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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
| Chromospheric activities and kinematics for solar type dwarfs and subgiants: analysis of the activity distribution and the AVR
Aims: In this work we present chromospheric activity indices,kinematics, radial-velocities, and rotational velocities for more than850 FGK-type dwarfs and subgiant stars in the southern hemisphere andtest how best to calibrate and measure S-indices from echelle spectra. Methods: We measured our parameters using the high-resolution andhigh-S/N FEROS echelle spectra acquired for this purpose. Results: We confirm the bimodal distribution of chromospheric activitiesfor such stars and highlight the role that the more active K-dwarfs playin biasing the number of active stars. We show that the age-activityrelationship does appear to continue to ages older than the Sun if wesimply compare main sequence stars and subgiant stars with an offset ofaround 2.5 Gyr between the peaks of both distributions. Also we showevidence of an increased spin-down timescale for cool K dwarfs comparedwith earlier F and G type stars. We highlight that activities drawn fromlow-resolution spectra (R < 2500) significantly increase the rmsscatter when calibrating onto common systems of measurements like theMt. Wilson system. Also we show that older and widely used catalogues ofactivities in the south appear to be offset compared to more recentworks at the 0.1 dex level in log R'HK through calibratordrift. In addition, we show how kinematics can be used to preselectinactive stars for future planet search projects. We see the well knowntrend between projected rotational velocity and activity, however wealso find a correlation between kinematic space velocity andchromospheric activity. It appears that after the Vaughan-Preston gapthere is a quick step function in the kinematic space motion towards asignificantly broader spread in velocities. We speculate on reasons forthis correlation and provide some model scenarios to describe thebimodal activity distribution through magnetic saturation, residual lowlevel gas accretion, or accretion by the star of planets orplanetesimals. Finally, we provide a new empirical measurement for thedisk-heating law, using the latest age-activity relationships toreconstruct the age-velocity distribution for local disk stars. We finda value of 0.337 ± 0.045 for the exponent of this power law (i.e.σtot ∝ t0.337), in excellent agreementwith those found using isochrone fitting methods and with theoreticaldisk-heating models.Based on observations made with the ESO telescopes at the La SillaParanal observatory under programme ID's 076.C-0578(B), 077.C-0192(A),082.C-0446(A) and 082.C-0446(B).Full Table 4 is only available at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/531/A8
| 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.
| The usage of Strömgren photometry in studies of local group dwarf spheroidal galaxies. Application to Draco: a new catalogue of Draco members and a study of the metallicity distribution function and radial gradients
Aims.In this paper we demonstrate how Strömgren uvby photometry canbe efficiently used to: 1. identify red giant branch stars that aremembers in a dwarf spheroidal galaxy; 2. derive age-independentmetallicities for the same stars and quantify the associated errors. Methods: Strömgren uvby photometry in a 11 × 22 arcmin fieldcentered on the Draco dwarf spheroidal galaxy was obtained using theIsaac Newton Telescope on La Palma. Members of the Draco dSph galaxywere identified using the surface gravity sensitive c1 indexwhich discriminates between red giant and dwarf stars. Thus enabling usto distinguish the (red giant branch) members of the dwarf spheroidalgalaxy from the foreground dwarf stars in our galaxy. The method isevaluated through a comparison of our membership list with membershipclassifications in the literature based on radial velocities and propermotions. The metallicity sensitive m1 index was used toderive individual and age-independent metallicities for the members ofthe Draco dSph galaxy. The derived metallicities are compared to studiesbased on high resolution spectroscopy and the agreement is found to bevery good. Results: We present metallicities for 169 members of the redgiant branch in the Draco dwarf spheroidal galaxy (the largest sample todate). The metallicity distribution function for the Draco dSph galaxyshows a mean [Fe/H] = -1.74 dex with a spread of 0.24 dex. Thecorrelation between metallicity and colour for the stars on the redgiant branch is consistent with a dominant old, and coeval population.There is a possible spatial population gradient over the field with themost metal-rich stars being more centrally concentrated than themetal-poor stars.Based on observations made with the Isaac Newton Telescope, operated onthe Island of La Palma by the Isaac Newton Group in the SpanishObservatorio del Roque de los Muchachos of the Instituto de Astrofisicade Canarias. Guest User, Canadian Astronomy Data Centre, which isoperated by the Herzberg Institute of Astrophysics, National ResearchCouncil of Canada. Full Tables 2 and 6 are only available athttp://www.aanda.org
