내용
사진
사진 업로드
DSS Images Other Images
관련 글
Radial Velocities of Late-Type Field Subgiant Stars
High-dispersion coudé spectra were observed and measured for 43field subgiants of the G and K spectral types, with the intent ofsearching for hitherto undiscovered spectroscopic binaries. Statisticalanalysis of the measurements revealed no definite but two possible newbinaries. We present the data and discuss the statistical analysis usedto test for new binaries. Additionally, we discuss the techniques forhigh precision of radial-velocity measurement, and the systematic errorsthat interfere with that goal.
| Synthetic Lick Indices and Detection of α-enhanced Stars. II. F, G, and K Stars in the -1.0 < [Fe/H] < +0.50 Range
We present an analysis of 402 F, G, and K solar neighborhood stars, withaccurate estimates of [Fe/H] in the range -1.0 to +0.5 dex, aimed at thedetection of α-enhanced stars and at the investigation of theirkinematical properties. The analysis is based on the comparison of 571sets of spectral indices in the Lick/IDS system, coming from fourdifferent observational data sets, with synthetic indices computed withsolar-scaled abundances and with α-element enhancement. We useselected combinations of indices to single out α-enhanced starswithout requiring previous knowledge of their main atmosphericparameters. By applying this approach to the total data set, we obtain alist of 60 bona fide α-enhanced stars and of 146 stars withsolar-scaled abundances. The properties of the detected α-enhancedand solar-scaled abundance stars with respect to their [Fe/H] values andkinematics are presented. A clear kinematic distinction betweensolar-scaled and α-enhanced stars was found, although a one-to-onecorrespondence to ``thin disk'' and ``thick disk'' components cannot besupported with the present data.
| The Globular Cluster Systems of the Sculptor Group
We use CTIO 4 m Mosaic II images taken with the Washington CM and HarrisR filters to identify candidate globular clusters in the six majorgalaxies of the Sculptor group: NGC 45, 55, 247, 254, 300, and 7793.From follow-up spectroscopy with Hydra-CTIO, we find 19 new globularclusters in NGC 55, 247, 253, and 300, bringing the total number ofknown Sculptor group globular clusters to 36. The newly discoveredclusters have spectroscopic ages consistent with those of old Milky Wayglobular clusters, and the majority are metal-poor. Their luminosityfunction closely resembles that of the Milky Way's globular clusters;their metallicity distribution is somewhat more metal-rich, but this maybe the result of our color selection of candidates. The mean[α/Fe] ratio in the clusters is -0.2+/-0.3, which is lower thanthe Milky Way average. The specific frequencies SN aresimilar to those of other late-type galaxies. However, if we calculatethe specific frequency using the K-band total magnitudes of the hostgalaxies, we find values that are more than a factor of 2 higher. Thekinematics of the globular cluster systems are consistent with rotationwith the H I disk in each of the four galaxies; however, only in NGC 253is this result based on more than seven objects. We suggest that theSculptor group galaxies add to evidence indicating that many of thefirst-generation globular clusters formed in disks, not halos.
