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Ýlgili Makaleler
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.
| Disk populations from HIPPARCOS kinematic data. Discontinuities in the local velocity distribution
The full space motions including radial velocities of a stellarsample drawn from HIPPARCOS catalogue are used to discriminatedifferentiated statistical behaviours that are associated with stellarpopulations in the solar neighbourhood. A sampling parameter is used tobuild a hierarchical set of nested samples, where a discontinuouspattern, based in a partition introduced by two normal distributions,scans the subsamples. Two quantities inform whether any subsample fitsproperly into the discontinuous model. A χ2 test measuresthe Gaussianity of both components, and the entropy of the mixtureprobability gives account of how informative the resulting segregationis. The less informative partition is the one with maximum populationentropy, which provides most representative kinematic parameters. Eachnew population merged to the cumulative subsample produces adiscontinuity in the plot entropy versus sampling parameter, that allowsto determine the number of populations contained in the whole sample.The resulting method has been named MEMPHIS, Maximum Entropy of theMixture Probability from HIerarchical Segregation. In addition to bothmain kinematic components, thin and thick disk, with respective velocitydispersions (28± 1, 16± 2, 13± 1) and (65±2, 39± 9, 41± 2) km s-1, two discretenon-Gaussian subcomponents are detected within the thin disk. Thesepopulations are identified with early-type and young disk stars.Moreover, a continuous old disk population is mixed with the foregoingsubcomponents composing all together the thin disk. Older thin diskstars have a velocity dispersion overlapping a wing of the thick disk.Although they could appear like an intermediate continuous population,nested subsamples distributions allow us to conclude that theydefinitively belong to the thin disk, and that a clear discontinuitydetaches thick from thin disk. Almost the same qualitative results, butwith less accuracy, are obtained whether MEMPHIS is applied tosubsamples from the Third Catalogue of Nearby Stars (CNS3). A dynamicmodel according to Chandrasekhar's approximation, under particularsymmetry hypotheses, allows to interpret the results. The non-vanishingvertex deviation lower for older stars of all Galactic components issuggesting that, at least, point-axial symmetry is required in order toexplain the local kinematic behaviour. According to this model, theoldest thick disk population, with no net radial movement, can beextrapolated, having heliocentric velocities of -76 ± 2 kms-1 in rotation, and -18 ± 1 km s-1 in theradial direction. Early-type stars show a worthy local singularity,nearly with no net radial motion, similarly to the oldest thick diskstars. Older populations half of the thin disk and the whole thickdisk share a common differential galactic movement, suggesting acommon dynamical origin for the rupture of the axial symmetry. Therelationship between the maximum stellar velocity of a sample and itsaverage age τ is discussed, finding an approximate relation|V|max ∝ τ. Local stellar populations can bedescribed from a Titius-Bode-like law for the radial velocitydispersion, σ1 = 6.6 (4/3)^x, so that for naturalvalues x=2,3,5,8 it determines average energy levels of discretepopulations, while for continuous intervals x≤ 5 and x≥ 7 itdescribes the velocity-age evolution of thin and thick disk components,according to x 1.5 ln τ.
| Astrometric orbits of SB^9 stars
Hipparcos Intermediate Astrometric Data (IAD) have been used to deriveastrometric orbital elements for spectroscopic binaries from the newlyreleased Ninth Catalogue of Spectroscopic Binary Orbits(SB^9). This endeavour is justified by the fact that (i) theastrometric orbital motion is often difficult to detect without theprior knowledge of the spectroscopic orbital elements, and (ii) suchknowledge was not available at the time of the construction of theHipparcos Catalogue for the spectroscopic binaries which were recentlyadded to the SB^9 catalogue. Among the 1374 binaries fromSB^9 which have an HIP entry (excluding binaries with visualcompanions, or DMSA/C in the Double and Multiple Stars Annex), 282 havedetectable orbital astrometric motion (at the 5% significance level).Among those, only 70 have astrometric orbital elements that are reliablydetermined (according to specific statistical tests), and for the firsttime for 20 systems. This represents a 8.5% increase of the number ofastrometric systems with known orbital elements (The Double and MultipleSystems Annex contains 235 of those DMSA/O systems). The detection ofthe astrometric orbital motion when the Hipparcos IAD are supplementedby the spectroscopic orbital elements is close to 100% for binaries withonly one visible component, provided that the period is in the 50-1000 drange and the parallax is >5 mas. This result is an interestingtestbed to guide the choice of algorithms and statistical tests to beused in the search for astrometric binaries during the forthcoming ESAGaia mission. Finally, orbital inclinations provided by the presentanalysis have been used to derive several astrophysical quantities. Forinstance, 29 among the 70 systems with reliable astrometric orbitalelements involve main sequence stars for which the companion mass couldbe derived. Some interesting conclusions may be drawn from this new setof stellar masses, like the enigmatic nature of the companion to theHyades F dwarf HIP 20935. This system has a mass ratio of 0.98 but thecompanion remains elusive.
