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Stellar Lyα Emission Lines in the Hubble Space Telescope Archive: Intrinsic Line Fluxes and Absorption from the Heliosphere and Astrospheres
We search the Hubble Space Telescope (HST) archive for previouslyunanalyzed observations of stellar H I Lyα emission lines, ourprimary purpose being to look for new detections of Lyα absorptionfrom the outer heliosphere and to also search for analogous absorptionfrom the astrospheres surrounding the observed stars. The astrosphericabsorption is of particular interest because it can be used to studysolar-like stellar winds that are otherwise undetectable. We find andanalyze 33 HST Lyα spectra in the archive. All the spectra weretaken with the E140M grating of the Space Telescope Imaging Spectrograph(STIS) instrument on board HST. The HST STIS spectra yield four newdetections of heliospheric absorption (70 Oph, ξ Boo, 61 Vir, and HD165185) and seven new detections of astrospheric absorption (EV Lac, 70Oph, ξ Boo, 61 Vir, δ Eri, HD 128987, and DK UMa), doubling theprevious number of heliospheric and astrospheric detections. Whencombined with previous results, 10 of 17 lines of sight within 10 pcyield detections of astrospheric absorption. This high detectionfraction implies that most of the ISM within 10 pc must be at leastpartially neutral, since the presence of H I within the ISM surroundingthe observed star is necessary for an astrospheric detection. Incontrast, the detection percentage is only 9.7% (3 out of 31) for starsbeyond 10 pc. Our Lyα analyses provide measurements of ISM H I andD I column densities for all 33 lines of sight, and we discuss someimplications of these results. Finally, we measure chromosphericLyα fluxes from the observed stars. We use these fluxes todetermine how Lyα flux correlates with coronal X-ray andchromospheric Mg II emission, and we also study how Lyα emissiondepends on stellar rotation.Based on observations with the NASA/ESA Hubble Space Telescope, obtainedat the Space Telescope Science Institute, which is operated by theAssociation of Universities for Research in Astronomy, Inc., under NASAcontract NAS5-26555.
| 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}
| Ca II K Emission-Line Asymmetries Among Red Giants
Measurements of the asymmetry of the K2 emission line of CaII have been made for a sample of bright field giants with B-V>1.15observed with the Cassegrain echelle spectrometer on the McDonaldObservatory 2.1 m telescope. The asymmetry of the Ca II K2line is quantified through measurement of a parameter V/R, which isdefined as the ratio between the maximum counts recorded in the violetand red components of the double-peaked emission profile. Red-maximumasymmetry (V/R<1.0) is found in our sample of 35 giants only amongstars with B-V>1.35, a trend that is still maintained (with oneexception) with the inclusion of an additional sample of giantspreviously observed by us with the same spectrograph. Althoughexceptional stars can be found in the literature, the data support anearlier finding by R. Stencel that among luminosity class III fieldgiants the occurrence of V/R<1.0 is generally restricted to effectivetemperatures cooler than 4320 K. This limit may coincide with the onsetof pulsation.
| A Revised Calibration of the MV-W(O I 7774) Relationship using Hipparcos Data: Its Application to Cepheids and Evolved Stars
A new calibration of the MV-W(O I 7774) relationship hasbeen calculated using better reddening and distance estimates for asample of 27 calibrator stars of spectral types A to G, based onaccurate parallaxes and proper motions from the Hipparcos and Tychocatalogues. The present calibration predicts absolute magnitude withaccuracies of +/-0.38mag for a sample covering a large range ofMV, from -9.5 to +0.35 mag. The color term included in aprevious paper has been dropped since its inclusion does not lead to anysignificant improvement in the calibration. The variation of the O I7774 feature in the classical cepheid SS Sct has been studied. Wecalculated a phase-dependent correction to random phase OI featurestrengths in Cepheids, such that it predicts mean absolute magnitudesusing the above calibration. After applying such a correction, we couldincrease the list of calibrators to 58 by adding MV and O Itriplet strength data for 31 classical Cepheids. The standard error ofthe calibration using the composite sample was comparable to thatobtained from the primary 27 calibrators, showing that it is possible tocalculate mean Cepheid luminosities from random phase observations ofthe O I 7774 feature. We use our derived calibrations to estimateMV for a set of evolved objects to be able to locate theirpositions in the HR diagram.