| The photospheric abundances of active binaries. III. Abundance peculiarities at high activity levels
We report the determination from high-resolution spectra of theatmospheric parameters and abundances of 13 chemical species (amongwhich lithium) in 8 single-lined active binaries. These data arecombined with our previous results for 6 other RS CVn systems to examinea possible relationship between the photospheric abundance patterns andthe stellar activity level. The stars analyzed are generally found toexhibit peculiar abundance ratios compared to inactive, Galactic diskstars of similar metallicities. We argue that this behaviour is unlikelyto be an artefact of errors in the determination of the atmosphericparameters or non-standard mixing processes along the red giant branch,but diagnoses instead the combined action of various physical processesrelated to activity. The most promising candidates are cool spot groupscovering a very substantial fraction of the stellar photosphere or NLTEeffects arising from nonthermal excitation. However, we cannot excludethe possibility that more general shortcomings in our understanding ofK-type stars (e.g. inadequacies in the atmospheric models) also play asignificant role. Lastly, we call attention to the unreliability of the(V-R) and (V-I) colour indices as temperature indicators inchromospherically active stars.Based on observations collected at the European Southern Observatory,Chile (Proposals 64.L-0249 and 071.D-0260).Table A.1 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/426/1007
| On the determination of oxygen abundances in chromospherically active stars
We discuss oxygen abundances derived from [O I] λ6300s and the OI triplet in stars spanning a wide range in chromospheric activitylevel, and show that these two indicators yield increasingly discrepantresults with higher chromospheric/coronal activity measures. While theforbidden and permitted lines give fairly consistent results forsolar-type disk dwarfs, spuriously high O I triplet abundances areobserved in young Hyades and Pleiades stars, as well as in individualcomponents of RS CVn binaries (up to 1.8 dex). The distinct behaviour ofthe [O I]-based abundances which consistently remain near-solar suggeststhat this phenomenon mostly results from large departures from LTEaffecting the O I triplet at high activity level that are currentlyunaccounted for, but also possibly from a failure to adequately modelthe atmospheres of K-type stars. These results suggest that some cautionshould be exercised when interpreting oxygen abundances in activebinaries or young open cluster stars.Based on observations collected at the European Southern Observatory,Chile (Proposals 64.L-0249 and 071.D-0260).Table \ref{tab_data} is only available in electronic form athttp://www.edpsciences.org
| Precise radial velocity measurements of G and K giants. Multiple systems and variability trend along the Red Giant Branch
We present the results of our radial velocity (RV) measurements of G andK giants, concentrating on the presence of multiple systems in oursample. Eighty-three giants have been observed for 2.5 years with thefiber-fed echelle spectrograph FEROS at the 1.52 m ESO telescope in LaSilla, Chile. Seventy-seven stars (93%) of the targets have beenanalyzed for RV variability using simultaneous Th-Ar calibration and across-correlation technique. We estimate the long-term precision of ourmeasurement as better than 25 m s-1. Projected rotationalvelocities have been measured for most stars of the sample. Within ourtime-base only 21 stars (or 27%) show variability below 2\sigma, whilethe others show RV variability with amplitudes up to several kms-1. The large amplitude (several km s-1) andshape (high eccentricity) of the RV variations for 11 of the programstars are consistent with stellar companions, and possibly brown dwarfcompanions for two of the program stars. In those systems for which afull orbit could be derived, the companions have minimum masses from0.6 M\sun down to 0.1 M\sun. To thesemultiple systems we add the two candidates of giant planets alreadydiscovered in the sample. This analysis shows that multiple systemscontribute substantially to the long-term RV variability of giant stars,with about 20% of the sample being composed of multiple systems despitescreening our sample for known binary stars. After removing binaries,the range of RV variability in the whole sample clearly decreases, butthe remaining stars retain a statistical trend of RV variability withluminosity: luminous cool giants with B-V≥1.2 show RV variationswith \sigma_{/lineRV} > 60 m s-1, while giants with B-V< 1.2 including those in the clump region exhibit less variability orthey are constant within our accuracy. The same trend is observed withrespect to absolute visual magnitudes: brighter stars show a largerdegree of variability and, when plotted in the RV variability vs.magnitude diagram a trend of increasing RV scatter with luminosity isseen. The amplitude of RV variability does not increase dramatically, aspredicted, for instance, by simple scaling laws. At least two luminousand cooler stars of the sample show a correlation between RV andchromospheric activity and bisector asymmetry, indicating that in thesetwo objects RV variability is likely induced by the presence of(chromospheric) surface structures.Based on observations collected at the 1.52 m-ESO telescope at the LaSilla Observatory from Oct 1999 to Feb. 2002 under ESO programs and theESO-Observatório Nacional, Brazil, agreement and in part onobservations collected on the Alfred Jensch 2 m telescope of theThüringer Landessternwarte Tautenburg.
| 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.
| Speckle Interferometry of New and Problem Hipparcos Binaries. II. Observations Obtained in 1998-1999 from McDonald Observatory
The Hipparcos satellite made measurements of over 9734 known doublestars, 3406 new double stars, and 11,687 unresolved but possible doublestars. The high angular resolution afforded by speckle interferometrymakes it an efficient means to confirm these systems from the ground,which were first discovered from space. Because of its coverage of adifferent region of angular separation-magnitude difference(ρ-Δm) space, speckle interferometry also holds promise toascertain the duplicity of the unresolved Hipparcos ``problem'' stars.Presented are observations of 116 new Hipparcos double stars and 469Hipparcos ``problem stars,'' as well as 238 measures of other doublestars and 246 other high-quality nondetections. Included in these areobservations of double stars listed in the Tycho-2 Catalogue andpossible grid stars for the Space Interferometry Mission.
