目录
图像
上传图像
DSS Images Other Images
相关文章
Improvement of Hipparcos Proper Motions in Declination
More than a decade elapsed after the HIPPARCOS ESA mission (ESA 1997)observations have been collected. This first astronomical satellitemission was less than 4 years long so that 1991.25 is the epoch of theHIPPARCOS Catalogue. Many other projects have checked or improvedHIPPARCOS data. Also, a long series of ground - based opticalobservations of some stars included in HIPPARCOS Catalogue, made withPhotographic Zenith Tubes (PZT) are useful for the task of improving theproper motions of these stars. The ARIHIP Catalogue (after ACT, TYCHO -2, FK6, GC+HIP, TYC2+HIP) is a combination of the HIPPARCOS and someground - based data, and the ARIHIP proper motions are more accuratethan the HIPPARCOS ones. Here we present a new step of our procedure ofcalculation; between PZT data we added the HIPPARCOS position withsuitable weight - the point with the coordinates (1991.25, 0ŭ0)in our case. The method was applied to 202 stars observed at RichmondPZTs in the course of a few decades. The result is better proper motionsin declination for these HIPPARCOS stars, and a good agreement withARIHIP proper motions (we found 128 common Richmond and ARIHIP stars tocheck our result). Also, we present the result for other 74 Richmondstars which are not found in ARIHIP.
| 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.
| A new Böhm-Vitense gap in the temperature range 5560 to 5610 K in the main sequence hm-Vitense gap in the main sequence
Highly precise temperatures (σ = 10-15 K) have been determinedfrom line depth ratios for a set of 248 F-K field dwarfs of about solarmetallicity (-0.5 < [Fe/H] < +0.4), based on high resolution (R=42000), high S/N echelle spectra. A new gap has been discovered in thedistribution of stars on the Main Sequence in the temperature range 5560to 5610 K. This gap coincides with a jump in the microturbulent velocityVt and the well-known Li depression near 5600 K in fielddwarfs and open clusters. As the principal cause of the observeddiscontinuities in stellar properties we propose the penetration of theconvective zone into the inner layers of stars slightly less massivethan the Sun and related to it, a change in the temperature gradient.Based on spectra collected with the ELODIE spectrograph at the 1.93-mtelescope of the Observatoire de Haute-Provence (France).Full Table 1 is only available in electronic form athttp://www.edpsciences.org
| 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
| Nearby stars of the Galactic disk and halo. III.
High-resolution spectroscopic observations of about 150 nearby stars orstar systems are presented and discussed. The study of these and another100 objects of the previous papers of this series implies that theGalaxy became reality 13 or 14 Gyr ago with the implementation of amassive, rotationally-supported population of thick-disk stars. The veryhigh star formation rate in that phase gave rise to a rapid metalenrichment and an expulsion of gas in supernovae-driven Galactic winds,but was followed by a star formation gap for no less than three billionyears at the Sun's galactocentric distance. In a second phase, then, thethin disk - our ``familiar Milky Way'' - came on stage. Nowadays ittraces the bright side of the Galaxy, but it is also embedded in a hugecoffin of dead thick-disk stars that account for a large amount ofbaryonic dark matter. As opposed to this, cold-dark-matter-dominatedcosmologies that suggest a more gradual hierarchical buildup throughmergers of minor structures, though popular, are a poor description forthe Milky Way Galaxy - and by inference many other spirals as well - if,as the sample implies, the fossil records of its long-lived stars do notstick to this paradigm. Apart from this general picture that emergeswith reference to the entire sample stars, a good deal of the presentwork is however also concerned with detailed discussions of manyindividual objects. Among the most interesting we mention the bluestraggler or merger candidates HD 165401 and HD 137763/HD 137778, thelikely accretion of a giant planet or brown dwarf on 59 Vir in itsrecent history, and HD 63433 that proves to be a young solar analog at\tau200 Myr. Likewise, the secondary to HR 4867, formerly suspectednon-single from the Hipparcos astrometry, is directly detectable in thehigh-resolution spectroscopic tracings, whereas the visual binary \chiCet is instead at least triple, and presumably even quadruple. Withrespect to the nearby young stars a complete account of