| 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.
| Radial Velocities for 889 Late-Type Stars
We report radial velocities for 844 FGKM-type main-sequence and subgiantstars and 45 K giants, most of which had either low-precision velocitymeasurements or none at all. These velocities differ from the standardstars of Udry et al. by 0.035 km s-1 (rms) for the 26 FGKstandard stars in common. The zero point of our velocities differs fromthat of Udry et al.: =+0.053km s-1. Thus, these new velocities agree with the best knownstandard stars both in precision and zero point, to well within 0.1 kms-1. Nonetheless, both these velocities and the standardssuffer from three sources of systematic error, namely, convectiveblueshift, gravitational redshift, and spectral type mismatch of thereference spectrum. These systematic errors are here forced to be zerofor G2 V stars by using the Sun as reference, with Vesta and day sky asproxies. But for spectral types departing from solar, the systematicerrors reach 0.3 km s-1 in the F and K stars and 0.4 kms-1 in M dwarfs. Multiple spectra were obtained for all 889stars during 4 years, and 782 of them exhibit velocity scatter less than0.1 km s-1. These stars may serve as radial velocitystandards if they remain constant in velocity. We found 11 newspectroscopic binaries and report orbital parameters for them. Based onobservations obtained at the W. M. Keck Observatory, which is operatedjointly by the University of California and the California Institute ofTechnology, and on observations obtained at the Lick Observatory, whichis operated by the University of California.
| A Strategy for Identifying the Grid Stars for the Space Interferometry Mission
We present a strategy to identify several thousand stars that areastrometrically stable at the microarcsecond level for use in the SpaceInterferometry Mission (SIM) astrometric grid. The requirements on thegrid stars make this a rather challenging task. Taking a variety ofconsiderations into account, we argue for K giants as the best type ofstars for the grid, mainly because they can be located at much largerdistances than any other type of star owing to their intrinsicbrightness. We show that it is possible to identify suitable candidategrid K giants from existing astrometric catalogs. However, double starshave to be eliminated from these candidate grid samples, since theygenerally produce much larger astrometric jitter than tolerable for thegrid. The most efficient way to achieve this is probably by means of aradial velocity survey. To demonstrate the feasibility of this approach,we repeatedly measured the radial velocities for a preselected sample of86 nearby Hipparcos K giants with precisions of 5-8 m s-1.The distribution of the intrinsic radial velocity variations for thebona fide single K giants shows a maximum around 20 m s-1,which is small enough not to severely affect the identification ofstellar companions around other K giants. We use the results of ourobservations as input parameters for Monte Carlo simulations on thepossible design of a radial velocity survey of all grid stars. Ourfavored scenario would result in a grid which consists to 68% of truesingle stars and to 32% of double or multiple stars with periods mostlylarger than 200 years, but only 3.6% of all grid stars would displayastrometric jitter larger than 1 μas. This contamination level isprobably tolerable.
