Contenidos
Imágenes
Subir su imagen
DSS Images Other Images
Artículos relacionados
Variability of Stars in the Pulkovo Spectrophotometric Catalog
We present the results of a statistical study of brightness variabilityfor 693 stars of the Pulkovo spectrophotometric database in fivespectral bands in the range λλ 320 1080 nm. Significantbrightness variations were detected in at least one spectral bandagainst the background of the random noise for one-third of the starsnot earlier believed to be variable. A comparison of the distributionsof these variations in amplitude and spectral band for the normal andvariable stars shows that variability is inherent to most stars to someextent and is often wavelength dependent.
| The Effective Temperature Scale of Galactic Red Supergiants: Cool, but Not As Cool As We Thought
We use moderate-resolution optical spectrophotometry and the new MARCSstellar atmosphere models to determine the effective temperatures of 74Galactic red supergiants (RSGs). The stars are mostly members of OBassociations or clusters with known distances, allowing a criticalcomparison with modern stellar evolutionary tracks. We find we canachieve excellent matches between the observations and the reddenedmodel fluxes and molecular transitions, although the atomic lines Ca Iλ4226 and Ca II H and K are found to be unrealistically strong inthe models. Our new effective temperature scale is significantly warmerthan those in the literature, with the differences amounting to 400 Kfor the latest type M supergiants (i.e., M5 I). We show that the newlyderived temperatures and bolometric corrections give much betteragreement with stellar evolutionary tracks. This agreement provides acompletely independent verification of our new temperature scale. Thecombination of effective temperature and bolometric luminosities allowsus to calculate stellar radii; the coolest and most luminous stars (KWSgr, Case 75, KY Cyg, HD 206936=μ Cep) have radii of roughly 1500Rsolar (7 AU), in excellent accordance with the largeststellar radii predicted from current evolutionary theory, althoughsmaller than that found by others for the binary VV Cep and for thepeculiar star VY CMa. We find that similar results are obtained for theeffective temperatures and bolometric luminosities using only thedereddened V-K colors, providing a powerful demonstration of theself-consistency of the MARCS models.
| 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
| 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}
| BD +59°224: A New ζ Aurigae System
The star BD +59°224 has an interesting history of spectroscopicclassification, having been described in the literature variously as acomposite G- and F-type star with helium, a K5 star, an O-type star, andan emission-line object similar to a planetary nebula. We present newspectra of this object that clearly show the star to be a binary with aK4.5 Ib primary and a B3 V secondary. We also calculate a reddening anddistance [E(B-V)~0.75, d~2.1 kpc] and point out similarities betweenthis object and the class of ζ Aurigae stars.
| 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.
| 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.
| High-Resolution Imaging of Dust Shells by Using Keck Aperture Masking and the IOTA Interferometer
We present first results of an experiment to combine data from Keckaperture masking and the Infrared-Optical Telescope Array to image thecircumstellar environments of evolved stars with ~20 mas resolution. Theunique combination of excellent Fourier coverage at short baselines andhigh-quality long-baseline fringe data allows us to determine thelocation and clumpiness of the innermost hot dust in the envelopes andto measure the diameters of the underlying stars themselves. We findevidence for large-scale inhomogeneities in some dust shells and alsosignificant deviations from uniform brightness for the photospheres ofthe most evolved M stars. Deviations from spherically symmetric massloss in the red supergiant NML Cyg could be related to recent evidencefor dynamically important magnetic fields and/or stellar rotation. Wepoint out that dust shell asymmetries, like those observed here, canqualitatively explain the difficulty recent workers have had insimultaneously fitting the broadband spectral energy distributions andhigh-resolution spatial information, without invoking unusual dustproperties or multiple distinct shells (from hypothetical``superwinds''). This paper is the first to combine opticalinterferometry data from multiple facilities for imaging, and we discussthe challenges and potential for the future of this method, givencurrent calibration and software limitations.
