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Population Synthesis in the Blue. IV. Accurate Model Predictions for Lick Indices and UBV Colors in Single Stellar Populations
We present a new set of model predictions for 16 Lick absorption lineindices from Hδ through Fe5335 and UBV colors for single stellarpopulations with ages ranging between 1 and 15 Gyr, [Fe/H] ranging from-1.3 to +0.3, and variable abundance ratios. The models are based onaccurate stellar parameters for the Jones library stars and a new set offitting functions describing the behavior of line indices as a functionof effective temperature, surface gravity, and iron abundance. Theabundances of several key elements in the library stars have beenobtained from the literature in order to characterize the abundancepattern of the stellar library, thus allowing us to produce modelpredictions for any set of abundance ratios desired. We develop a methodto estimate mean ages and abundances of iron, carbon, nitrogen,magnesium, and calcium that explores the sensitivity of the variousindices modeled to those parameters. The models are compared to high-S/Ndata for Galactic clusters spanning the range of ages, metallicities,and abundance patterns of interest. Essentially all line indices arematched when the known cluster parameters are adopted as input.Comparing the models to high-quality data for galaxies in the nearbyuniverse, we reproduce previous results regarding the enhancement oflight elements and the spread in the mean luminosity-weighted ages ofearly-type galaxies. When the results from the analysis of blue and redindices are contrasted, we find good consistency in the [Fe/H] that isinferred from different Fe indices. Applying our method to estimate meanages and abundances from stacked SDSS spectra of early-type galaxiesbrighter than L*, we find mean luminosity-weighed ages of theorder of ~8 Gyr and iron abundances slightly below solar. Abundanceratios, [X/Fe], tend to be higher than solar and are positivelycorrelated with galaxy luminosity. Of all elements, nitrogen is the morestrongly correlated with galaxy luminosity, which seems to indicatesecondary nitrogen enrichment. If that interpretation is correct, thisresult may impose a lower limit of 50-200 Myr to the timescale of starformation in early-type galaxies. Unlike clusters, galaxies show asystematic effect whereby higher order, bluer, Balmer lines yieldyounger ages than Hβ. This age discrepancy is stronger for lowerluminosity galaxies. We examine four possible scenarios to explain thistrend. Contamination of the bluer indices by a metal-poor stellarpopulation with a blue horizontal branch cannot account for the data.Blue stragglers and abundance-ratio effects cannot be ruled out, as theycan potentially satisfy the data, even though this can only be achievedby resorting to extreme conditions, such as extremely high [O/Fe] orspecific blue-straggler frequencies. The most likely explanation is thepresence of small amounts of a young/intermediate-age stellar populationcomponent. We simulate this effect by producing two-component models andshow that they provide a reasonably good match to the data when the massfraction of the young component is typically a few percent. Ifconfirmed, this result implies star formation has been extended inearly-type galaxies, and more so in less massive galaxies, which seemsto lend support to the ``downsizing'' scenario. Moreover, it impliesthat stellar population synthesis models are capable of constraining notonly the mean ages of stellar populations in galaxies, but also theirage spread.
| Giants in the Local Region
We present parameter and abundance data for a sample of 298 nearbygiants. The spectroscopic data for this work have a resolution ofR~60,000, S/N>150, and spectral coverage from 475 to 685 nm. Overalltrends in the Z>10 abundances are dominated by Galactic chemicalevolution, while the light-element abundances are influenced by stellarevolution, as well as Galactic evolution. We find several super-Li starsin our sample and confirm that Li abundances in the first giant branchare related to mixing depths. Once astration of lithium on the mainsequence along with the overall range of main-sequence lithiumabundances are taken into account, the lithium abundances of the giantsare not dramatically at odds with the predictions of standard stellarevolution. We find the giants to be carbon-diluted in accord withstandard stellar evolution and that the carbon and oxygen abundancesdetermined for the local giants are consistent with those found in localfield dwarfs. We find that there is evidence for systematic carbonvariations in the red giant clump in the sense that the blue side of theclump is carbon-poor (more diluted) than the red side.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| A New Definition for the Ca4227 Feature: Is Calcium Really Underabundant in Early-Type Galaxies?
