Contents
Images
Upload your image
DSS Images Other Images
Related articles
Spectroscopic Properties of Cool Stars (SPOCS). I. 1040 F, G, and K Dwarfs from Keck, Lick, and AAT Planet Search Programs
We present a uniform catalog of stellar properties for 1040 nearby F, G,and K stars that have been observed by the Keck, Lick, and AAT planetsearch programs. Fitting observed echelle spectra with synthetic spectrayielded effective temperature, surface gravity, metallicity, projectedrotational velocity, and abundances of the elements Na, Si, Ti, Fe, andNi, for every star in the catalog. Combining V-band photometry andHipparcos parallaxes with a bolometric correction based on thespectroscopic results yielded stellar luminosity, radius, and mass.Interpolating Yonsei-Yale isochrones to the luminosity, effectivetemperature, metallicity, and α-element enhancement of each staryielded a theoretical mass, radius, gravity, and age range for moststars in the catalog. Automated tools provide uniform results and makeanalysis of such a large sample practical. Our analysis method differsfrom traditional abundance analyses in that we fit the observed spectrumdirectly, rather than trying to match equivalent widths, and wedetermine effective temperature and surface gravity from the spectrumitself, rather than adopting values based on measured photometry orparallax. As part of our analysis, we determined a new relationshipbetween macroturbulence and effective temperature on the main sequence.Detailed error analysis revealed small systematic offsets with respectto the Sun and spurious abundance trends as a function of effectivetemperature that would be inobvious in smaller samples. We attempted toremove these errors by applying empirical corrections, achieving aprecision per spectrum of 44 K in effective temperature, 0.03 dex inmetallicity, 0.06 dex in the logarithm of gravity, and 0.5 kms-1 in projected rotational velocity. Comparisons withprevious studies show only small discrepancies. Our spectroscopicallydetermined masses have a median fractional precision of 15%, but theyare systematically 10% higher than masses obtained by interpolatingisochrones. Our spectroscopic radii have a median fractional precisionof 3%. Our ages from isochrones have a precision that variesdramatically with location in the Hertzsprung-Russell diagram. We planto extend the catalog by applying our automated analysis technique toother large stellar samples.
| The Planet-Metallicity Correlation
We have recently carried out spectral synthesis modeling to determineTeff, logg, vsini, and [Fe/H] for 1040 FGK-type stars on theKeck, Lick, and Anglo-Australian Telescope planet search programs. Thisis the first time that a single, uniform spectroscopic analysis has beenmade for every star on a large Doppler planet search survey. We identifya subset of 850 stars that have Doppler observations sufficient todetect uniformly all planets with radial velocity semiamplitudes K>30m s-1 and orbital periods shorter than 4 yr. From this subsetof stars, we determine that fewer than 3% of stars with-0.5<[Fe/H]<0.0 have Doppler-detected planets. Above solarmetallicity, there is a smooth and rapid rise in the fraction of starswith planets. At [Fe/H]>+0.3 dex, 25% of observed stars have detectedgas giant planets. A power-law fit to these data relates the formationprobability for gas giant planets to the square of the number of metalatoms. High stellar metallicity also appears to be correlated with thepresence of multiple-planet systems and with the total detected planetmass. This data set was examined to better understand the origin of highmetallicity in stars with planets. None of the expected fossilsignatures of accretion are observed in stars with planets relative tothe general sample: (1) metallicity does not appear to increase as themass of the convective envelopes decreases, (2) subgiants with planetsdo not show dilution of metallicity, (3) no abundance variations for Na,Si, Ti, or Ni are found as a function of condensation temperature, and(4) no correlations between metallicity and orbital period oreccentricity could be identified. We conclude that stars with extrasolarplanets do not have an accretion signature that distinguishes them fromother stars; more likely, they are simply born in higher metallicitymolecular clouds.Based on observations obtained at Lick and Keck Observatories, operatedby the University of California, and the Anglo-Australian Observatories.
| 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.
