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Newly discovered active binaries in the RasTyc sample of stellar X-ray sources. I. Orbital and physical parameters of six new binaries
We present the first results from follow-up optical observations, bothphotometric and spectroscopic, of stellar X-ray sources, selected fromthe RasTyc sample, resulting from the cross-correlation of ROSAT All-SkySurvey (RASS) and TYCHO catalogues. In particular, we report on thediscovery of six late-type binaries, for which we obtained good radialvelocity curves and solved their orbits. We performed an automaticspectral classification of both single-lined and double-lined binarieswith codes developed by us and found two binaries composed of twomain-sequence stars and four binaries with an evolved (giant orsubgiant) component. Filled-in or pure emission Hα profilesindicative of a moderate or high level of chromospheric activity wereobserved. In nearly all the systems, we also detected a photometricmodulation ascribable to surface inhomogeneities that is correlated withthe orbital period, suggesting a synchronization between rotational andorbital periods. The position on the HR diagram of the components of thefive sources with a known parallax indicates three binaries containingonly main-sequence stars and two single-lined systems with a giantcomponent. The kinematical properties of two, or possibly four, of theobserved systems are consistent with a young disk population.
| Predicting accurate stellar angular diameters by the near-infrared surface brightness technique
I report on the capabilities of the near-infrared (near-IR) surfacebrightness technique to predict reliable stellar angular diameters asaccurate as <~2 per cent using standard broad-band Johnson photometryin the colour range -0.1 <= (V-K)O<= 3.7 includingstars of A, F, G, K spectral type. This empirical approach is fast toapply and leads to estimated photometric diameters in very goodagreement with recent high-precision interferometric diametermeasurements available for non-variable dwarfs and giants, as well asfor Cepheid variables. Then I compare semi-empirical diameters predictedby model-dependent photometric and spectrophotometric (SP) methods withnear-IR surface brightness diameters adopted as empirical referencecalibrators. The overall agreement between all these methods is withinapproximately +/-5 per cent, confirming previous works. However, on thesame scale of accuracy, there is also evidence for systematic shiftspresumably as a result of an incorrect representation of the stellareffective temperature in the model-dependent results. I also comparemeasurements of spectroscopic radii with near-IR surface brightnessradii of Cepheids with known distances. Spectroscopic radii are found tobe affected by a scatter as significant as >~9 per cent, which is atleast three times greater than the formal error currently claimed by thespectroscopic technique. In contrast, pulsation radii predicted by theperiod-radius (PR) relation according to the Cepheid period result aresignificantly less dispersed, indicating a quite small scatter as aresult of the finite width of the Cepheid instability strip, as expectedfrom pulsation theory. The resulting low level of noise stronglyconfirms our previous claims that the pulsation parallaxes are the mostaccurate empirical distances presently available for Galactic andextragalactic Cepheids.
| Spectral analysis of red clump giants and their use as standard candles in the wavebands I and K
Using high resolution and high signal-to-noise ratio observational data,we determined the stellar atmospheric parameters of 19 metal-poor redclump giants and their chemical abundances of the four α elements(i.e., O, Mg, Ca, Si). We discuss the variations, with the ironabundance, of the atmospheric parameters and of the α elementsabundances. We examined the absolute stellar magnitudes of 58 red clumpgiants in the I and K wavebands as well as their relations with the ironabundance, and found that for the analysed range of iron abundance, thecorrelation with the iron abundance is weaker for the absolute magnitudein the K band than that in the I band, in agreement with theoreticalexpectations.
| 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.
