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Reliability Checks on the Indo-US Stellar Spectral Library Using Artificial Neural Networks and Principal Component Analysis
The Indo-US coudé feed stellar spectral library (CFLIB) madeavailable to the astronomical community recently by Valdes et al. (2004,ApJS, 152, 251) contains spectra of 1273 stars in the spectral region3460 to 9464Å at a high resolution of 1Å (FWHM) and a widerange of spectral types. Cross-checking the reliability of this databaseis an important and desirable exercise since a number of stars in thisdatabase have no known spectral types and a considerable fraction ofstars has not so complete coverage in the full wavelength region of3460-9464Å resulting in gaps ranging from a few Å to severaltens of Å. We use an automated classification scheme based onArtificial Neural Networks (ANN) to classify all 1273 stars in thedatabase. In addition, principal component analysis (PCA) is carried outto reduce the dimensionality of the data set before the spectra areclassified by the ANN. Most importantly, we have successfullydemonstrated employment of a variation of the PCA technique to restorethe missing data in a sample of 300 stars out of the CFLIB.
| 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.
| 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.
| 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
| K-Band Calibration of the Red Clump Luminosity
The average near-infrared (K-band) luminosity of 238 Hipparcos red clumpgiants is derived and then used to measure the distance to the Galacticcenter. These Hipparcos red clump giants have been previously employedas I-band standard candles. The advantage of the K-band is a decreasedsensitivity to reddening and perhaps a reduced systematic dependence onmetallicity. In order to investigate the latter, and also to refer ourcalibration to a known metallicity zero point, we restrict our sample ofred clump calibrators to those with abundances derived fromhigh-resolution spectroscopic data. The mean metallicity of the sampleis [Fe/H]=-0.18 dex (σ=0.17 dex). The data are consistent with nocorrelation between MK and [Fe/H] and only weakly constrainthe slope of this relation. The luminosity function of the sample peaksat MK=-1.61+/-0.03 mag. Next, we assemble published opticaland near-infrared photometry for ~20 red clump giants in a Baade'swindow field with a mean metallicity of [Fe/H]=-0.17+/-0.09 dex, whichis nearly identical to that of the Hipparcos red clump. Assuming thatthe average (V-I)0 and (V-K)0 colors of these twored clumps are the same, the extinctions in the Baade's window field arefound to be AV=1.56, AI=0.87, andAK=0.15, in agreement with previous estimates. We derive thedistance to the Galactic center: (m-M)0=14.58+/-0.11 mag, orR=8.24+/-0.42 kpc. The uncertainty in this distance measurement isdominated by the small number of Baade's window red clump giantsexamined here.
| A catalog of rotational and radial velocities for evolved stars
Rotational and radial velocities have been measured for about 2000evolved stars of luminosity classes IV, III, II and Ib covering thespectral region F, G and K. The survey was carried out with the CORAVELspectrometer. The precision for the radial velocities is better than0.30 km s-1, whereas for the rotational velocity measurementsthe uncertainties are typically 1.0 km s-1 for subgiants andgiants and 2.0 km s-1 for class II giants and Ib supergiants.These data will add constraints to studies of the rotational behaviourof evolved stars as well as solid informations concerning the presenceof external rotational brakes, tidal interactions in evolved binarysystems and on the link between rotation, chemical abundance and stellaractivity. In this paper we present the rotational velocity v sin i andthe mean radial velocity for the stars of luminosity classes IV, III andII. Based on observations collected at the Haute--Provence Observatory,Saint--Michel, France and at the European Southern Observatory, LaSilla, Chile. Table \ref{tab5} also available in electronic form at CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| 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
| Photometric Separation of Stellar Properties Using SDSS Filters
Using synthetic photometry of Kurucz model spectra, we explore thecolors of stars as a function of temperature, metallicity, and surfacegravity with Sloan Digital Sky Survey (SDSS) filters, u'g'r'i'z'. Thesynthetic colors show qualitative agreement with the few publishedobservations in these filters. We find that the locus of synthetic starsis basically two-dimensional for 4500 < T < 8000 K, whichprecludes simultaneous color separation of the three basic stellarcharacteristics we consider. Colors including u' contain the mostinformation about normal stellar properties; measurements in this filterare also important for selecting white dwarfs. We identify two differentsubsets of the locus in which the loci separate by either metallicity orsurface gravity. For 0.5 < g' - r' < 0.8 (corresponding roughly toG stars), the locus separates by metallicity; for photometric error of afew percent, we estimate metallicity to within ~0.5 dex in this range.In the range -0.15 < g' - r' < 0.00 (corresponding roughly to Astars), the locus shows separation by surface gravity. In both cases, weshow that it is advantageous to use more than two colors whendetermining stellar properties by color. Strategic observations in SDSSfilters are required to resolve the source of a ~5% discrepancy betweensynthetic colors of Gunn-Stryker stars, Kurucz models, and externaldeterminations of the metallicities and surface gravities. The syntheticstar colors can be used to investigate the properties of any normal starand to construct analytic expressions for the photometric prediction ofstellar properties in special cases.