| Aldebaran's angular diameter: How well do we know it?
The bright, well-known K5 giant Aldebaran,α Tau, is probably the star with the largestnumber of direct angular diameter determinations, achieved over a longtime by several authors using various techniques. In spite of thiswealth of data, or perhaps as a direct result of it, there is not a verygood agreement on a single angular diameter value. This is particularlyunsettling if one considers that Aldebaran is also used as a primarycalibrator for some angular resolution methods, notably for optical andinfrared long baseline interferometry. Directly connected to Aldebaran'sangular diameter and its uncertainties is its effective temperature,which also has been used for several empirical calibrations. Among theproposed explanations for the elusiveness of an accurate determinationof the angular diameter of Aldebaran are the possibility of temporalvariations as well as a possible dependence of the angular diameter onthe wavelength. We present here a few, very accurate new determinationsobtained by means of lunar occultations and long baselineinterferometry. We derive an average value of 19.96±0.03milliarcsec for the uniform disk diameter. The correspondinglimb-darkened value is 20.58±0.03 milliarcsec, or 44.2±0.9Rȯ. We discuss this result, in connection with previousdeterminations and with possible problems that may affect suchmeasurements.Based on observations collected at TIRGO (Gornergrat, Switzerland). TIRGO is operated by CNR - CAISMI Arcetri, Italy.
| 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 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.
| The Wilson-Bappu effect: A tool to determine stellar distances
Wilson & Bappu (\cite{orig}) have shown the existence of aremarkable correlation between the width of the emission in the core ofthe K line of Ca II and the absolute visual magnitude of late-typestars.Here we present a new calibration of the Wilson-Bappu effect based on asample of 119 nearby stars. We use, for the first time, widthmeasurements based on high resolution and high signal to noise ratio CCDspectra and absolute visual magnitudes from the Hipparcos database.Our primary goal is to investigate the possibility of using theWilson-Bappu effect to determine accurate distances to single stars andgroups.The result of our calibration fitting of the Wilson-Bappu relationshipis MV=33.2-18.0 log W0, and the determinationseems free of systematic effects. The root mean square error of thefitting is 0.6 mag. This error is mostly accounted for by measurementerrors and intrinsic variability of W0, but in addition apossible dependence on the metallicity is found, which becomes clearlynoticeable for metallicities below [Fe/H] ~ -0.4. This detection ispossible because in our sample [Fe/H] ranges from -1.5 to 0.4.The Wilson-Bappu effect can be used confidently for all metallicitiesnot lower than ~ -0.4, including the LMC. While it does not provideaccurate distances to single stars, it is a useful tool to determineaccurate distances to clusters and aggregates, where a sufficient numberof stars can be observed.We apply the Wilson-Bappu effect to published data of the open cluster M67; the retrieved distance modulus is of 9.65 mag, in very goodagreement with the best distance estimations for this cluster, based onmain sequence fitting.Observations collected at ESO, La Silla.
| Reprocessing the Hipparcos Intermediate Astrometric Data of spectroscopic binaries. II. Systems with a giant component
By reanalyzing the Hipparcos Intermediate Astrometric Data of a largesample of spectroscopic binaries containing a giant, we obtain a sampleof 29 systems fulfilling a carefully derived set of constraints andhence for which we can derive an accurate orbital solution. Of these,one is a double-lined spectroscopic binary and six were not listed inthe DMSA/O section of the catalogue. Using our solutions, we derive themasses of the components in these systems and statistically analyzethem. We also briefly discuss each system individually.Based on observations from the Hipparcos astrometric satellite operatedby the European Space Agency (ESA 1997) and on data collected with theSimbad database.