| The Effective Temperature Scale of FGK Stars. II. Teff:Color:[Fe/H] Calibrations
We present up-to-date metallicity-dependent temperature versus colorcalibrations for main-sequence and giant stars based on temperaturesderived with the infrared flux method (IRFM). Seventeen colors in thephotometric systems UBV, uvby, Vilnius, Geneva, RI(Cousins), DDO,Hipparcos-Tycho, and Two Micron All Sky Survey (2MASS) have beencalibrated. The spectral types covered by the calibrations range from F0to K5 (7000K>~Teff>~4000K) with some relationsextending below 4000 K or up to 8000 K. Most of the calibrations arevalid in the metallicity range -3.5>~[Fe/H]>~0.4, although some ofthem extend to as low as [Fe/H]~-4.0. All fits to the data have beenperformed with more than 100 stars; standard deviations range from 30 to120 K. Fits were carefully performed and corrected to eliminate thesmall systematic errors introduced by the calibration formulae. Tablesof colors as a function of Teff and [Fe/H] are provided. Thiswork is largely based on the study by A. Alonso and collaborators; thus,our relations do not significantly differ from theirs except for thevery metal-poor hot stars. From the calibrations, the temperatures of 44dwarf and giant stars with direct temperatures available are obtained.The comparison with direct temperatures confirms our finding in Paper Ithat the zero point of the IRFM temperature scale is in agreement, tothe 10 K level, with the absolute temperature scale (that based onstellar angular diameters) within the ranges of atmospheric parameterscovered by those 44 stars. The colors of the Sun are derived from thepresent IRFM Teff scale and they compare well with those offive solar analogs. It is shown that if the IRFM Teff scaleaccurately reproduces the temperatures of very metal-poor stars,systematic errors of the order of 200 K, introduced by the assumption of(V-K) being completely metallicity independent when studying verymetal-poor dwarf stars, are no longer acceptable. Comparisons with otherTeff scales, both empirical and theoretical, are also shownto be in reasonable agreement with our results, although it seems thatboth Kurucz and MARCS synthetic colors fail to predict the detailedmetallicity dependence, given that for [Fe/H]=-2.0, differences as highas approximately +/-200 K are found.
| Survey for Transiting Extrasolar Planets in Stellar Systems. II. Spectrophotometry and Metallicities of Open Clusters
We present metallicity estimates for seven open clusters based onspectrophotometric indices from moderate-resolution spectroscopy.Observations of field giants of known metallicity provide a correlationbetween the spectroscopic indices and the metallicity of open clustergiants. We use χ2 analysis to fit the relation ofspectrophotometric indices to metallicity in field giants. The resultingfunction allows an estimate of the target-cluster giants' metallicitieswith an error in the method of +/-0.08 dex. We derive the followingmetallicities for the seven open clusters: NGC 1245, [M/H]=-0.14+/-0.04NGC 2099, [M/H]=+0.05+/-0.05 NGC 2324, [M/H]=-0.06+/-0.04 NGC 2539,[M/H]=-0.04+/-0.03 NGC 2682 (M67), [M/H]=-0.05+/-0.02 NGC 6705,[M/H]=+0.14+/-0.08 NGC 6819, [M/H]=-0.07+/-0.12. These metallicityestimates will be useful in planning future extrasolar planet transitsearches, since planets may form more readily in metal-richenvironments.
| Broad-band photometric colors and effective temperature calibrations for late-type giants. I. Z = 0.02
We present new synthetic broad-band photometric colors for late-typegiants based on synthetic spectra calculated with the PHOENIX modelatmosphere code. The grid covers effective temperatures T_eff=3000dots5000 K, gravities log g=-0.5dots{+3.5}, and metallicities[M/H]=+0.5dots{-4.0}. We show that individual broad-band photometriccolors are strongly affected by model parameters such as molecularopacities, gravity, microturbulent velocity, and stellar mass. Ourexploratory 3D modeling of a prototypical late-type giant shows thatconvection has a noticeable effect on the photometric colors too, as italters significantly both the vertical and horizontal thermal structuresin the outer atmosphere. The differences between colors calculated withfull 3D hydrodynamical and 1D model atmospheres are significant (e.g.,Δ(V-K)0.2 mag), translating into offsets in effectivetemperature of up to 70 K. For a sample of 74 late-type giants in theSolar neighborhood, with interferometric effective temperatures andbroad-band photometry available in the literature, we compare observedcolors with a new PHOENIX grid of synthetic photometric colors, as wellas with photometric colors calculated with the MARCS and ATLAS modelatmosphere codes. We find good agreement of the new synthetic colorswith observations and published T_eff-color and color-color relations,especially in the T_eff-(V-K), T_eff-(J-K) and (J-K)-(V-K) planes.Deviations from the observed trends in the T_eff-color planes aregenerally within ±100 K for T_eff=3500 to 4800 K. Syntheticcolors calculated with different stellar atmosphere models agree to±100 K, within a large range of effective temperatures andgravities. The comparison of the observed and synthetic spectra oflate-type giants shows that discrepancies result from the differencesboth in the strengths of various spectral lines/bands (especially thoseof molecular bands, such as TiO, H2O, CO) and the continuum level.Finally, we derive several new T_eff-log g-color relations for late-typegiants at solar-metallicity (valid for T_eff=3500 to 4800 K), based bothon the observed effective temperatures and colors of the nearby giants,and synthetic colors produced with PHOENIX, MARCS and ATLAS modelatmospheres.