| UBVJHKLM photometry of the symbiotic Mira V407 Cyg in 1998 2002
New results of UBV JHKLM photometry of the symbiotic Mira V407 Cygperformed in 1998 2002 are reported. In 2002, these observations weresupplemented with RI observations and a search for rapid variability inthe V band. The hot component of V407 Cyg experienced a strong flare in1998, which was the second in the history of photometric observations ofthis star; this flare is still continuing. During the flare, thespectral energy distribution of the hot component can be approximated byblackbody radiation with a temperature of 7200 K. At the maximumbrightness, the bolometric flux from the hot component did not exceed 3%of the Mira's mean bolometric flux, while its bolometric luminosity was400Lȯ. Appreciable variations of the star's BV brightness on atimescale of several days have been observed. These variations are notcorrelated with variations of B-V. Flickering on a timescale of severalminutes with an amplitude of has been detected in the V band. Theobservations suggest that the hot component can be in threequalitatively different states. In a model with a rapidly rotating whitedwarf, these states can be associated with (i) the quiescent state ofthe white dwarf (with a very low accretion rate), (ii) an ejectionstate, and (iii) an accretion state. The Mira pulsation period P is&$ ≈ 762mathop dlimits_. 9$; , with its infrared maximum occurring 0.15P after the visualmaximum. A “step” is observed on the ascending branch of theMira infrared light curves. In 1998, the gradual increase of the mean Kbrightness of the Mira that had been observed since 1984 was interruptedby an unusually deep minimum, after which the mean level of the Kbrightness considerably decreased.
| Kinematic Masses of Super-Star Clusters in M82 from High-Resolution Near-Infrared Spectroscopy
Using high-resolution (R~22,000) near-infrared (1.51-1.75 μm) spectrafrom Keck Observatory, we measure the kinematic masses of two super-starclusters in M82. Cross-correlation of the spectra with template spectraof cool evolved stars gives stellar velocity dispersions ofσr=15.9+/-0.8 km s-1 for J0955505+694045(MGG-9) and σr=11.4+/-0.8 km s-1 forJ0955502+694045 (MGG-11). The cluster spectra are dominated by the lightof red supergiants and correlate most closely with template supergiantsof spectral types M0 and M4.5. King model fits to the observed profilesof the clusters in archival Hubble Space Telescope/Near-Infrared Cameraand Multi-Object Spectometer images give half-light radii ofrhp=2.6+/-0.4 pc for MGG-9 and rhp=1.2+/-0.17 pcfor MGG-11. Applying the virial theorem, we determine masses of1.5+/-0.3×106 Msolar for MGG-9 and3.5+/-0.7×105 Msolar for MGG-11 (where thequoted errors include σr, rhp, and thedistance). Population synthesis modeling suggests that MGG-9 isconsistent with a standard initial mass function (IMF), whereas MGG-11appears to be deficient in low-mass stars relative to a standard IMF.There is, however, evidence of mass segregation in the clusters, inwhich case the virial mass estimates would represent lower limits.Based on observations made at the W. M. Keck Observatory, which isoperated as a scientific partnership among the California Institute ofTechnology, the University of California, and the National Aeronauticsand Space Administration. The Observatory was made possible by thegenerous financial support of the W. M. Keck Foundation.
| Onset of Mass Loss in Red Giants: Association with an Evolutionary Event
Stencel & Mullan used asymmetries in the Mg II k emission lineprofile to determine the location of a ``velocity dividing line'' (VDL)in the H-R diagram. Stars to the right of (and above) the VDL wereobserved to have asymmetries that are consistent with the presence ofcool massive winds. Stars to the left of (and below) the VDL showed noevidence for winds. We show that the VDL lies close to a certain eventof stellar evolution on the red giant branch (RGB). The event occurswhen the hydrogen-burning shell evolves outward through a discontinuityin molecular weight. In some low-mass stars, this event causes a kink inthe evolutionary track of an individual low-mass star. In a cluster, thecombined effects of such kinks create a ``bump'' in the luminosityfunction. Our result suggests that evolution through the kink (or bump)on the RGB is associated with the onset of a cool massive wind.Theoretical possibilities to explain this association will be exploredin a subsequent paper.
| 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.
| Spectral Classification of the Hot Components of a Large Sample of Stars with Composite Spectra, and Implication for the Absolute Magnitudes of the Cool Supergiant Components.