| Chemical enrichment and star formation in the Milky Way disk. III. Chemodynamical constraints
In this paper, we investigate some chemokinematical properties of theMilky Way disk, by using a sample composed by 424 late-type dwarfs. Weshow that the velocity dispersion of a stellar group correlates with theage of this group, according to a law proportional to t0.26,where t is the age of the stellar group. The temporal evolution of thevertex deviation is considered in detail. It is shown that the vertexdeviation does not seem to depend strongly on the age of the stellargroup. Previous studies in the literature seem to not have found it dueto the use of statistical ages for stellar groups, rather thanindividual ages. The possibility to use the orbital parameters of a starto derive information about its birthplace is investigated, and we showthat the mean galactocentric radius is likely to be the most reliablestellar birthplace indicator. However, this information cannot bepresently used to derive radial evolutionary constraints, due to anintrinsic bias present in all samples constructed from nearby stars. Anextensive discussion of the secular and stochastic heating mechanismscommonly invoked to explain the age-velocity dispersion relation ispresented. We suggest that the age-velocity dispersion relation couldreflect the gradual decrease in the turbulent velocity dispersion fromwhich disk stars form, a suggestion originally made by Tinsley &Larson (\cite{tinsley}, ApJ, 221, 554) and supported by several morerecent disk evolution calculations. A test to distinguish between thetwo types of models using high-redshift galaxies is proposed.Full Table 1 is 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/423/517
| 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
| Some anomalies in the occurrence of debris discs around main-sequence A and G stars
Debris discs consist of large dust grains that are generated bycollisions of comets or asteroids around main-sequence stars, and thequantity and distribution of debris may be used to detect the presenceof perturbing planets akin to Neptune. We use stellar and disc surveysto compare the material seen around A- and G-type main-sequence stars.Debris is detected much more commonly towards A stars, even when acomparison is made only with G stars of comparable age. Detection ratesare consistent with disc durations of ~0.5 Gyr, which may occur at anytime during the main sequence. The higher detection rate for A stars canresult from this duration being a larger fraction of the main-sequencelifetime, possibly boosted by a globally slightly larger disc mass thanfor the G-type counterparts. The disc mass range at any given age is afactor of at least ~100 and any systematic decline with time is slow,with a power law estimated to not be steeper than t-1/2.Comparison with models shows that dust can be expected as late as a fewGyr when perturbing planetesimals form slowly at large orbital radii.Currently, the Solar system has little dust because the radius of theKuiper Belt is small and hence the time-scale to produce planetesimalswas less than 1 Gyr. However, the apparently constant duration of ~0.5Gyr when dust is visible is not predicted by the models.
| 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.
| Extrasolar planets around HD 196050, HD 216437 and HD 160691
We report precise Doppler measurements of the stars HD 216437, HD 196050and HD 160691 obtained with the Anglo-Australian Telescope using theUCLES spectrometer together with an iodine cell as part of theAnglo-Australian Planet Search. Our measurements reveal periodicKeplerian velocity variations that we interpret as evidence for planetsin orbit around these solar type stars. HD 216437 has a period of 1294+/- 250 d, a semi-amplitude of 38 +/- 3 m s-1 and aneccentricity of 0.33 +/- 0.09. The minimum (M sin i) mass of thecompanion is 2.1 +/- 0.3 MJUP and the semi-major axis is 2.4+/- 0.5 au. HD 196050 has a period of 1300 +/- 230 d, a semi-amplitudeof 49 +/- 8 m s-1 and an eccentricity of 0.19 +/- 0.09. Theminimum mass of the companion is 2.8 +/- 0.5 MJUP and thesemi-major axis is 2.4 +/- 0.5 au. We also report further observationsof the metal-rich planet bearing star HD 160691. Our new solutionconfirms the previously reported planet and shows a trend indicating asecond, longer-period companion. These discoveries add to the growingnumbers of mildly eccentric, long-period extrasolar planets aroundmetal-rich Sun-like stars.