| CHARM2: An updated Catalog of High Angular Resolution Measurements
We present an update of the Catalog of High Angular ResolutionMeasurements (CHARM, Richichi & Percheron \cite{CHARM}, A&A,386, 492), which includes results available until July 2004. CHARM2 is acompilation of direct measurements by high angular resolution methods,as well as indirect estimates of stellar diameters. Its main goal is toprovide a reference list of sources which can be used for calibrationand verification observations with long-baseline optical and near-IRinterferometers. Single and binary stars are included, as are complexobjects from circumstellar shells to extragalactic sources. The presentupdate provides an increase of almost a factor of two over the previousedition. Additionally, it includes several corrections and improvements,as well as a cross-check with the valuable public release observationsof the ESO Very Large Telescope Interferometer (VLTI). A total of 8231entries for 3238 unique sources are now present in CHARM2. Thisrepresents an increase of a factor of 3.4 and 2.0, respectively, overthe contents of the previous version of CHARM.The catalog is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/431/773
| Improved Baade-Wesselink surface brightness relations
Recent, and older accurate, data on (limb-darkened) angular diameters iscompiled for 221 stars, as well as BVRIJK[12][25] magnitudes for thoseobjects, when available. Nine stars (all M-giants or supergiants)showing excess in the [12-25] colour are excluded from the analysis asthis may indicate the presence of dust influencing the optical andnear-infrared colours as well. Based on this large sample,Baade-Wesselink surface brightness (SB) relations are presented fordwarfs, giants, supergiants and dwarfs in the optical and near-infrared.M-giants are found to follow different SB relations from non-M-giants,in particular in V versus V-R. The preferred relation for non-M-giantsis compared to the earlier relation by Fouqué and Gieren (basedon 10 stars) and Nordgren et al. (based on 57 stars). Increasing thesample size does not lead to a lower rms value. It is shown that theresiduals do not correlate with metallicity at a significant level. Thefinally adopted observed angular diameters are compared to thosepredicted by Cohen et al. for 45 stars in common, and there isreasonable overall, and good agreement when θ < 6 mas.Finally, I comment on the common practice in the literature to average,and then fix, the zero-point of the V versus V-K, V versus V-R and Kversus J-K relations, and then rederive the slopes. Such a commonzero-point at zero colour is not expected from model atmospheres for theV-R colour and depends on gravity. Relations derived in this way may bebiased.
| Determination of fundamental characteristics for stars of the F, G, and K spectral types. The surface gravities and metallicity parameters.
Not Available
| A near-infrared stellar spectral library: I. H-band spectra.
This paper presents the H band near-infrared (NIR) spectral library of135 solar type stars covering spectral types O5-M3 and luminosityclasses I-V as per MK classification. The observations were carried outwith 1.2 meter Gurushikhar Infrared Telescope (GIRT), at Mt. Abu, Indiausing a NICMOS3 HgCdTe 256 x 256 NIR array based spectrometer. Thespectra have a moderate resolution of 1000 (about 16 A) at the H bandand have been continuum shape corrected to their respective effectivetemperatures. This library and the remaining ones in J and K bands oncereleased will serve as an important database for stellar populationsynthesis and other applications in conjunction with the newly formedlarge optical coude feed stellar spectral library of Valdes et al.(2004). The complete H-Band library is available online at: http://vo.iucaa.ernet.in/~voi/NIR_Header.html
| 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.
| 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.