A sample of 135 stars with composite spectra has been observed in thenear-UV spectral region with the Aurélie spectrograph at theObservatoire de Haute-Provence. Using the spectral classifications ofthe cool components previously determined with near infrared spectra, weobtained reliable spectral types of the hot components of the samplesystems. The hot components were isolated by the subtraction methodusing MK standards as surrogates of the cool components. We also derivedthe visual magnitude differences between the components usingWillstrop's normalized stellar flux ratios. We propose a photometricmodel for each of these systems on the basis of our spectroscopic dataand the Hipparcos data. We bring to light a discrepancy for the Gsupergiant primaries between the visual absolute magnitudes deduced fromHipparcos parallaxes and those tabulated by Schmidt-Kaler for the GIbstars: we propose a scale of Mv-values for these stars incomposite systems. By way of statistics, about 75% of the hot componentsare dwarf or subgiant stars, and 25% should be giants. The distributionin spectral types is as follows: 41% of B-type components, 57% of typeA, and 2% of type F; 68% of the hot components have a spectral type inthe range B7 to A2. The distribution of the ΔMv-valuesshows a maximum near 0.75 mag.
| The Effect of TiO Absorption on Optical and Infrared Angular Diameters of Cool Stars
We review the systematic variation between optical- andinfrared-wavelength angular diameters reported for stars in theapproximate range of spectral types K0-M6. We show that there is acorrelation between the ratio of angular diameters and the depth of TiOabsorption, in the sense that the optical diameters are larger. We arguethat this validates a recent proposal by Houdashelt et al. that TiOabsorption affects certain, but not all, optical-wavelength angulardiameters significantly. Those authors pointed out that the infraredangular diameters appear to yield better effective temperatures than dothe optical diameters, even though the latter are of higher precision.The observed angular diameter differences may arise either from limbdarkening, atmospheric extension, or a combination of these twoprocesses. Model atmosphere calculations of limb-darkening coefficientsare needed to see whether the diameter discrepancy may be resolved.These models need to contain the correct opacity sources and a realisticestimate of the atmospheric geometry and dynamics. A comparison withobservations such as those described in this paper will be useful fortesting the validity of atmosphere models.
| A catalog of rotational and radial velocities for evolved stars. II. Ib supergiant stars
Rotational velocity vsin i and mean radial velocity are presented for asample of 231 Ib supergiant stars covering the spectral region F, G andK. This work is the second part of the large survey carried out with theCORAVEL spectrometer to establish the behavior of the rotation for starsevolving off the main sequence (De Medeiros & Mayor 1999). Thesedata will add constraints to the study of the rotational behavior inevolved stars, as well as solid information concerning tidalinteractions in binary systems and on the link between rotation,chemical abundance and activity in stars of intermediate masses. Basedon observations collected at the Haute-Provence Observatory,Saint-Michel, France and at the European Southern Observatory, La Silla,Chile Table 1 is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/395/97
| 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.
| A Large Spectral Class Dependence of the Wilson-Bappu Effect among Luminous Stars
The striking correlation between Ca II K-line emission width andabsolute visual magnitude has not previously been well calibrated forstars more luminous than giants. From a sample of binary systems fit toisochrones, we find deviations of more than 2 mag, correlated withspectral class, between these binarity Mv values and theWilson-Bappu relation. Additional Mv values derived fromHipparcos parallaxes are used to explore the systematics. The spectralclass dependence vanishes for K-line parameterlogW0<=1.80. Linear spectral class corrections are derivedfor the more luminous stars, with logW0>=2.00, while atable is provided for the transition region. The dispersion from theserelations is about +/-0.6 mag. This recalibration extends thedemonstrated applicability of the Wilson-Bappu technique toMv~=-5 or distance ~20 kpc.
| Absolute spectrophotometry of late-type stars.
Not Available
| 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.
| 4 μm spectra of AGB stars I. Observations
We present times series of high resolution spectra of AGB variables at 4mu m. Line profiles from the major contributors to the spectra ofoxygen-rich stars at 4 mu m, OH, H_2O, HCl and SiO, are examined. Thevelocity as well as shape variations of these profiles with time arediscussed. The line profiles investigated frequently have emission andmultiple absorption components. The changes with time of the 4 mu mregion lines do not always follow the cyclic variability seen in NIRspectra and in the photometric light curve. We interpret and discuss theresults qualitatively considering comparing the spectral variabilitywith that of the well behaved 1.6 mu m region and of dynamical modelatmospheres. Miras and semiregular variables are compared. The originsof non-periodic behavior are discussed, including the role of spatialinhomogeneities in the stellar atmosphere.