| 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
| Chromospherically young, kinematically old stars
We have investigated a group of stars known to have low chromosphericages, but high kinematical ages. Isochrone, chemical and lithium agesare estimated for them. The majority of stars in this group show lithiumabundances much smaller than expected for their chromospheric ages,which is interpreted as an indication of their old age. Radial velocitymeasurements in the literature also show that they are not closebinaries. The results suggest that they can be formed from thecoalescence of short-period binaries. Coalescence rates, calculatedtaking into account several observational data and a maximum theoreticaltime scale for contact, in a short-period pair, predict a number ofcoalesced stars similar to what we have found in the solarneighbourhood.
| A revision of the solar neighbourhood metallicity distribution
We present a revised metallicity distribution of dwarfs in the solarneighbourhood. This distribution is centred on solar metallicity. Weshow that previous metallicity distributions, selected on the basis ofspectral type, are biased against stars with solar metallicity orhigher. A selection of G-dwarf stars is inherently biased againstmetal-rich stars and is not representative of the solar neighbourhoodmetallicity distribution. Using a sample selected on colour, we obtain adistribution where approximately half the stars in the solarneighbourhood have metallicities higher than [Fe/H]=0. The percentage ofmid-metal-poor stars ([Fe/H]<-0.5) is approximately 4 per cent, inagreement with present estimates of the thick disc. In order to have ametallicity distribution comparable to chemical evolution modelpredictions, we convert the star fraction to mass fraction, and showthat another bias against metal-rich stars affects dwarf metallicitydistributions, due to the colour (or spectral type) limits of thesamples. Reconsidering the corrections resulting from the increasingthickness of the stellar disc with age, we show that the simpleclosed-box model with no instantaneous recycling approximation gives areasonable fit to the observed distribution. Comparisons with theage-metallicity relation and abundance ratios suggest that the simpleclosed-box model may be a viable model of the chemical evolution of theGalaxy at solar radius.
| High proper motion stars with declinations between -30o and -40o, and right ascensions between 00 h and 10 h 40 m
Proper motions, positions, finding charts and magnitudes are given for147 newly discovered stars with proper motions larger than 0.15arcsec/year. They were found in a search for high proper motion starscarried out in thirteen 5o x 5o areas, locatedbetween -30o and -40o in declination, and 00 h and10 h 40 m in right ascension. Their blue photographic magnitudes rangefrom approximately 9.0 to 18.5. Nine objects from the above sample haveproper motions larger than 0.4 (0.404 to 0.550) arcsec/year. The sametype of data is also presented for 149 Luyten Catalogue (LTT, Luyten\cite{Luyten57}) stars re-discovered during the above search. Anestimated precision level between 6 and 22 mas/year was achieved for theproper motions. Tables 2 and 3 are only available in electronic form atthe CDS, via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5), or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/367/725 Figures 4 and 5are only available in electronic form at http://www.edpsciences.org
| 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
| Unlocking the Keyhole: H2 and PAH emission from molecular clumps in the Keyhole Nebula
To better understand the environment surrounding CO emission clumps inthe Keyhole Nebula, we have made images of the region in H21-0 S(1) (2.122-μm) emission and polycyclic aromatic hydrocarbon(PAH) emission at 3.29μm. Our results show that the H2 andPAH emission regions are morphologically similar, existing as severalclumps, all of which correspond to CO emission clumps and dark opticalfeatures. The emission confirms the existence of photodissociationregions (PDRs) on the surface of the clumps. By comparing the velocityrange of the CO emission with the optical appearance of theH2 and PAH emission, we present a model of the Keyhole Nebulawhereby the most negative velocity clumps are in front of the ionizationregion, the clumps at intermediate velocities are in it and those whichhave the least negative velocities are at the far side. It may be thatthese clumps, which appear to have been swept up from molecular gas bythe stellar winds from ηCar, are now being overrun by the ionizationregion and forming PDRs on their surfaces. These clumps comprise thelast remnants of the ambient molecular cloud around η Car.