the Ursa MajorAssociation is presented, and we provide as well plain evidence foranother, the ``Hercules-Lyra Association'', the likely existence ofwhich was only realized in recent years. On account of its rotation,chemistry, and age we do confirm that the Sun is very typical among itsG-type neighbors; as to its kinematics, it appears however not unlikelythat the Sun's known low peculiar space velocity could indeed be thecause for the weak paleontological record of mass extinctions and majorimpact events on our parent planet during the most recent Galactic planepassage of the solar system. Although the significance of thiscorrelation certainly remains a matter of debate for years to come, wepoint in this context to the principal importance of the thick disk fora complete census with respect to the local surface and volumedensities. Other important effects that can be ascribed to this darkstellar population comprise (i) the observed plateau in the shape of theluminosity function of the local FGK stars, (ii) a small thoughsystematic effect on the basic solar motion, (iii) a reassessment of theterm ``asymmetrical drift velocity'' for the remainder (i.e. the thindisk) of the stellar objects, (iv) its ability to account for the bulkof the recently discovered high-velocity blue white dwarfs, (v) itsmajor contribution to the Sun's 220 km s-1 rotationalvelocity around the Galactic center, and (vi) the significant flatteningthat it imposes on the Milky Way's rotation curve. Finally we note ahigh multiplicity fraction in the small but volume-complete local sampleof stars of this ancient population. This in turn is highly suggestivefor a star formation scenario wherein the few existing single stellarobjects might only arise from either late mergers or the dynamicalejection of former triple or higher level star systems.
| 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.
| Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 Parsecs: The Northern Sample. I.
We have embarked on a project, under the aegis of the Nearby Stars(NStars)/Space Interferometry Mission Preparatory Science Program, toobtain spectra, spectral types, and, where feasible, basic physicalparameters for the 3600 dwarf and giant stars earlier than M0 within 40pc of the Sun. In this paper, we report on the results of this projectfor the first 664 stars in the northern hemisphere. These resultsinclude precise, homogeneous spectral types, basic physical parameters(including the effective temperature, surface gravity, and overallmetallicity [M/H]), and measures of the chromospheric activity of ourprogram stars. Observed and derived data presented in this paper arealso available on the project's Web site.
| 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.
| 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.
| 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
| Nearby Young Solar Analogs. I. Catalog and Stellar Characteristics
We present a catalog of 38 young solar analogs within 25 pc, stars thatare uniquely well suited for observations of their circumstellarenvironments to improve our understanding of conditions within the solarsystem during the Hadean/early Archean eons (prior to 3.8 Gyr ago).These G and early K stars were selected from the Hipparcos astrometriccatalog based on lack of known stellar companions within 800 AU,bolometric luminosities close to that of the zero-age Sun and consistentwith the zero-age main sequence, and ROSAT X-ray luminositiescommensurate with the higher rotation rate and level of dynamo-drivenactivity in solar-mass stars less than 0.8 Gyr old. While many of theseobjects have been previously identified, this sample is novel in tworespects: The selection criteria specifically consider the planetaryenvironment, and the selection is uniform and all-sky. The X-rayemission from these young analogs is spectrally soft and consistent witha coronal origin. Calcium H and K emission, rotation periods, lithiumabundances, and kinematics support an age range of 0.2-0.8 Gyr for mostof these stars. Three stars have exceptionally high space motions withrespect to the local standard of rest and may be old disk or halo starsthat are anomalously X-ray luminous.
| Reality Tests of Superclusters in the Young Disk Population
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....110.2862E&db_key=AST
| 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.
| Spectroscopic binary orbits from photoelectric radial velocities Paper 120: HR 3325
Not Available
| Radio continuum emission from stars: a catalogue update.