| Empirically Constrained Color-Temperature Relations. II. uvby
A new grid of theoretical color indices for the Strömgren uvbyphotometric system has been derived from MARCS model atmospheres and SSGsynthetic spectra for cool dwarf and giant stars having-3.0<=[Fe/H]<=+0.5 and 3000<=Teff<=8000 K. Atwarmer temperatures (i.e., 8000-2.0. To overcome thisproblem, the theoretical indices at intermediate and high metallicitieshave been corrected using a set of color calibrations based on fieldstars having well-determined distances from Hipparcos, accurateTeff estimates from the infrared flux method, andspectroscopic [Fe/H] values. In contrast with Paper I, star clustersplayed only a minor role in this analysis in that they provided asupplementary constraint on the color corrections for cool dwarf starswith Teff<=5500 K. They were mainly used to test thecolor-Teff relations and, encouragingly, isochrones thatemploy the transformations derived in this study are able to reproducethe observed CMDs (involving u-v, v-b, and b-y colors) for a number ofopen and globular clusters (including M67, the Hyades, and 47 Tuc)rather well. Moreover, our interpretations of such data are verysimilar, if not identical, with those given in Paper I from aconsideration of BV(RI)C observations for the sameclusters-which provides a compelling argument in support of thecolor-Teff relations that are reported in both studies. Inthe present investigation, we have also analyzed the observedStrömgren photometry for the classic Population II subdwarfs,compared our ``final'' (b-y)-Teff relationship with thosederived empirically in a number of recent studies and examined in somedetail the dependence of the m1 index on [Fe/H].Based, in part, on observations made with the Nordic Optical Telescope,operated jointly on the island of La Palma by Denmark, Finland, Iceland,Norway, and Sweden, in the Spanish Observatorio del Roque de losMuchachos of the Instituto de Astrofisica de Canarias.Based, in part, on observations obtained with the Danish 1.54 mtelescope at the European Southern Observatory, La Silla, Chile.
| Angular Diameters of Stars from the Mark III Optical Interferometer
Observations of 85 stars were obtained at wavelengths between 451 and800 nm with the Mark III Stellar Interferometer on Mount Wilson, nearPasadena, California. Angular diameters were determined by fitting auniform-disk model to the visibility amplitude versus projected baselinelength. Half the angular diameters determined at 800 nm have formalerrors smaller than 1%. Limb-darkened angular diameters, effectivetemperatures, and surface brightnesses were determined for these stars,and relationships between these parameters are presented. Scatter inthese relationships is larger than would be expected from themeasurement uncertainties. We argue that this scatter is not due to anunderestimate of the angular diameter errors; whether it is due tophotometric errors or is intrinsic to the relationship is unresolved.The agreement with other observations of the same stars at the samewavelengths is good; the width of the difference distribution iscomparable to that estimated from the error bars, but the wings of thedistribution are larger than Gaussian. Comparison with infraredmeasurements is more problematic; in disagreement with models, coolerstars appear systematically smaller in the near-infrared than expected,warmer stars larger.
| Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 Parsecs: The Northern Sample. I.
We have embarked on a project, under the aegis of the Nearby Stars(NStars)/Space Interferometry Mission Preparatory Science Program, toobtain spectra, spectral types, and, where feasible, basic physicalparameters for the 3600 dwarf and giant stars earlier than M0 within 40pc of the Sun. In this paper, we report on the results of this projectfor the first 664 stars in the northern hemisphere. These resultsinclude precise, homogeneous spectral types, basic physical parameters(including the effective temperature, surface gravity, and overallmetallicity [M/H]), and measures of the chromospheric activity of ourprogram stars. Observed and derived data presented in this paper arealso available on the project's Web site.
| STELIB: A library of stellar spectra at R ~ 2000
We present STELIB, a new spectroscopic stellar library, available athttp://webast.ast.obs-mip.fr/stelib. STELIB consists of an homogeneouslibrary of 249 stellar spectra in the visible range (3200 to 9500Å), with an intermediate spectral resolution (la 3 Å) andsampling (1 Å). This library includes stars of various spectraltypes and luminosity classes, spanning a relatively wide range inmetallicity. The spectral resolution, wavelength and spectral typecoverage of this library represents a substantial improvement overprevious libraries used in population synthesis models. The overallabsolute photometric uncertainty is 3%.Based on observations collected with the Jacobus Kaptein Telescope,(owned and operated jointly by the Particle Physics and AstronomyResearch Council of the UK, The Nederlandse Organisatie voorWetenschappelijk Onderzoek of The Netherlands and the Instituto deAstrofísica de Canarias of Spain and located in the SpanishObservatorio del Roque de Los Muchachos on La Palma which is operated bythe Instituto de AstrofÃsica de Canarias), the 2.3 mtelescope of the Australian National University at Siding Spring,Australia, and the VLT-UT1 Antu Telescope (ESO).Tables \ref{cat1} to \ref{cat6} and \ref{antab1} to A.7 are onlyavailable in electronic form at http://www.edpsciences.org. The StellarLibrary STELIB library is also available at the CDS, via anonymous ftpto cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/402/433
| Line Absorption as a Metallicity Index for Giant Stars
The fraction of light removed from a star's spectrum by the spectrallines, the line absorption, is shown to be a precise empirical indicatorof metallicity. We measured the line absorption in 89 class III giantstars in a 42.5 Å window between 6219.0 and 6261.5 Å andthen calibrated these values against published metallicities. We showthat the line absorption can be measured precisely enough to improve themetallicity precision about fivefold over the original calibrationmetallicities, reaching a precision of 0.01 dex in favorable cases.
