Ýçindekiler
Görüntüler
Resim Yükleyin
DSS Images Other Images
Ýlgili Makaleler
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.
| Medium-resolution Isaac Newton Telescope library of empirical spectra - II. The stellar atmospheric parameters
We present a homogeneous set of stellar atmospheric parameters(Teff, logg, [Fe/H]) for MILES, a new spectral stellarlibrary covering the range λλ 3525-7500Å at2.3Å (FWHM) spectral resolution. The library consists of 985 starsspanning a large range in atmospheric parameters, from super-metal-rich,cool stars to hot, metal-poor stars. The spectral resolution, spectraltype coverage and number of stars represent a substantial improvementover previous libraries used in population synthesis models. Theatmospheric parameters that we present here are the result of aprevious, extensive compilation from the literature. In order toconstruct a homogeneous data set of atmospheric parameters we have takenthe sample of stars of Soubiran, Katz & Cayrel, which has very welldetermined fundamental parameters, as the standard reference system forour field stars, and have calibrated and bootstrapped the data fromother papers against it. The atmospheric parameters for our clusterstars have also been revised and updated according to recent metallicityscales, colour-temperature relations and improved set of isochrones.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| Medium-resolution Isaac Newton Telescope library of empirical spectra
A new stellar library developed for stellar population synthesismodelling is presented. The library consists of 985 stars spanning alarge range in atmospheric parameters. The spectra were obtained at the2.5-m Isaac Newton Telescope and cover the range λλ3525-7500 Å at 2.3 Å (full width at half-maximum) spectralresolution. The spectral resolution, spectral-type coverage,flux-calibration accuracy and number of stars represent a substantialimprovement over previous libraries used in population-synthesis models.
| 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.
| 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.
| Mesures de vitesses radiales. VIII. Accompagnement AU sol DU programme d'observation DU satellite HIPPARCOS
We publish 1879 radial velocities of stars distributed in 105 fields of4^{\circ} \times 4^{\circ}. We continue the PPO series \cite[(Fehrenbachet al. 1987;]{Feh87} \cite[Duflot et al. 1990, 1992 and 1995),]{Du90}using the Fehrenbach objective prism method. Table 1 only available inelectronic form at CDS via to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| 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.
| 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.
| Transformation equations and other aids for VRI photometry
Transformations among VRI systems are commonly beset by Paschen-jumpeffects, for which fully satisfactory allowance has not previously beenmade. This paper describes two new techniques which are based on thework of Gutierrez-Moreno, and which allow fully for the effects of thePaschen jump. Values of E(V-R)/E(B-V) and E(R-I)/E(B-V) are also givenfor the Cousins system for a wide range of temperatures. These and thenew techniques contribute to a set of new transformation relations whichapply for most VRI systems; the status of the remaining systems isreviewed, and future work needed for them is described. Two majorsources of Cousins VRI data underlie the new relations; the consistencyof these sources is reviewed and found to be generally satisfactory,although more work on this question is needed. Finally, three tables oftransformed standard-star and other data are given for the Cousins andJohnson systems, and a description of ways to reproduce the latter ispresented.
| 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
| Stellar radial velocities derived from microphotometer measurements.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1969AJ.....74...91L&db_key=AST
| Red and infra-red magnitudes and colours for 300 F. G and K type stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1967MNRAS.135...23A&db_key=AST
| La mesure des vitesses radiales au prisme objectif. XX. Liste de 309 vitesses radiales determinees au prisme objectif a vision directe.
Not Available
| UBV photometry of 550 F, G and K type stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1966MNRAS.133..475A&db_key=AST
| Hα Photometry of late-type stars I. F, G and K-type stars north of the equator
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1964MNRAS.128..435P&db_key=AST
| Relationship between CN anomaly and U V W components of space velocity.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1962AJ.....67..757Y&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
| Photoelectric measurements of the λ4200 A CN band and the G band in G8-K5 spectra
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1960MNRAS.120..287G&db_key=AST
| A Catalogue of High-Velocity Stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1955ApJS....2..195R&db_key=AST
|
Yeni bir Makale Öner
Ýlgili Baðlantýlar
Yeni Bir Baðlantý Öner
sonraki gruplarýn üyesi:
|
Gözlemler ve gökölçümü verileri
| Takýmyýldýz: | Kral-Sefe |
| Sað Açýklýk: | 21h37m10.42s |
| Yükselim: | +62°18'15.3" |
| Görünürdeki Parlaklýk: | 7.153 |
| Uzaklýk: | 156.006 parsek |
| özdevim Sað Açýklýk: | 43.4 |
| özdevim Yükselim: | 114.8 |
| B-T magnitude: | 8.373 |
| V-T magnitude: | 7.254 |
Kataloglar ve belirtme:
|