| Long-term starspot evolution, activity cycle and orbital period variation of SZ Piscium
A sequence of V-band light curves of the active close binary SZ Piscium(F8 V-IV+ K1 IV), extending from 1957 to 1998, is presented and analysedto derive the spot distribution and evolution on the component stars. Inour modelling approach the Roche geometry and Kurucz's atmosphericmodels were adopted. The resulting maps of the spot surface distributionwere regularized by means of the Maximum Entropy and Tikhonov criteriato take full advantage of the increased geometrical resolution duringeclipses. By comparing the maps obtained with these two criteria, it waspossible to discriminate between surface features actually required bythe data and artifacts introduced by the regularization process.Satisfactory fits were obtained assuming spots on both components andthe unspotted V-band luminosity ratio: L1/L2 =0.35 +/- 0.035. The derived yearly spot distributions indicate that thespot patterns consist of two components, one uniformly and the othernon-uniformly distributed in longitude, the latter suggesting thepresence of preferential longitudes. Starspots at latitudes higher than~ 75deg were not required to reproduce the photometricmodulation. For the spot pattern on the less luminous F8 V primarycomponent there are only some hints of the possible presence of spotsaround the substellar point facing the K1 IV secondary component. On themore luminous and larger secondary component there is clear evidence forthe presence of three active longitudes. A stable active longitudearound the substellar point facing the primary star appears to be quitecompact with an extension of ~ 40deg on several maps. Theother two active longitudes display irregular changes of the spot areaand location. The variation of the total spotted area on the secondarycomponent shows sizeable fluctuations and a possible short-term cycle ofabout 13 yr, which is more clearly apparent in the variation of thespotted area unevenly distributed in longitude. A longer-term cycle ofabout 30 yr with a markedly non-sinusoidal variation might also bepresent. The spatial association between photospheric spots andchromospheric plages (as detected in the UV lines) appears significantfor the active region around the substellar point in the K1 IVcomponent. A possible connection between magnetic activity and orbitalperiod variation is suggested by comparing the variation of the totalspotted area with the O-C diagram of the primary eclipse times. The timespan covered by the available data is, however, not long enough for usto draw any definite conclusions.
| 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
| CaII K Emission-Line Asymmetry among Red Giants Detected by the ROSAT Satellite
Spectra of the Ca II H and K lines are reported for a number of fieldgiants from which soft X-ray emission was detected by the ROSATsatellite. Several of these stars are RS CVn systems and exhibit verystrong Ca II emission. The majority of the noninteracting giants in thesample have MV>-2.0, as determined from Hipparcosparallaxes, and spectral types earlier than K3. The Ca II Kemission-line profile for these stars is most often double-peaked andasymmetric, with the short-wavelength peak being stronger than thelongward peak. This asymmetry is in the same sense as for the integrateddisk of the Sun. The X-ray and Ca II K-line data indicate that giants ofspectral types G and early K have coronae and chromospheres seeminglyanalogous to those of the Sun. Four M giants that were detected by ROSATwere also observed. Their Ca II emission spectra show asymmetries inwhich the violet wing is weaker than the red wing, a phenomenon that istypical of M giants in general and indicative of mass outflows in theirchromospheres. The majority of these M giants, but not all, are known tobe in binary systems, so it is possible that the X-ray emission for atleast some of them may come from a companion. Alternatively, some or allof these M giants may be examples of hybrid stars.
| Speckle Interferometry of New and Problem HIPPARCOS Binaries
The ESA Hipparcos satellite made measurements of over 12,000 doublestars and discovered 3406 new systems. In addition to these, 4706entries in the Hipparcos Catalogue correspond to double star solutionsthat did not provide the classical parameters of separation and positionangle (rho,theta) but were the so-called problem stars, flagged ``G,''``O,'' ``V,'' or ``X'' (field H59 of the main catalog). An additionalsubset of 6981 entries were treated as single objects but classified byHipparcos as ``suspected nonsingle'' (flag ``S'' in field H61), thusyielding a total of 11,687 ``problem stars.'' Of the many ground-basedtechniques for the study of double stars, probably the one with thegreatest potential for exploration of these new and problem Hipparcosbinaries is speckle interferometry. Results are presented from aninspection of 848 new and problem Hipparcos binaries, using botharchival and new speckle observations obtained with the USNO and CHARAspeckle cameras.
