Gradual modifications to this instrumentover its first eight years of operation have reduced the observationalerror for high-quality dip observations to + or - 0.8 km/s.
| Photometry of stars in the uvgr system
Photoelectric photometry is presented for over 400 stars using the uvgrsystem of Thuan and Gunn. Stars were selected to cover a wide range ofspectral type, luminosity class, and metallicity. A mean main sequenceis derived along with reddening curves and approximate transformationsto the UBVR system. The calibration of the standard-star sequence issignificantly improved.
| An Investigation of Short-Period Variable Stars. I. The Delta Scuti Stars
Abstract image available at:http://adsabs.harvard.edu/abs/1969ApJS...18..167B
| Relationship between CN anomaly and U V W components of space velocity.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1962AJ.....67..757Y&db_key=AST
| Spectral and Luminosity Classifications and Measurements of the Strength of Cyanogen Absorption for Late-Type Stars from Objective-Prism Spectra.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1961ApJ...134..809Y&db_key=AST
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Miembro de los siguientes grupos:
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Datos observacionales y astrométricos
| Constelación: | Zorra |
| Ascensión Recta: | 21h18m58.22s |
| Declinación: | +26°13'49.9" |
| Magnitud Aparente: | 8.433 |
| Distancia: | 40.85 parsecs |
| Movimiento Propio en Ascensión Recta: | 131.3 |
| Movimiento Propio en Declinación: | 8.9 |
| B-T magnitude: | 9.393 |
| V-T magnitude: | 8.513 |
Catálogos y designaciones:
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