| On the possibility of ground-based direct imaging detection of extra-solar planets: the case of TWA-7
We show that ground-based direct imaging detection of extra-solarplanets is possible with current technology. As an example, we presentevidence for a possible planetary companion to the young T Tauri star1RXSJ104230.3-334014 (=TWA-7), discovered by ROSAT as a member of thenearby TW Hya association. In an HST NICMOS F160W image, an object isdetected that is more than 9 mag fainter than TWA-7, located 2.445 +/-0.035'' south-east at a position angle of 142.24 +/- 1.34deg.One year later using the ESO-NTT with the SHARP speckle camera, weobtained H- and K-band detections of this faint object at a separationof 2.536 +/- 0.077'' and a position angle of 139.3 +/-2.1deg. Given the known proper motion of TWA-7, the pair mayform a proper motion pair. If the faint object orbits TWA-7, then itsapparent magnitudes of H=16.42 +/- 0.11 and K=16.34 +/- 0.15 mag yieldabsolute magnitudes consistent with a ~ 106.5 yr old ~ 3M_jup mass object according to the non-gray theory by Burrows et al.(1997). At ~ 55 pc, the angular separation of ~ 2.5'' corresponds to ~138 AU, clearly within typical disk sizes. However, position angles andseparations are slightly more consistent with a background object thanwith a companion. Based on observations obtained at the EuropeanSouthern Observatory, La Silla (ESO Proposals 62.I-0418 and 63.N-0178),and on observations made with the NASA/ESA Hubble Space Telescope,obtained from the data archive at the Space Telescope Science Institute.STScI is operated by the Association of Universities for Research inAstronomy, Inc., under the NASA contract NAS 5-26555.
| 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
| Metallicity effects on the chromospheric activity-age relation for late-type dwarfs
We show that there is a relationship between the age excess, defined asthe difference between the stellar isochrone and chromospheric ages, andthe metallicity as measured by the index [Fe/H] for late-type dwarfs.The chromospheric age tends to be lower than the isochrone age formetal-poor stars, and the opposite occurs for metal-rich objects. Wesuggest that this could be an effect of neglecting the metallicitydependence of the calibrated chromospheric emission-age relation. Wepropose a correction to account for this dependence. We also investigatethe metallicity distributions of these stars, and show that there aredistinct trends according to the chromospheric activity level. Inactivestars have a metallicity distribution which resembles the metallicitydistribution of solar neighbourhood stars, while active stars appear tobe concentrated in an activity strip on the logR'_HKx[Fe/H] diagram. Weprovide some explanations for these trends, and show that thechromospheric emission-age relation probably has different slopes on thetwo sides of the Vaughan-Preston gap.
| A Multiplicity Survey of Chromospherically Active and Inactive Stars
Surveys of three samples of solar-type stars, segregated bychromospheric emission level, were made to determine their multiplicityfractions and to investigate the evolution of multiplicity with age. Intotal, 245 stars were searched for companions with DeltaV <= 3.0 andseparations of 0.035" to 1.08" using optical speckle interferometry. Byincorporating the visual micrometer survey for duplicity of theLamontHussey Observatory, the angular coverage was extended to 5.0" withno change in the DeltaV limit. This magnitude difference allows massratios of 0.63 and larger to be detected throughout a search region of2-127 AU for the stars observed. The 84 primaries observed in thechromospherically active sample are presumably part of a youngpopulation and are found to have a multiplicity fraction of 17.9% +/-4.6%. The sample of 118 inactive, presumably older, primaries wereselected and observed using identical methods and are found to have amultiplicity fraction of only 8.5% +/- 2.7%. Given the known linkbetween chromospheric activity and age, these results tentatively implya decreasing stellar multiplicity fraction from 1 to 4 Gyr, theapproximate ages of the two samples. Finally, only two of the 14 veryactive primaries observed were found to have a companion meeting thesurvey detection parameters. In this case, many of the systems areeither very young, or close, RS CVn type multiples that are unresolvableusing the techniques employed here.