| Catalogs of temperatures and [Fe/H] averages for evolved G and K stars
A catalog of mean values of [Fe/H] for evolved G and K stars isdescribed. The zero point for the catalog entries has been establishedby using differential analyses. Literature sources for those entries areincluded in the catalog. The mean values are given with rms errors andnumbers of degrees of freedom, and a simple example of the use of thesestatistical data is given. For a number of the stars with entries in thecatalog, temperatures have been determined. A separate catalogcontaining those data is briefly described. Catalog only available atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Late-type giants with infrared excess. I. Lithium abundances
de la Reza et al. (1997) suggested that all K giants become Li-rich fora short time. During this period the giants are associated with anexpanding thin circumstellar shell supposedly triggered by an abruptinternal mixing mechanism resulting in the surface Li enrichment. Inorder to test this hypothesis twenty nine late-type giants withfar-infrared excess from the list of Zuckerman et al. (1995) wereobserved in the Li-region to study the connection between thecircumstellar shells and Li abundance. Eight giants have been found tohave log epsilon (Li) > 1.0. In the remaining giants the Li abundanceis found to be much lower. HD 219025 is found to be a rapidly rotating(projected rotational velocity of 23 +/-3 km s(-1) ), dusty and Li-rich(log epsilon (Li) = 3.0+/-0.2) K giant. Absolute magnitude derived fromthe Hipparcos parallax reveals that it is a giant and not apre-main-sequence star. The evolutionary status of HD 219025 seems to besimilar to that of HDE 233517 which is also a rapidly rotating, dustyand Li-rich K giant. The Hipparcos parallaxes of all the well studiedLi-rich K giants show that most of them are brighter than the ``clump"giants. Their position in the H-R diagram indicates that they have gonethrough mixing and the initial abundance of Li is not preserved. Thereseems to be no correlations between Li abundances, rotational velocitiesand carbon isotope ratios. The only satisfactory explanation for theoverabundance of lithium in these giants is the creation of Li by theextra deep mixing and the associated ``cool bottom processing". Based onobservations obtained at the European Southern Observatory, La Silla,Chile, and at the Observatoire de Haute Provence, France.
| A Search for Lithium-Rich Giants among Stars with Infrared Excesses
The unusual nature of the single, rapidly rotating, lithium-rich K giantHDE 233517, which is currently undergoing significant mass loss,prompted a search for giants with similar properties. High-dispersionspectroscopic observations were obtained of HD 219025, a knownlithium-rich infrared-excess giant, plus 39 stars from a list of G and Kgiants with excess far-infrared emission. The projected rotationalvelocities of the vast majority of infrared-excess giants appear to besimilar to those of normal G and K giants. Six giants have lithiumabundances at or above theoretical upper envelope values. The percentageof such stars in the sample of 39 infrared-excess giants is similar tothat of normal giants. The three giants with the largest lithiumabundances have previously been discovered. None of the sample of 39giants have an Hα line similar to the broadened and veryasymmetric line of HDE 233517. The star with optical properties mostsimilar to HDE 233517 is HD 219025.
| The ROSAT all-sky survey catalogue of optically bright late-type giants and supergiants
We present X-ray data for all late-type (A, F, G, K, M) giants andsupergiants (luminosity classes I to III-IV) listed in the Bright StarCatalogue that have been detected in the ROSAT all-sky survey.Altogether, our catalogue contains 450 entries of X-ray emitting evolvedlate-type stars, which corresponds to an average detection rate of about11.7 percent. The selection of the sample stars, the data analysis, thecriteria for an accepted match between star and X-ray source, and thedetermination of X-ray fluxes are described. Catalogue only available atCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| H gamma and H delta Absorption Features in Stars and Stellar Populations
The H gamma and H delta absorption features are measured in a sample of455 (out of an original 460) Lick/IDS stars with pseudo--equivalentwidth indices. For each Balmer feature, two definitions, involving anarrow (~20 Angstroms) and a wide (~40 Angstroms) central bandpass, aremeasured. These four new Balmer indices augment 21 indices previouslydetermined by Worthey et al., and polynomial fitting functions that giveindex strengths as a function of stellar temperature, gravity, and[Fe/H] are provided. The new indices are folded into models for theintegrated light of stellar populations, and predictions are given forsingle-burst stellar populations of a variety of ages and metallicities.Contrary to our initial hopes, the indices cannot break a degeneracybetween burst age and burst strength in post-starburst objects, but theyare successful mean-age indicators when used with sensitive metallicityindicators. An appendix gives data, advice, and examples of how totransform new spectra to the 25-index Lick/IDS system.