We have investigated the abundance of calcium in early-type galaxies bymeasuring the strength of the Ca I λ4227 absorption line in theirintegrated spectra. The database used is the large sample of early-typegalaxy integrated spectra in Caldwell and coworkers. We have measured Caabundances from the Ca I λ4227 feature both by using the LickCa4227 index and by defining a new index, Ca4227r, thatavoids the CN4216 molecular band in the continuum on the blueward sideof the line. With the new index definition we measure Ca abundances thatare systematically ~0.3 dex higher than with the Lick Ca4227 index. Theresult is that with the new index definition we obtain higher [Ca/Fe]abundances in early-type galaxies, which are more consistent with theirwell-known [Mg/Fe] overabundances. Hence, we suggest that Ca might beslightly enhanced, relative to Fe, in early-type galaxies.
| Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data. Revisiting the concept of superclusters
The availability of the Hipparcos Catalogue has triggered many kinematicand dynamical studies of the solar neighbourhood. Nevertheless, thosestudies generally lacked the third component of the space velocities,i.e., the radial velocities. This work presents the kinematic analysisof 5952 K and 739 M giants in the solar neighbourhood which includes forthe first time radial velocity data from a large survey performed withthe CORAVEL spectrovelocimeter. It also uses proper motions from theTycho-2 catalogue, which are expected to be more accurate than theHipparcos ones. An important by-product of this study is the observedfraction of only 5.7% of spectroscopic binaries among M giants ascompared to 13.7% for K giants. After excluding the binaries for whichno center-of-mass velocity could be estimated, 5311 K and 719 M giantsremain in the final sample. The UV-plane constructed from these datafor the stars with precise parallaxes (σπ/π≤20%) reveals a rich small-scale structure, with several clumpscorresponding to the Hercules stream, the Sirius moving group, and theHyades and Pleiades superclusters. A maximum-likelihood method, based ona Bayesian approach, has been applied to the data, in order to make fulluse of all the available stars (not only those with precise parallaxes)and to derive the kinematic properties of these subgroups. Isochrones inthe Hertzsprung-Russell diagram reveal a very wide range of ages forstars belonging to these groups. These groups are most probably relatedto the dynamical perturbation by transient spiral waves (as recentlymodelled by De Simone et al. \cite{Simone2004}) rather than to clusterremnants. A possible explanation for the presence of younggroup/clusters in the same area of the UV-plane is that they have beenput there by the spiral wave associated with their formation, while thekinematics of the older stars of our sample has also been disturbed bythe same wave. The emerging picture is thus one of dynamical streamspervading the solar neighbourhood and travelling in the Galaxy withsimilar space velocities. The term dynamical stream is more appropriatethan the traditional term supercluster since it involves stars ofdifferent ages, not born at the same place nor at the same time. Theposition of those streams in the UV-plane is responsible for the vertexdeviation of 16.2o ± 5.6o for the wholesample. Our study suggests that the vertex deviation for youngerpopulations could have the same dynamical origin. The underlyingvelocity ellipsoid, extracted by the maximum-likelihood method afterremoval of the streams, is not centered on the value commonly acceptedfor the radial antisolar motion: it is centered on < U > =-2.78±1.07 km s-1. However, the full data set(including the various streams) does yield the usual value for theradial solar motion, when properly accounting for the biases inherent tothis kind of analysis (namely, < U > = -10.25±0.15 kms-1). This discrepancy clearly raises the essential questionof how to derive the solar motion in the presence of dynamicalperturbations altering the kinematics of the solar neighbourhood: doesthere exist in the solar neighbourhood a subset of stars having no netradial motion which can be used as a reference against which to measurethe solar motion?Based on observations performed at the Swiss 1m-telescope at OHP,France, and on data from the ESA Hipparcos astrometry satellite.Full Table \ref{taba1} is 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/430/165}
| The Indo-US Library of Coudé Feed Stellar Spectra
We have obtained spectra for 1273 stars using the 0.9 m coudéfeed telescope at Kitt Peak National Observatory. This telescope feedsthe coudé spectrograph of the 2.1 m telescope. The spectra havebeen obtained with the no. 5 camera of the coudé spectrograph anda Loral 3K×1K CCD. Two gratings have been used to provide spectralcoverage from 3460 to 9464 Å, at a resolution of ~1 Å FWHMand at an original dispersion of 0.44 Å pixel-1. For885 stars we have complete spectra over the entire 3460 to 9464 Åwavelength region (neglecting small gaps of less than 50 Å), andpartial spectral coverage for the remaining stars. The 1273 stars havebeen selected to provide broad coverage of the atmospheric parametersTeff, logg, and [Fe/H], as well as spectral type. The goal ofthe project is to provide a comprehensive library of stellar spectra foruse in the automated classification of stellar and galaxy spectra and ingalaxy population synthesis. In this paper we discuss thecharacteristics of the spectral library, viz., details of theobservations, data reduction procedures, and selection of stars. We alsopresent a few illustrations of the quality and information available inthe spectra. The first version of the complete spectral library is nowpublicly available from the National Optical Astronomy Observatory(NOAO) via ftp and http.