| 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.
| The tidal effects on the lithium abundance of binary systems with giant component
We analyse the behavior of lithium abundance as a function of effectivetemperature, projected rotational velocity, orbital period andeccentricity for a sample of 68 binary systems with giant component andorbital period ranging from about 10 to 6400 days. For these binarysystems the Li abundances show a gradual decrease with temperature,paralleling the well established result for single giants. We have alsoobserved a dependence of lithium content on rotation. Binary systemswith moderate to high rotation present also moderate to high Li content.This study shows also that synchronized binary systems with giantcomponent seem to retain more of their original lithium than theunsynchronized systems. For orbital periods lower than 100 to 250 days,typically the period of synchronization for this kind of binary systems,lithium depleted stars seems to be unusual. The suggestion is made thatthere is an ``inhibited zone" in which synchronized binary systems withgiant component having lithium abundance lower than a threshold levelshould be unusual. Based on observations collected at ESO, La Silla.
| 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
| High-Precision Radial Velocity Measurements of Some Southern Stars
Precise absolute radial velocities have been obtained at Mount JohnUniversity Observatory for a number of southern stars, using the 1 mtelescope and fiber-fed echelle spectrograph. Only the stars that havebeen observed three or more times are presented, including 14 IAUstandards and 11 program stars. Six echelle orders in the green(5000-5600 Å) are used. Many delicate steps have been undertakenin order to maintain the same conditions in both recording and reducingthe spectra over a period of 27 months. The Th-Ar lamp has been used forthe wavelength calibration. The absolute radial velocities have beendetermined by cross-correlation with synthetic spectra computed by R. L.Kurucz. The zero point has been adjusted using blue-sky spectra. Anadditional strong correlation, between the measured velocities andphoton counts in stellar and Th-Ar spectra, has been detected for thePM3000 CCD camera and has been eliminated. A resulting precision ofabout 20-30 m s-1 has been obtained. The overall uncertaintyof the absolute radial velocities was estimated to be about 100-200 ms-1. The present paper is a continuation of our recentprevious work, including more details on the reduction process and thepresentation of the radial velocities for more stars.
| A statistical analysis of the metallicities of nine old superclusters and moving groups
Using both high-dispersion and low-resolution data, the metallicities ofnine old moving groups and superclusters are analyzed. These stellargroupings include the HR 1614 and Hyades superclusters and the Wolf 630,zeta Her, 61 Cyg, HR 1614, sigma Pup, eta Cep, and Arcturus groups.Samples of these stellar groupings are drawn from Eggen's membershiplists. Precautions are taken against problems posed by reddening, visualand spectroscopic binaries, and typographical errors in Eggen's lists.When required, the analyses allow for systematic differences betweenlow-resolution and high-dispersion metallicities. It is found that noneof the stellar groupings have the small metallicity dispersion found fora selection of galactic clusters. Instead, the metallicity dispersionsturn out to be comparable to the dispersion for a random selection offield stars. For most of the stellar groupings, it does not seempossible at present to learn more by analyzing metallicities. However,one can be more definite about three of them: the HR 1614 supercluster,the HR 1614 group, and the Hyades supercluster. Using a membership listfrom Eggen (\cite{e98c}) that is based on Hipparcos astrometry, noevidence is found for the existence of an HR 1614 supercluster. Toisolate an HR 1614 group, results from a kinematic analysis (Dehnen\cite{d98}) are then used to select a tentative list of members fromEggen's group and supercluster lists. From the mean metallicity of theredefined group, it is found that the group is very unlikely to be arandom, magnitude-limited sample of stars. A similar result is obtainedfor a version of the Hyades supercluster derived from 18 of Eggen'smembership lists. About 43% of the stars in this version turn out to bemembers of the supercluster.
| The 74th Special Name-list of Variable Stars
We present the Name-list introducing GCVS names for 3153 variable starsdiscovered by the Hipparcos mission.