| On a Rapid Lithium Enrichment and Depletion of K Giant Stars
A model scenario has recently been introduced by de la Reza andcolleagues to explain the presence of very strong Li lines in thespectra of some low-mass K giant stars. In this scenario all ordinary,Li-poor, K giants become Li rich during a short time (~105 yr) whencompared to the red giant phase of 5 x 107 yr. In this "Li period," alarge number of the stars are associated with an expanding thincircumstellar shell supposedly triggered by an abrupt internal mixingmechanism resulting in a surface new 7Li enrichment. This Letterpresents nearly 40 Li-rich K giants known up to now. The distribution ofthese Li-rich giants, along with 41 other observed K giants that haveshells but are not Li rich, in a color-color IRAS diagram confirms thisscenario, which indicates, also as a new result, that a rapid Lidepletion takes place on a timescale of between ~103 and 105 yr. Thismodel explains the problem of the presence of K giants with far-infraredexcesses presented by Zuckerman and colleagues. Other present and futuretests of this scenario are briefly discussed.
| A catalogue of [Fe/H] determinations: 1996 edition
A fifth Edition of the Catalogue of [Fe/H] determinations is presentedherewith. It contains 5946 determinations for 3247 stars, including 751stars in 84 associations, clusters or galaxies. The literature iscomplete up to December 1995. The 700 bibliographical referencescorrespond to [Fe/H] determinations obtained from high resolutionspectroscopic observations and detailed analyses, most of them carriedout with the help of model-atmospheres. The Catalogue is made up ofthree formatted files: File 1: field stars, File 2: stars in galacticassociations and clusters, and stars in SMC, LMC, M33, File 3: numberedlist of bibliographical references The three files are only available inelectronic form at the Centre de Donnees Stellaires in Strasbourg, viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5), or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Classification of Population II Stars in the Vilnius Photometric System. I. Methods
The methods used for classification of Population II stars in theVilnius photometric system are described. An extensive set of standardswith known astrophysical parameters compiled from the literature sourcesis given. These standard stars are classified in the Vilnius photometricsystem using the methods described. The accuracy of classification isevaluated by a comparison of the astrophysical parameters derived fromthe Vilnius photometric system with those estimated from spectroscopicstudies as well as from photometric data in other systems. For dwarfsand subdwarfs, we find a satisfactory agreement between our reddeningsand those estimated in the uvbyscriptstyle beta system. The standarddeviation of [Fe/H] deter mined in the Vilnius system is about 0.2 dex.The absolute magnitude for dwarfs and subdwarfs is estimated with anaccuracy of scriptstyle <=0.5 mag.
| Luminosity Class III Stars with Excess Far-Infrared Emission
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...446L..79Z&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
| 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.
| Old stellar populations. 5: Absorption feature indices for the complete LICK/IDS sample of stars
Twenty-one optical absorption features, 11 of which have been previouslydefined, are automatically measured in a sample of 460 stars. FollowingGorgas et al., the indices are summarized in fitting functions that giveindex strengths as functions of stellar temperature, gravity, and(Fe/H). This project was carried out with the purpose of predictingindex strengths in the integrated light of stellar populations ofdifferent ages and metallicities, but the data should be valuable forstellar studies in the Galaxy as well. Several of the new indices appearto be promising indicators of metallicity for old stellar populations. Acomplete list of index data and atmospheric parameters is available incomputer-readable form.