| 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
| 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.
| Continuum and line emission in Cygnus A
We present the results from (1) imaging observations of Cygnus A in fiveessentially line-free continuum bands with central wavelengths rangingfrom 0.34 to 2.1 microns. (2) imaging observations in five narrowbandfilters centered on the emission lines H beta(O III) lambda5007, Halpha(N II) lambda6583, and (S II) lambda lambda6716, 6731, and (3) deepspectroscopy covering the entire central region of Cyg A. We confirmthat the featureless spectrum component is to be identified with theprominent double morphology at the center of Cyg A, but uncertainties inthe distribution of the dust in this region tend to limit the accuracywith which we can determine its morphology and spectral-energydistribution (SED). From regions that appear to be least affected byobscuration, we find fv is approximately v-0.1 forthis component. This SED could be consistent with free-free emission, apopulation of young stars, or a quasar continuum scattered by electrons,but probably not with a quasar continuum scattered by dust, which wouldbe bluer. Our spectroscopy places an upper limit on the equivalent widthof broad H beta that is well below that of typical quasars, showing thatthis flat-spectrum component (FSC) is almost certainly not dominated byscattered quasar radiation. Appeals to scattering by hot electrons tosmear the scattered broad lines into invisibility appear to fail becausethe large density scale height of the electrons and the inefficiency ofelectron scattering should result in smoother and more extensivestructure than we observe. Although the relative SED is consistent withfree-free emission, the required amount of hot gas violates otherobservational constraints. At high angular resolution, the apparentmorphology of the FSC is spiral-like. Although this impression may bepartly due to obscuration, the distribution of the dust itself onlyserves to reinforce the spiral-like nature of the material with which itis associated. We conclude that the FSC is most likely radiation from astarburst at the center of Cyg A. Fits to the radial surface-brightnessprofile of the late-type component after our best efforts at removingthe FSC allow us to estimate the wavelength dependence of extinction inthe central region.
| 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.
| Velocity dispersions and mean abundances for Roman's G5-K1 spectroscopic groups
The velocity dispersions and U-V distributions of Roman's (1950, 1952)four spectroscopic groups (weak CN, weak line, strong line, and 4150)are compared with those of groups based only on Fe/H ratio. It is shownthat the velocity-dispersion gradient for the Roman spectroscopic groupsis greater than for the comparison group for all three velocitycomponents and for the mean orbital eccentricity, with a clearly definedminimum for the strong-line stars and a sharp upturn for the 4150 stars.The results suggest that the Roman's assignment to distinctspectroscopic groups results in more homogeneous groups than the binningon the basis of metallicity.
| Theoretical colours and isochrones for some Hubble Space Telescope colour systems. II
A grid of synthetic surface brightness magnitudes for 14 bandpasses ofthe Hubble Space Telescope Faint Object Camera is presented, as well asa grid of UBV, uvby, and Faint Object Camera surface brightnessmagnitudes derived from the Gunn-Stryker spectrophotometric atlas. Thesynthetic colors are used to examine the transformations between theground-based Johnson UBV and Stromgren uvby systems and the Faint ObjectCamera UBV and uvby. Two new four-color systems, similar to theStromgren system, are proposed for the determination of abundance,temperature, and surface gravity. The synthetic colors are also used tocalculate color-magnitude isochrones from the list of theoretical tracksprovided by VandenBerg and Bell (1990). It is shown that by using theappropriate filters it is possible to minimize the dependence of thiscolor difference on metallicity. The effects of interstellar reddeningon various Faint Object Camera colors are analyzed as well as theobservational requirements for obtaining data of a given signal-to-noisefor each of the 14 bandpasses.
| 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.
| Photoelectric photometry of G-M stars in the Vilnius system
Not Available
| 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.
| Photoelectric photometry of bright stars in the vicinity of the North Galactic Pole
Not Available
| A search for lithium-rich giant stars
Lithium abundances or upper limits have been determined for 644 brightG-K giant stars selected from the DDO photometric catalog. Two of thesegiants possess surface lithium abundances approaching the 'cosmic' valueof the interstellar medium and young main-sequence stars, and eight moregiants have Li contents far in excess of standard predictions. At leastsome of these Li-rich giants are shown to be evolved to the stage ofhaving convectively mixed envelopes, either from the direct evidence oflow surface carbon isotope ratios, or from the indirect evidence oftheir H-R diagram positions. Suggestions are given for the uniqueconditions that might have allowed these stars to produce or accrete newlithium for their surface layers, or simply to preserve from destructiontheir initial lithium contents. The lithium abundance of the remainingstars demonstrates that giants only very rarely meet the expectations ofstandard first dredge-up theories; the average extra Li destructionrequired is about 1.5 dex. The evolutionary states of these giants andtheir average masses are discussed briefly, and the Li distribution ofthe giants is compared to predictions of Galactic chemical evolution.