| A Second Catalog of Orbiting Astronomical Observatory 2 Filter Photometry: Ultraviolet Photometry of 614 Stars
Ultraviolet photometry from the Wisconsin Experiment Package on theOrbiting Astronomical Observatory 2 (OAO 2) is presented for 614 stars.Previously unpublished magnitudes from 12 filter bandpasses withwavelengths ranging from 1330 to 4250 Å have been placed on thewhite dwarf model atmosphere absolute flux scale. The fluxes wereconverted to magnitudes using V=0 for F(V)=3.46x10^-9 ergs cm^-2 s^-1Å^-1, or m_lambda=-2.5logF_lambda-21.15. This second catalogeffectively doubles the amount of OAO 2 photometry available in theliterature and includes many objects too bright to be observed withmodern space observatories.
| Spectral Irradiance Calibration in the Infrared. X. A Self-Consistent Radiometric All-Sky Network of Absolutely Calibrated Stellar Spectra
We start from our six absolutely calibrated continuous stellar spectrafrom 1.2 to 35 μm for K0, K1.5, K3, K5, and M0 giants. These wereconstructed as far as possible from actual observed spectral fragmentstaken from the ground, the Kuiper Airborne Observatory, and the IRAS LowResolution Spectrometer, and all have a common calibration pedigree.From these we spawn 422 calibrated ``spectral templates'' for stars withspectral types in the ranges G9.5-K3.5 III and K4.5-M0.5 III. Wenormalize each template by photometry for the individual stars usingpublished and/or newly secured near- and mid-infrared photometryobtained through fully characterized, absolutely calibrated,combinations of filter passband, detector radiance response, and meanterrestrial atmospheric transmission. These templates continue ourongoing effort to provide an all-sky network of absolutely calibrated,spectrally continuous, stellar standards for general infrared usage, allwith a common, traceable calibration heritage. The wavelength coverageis ideal for calibration of many existing and proposed ground-based,airborne, and satellite sensors, particularly low- tomoderate-resolution spectrometers. We analyze the statistics of probableuncertainties, in the normalization of these templates to actualphotometry, that quantify the confidence with which we can assert thatthese templates truly represent the individual stars. Each calibratedtemplate provides an angular diameter for that star. These radiometricangular diameters compare very favorably with those directly observedacross the range from 1.6 to 21 mas.
| The central depth of the Ca II triplet lines as a discriminant of chromospheric activity in late type stars
Not Available
| Classification and Identification of IRAS Sources with Low-Resolution Spectra
IRAS low-resolution spectra were extracted for 11,224 IRAS sources.These spectra were classified into astrophysical classes, based on thepresence of emission and absorption features and on the shape of thecontinuum. Counterparts of these IRAS sources in existing optical andinfrared catalogs are identified, and their optical spectral types arelisted if they are known. The correlations between thephotospheric/optical and circumstellar/infrared classification arediscussed.
| MSC - a catalogue of physical multiple stars
The MSC catalogue contains data on 612 physical multiple stars ofmultiplicity 3 to 7 which are hierarchical with few exceptions. Orbitalperiods, angular separations and mass ratios are estimated for eachsub-system. Orbital elements are given when available. The catalogue canbe accessed through CDS (Strasbourg). Half of the systems are within 100pc from the Sun. The comparison of the periods of close and widesub-systems reveals that there is no preferred period ratio and allpossible combinations of periods are found. The distribution of thelogarithms of short periods is bimodal, probably due to observationalselection. In 82\% of triple stars the close sub-system is related tothe primary of a wide pair. However, the analysis of mass ratiodistribution gives some support to the idea that component masses areindependently selected from the Salpeter mass function. Orbits of wideand close sub-systems are not always coplanar, although thecorresponding orbital angular momentum vectors do show a weak tendencyof alignment. Some observational programs based on the MSC aresuggested. Tables 2 and 3 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| The Pulkovo Spectrophotometric Catalog of Bright Stars in the Range from 320 TO 1080 NM
A spectrophotometric catalog is presented, combining results of numerousobservations made by Pulkovo astronomers at different observing sites.The catalog consists of three parts: the first contains the data for 602stars in the spectral range of 320--735 nm with a resolution of 5 nm,the second one contains 285 stars in the spectral range of 500--1080 nmwith a resolution of 10 nm and the third one contains 278 stars combinedfrom the preceding catalogs in the spectral range of 320--1080 nm with aresolution of 10 nm. The data are presented in absolute energy unitsW/m(2) m, with a step of 2.5 nm and with an accuracy not lower than1.5--2.0%.