| Evolved GK stars near the sun. I - The old disk population
A sample of nearly two thousand GK giants with intermediate band, (R,I),DDO and Geneva photometry has been assembled. Astrometric data is alsoavailable for most of the stars. The some 800 members of the old diskpopulation in the sample yield accurate luminosities (from two sources),reddening values and chemical abundances from calibrations of thephotometric parameters. Less than one percent of the objects arepeculiar in the sense that the flux distribution is abnormal. Thepeculiarity is signaled by strong CH (and Ba II) and weak CH. The CH+stars are all spectroscopic binaries, probably with white dwarfcompanions, whereas the CH- stars are not. A broad absorption band,centered near 3500 A, is found in the CH+ stars whereas the CH- objectshave a broad emission feature in the same region. The intensity of theseabsorptions and emissions are independent of the intensity of abnormalspectral features. Ten percent of the old disk sample have a heavyelement abundance from one and a half to three times the solar value.The distribution of the heavy element abundances is nearly a normal onewith a peak near solar abundance and ranges three times to one sixthsolar. The distribution of the (U, V) velocities is independent of theheavy element abundance and does not appear to be random. Ten percent ofthe old disk stars show a CN anomaly, equally divided between CN strongand CN weak. Several stars of individual astrometric or astrophysicalimportance are isolated.
| Fifth fundamental catalogue. Part 2: The FK5 extension - new fundamental stars
The mean positions and proper motions for 3117 new fundamental starsessentially in the magnitude range about 4.5 to 9.5 are given in thisFK5 extension. Mean apparent visual magnitude is 7.2 and is on average2.5 magnitudes fainter then the basic FK5 which has a mean magnitude of4.7. (The basic FK5 gives the mean positions and proper motions for theclassical 1535 fundamental stars). The following are discussed: theobservational material, reduction of observations, star selection, andthe system for the FK5 extension. An explanation and description of thecatalog are given. The catalog of 3117 fundamental stars for the equinoxand epoch J2000.0 and B1950.0 is presented. The parallaxes and radialvelocities for 22 extension stars with large forecasting effects aregiven. Catalogs used in the compilation of the FK5 fundamental catalogare listed.
| Ca II H and K filter photometry on the UVBY system. I - The standard system
A fifth filter (fwhm = 90 A) centered on Ca II H and K has beendeveloped for use with the standard uvby system. The filter, called Ca,is designed primarily for applications to metal-poor dwarfs and redgiants, regions where the uvby metallicity index, m(l), loses somesensitivity. An index, hk, is defined by replacing v in m(l) by Ca. Theeffects of interstellar extinction on the index are modeled anddemonstrated to be modest and relatively insensitive to spectral type.Observations of V, (b-y), and hk for 163 primary standards are detailedand transformed to the standard V and (b-y) system. A qualitativeanalysis using only the primary standards indicates that hk is moresensitive than m(l) over the regions of interest by about a factor of 3.
| High-resolution spectroscopic survey of 671 GK giants. I - Stellar atmosphere parameters and abundances
A high-resolution spectroscopic survey of 671 G and K field giants isdescribed. Broad-band Johnson colors have been calibrated againstrecent, accurate effective temperature, T(eff), measurements for starsin the range 3900-6000 K. A table of polynomial coefficients for 10color-T(eff) relations is presented. Stellar atmosphere parameters,including T(eff), log g, Fe/H, and microturbulent velocity, are computedfor each star, using the high-resolution spectra and various publishedphotometric catalogs. For each star, elemental abundances for a varietyof species have been computed using a LTE spectrum synthesis program andthe adopted atmosphere parameters.
| The Perkins catalog of revised MK types for the cooler stars
A catalog is presented listing the spectral types of the G, K, M, and Sstars that have been classified at the Perkins Observatory in therevised MK system. Extensive comparisons have been made to ensureconsistency between the MK spectral types of stars in the Northern andSouthern Hemispheres. Different classification spectrograms have beengradually improved in spite of some inherent limitations. In thecatalog, the full subclasses used are the following: G0, G5, G8, K0, K1,K2, K3, K4, K5, M0, M1, M2, M3, M4, M5, M6, M7, and M8. Theirregularities are the price paid for keeping the general scheme of theoriginal Henry Draper classification.
| A catalog of precise reference star positions for the astrometry network of the international comet P/Halley compaign
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1987A&AS...71..525D&db_key=AST
|
새 글 등록
관련 링크
새 링크 등록
다음 그룹에 속해있음:
|
관측 및 측정 데이터
천체목록:
|