| Kinematics and Metallicity of Stars in the Solar Region
Several samples of nearby stars with the most accurate astrometric andphotometric parameters are searched for clues to their evolutionaryhistory. The main samples are (1) the main-sequence stars with b - ybetween 0.29 and 0.59 mag (F3 to K1) in the Yale parallax catalog, (2) agroup of high-velocity subgiants studied spectroscopically by Ryan &Lambert, and (3) high-velocity main-sequence stars in the extensiveinvestigation by Norris, Bessel, & Pickles. The major conclusionsare as follows: (1) The oldest stars (halo), t >= 10-12 Gyr, haveV-velocities (in the direction of Galactic rotation and referred to theSun) in the range from about -50 to -800 km s^-1 and have aheavy-element abundance [Fe/H] of less than about -0.8 dex. The agerange of these objects depends on our knowledge of globular clusterages, but if age is correlated with V-velocity, the youngest may be M22and M28 (V ~ -50 km s^-1) and the oldest NGC 3201 (V ~ -500 km s^-1) andassorted field stars. (2) The old disk population covers the large agerange from about 2 Gyr (Hyades, NGC 752) to 10 or 12 Gyr (Arcturusgroup, 47 Tuc), but the lag (V) velocity is restricted to less thanabout 120 km s^-1 and [Fe/H] >= -0.8 or -0.9 dex. The [Fe/H] ~ -0.8dex division between halo and old disk, near t ~ 10-12 Gyr, is marked bya change in the character of the CN index (C_m) and of the blanketingparameter K of the DDO photometry. (3) The young disk population, t <2 Gyr, is confined exclusively to a well-defined area of the (U, V)velocity plane. The age separating young and old disk stars is also thatseparating giant evolution of the Hyades (near main-sequence luminosity)and M67 (degenerate helium cores and a large luminosity rise) kinds. Thetwo disk populations are also separated by such indexes as the g-indexof Geveva photometry. There appears to be no obvious need to invokeexogeneous influences to understand the motion and heavy-elementabundance distributions of the best-observed stars near the Sun.Individual stars of special interest include the parallax star HD 55575,which may be an equal-component binary, and the high-velocity star HD220127, with a well-determined space velocity near 1000 km s^-1.
| The ROSAT all-sky survey catalogue of optically bright main-sequence stars and subgiant stars
We present X-ray data for all main-sequence and subgiant stars ofspectral types A, F, G, and K and luminosity classes IV and V listed inthe Bright Star Catalogue that have been detected as X-ray sources inthe ROSAT all-sky survey; several stars without luminosity class arealso included. The catalogue contains 980 entries yielding an averagedetection rate of 32 percent. In addition to count rates, sourcedetection parameters, hardness ratios, and X-ray fluxes we also listX-ray luminosities derived from Hipparcos parallaxes. The catalogue isalso available in electronic form via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Determination of the temperatures of selected ISO flux calibration stars using the Infrared Flux Method
Effective temperatures for 420 stars with spectral types between A0 andK3, and luminosity classes between II and V, selected for a fluxcalibration of the Infrared Space Observatory, ISO, have been determinedusing the Infrared Flux Method (IRFM). The determinations are based onnarrow and wide band photometric data obtained for this purpose, andtake into account previously published narrow-band measures oftemperature. Regression coefficients are given for relations between thedetermined temperatures and the photometric parameters (B2-V1), (b-y)and (B-V), corrected for interstellar extinction through use ofHipparcos parallaxes. A correction for the effect of metallicity on thedetermination of integrated flux is proposed. The importance of aknowledge of metallicity in the representation of derived temperaturesfor Class V, IV and III stars by empirical functions is discussed andformulae given. An estimate is given for the probable error of eachtemperature determination. Based on data from the ESA HipparcosAstrometry Satellite.