| Kurucz Model Energy Distributions: A Comparison With Real Stars. II. Metal-Deficient Stars
Energy distributions of synthetic spectra for Kurucz model atmospheresare compared with observed energy distributions of metal-deficient starsof the blue horizontal-branch (BHB), F--G--K subdwarf (SD) and G--Kgiant (MDG) types. The best coincidence of the synthetic and observedenergy curves is found for BHB stars. The largest differences are foundin the ultraviolet wavelengths for subdwarfs and cool MDGs. Theinfluence of errors of effective temperatures, gravities andmetallicities is estimated.
| The Rotation of Binary Systems with Evolved Components
In the present study we analyze the behavior of the rotational velocity,vsini, for a large sample of 134 spectroscopic binary systems with agiant star component of luminosity class III, along the spectral regionfrom middle F to middle K. The distribution of vsini as a function ofcolor index B-V seems to follow the same behavior as their singlecounterparts, with a sudden decline around G0 III. Blueward of thisspectral type, namely, for binary systems with a giant F-type component,one sees a trend for a large spread in the rotational velocities, from afew to at least 40 km s-1. Along the G and K spectral regionsthere are a considerable number of binary systems with moderate tomoderately high rotation rates. This reflects the effects ofsynchronization between rotation and orbital motions. These rotatorshave orbital periods shorter than about 250 days and circular or nearlycircular orbits. Except for these synchronized systems, the largemajority of binary systems with a giant component of spectral type laterthan G0 III are composed of slow rotators.
| CHARM: A Catalog of High Angular Resolution Measurements
The Catalog of High Angular Resolution Measurements (CHARM) includesmost of the measurements obtained by the techniques of lunaroccultations and long-baseline interferometry at visual and infraredwavelengths, which have appeared in the literature or have otherwisebeen made public until mid-2001. A total of 2432 measurements of 1625sources are included, along with extensive auxiliary information. Inparticular, visual and infrared photometry is included for almost allthe sources. This has been partly extracted from currently availablecatalogs, and partly obtained specifically for CHARM. The main aim is toprovide a compilation of sources which could be used as calibrators orfor science verification purposes by the new generation of largeground-based facilities such as the ESO Very Large Interferometer andthe Keck Interferometer. The Catalog is available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/386/492, and from theauthors on CD-Rom.
| New algorithms for reducing cross-dispersed echelle spectra
We describe advanced image processing algorithms, implemented in a dataanalysis package for conventional and cross-dispersed echelle spectra.Comparisons with results from other packages illustrate the outstandingquality of the new REDUCE package, particularly in terms of resultingnoise level and treatment of CCD defects and cosmic ray spikes. REDUCEcan be adapted relatively easily to handle a variety of instrumenttypes, including spectrographs with prism or grating cross-dispersers,possibly fed by a fiber or image slicer, etc. In addition to reducedspectra, an accurate spatial profile is recovered, providing valuableinformation about the spectrograph PSF and simplifying scattered lightcorrections. Based on data obtained with the VLT UVES and SAAO Giraffespectrometers.