| ICCD speckle observations of binary stars. IV - Measurements during 1986-1988 from the Kitt Peak 4 M telescope
One thousand five hundred and fifty measurements of 1006 binary starsystems observed mostly during 1986 through mid-1988 by means of speckleinterferometry with the KPNO 4-m telescope are presented. Twenty-onesystems are directly resolved for the first time, including newcomponents to the cool supergiant Alpha Her A and the Pleiades shellstar Pleione. A continuing survey of The Bright Star Catalogue yieldedeight new binaries from 293 bright stars observed. Corrections tospeckle measures from the GSU/CHARA ICCD speckle camera previouslypublished are presented and discussed.
| 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.
| Stellar spectrophotometric atlas, wavelengths from 3130 to 10800 A
Over the course of the past 10 years, a large body of homogeneousspectrophotometric data on relatively bright stars has been gathered toserve as a library with which to synthesize galaxy spectra in populationstudies. As the data might be generally useful, they are presented inthree tables. One hundred seventy-five (175) stars were selected, mostfrom the Navy photometric catalog. Covered are complete ranges ofspectral type and luminosity class. Normalized spectral energydistributions of these stars in pictorial form are provided along withtables of calculated colors, scan line and continuum indices, and someinformation on the relation of the scan colors to real photometricsystems.
| Evolutionary synthesis of the stellar population in elliptical galaxies. III - Detailed optical spectra
The evolutionary synthesis technique is used to construct populationmodels for giant elliptical galaxies, using detailed spectrophotometricdata for the galaxies and for stars obtained with the Oke multichannelspectrometer on the Hale telescope. It is found that ellipticals arewell represented by an old, metal-rich population with a turnoff at B-Vof about 0.80 and a turnoff mass function slope of x approximately equalto or less than 1, plus a quite significant contribution from starsabove the turnoff. The nature of these objects is discussed, and it isconcluded that the present data and astrophysical constraints cannotdistinguish between a small young population and a blue stragglerpopulation augmented by a few O stars.
| Catalogue of stars with CaII H and K emissions
Not Available
| Multivariate analysis of spectrophotometry
Multivariate analysis is applied to various photometric indices of Kstars in order to determine the number of independent factors thataccount for the variations observed in the data. Temperature is found tobe the overwhelmingly dominant factor, so low-resolution scannerobservations of 26 K0 stars are analyzed to reduce the temperaturedomination. Factor analysis of various combinations of continuum colorsyields one dominant factor ('index one') that is correlated withtemperature and gravity but not with abundance. Two significant factorsare obtained from factor analysis of the five reddest continuum colors;one is shown to be basically equivalent to index one, and the other isidentified as an abundance factor. The possible existence of a thirdfactor that may be a measure of CN abundance variation is indicated.
| Luminosity functions and the evolution of low-mass population I giants
Luminosity functions in terms of bolometric magnitudes are constructedfor M67 and for two samples of old-disk field giants. These are comparedwith theoretical rates of evolution on the giant branch. M67 has too fewstars to give a useful comparison. The field giants show good agreementwith theory, and the number of stars at the 'clump' suggests that corehelium-burning is prolonged by overshoot with semiconvective mixing. Thefuel consumption derived from the luminosity functions is consistentwith core helium ignition at the theoretically predicted core mass, andwith a final core mass in agreement with observed white dwarf masses.Data are needed for a larger complete sample of field giants for theluminosity function to be better determined. Further details, especiallyfor the variable M giants at the top of the giant branch, are needed forpopulation syntheses of elliptical galaxies.
| Absolute magnitudes of stars from widths of chromospheric CaII emission lines.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1976ApJ...205..823W&db_key=AST
| DDO intermediate-band photometry of moving-group stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1975PASP...87...17B&db_key=AST
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| קבוצת-כוכבים: | שומר הדובים |
| התרוממות ימנית: | 14h50m29.60s |
| סירוב: | +37°16'19.0" |
| גודל גלוי: | 5.48 |
| מרחק: | 61.312 פארסק |
| תנועה נכונה: | -212.6 |
| תנועה נכונה: | 95.8 |
| B-T magnitude: | 6.785 |
| V-T magnitude: | 5.59 |
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