| Spectroscopic and photometric behaviour of the FU Orionis variable Z Canis Majoris
We present optical and IR photometry, optical multi-dispersionspectroscopy, and IR spectrophotometry of the FU Ori variable Z CanisMajoris, obtained in the years 1984, 1985, 1989 and 1996. A comparisonof data obtained in 1984 and 1985 confirms that in 1985 Z CMa underwenta low-power eruption. The enhancement of H alpha emission line, thetransition of H beta and Fe ii lines from pure absorption to emissionwith or without a P~Cygni profile, the appearance of the He i 6678Angstrom absorption line, a radial velocity increase of about 30% of theP Cygni absorption components, and finally a 0.2-0.3 mag increase of IRluminosity, were all dinstinctive characteristics of this state. Furtherobservations in 1996 show that Z CMa is in a low-luminosity state at V =10.24 while the appearance of a double-peaked H alpha emission, with theblue component much weaker than the red one, is the most significantspectroscopic variation. Energy distributions in the range 0.4-5microns, obtained during 1984 and 1985 observational runs, are alsopresented. Based on observations collected at the European SouthernObservatory in La Silla, Chile.
| The catalogue of nearby stars metallicities.
Not Available
| A Survey of Ca II H and K Chromospheric Emission in Southern Solar-Type Stars
More than 800 southern stars within 50 pc have been observed forchromospheric emission in the cores of the Ca II H and K lines. Most ofthe sample targets were chosen to be G dwarfs on the basis of colors andspectral types. The bimodal distribution in stellar activity first notedin a sample of northern stars by Vaughan and Preston in 1980 isconfirmed, and the percentage of active stars, about 30%, is remarkablyconsistent between the northern and southern surveys. This is especiallycompelling given that we have used an entirely different instrumentalsetup and stellar sample than used in the previous study. Comparisons tothe Sun, a relatively inactive star, show that most nearby solar-typestars have a similar activity level, and presumably a similar age. Weidentify two additional subsamples of stars -- a very active group, anda very inactive group. The very active group may be made up of youngstars near the Sun, accounting for only a few percent of the sample, andappears to be less than ~0.1 Gyr old. Included in this high-activitytail of the distribution, however, is a subset of very close binaries ofthe RS CVn or W UMa types. The remaining members of this population maybe undetected close binaries or very young single stars. The veryinactive group of stars, contributting ~5%--10% to the total sample, maybe those caught in a Maunder Minimum type phase. If the observations ofthe survey stars are considered to be a sequence of snapshots of the Sunduring its life, we might expect that the Sun will spend about 10% ofthe remainder of its main sequence life in a Maunder Minimum phase.
| Chemistry and Kinematics in the Solar Neighborhood: Implications for Stellar Populations and for Galaxy Evolution
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....110.2771W&db_key=AST
| 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
| Photometric discriminate for GK dwarfs of disk populations
The young and old disk populations, with ages respectively less than andgreater than about 2 x 109 yr, are separated in the (R - I,42 - 45) plane, where the 42 - 45 index of the DDO system is based onbandpasses of 75 A half-width and effective wavelengths of 4257 and 4571A. A similar, but smaller separation is seen in the (g,B2 - VI) planewhere g is the Geneva system alternative to 42 - 45 but with bandpassesof 175 A half-width and effective wavelengths of 4015 and 4476 A.Although models, based on the assumption that this separation resultsfrom a veil of weak metal lines (Magain 1983), may explain thesephenomena in the (g,B2 - VI) plane for the hotter stars, more models arerequired to test it for the DDO system and for cooler objects. Theavailable evidence suggests that an additional causation, probablyconnected with the CN abundance, also exists.
| 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.
| SANTIAGO 91, a right ascension catalogue of 3387 stars (equinox J2000).
The positions in right ascension of 3387 stars belonging to the Santiago67 Catalogue, observed with the Repsold Meridian Circle at Cerro Calan,National Astronomical Observatory, during the period 1989 to 1994, aregiven. The average mean square error of a position, for the wholeCatalogue, is +/-0.009 s. The mean epoch of the catalogue is 1991.84.
| Vilnius Photometric System - Part Two - the Bright Southern Standard Stars
Not Available
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
| Constellation: | Antlia |
| Right ascension: | 10h13m24.80s |
| Declination: | -33°01'55.0" |
| Apparent magnitude: | 6.38 |
| Distance: | 22.738 parsecs |
| Proper motion RA: | -369.8 |
| Proper motion Dec: | 65.3 |
| B-T magnitude: | 7.081 |
| V-T magnitude: | 6.429 |
Catalogs and designations:
|