| 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.
| A critical appraisal of published values of (Fe/H) for K II-IV stars
'Primary' (Fe/H) averages are presented for 373 evolved K stars ofluminosity classes II-IV and (Fe/H) values beween -0.9 and +0.21 dex.The data define a 'consensus' zero point with a precision of + or -0.018 dex and have rms errors per datum which are typically 0.08-0.16dex. The primary data base makes recalibration possible for the large(Fe/H) catalogs of Hansen and Kjaergaard (1971) and Brown et al. (1989).A set of (Fe/H) standard stars and a new DDO calibration are given whichhave rms of 0.07 dex or less for the standard star data. For normal Kgiants, CN-based values of (Fe/H) turn out to be more precise than manyhigh-dispersion results. Some zero-point errors in the latter are alsofound and new examples of continuum-placement problems appear. Thushigh-dispersion results are not invariably superior to photometricmetallicities. A review of high-dispersion and related work onsupermetallicity in K III-IV star is also given.
| CA II H and K measurements made at Mount Wilson Observatory, 1966-1983
Summaries are presented of the photoelectric measurements of stellar CaII H and K line intensity made at Mount Wilson Observatory during theyears 1966-1983. These results are derived from 65,263 individualobservations of 1296 stars. For each star, for each observing season,the maximum, minimum, mean, and variation of the instrumental H and Kindex 'S' are given, as well as a measurement of the accuracy ofobservation. A total of 3110 seasonal summaries are reported. Factorswhich affect the ability to detect stellar activity variations andaccurately measure their amplitudes, such as the accuracy of the H and Kmeasurements and scattered light contamination, are discussed. Relationsare given which facilitate intercomparison of 'S' values with residualintensities derived from ordinary spectrophotometry, and for convertingmeasurements to absolute fluxes.
| Photometry of 50 suspected variable stars
Fifty stars have been chosen as suspected variable stars and analyzedfor variability. A large portion of this sample are stars that areeither proved active chromosphere stars or are candidates for suchactivity. The photometric data base consists of differential Vmeasurements of the Vanderbilt 16 inch (41 cm) automatic photoelectrictelescope and 25 observers at 26 observatories worldwide. Publishedphotometric data have also been utilized, with proper adjustments madeto ensure that all magnitudes are differential. Searches for photometricperiod, amplitudes, and times of minimum light showed 68 percent of thesample to be photometrically variable with periods found for 34. Twostars were deemed norvariable for the period of observation. Conclusivestatements could not be made concerning the photometric variability ofthe 14 remaining stars.
| Determination of atmospheric parameters for G and K giants by means of photoelectric indices.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1971A&A....15..123H&db_key=AST
| Strong-Cyanogen Stars: Photometry and Kinematics
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1971ApJ...165..561J&db_key=AST
| Photoelectric photometry of selected AG stars in the 25D to 30D zone.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1968AJ.....73..187B&db_key=AST
| Abundances of sodium, magnesium and calcium in K-type giant stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1968MNRAS.140...21P&db_key=AST
| Spectral and Luminosity Classifications and Measurements of the Strength of Cyanogen Absorption for Late-Type Stars from Objective-Prism Spectra.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1961ApJ...134..809Y&db_key=AST
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | ברבור |
| התרוממות ימנית: | 21h29m15.39s |
| סירוב: | +28°34'58.8" |
| גודל גלוי: | 6.754 |
| מרחק: | 97.561 פארסק |
| תנועה נכונה: | -32.8 |
| תנועה נכונה: | -142.4 |
| B-T magnitude: | 8.162 |
| V-T magnitude: | 6.871 |
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