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| 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 age-metallicity relation of the solar neighbourhood disc stars
We derive age-metallicity relations (AMRs) and orbital parameters forthe 1658 solar neighbourhood stars to which accurate distances aremeasured by the HIPPARCOS satellite. The sample stars comprise 1382 thindisc stars, 229 thick disc stars, and 47 halo stars according to theirorbital parameters. We find a considerable scatter for thin disc AMRalong the one-zone Galactic chemical evolution (GCE) model. Orbits andmetallicities of thin disc stars show now clear relation each other. Thescatter along the AMR exists even if the stars with the same orbits areselected. We examine simple extension of one-zone GCE models whichaccount for inhomogeneity in the effective yield and inhomogeneous starformation rate in the Galaxy. Both extensions of the one-zone GCE modelcannot account for the scatter in age - [Fe/H] - [Ca/Fe] relationsimultaneously. We conclude, therefore, that the scatter along the thindisc AMR is an essential feature in the formation and evolution of theGalaxy. The AMR for thick disc stars shows that the star formationterminated 8 Gyr ago in the thick disc. As already reported by Grattonet al. (\cite{Gratton_et.al.2000}) and Prochaska et al.(\cite{Prochaska_et.al.2000}), thick disc stars are more Ca-rich thanthin disc stars with the same [Fe/H]. We find that thick disc stars showa vertical abundance gradient. These three facts, the AMR, verticalgradient, and [Ca/Fe]-[Fe/H] relation, support monolithic collapseand/or accretion of satellite dwarf galaxies as likely thick discformation scenarios. Tables 2 and 3 are only available in electronicform at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)or via http:/ /cdsweb.u-strasbg.fr/ cgi-bin/qcat?J/ A+A/394/927
| Resolving the 47 Tucanae Distance Problem
We present new B-, V-, and I-band photometry for a sample of 43 localsubdwarfs with Hipparcos parallax errors less than 13%, in themetallicity range -1.0<[Fe/H]<-0.3, which we use to performmain-sequence (MS) fitting to the Galactic globular cluster 47 Tuc. Thissample is many times larger than those used in previous MS-fittingstudies and also enables us to fit in two color planes, V/(B-V) andV/(V-I). With this enlarged subdwarf sample we investigate whether thecurrent discrepancy in empirical distance estimates for 47 Tuc, arisingfrom recent MS-fitting and white dwarf fitting results, is due toinaccuracies in the MS-fitting method. Comparison of publishedphotometries for 47 Tuc has revealed systematic offsets, which meansthat the (B-V) main line used in previous studies may be too blue by~0.02 mag, which would have the effect of making any derived distancemodulus too large by around 0.1 mag. Preliminary work has alsohighlighted discrepancies between results obtained in the two colorplanes, V/(B-V) and V/(V-I). We have derived main lines in V/(B-V) andV/(V-I) from the data of Kaluzny et al., which we have recalibrated fromthe ``secondary'' standards in 47 Tuc of Stetson (2000). Using anassumed cluster reddening of E(B-V)=0.04, our best-fit apparent distancemodulus is (m-M)V=13.37+0.10-0.11 inboth color planes, which implies a cluster age of 11.0+/-1.4 Gyr andleads to a dereddened distance modulus of(m-M)0=13.25+0.06-0.07. Comparison withprevious work shows that our apparent distance modulus is ~0.2 magsmaller than those derived in previous MS-fitting studies. Thedifference is accounted for by our preferred cluster reddening and therecalibration of the cluster photometry, which has made the main lineredder by an average of 0.02 mag in (B-V). Our derived distance modulusis also now plausibly consistent with the short distance recentlyderived from white dwarf fitting. Independent support for our MS-fittingdistance comes from consideration of the red clump in the cluster, fromwhich we derive a dereddened distance modulus of(m-M)0=13.31+/-0.05, which is in agreement with theMS-fitting result.
| New proper motion determination of Luyten catalogue stars (LTT) with declination between -5(deg) and -30(deg) and right ascension between 0h and 13h 30m
Data are given for 353 LTT stars found on 42 areas, covering 25 squaredegrees each, with declination between -5(deg) and -30(deg) and rightascension between 0h and 13h 30m. Nineteen stars present differences inproper motion >= 0('') 10, twenty present differences in positionangle >= 20(deg) and six present those differences in both values.Table 2 only available in electronic foun at CDS viahttp://cdsweb.u-strasbg.fr/Abstract.html. Finding charts only availablein the electronic version.
| GPM - compiled catalogue of absolute proper motions of stars in selected areas of sky with galaxies.