| Statistics of spectroscopic sub-systems in visual multiple stars
A large sample of visual multiples of spectral types F5-M has beensurveyed for the presence of spectroscopic sub-systems. Some 4200 radialvelocities of 574 components were measured in 1994-2000 with thecorrelation radial velocity meter. A total of 46 new spectroscopicorbits were computed for this sample. Physical relations are establishedfor most of the visual systems and several optical components areidentified as well. The period distribution of sub-systems has a maximumat periods from 2 to 7 days, likely explained by a combination of tidaldissipation with triple-star dynamics. The fraction of spectroscopicsub-systems among the dwarf components of close visual binaries withknown orbits is similar to that of field dwarfs, from 11% to 18% percomponent. Sub-systems are more frequent among the components of widevisual binaries and among wide tertiary components to the known visualor spectroscopic binaries - 20% and 30%, respectively. In triple systemswith both outer (visual) and inner (spectroscopic) orbits known, we findan anti-correlation between the periods of inner sub-systems and theeccentricities of outer orbits which must be related to dynamicalstability constraints. Tables 1, 2, and 6 are only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/382/118
| Line-Depth Ratios: Temperature Indices for Giant Stars
Ratios of the depths of appropriately chosen spectral lines are shown tobe excellent indicators of stellar temperatures for giant stars in theG3 to K3 spectral type range. We calibrate five line-depth ratiosagainst B-V and R-I color indices and then translate these intotemperatures. Our goal is to set up line-depth ratios to (1) accuratelymonitor any temperature variations of a few degrees or less that mayoccur during magnetic cycles or oscillations and (2) rank giantsprecisely on a temperature coordinate. This is not an absolutecalibration of stellar temperatures. We show how giant spectra can bemisleading because of the complex dependences of spectral lines onmetallicity and absolute magnitude as well as temperature, and it isessential to make corrections to accommodate these complications. Thefive line-depth ratios we use yield precision for monitoring, i.e.,detecting temperature variations, of 4 K from a single exposure. Rankinggiants by temperature can be done with errors of ~25 K but could beimproved with better determinations of the metallicity andabsolute-magnitude corrections.
| Absolute spectrophotometry of late-type stars.
Not Available
| On the Photometric Variability of Red Clump Giants
Hipparcos photometry of the 308 red clump giants identified by Paczynskiet al. (1999) is investigated. These stars are found to be quite stableduring the three years of observation, but questions remain about longerterm stability.
| Galaxy Populations and Evolution in Clusters. I. Dynamics and the Origin of Low-Mass Galaxies in the Virgo Cluster
Early-type dwarfs are the most common galaxy in the local universe, yettheir origin and evolution remain a mystery. Various cosmologicalscenarios predict that dwarf-like galaxies in dense areas are the firstto form and hence should be the oldest stellar systems in clusters. Byusing radial velocities of early-type dwarfs in the Virgo cluster wedemonstrate that these galaxies are not an old cluster population buthave signatures of production from the infall of field galaxies.Evidence of this includes the combined large dispersions andsubstructure in spatial and kinematic distributions for Virgo early-typedwarfs and a velocity dispersion ratio with giant ellipticals expectedfor virialized and accreted populations. We also argue that thesegalaxies cannot originate from accreted field dwarfs, but must havephysically evolved from a precursor population, of different morphology,that fell into Virgo some time in the past.
| Comparison of Stellar Angular Diameters from the NPOI, the Mark III Optical Interferometer, and the Infrared Flux Method
The Navy Prototype Optical Interferometer (NPOI) has been used tomeasure the angular diameters of 41 late-type giant and supergiant starspreviously observed with the Mark III optical interferometer. Sixteen ofthese stars have published angular diameters based on model atmospheres(infrared flux method, IRFM). Comparison of these angular diametersshows that there are no systematic offsets between any pair of datasets. Furthermore, the reported uncertainties in the angular diametersmeasured using both interferometers are consistent with the distributionof the differences in the diameters. The distribution of diameterdifferences between the interferometric and model atmosphere angulardiameters are consistent with uncertainties in the IRFM diameters of1.4%. Although large differences in angular diameter measurements areseen for three stars, the data are insufficient to determine whetherthese differences are due to problems with the observations or are dueto temporal changes in the stellar diameters themselves.
| On the Wilson-Bappu relationship in the Mg II k line
An investigation is carried out on the Wilson-Bappu effect in the Mg Iik line at 2796.34 Å. The work is based on a selection of 230 starsobserved by both the IUE and HIPPARCOS satellites, covering a wide rangeof spectral types (F to M) and absolute visual magnitudes (-5.4<=MV <=9.0). A semi-automatic procedure is used to measurethe line widths, which applies also in the presence of strong centralabsorption reversal. The Wilson-Bappu relationship here provided isconsidered to represent an improvement over previous recent results forthe considerably larger data sample used, as well as for a properconsideration of the measurement errors. No evidence has been found fora possible dependence of the WB effect on stellar metallicity andeffective temperature.
| 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
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| Csillagkép: | Ökörhajcsár |
| Rektaszcenzió: | 15h15m30.20s |
| Deklináció: | +33°18'53.0" |
| Vizuális fényesség: | 3.47 |
| Távolság: | 35.791 parszek |
| RA sajátmozgás: | 84.7 |
| Dec sajátmozgás: | -110.9 |
| B-T magnitude: | 4.669 |
| V-T magnitude: | 3.563 |
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