| 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
| The proper motions of fundamental stars. I. 1535 stars from the Basic FK5
A direct combination of the positions given in the HIPPARCOS cataloguewith astrometric ground-based catalogues having epochs later than 1939allows us to obtain new proper motions for the 1535 stars of the BasicFK5. The results are presented as the catalogue Proper Motions ofFundamental Stars (PMFS), Part I. The median precision of the propermotions is 0.5 mas/year for mu alpha cos delta and 0.7mas/year for mu delta . The non-linear motions of thephotocentres of a few hundred astrometric binaries are separated intotheir linear and elliptic motions. Since the PMFS proper motions do notinclude the information given by the proper motions from othercatalogues (HIPPARCOS, FK5, FK6, etc.) this catalogue can be used as anindependent source of the proper motions of the fundamental stars.Catalogue (Table 3) is only available at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strastg.fr/cgi-bin/qcat?J/A+A/365/222
| The intermediate-band approach to the surface-brightness method for Cepheid radii and distance determination
The surface-brightness parameter Fν is calibrated in termsof the Strömgren intermediate-band colour b-y. The relationFν-(b-y)o valid for Cepheids is calibratedusing accurate near-infrared radii and distances for selected Cepheids.We have obtained uvby photometry for non-Cepheid giant and supergiantstars with known angular diameters and compared the slope and zero-pointof their Fν-(b-y)o relation with the Cepheidcalibration. We found that the two calibrations are significantlydifferent. The theoretical models lie in between the two calibrations.It is remarked that Fν-colour relations derived fromnon-Cepheids and involving blue colours (e.g. B-V or b-y) are notapplicable to Cepheids, while those involving redder colours (e.g. V-R,V-K or V-J) also produce good radii for Cepheids. Selected Cepheids ascalibrators lead to the accurate relationFν=3.898(+/-0.003)-0.378(+/-0.006)(b-y)o, whichallowed the calculation of radii and distances for a sample of 59Galactic Cepheids. The uncertainties in the zero-point and slope of theabove relation are similar to those obtained from near-infrared colours,and determine the accuracies in radii and distance calculations. Whileinfrared light and colour curves for Cepheids may be superior inprecision, the intermediate-band b-y colour allows the recovery of meanradii with an accuracy comparable to those obtained from the infraredsolutions. The derived distances are consistent within the uncertaintieswith those predicted by a widely accepted period-luminosityrelationship. Likewise, the resulting period-radius relation from theintermediate-band approach is in better agreement with infrared versionsthan with optical versions of this law. It is highlighted that theintermediate-band calibration of the surface-brightness method in thiswork is of comparable accuracy to the near-infrared calibrations. Thepresent results stress the virtues of uvby in determining the physicalparameters of supergiant stars of intermediate temperature.
| Trend analysis of 51 carbon long-period variables.
Not Available
| Near-Infrared Classification Spectroscopy: J-Band Spectra of Fundamental MK Standards
We present a catalog of J-band spectra for 88 fundamental MK standardstars observed at a resolving power of R~3000. This contribution servesas a companion atlas to the K-band spectra recently published by Wallace& Hinkle and the H-band atlas by Meyer and coworkers. We report datafrom 7400 to 9550 cm-1 (1.05-1.34 μm) for stars ofspectral types O7-M6 and luminosity classes I-V as defined in the MKsystem. In reducing these data, special care has been taken to removetime-variable telluric features of water vapor. We identify atomic andmolecular indexes that are both temperature and luminosity sensitivethat aid in the classification of stellar spectra in the J band. Inaddition to being useful in the classification of late-type stars, the Jband contains several features of interest in the study of early-typestellar photospheres. These data are available electronically foranonymous FTP in addition to being served on the World Wide Web.