| The Stellar Content of Star Stream I
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....111.1615E&db_key=AST
| 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.
| SANTIAGO 91, a right ascension catalogue of 3387 stars (equinox J2000).
The positions in right ascension of 3387 stars belonging to the Santiago67 Catalogue, observed with the Repsold Meridian Circle at Cerro Calan,National Astronomical Observatory, during the period 1989 to 1994, aregiven. The average mean square error of a position, for the wholeCatalogue, is +/-0.009 s. The mean epoch of the catalogue is 1991.84.
| Radio continuum emission from stars: a catalogue update.
An updated version of my catalogue of radio stars is presented. Somestatistics and availability are discussed.
| The position corrections of 1400 stars observed with PA II in San Juan.
Not Available
| A Spectrophotometric Catalogue of 60 Selected Southern Stars
Not Available
| Second astrolabe catalogue of Santiago.
Positions for 350 FK5 and 164 FK5 Extension stars as determined with theDanjon astrolabe of Santiago and differences astrolabe-catalogue aregiven for Equinox J2000.0 and for the mean observation epoch of eachstar. The average mean error in alpha is +/-0.005s and +/-0.07" indelta. The mean epoch of observation of the catalogue is J1979.96.
| The CA II triplet lines in cool stars
Observations of the infrared triplet lines of ionized calcium arepresented for 91 stars brighter than m_v_=+7.0 in the spectral rangeF8-M4 of all luminosity classes and over a range of metallicities [Fe/H]from -0.65 to +0.60. The above spectra have been obtained at a spectralresolution of 0.4 A with a coude echelle spectrograph using the ThomsonCCD as the detector. This study has been undertaken primarily toinvestigate the dependence of the Ca II triplet strengths over the broadrange of atmospheric parameters like luminosity, temperature andmetallicity. The Ca II triplet lines are a powerful diagnostic of thestellar populations in galaxies because of their sensitivity to theabove parameters. Our detailed analysis indicates a strong correlationbetween the equivalent width of the Ca II triplet lines and surfacegravity, much stronger in metal rich stars than in metal poor stars. TheCa II equivalent widths are fairly insensitive to temperature over therange of luminosity covered. However, they are found to be quitesensitive to metallicity, more conspicuously in supergiants than ingiants and dwarfs. Observations are compared with recent theoreticalcalculations of these lines in NLTE atmospheres.
| A catalog of stellar Lyman-alpha fluxes
We present a catalog of stellar Ly-alpha emission fluxes, based on newand archival images obtained with the IUE spacecraft. The catalogincludes 227 stars with detectable Ly-alpha emission fluxes, and upperlimits on the Ly-alpha emission flux for another 48 stars. Multiple fluxmeasurements are given for 52 stars. We present a model for correctingthe observed Ly-alpha flux for attenuation by the local interstellarmedium, and we apply this model to derive intrinsic Ly-alpha fluxes for149 catalog stars which are located in low H I column density directionsof the local interstellar medium. In our catalog, there are 14 late-Aand early-F stars at B-V = 0.29 or less that show detectable emission atLy-alpha. We find a linear correlation between the intrinsic Ly-alphaflux and C II 1335 A flux for stars with B-V greater than 0.60, but theA and F stars deviate from this relation in the sense that theirLy-alpha flux is too low. We also find a good correlation betweenLy-alpha strength and coronal X-ray emission. This correlation holdsover most of the H-R diagram, even for the F stars, where an X-raydeficit has previously been found relative to the transition regionlines of C II and C IV.
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| Sað Açýklýk: | 07h29m13.80s |
| Yükselim: | -43°18'05.0" |
| Görünürdeki Parlaklýk: | 3.25 |
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