An updated version of my catalogue of radio stars is presented. Somestatistics and availability are discussed.
| Stroemgren photometry of F- and G-type stars brighter than V = 9.6. I. UVBY photometry
Within the framework of a large photometric observing program, designedto investigate the Galaxy's structure and evolution, Hβ photometryis being made for about 9000 stars. As a by-product, supplementary uvbyphotometry has been made. The results are presented in a cataloguecontaining 6924 uvby observations of 6190 stars, all south ofδ=+38deg. The overall internal rms errors of one observation(transformed to the standard system) of a program star in the interval6.5
| 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.
| Spectroscopic binaries - 15th complementary catalog
Published observational data on the orbital characteristics of 436spectroscopic binaries, covering the period 1982-1986, are compiled intables. The data sources and the organization of the catalog are brieflydiscussed, and notes are provided for each item.
| 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.
| Visual multiples. VIII - 1000 MK types
A total of 1000 new classifications are given for stars brighter than B= 8.0 mag in the Aitken double star catalog. The classificationssupplement 865 classifications obtained in 1981 and 1984. Among thenewly discovered stars are 12 new Ap stars, eight Lambda Bootis stars,one Ba II star, and 60 Am stars. A detailed list of the newclassifications is given.
| Radial-velocity orbits for six single-line spectroscopic binaries
Orbital elements are reported for three single-line spectroscopicbinaries, HR 2692, HR 3725, and HR 5911, none of which have previouslydetermined orbits. In addition, improved orbital elements are reportedfor three stars with previously determined orbits of low quality.
| Preliminary UVBY calibrations for G and K type dwarf stars
Four-color uvby photometry for several hundred late-type dwarf stars oftypes G, K and M is discussed. Mean values of photometric indices aregiven for MK spectral types between F8/G0V and M2V. Preliminary standardrelations between the four-color indices are derived. Based onparallaxes and results from high-dispersion spectroscopic analyses,calibrations of the observed indices in terms of Mv, log Te and Fe/Hhave been derived. The means errors are 0.29 mag, 0.009 dex, and 0.17dex, respectively. The calibrations are valid for class-V stars of allpopulations between G0 and M2. If extreme population-II dwarfs areexcluded, the mean error of the abundance calibration decreases to 0.13dex. Calibrations in terms of log g have been attempted,, but the lowaccuracy of the spectroscopic g determinations does not inspireconfidence in the results. The possible contribution of a'fourth-parameter' variation to the mean errors of the calibrations isbriefly discussed. This fourth parameter could be the intrinsic heliumabundance of the stars.
| The period distribution of unevolved close binary systems
Period distributions have been examined for various spectral types ofabout 600 (eclipsing and spectroscopic) close binaries, which are likelyto be substantially unevolved. The comparison with the previouscorresponding analyses of extensive (but heterogeneous) binary samplesallows a clarification of the extent of the evolutionary andobservational selection effects. Remarkably, this analysis reveals agreat deficiency of short period binaries (with periods corresponding tocase A mass transfer) in the whole spectral range. For the late spectraltypes, this result may be connected with postformation angular momentumloss caused by stellar wind magnetic braking; at least for the late Band A spectral range, a ready interpretation of this finding is thatclose binaries of corresponding periods and spectral types are rarelyformed.
| 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.
| Seventh catalogue of the orbital elements of spectroscopic binary systems.
Not Available
| Radio survey of close binary stars
Results are presented for a deep (5 mJy) 6-cm survey of 145 close binarystars. Eleven stars were detected (including five not previously knownto be radio binaries), and seven possibly detected (six of which werenot previously suspected to be radio sources). The short-period (lessthan 1 day) binary UV Psc was detected, the first star of this periodrange found to be a radio binary. The discovery of a radio source in thesystem HD 216489 brings to two the number of long-period (periodsexceeding 14 days) radio binaries. This relatively unbiased surveyconfirms that radio binaries later than A0 are predominantly of spectralclasses G and K. In an HR diagram, the radio binaries tend to besignificantly to the right of radio-quiet binaries.
| Spectroscopic binaries with circular orbits.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1971AJ.....76..544L&db_key=AST
| MK classifications for F and G-type stars. I.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1969AJ.....74..916H&db_key=AST
| A catalogue of four-color photometry of late F-type stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1969AJ.....74..705P&db_key=AST
|
提交文章
相关链接
提交链接
下列团体成员
|
观测天体数据
目录:
|
INHABITED SKY