| Ca II activity and rotation in F-K evolved stars
Ca II H and K high resolution observations for 60 evolved stars in thefield and in 5 open clusters are presented. From these spectrachromospheric fluxes are derived, and a homogeneous sample of more than100 giants is built adding data from the literature. In addition, formost stars, rotational velocities were derived from CORAVELobservations. By comparing chromospheric emission in the cluster starswe confirm the results of Pasquini & Brocato (1992): chromosphericactivity depends on the stellar effective temperature, and mass, whenintermediate mass stars (M ~ 4 Msun) are considered. TheHyades and the Praesepe clump giants show the same level of activity, asexpected from stars with similar masses and effective temperatures. Adifference of up to 0.4 dex in the chromospheric fluxes among the Hyadesgiants is recorded and this sets a clear limit to the intrinsic spreadof stellar activity in evolved giants. These differences in otherwisevery similar stars are likely due to stellar cycles and/or differencesin the stellar initial angular momentum. Among the field stars none ofthe giants with (V-R)o < 0.4 and Ia supergiants observedshows a signature of Ca II activity; this can be due either to the realabsence of a chromosphere, but also to other causes which preclude theappearance of Ca II reversal. By analyzing the whole sample we find thatchromospheric activity scales linearly with stellar rotational velocityand a high power of stellar effective temperature: F'k ~Teff7.7 (Vsini)0.9. This result can beinterpreted as the effect of two chromospheric components of differentnature: one mechanical and one magnetic. Alternatively, by using theHipparcos parallaxes and evolutionary tracks, we divide the sampleaccording to the stellar masses, and we follow the objects along anevolutionary track. For each range of masses activity can simply beexpressed as a function of only one parameter: either theTeff or the angular rotation Omega , with laws F'k~ Omega alpha , because angular velocity decreases witheffective temperature along an evolutionary track. By using theevolutionary tracks and the observed Vsini we investigate the evolutionof the angular momentum for evolved stars in the range 1-5Msun. For the 1.6-3 solar mass stars the data are consistentwith the IOmega =const law while lower and higher masses follow a lawsimilar to IOmega 2=const, where I is the computed stellarmomentum of inertia. We find it intriguing that Vsini remains almostconstant for 1Msun stars along their evolution; if a similarbehavior is shared by Pop II stars, this could explain the relativelyhigh degree of activity observed in Pop II giants. Finally, through theuse of models, we have verified the consistency of the F'k ~Omega alpha and the IOmega beta = Const lawsderived, finding an excellent agreement. This representation, albeitcrude (the models do not consider, for instance, mass losses) representsthe evolution of Ca II activity and of the angular momentum in asatisfactory way in most of the portion of HR diagram analyzed.Different predictions could be tested with observations in selectedclusters. Based on observations collected at ESO, La Silla. Tables 1-3are only available in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| The CaII-M_v Correlation (Wilson-Bappu Effect) Calibrated by HIPPARCOS Parallaxes
We have used Hipparcos parallaxes to derive absolute visual magnitudesof G, K, and M stars with Ca II emission line widths previously measuredby O. C. Wilson. A linear relationship similar to the one derivedoriginally by Wilson & Bappu and improved by Lutz & Kelker wasfound from M_v=+7 to -2. For stars brighter than M_v=-2 a substantialnumber of stars show Ca II emission lines that are broader than expectedfrom the linear fit. Most of those stars are bright giants andsupergiants of type G. In appendices we show some sample Ca II profilesand identify emission lines of Fe II as well as the Hepsilon line insome stars.
| Spectral classification of the cool components of symbiotic stars
We have made near infrared spectroscopic observations of 10 symbioticand 27 K-M comparison stars. For stars later than M3, we found the banddepth of the triple-headed TiO absorption band to be sensitive totemperature and insensitive to gravity. We fitted the spectral type tothe band depth with a standard error of 0.22 of a subtype and derivedthe spectral types for 6 symbiotic stars. We measured the EW of a largenumber of lines including the CaII lines (very sensitive to luminosity),the FeI and TiO lines (moderately sensitive) and the NaI lines (notsensitive). The EW of these lines vary with the spectral type,particularly for stars later than M3, both spectral type and luminosityeffects must be considered. We give the luminosity classes for 10 of thebrighter symbiotic stars, they are all giant stars, showing no featuresof bright giants or supergiants.
|
Enviar un nuevo artículo
Enlaces relacionados
- - No se han encontrado enlaces -
En viar un nuevo enlace
Miembro de los siguientes grupos:
|
Datos observacionales y astrométricos
| Constelación: | Cisne |
| Ascensión Recta: | 21h04m55.90s |
| Declinación: | +43°55'40.0" |
| Magnitud Aparente: | 3.72 |
| Distancia: | 361.011 parsecs |
| Movimiento Propio en Ascensión Recta: | 9 |
| Movimiento Propio en Declinación: | 0.1 |
| B-T magnitude: | 5.829 |
| V-T magnitude: | 3.88 |
Catálogos y designaciones:
|
INHABITED SKY