Not Available
| GPM1 - a catalog of absolute proper motions of stars with respect to galaxies
The description of the first version of the General Compiled Catalogueof Absolute Proper Motions (GPM1) for a sample of HIPPARCOS stars,derived with respect to galaxies within the plan called Catalogue ofFaint Stars (KSZ, Deutch 1952), is presented. The principal aim of theGPM1 construction was to provide absolute proper motions of stars todetermine the rotation of the HIPPARCOS system. The GPM1 cataloguecontains 977 HIPPARCOS Input Catalogue stars with V magnitudes $5^m -11^m in 180 fields north of -25 degrees of declination. The accuracy ofthe proper motions is 8 mas/yr (milliarcseconds per year). Comparison ofproper motions of GPM1 with those of the PPM and ACRS was performed andanalyzed with respect to systematic errors caused by spurious rotationof the FK5 system. The standard errors show that the rotation may bedetermined with an accuracy better than 1 mas/yr. Catalog is onlyavailable in electronic form at the CDS via anonymous ftpcdsarc.u-strasbg.fr or ftp 130.79.128.5.
| Ultraviolet Imaging Telescope Near-Ultraviolet Bright Object Catalog
We present a photometric catalog of 2244 objects detected by theUltraviolet Imaging Telescope in the near-ultraviolet (NUV; 1650A <λ < 2900 A) during the Astro Space Shuttle mission. Sources inthe catalog are as faint as m_nuv_ ~ 18.8, or f_nuv_ ~ 1.1 x 10^16^ ergss^-1^ cm^-2^ A^-1^, but the survey is not complete to this level.Optical catalogs were used to cross identify sources and derive NUV - Vcolors. A majority of the objects (88%) do indeed have proposed opticalidentifications from catalogs, and most are stars. Our purpose increating the catalog is to form a database useful for identifying veryblue objects and performing Galactic UV stellar population studies.
| 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.
| Ca II H and K Filter Photometry on the UVBY System. II. The Catalog of Observations
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....109.2828T&db_key=AST
| The general catalogue of trigonometric [stellar] paralaxes
Not Available
| Four-color UVBY and H-beta photometry of high-velocity and metal-poor stars. I - The catalogue of observations
A catalog of four-color uvby and H-beta photometry for 711 high-velocityand metal-poor stars is given. The selection of the stars and theobserving and reduction techniques used to obtain these data arediscussed. The photometry has been transformed closely onto the standarduvby-beta system. The errors of the data have been estimated using bothinternal and external comparisons. The data are uniform over the sky;that is, there are no significant north-south differences. For the largemajority of stars the mean errors of V, m1, c1, and beta are less than +or - 0.008 mag, and the error of b-y is less than + or - 0.005 mag.Values of V, b-y and beta and rough photometric classifications aregiven for 63 red and/or evolved stars that fall outside the range of thephotometric transformations.
| G. P. Kuiper's spectral classifications of proper-motion stars
Spectral classifications are listed for over 3200 stars, mainly of largeproper motion, observed and classified by Kuiper during the years1937-1944 at the Yerkes and McDonald Observatories. While Kuiper himselfpublished many of his types, and while improved classifications are nowavailable for many of these stars, much of value remains. For many ofthe objects, no other spectral data exist.
| Kinematical and orbital properties for selected southern high-velocity stars
Using the model of the Galaxy presented by Eggen, Lynden-Bell, andSandage (1962), plane galactic orbits have been calculated for severalsouthern high-velocity stars which possess parallax, proper motion, andradial velocity data. Extensive lists of both raw and computed data forthese stars are included. Published values of U-B and B-V for some ofthese stars were used in plots of each of the orbital parameters versusU-B, B-V, or the ultraviolet excess. Also, a comparison is made betweenthe H-R diagrams for the southern high-velocity star group and that ofM3, a globular cluster, and again for M67, an old open cluster. Thehigh-velocity star group is found to resemble an old open cluster morethan a globular cluster.
| Catalog of Indidual Radial Velocities, 0h-12h, Measured by Astronomers of the Mount Wilson Observatory
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1970ApJS...19..387A&db_key=AST
| Discussion of five-colour observations of stars of high velocity
Not Available
| Photoelectric Three Colour Magnitudes for Southern Stars
Not Available
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הכנס מאמר חדש
לינקים קשורים
הכנס לינק חדש
משמש של הקבוצה הבאה
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | נחש מים |
| התרוממות ימנית: | 09h46m25.99s |
| סירוב: | -14°31'45.5" |
| גודל גלוי: | 9.421 |
| תנועה נכונה: | -254.5 |
| תנועה נכונה: | 173.7 |
| B-T magnitude: | 10.336 |
| V-T magnitude: | 9.497 |
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