| 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
| Rotation and lithium in single giant stars
In the present work, we study the link between rotation and lithiumabundance in giant stars of luminosity class III, on the basis of alarge sample of 309 single stars of spectral type F, G and K. We havefound a trend for a link between the discontinuity in rotation at thespectral type G0III and the behavior of lithium abundances around thesame spectral type. The present work also shows that giant starspresenting the highest lithium contents, typically stars earlier thanG0III, are those with the highest rotation rates, pointing for adependence of lithium content on rotation, as observed for otherluminosity classes. Giant stars later than G0III present, as a rule, thelowest rotation rates and lithium contents. A large spread of about fivemagnitudes in lithium abundance is observed for the slow rotators.Finally, single giant stars with masses 1.5 < M/Msun<=2.5 show a clearest trend for a correlation between rotational velocityand lithium abundance. Based on observations collected at theObservatoire de Haute -- Provence (France) and at the European SouthernObservatory, La Silla (Chile). Table 2 is only available electronicallywith the On-Line publication athttp://link.springer.de/link/service/00230/
| A catalog of rotational and radial velocities for evolved stars
Rotational and radial velocities have been measured for about 2000evolved stars of luminosity classes IV, III, II and Ib covering thespectral region F, G and K. The survey was carried out with the CORAVELspectrometer. The precision for the radial velocities is better than0.30 km s-1, whereas for the rotational velocity measurementsthe uncertainties are typically 1.0 km s-1 for subgiants andgiants and 2.0 km s-1 for class II giants and Ib supergiants.These data will add constraints to studies of the rotational behaviourof evolved stars as well as solid informations concerning the presenceof external rotational brakes, tidal interactions in evolved binarysystems and on the link between rotation, chemical abundance and stellaractivity. In this paper we present the rotational velocity v sin i andthe mean radial velocity for the stars of luminosity classes IV, III andII. Based on observations collected at the Haute--Provence Observatory,Saint--Michel, France and at the European Southern Observatory, LaSilla, Chile. Table \ref{tab5} also available in electronic form at CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Catalogs of temperatures and [Fe/H] averages for evolved G and K stars
A catalog of mean values of [Fe/H] for evolved G and K stars isdescribed. The zero point for the catalog entries has been establishedby using differential analyses. Literature sources for those entries areincluded in the catalog. The mean values are given with rms errors andnumbers of degrees of freedom, and a simple example of the use of thesestatistical data is given. For a number of the stars with entries in thecatalog, temperatures have been determined. A separate catalogcontaining those data is briefly described. Catalog only available atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| 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.
| A catalogue of [Fe/H] determinations: 1996 edition
A fifth Edition of the Catalogue of [Fe/H] determinations is presentedherewith. It contains 5946 determinations for 3247 stars, including 751stars in 84 associations, clusters or galaxies. The literature iscomplete up to December 1995. The 700 bibliographical referencescorrespond to [Fe/H] determinations obtained from high resolutionspectroscopic observations and detailed analyses, most of them carriedout with the help of model-atmospheres. The Catalogue is made up ofthree formatted files: File 1: field stars, File 2: stars in galacticassociations and clusters, and stars in SMC, LMC, M33, File 3: numberedlist of bibliographical references The three files are only available inelectronic form at the Centre de Donnees Stellaires in Strasbourg, viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5), or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Intrinsic Energy Distribution in Stellar Spectra in the Wavelength Interval 320--760 NM
The intrinsic energy distributions in the interval 320--760 nm ofspectral types B5--G8 of luminosity V, F0--F5 of luminosity IV andG8--M2 of luminosity III, determined by authors, are intercompared withthe catalogue of the mean energy distribution data published bySviderskiene (1988).
| The photoelectric astrolabe catalogue of Yunnan Observatory (YPAC).
The positions of 53 FK5, 70 FK5 Extension and 486 GC stars are given forthe equator and equinox J2000.0 and for the mean observation epoch ofeach star. They are determined with the photoelectric astrolabe ofYunnan Observatory. The internal mean errors in right ascension anddeclination are +/- 0.046" and +/- 0.059", respectively. The meanobservation epoch is 1989.51.
| Chemical Abundances for Very Strong-Lined Giants
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....110.2968L&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.
| SMR stars, strong-CN stars and R stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1994RMxAA..29..103K&db_key=AST
| Carbon and nitrogen abundances determined from transition layer lines
The possibility of determining relative carbon, nitrogen, and siliconabundances from the emission-line fluxes in the lower transition layersbetween stellar chromospheres and coronae is explored. Observations formain-sequence and luminosity class IV stars with presumably solarelement abundances show that for the lower transition layers Em =BT-gamma. For a given carbon abundance the constants gammaand B in this relation can be determined from the C II and C IVemission-line fluxes. From the N V and S IV lines, the abundances ofthese elements relative to carbon can be determined from their surfaceemission-line fluxes. Ratios of N/C abundances determined in this wayfor some giants and supergiants agree within the limits of errors withthose determined from molecular bands. For giants, an increase in theratio of N/C at B-V of about 0.8 is found, as expected theoretically.
| The metallicity and luminosity of RV Tauri variables from medium-resolution spectra
Results are reported from spectroscopic observations of members of theRV Tauri class of pulsating variable stars at moderate resolution, andfrom photometric observations of these stars with the B and V filters ofthe Johnson UBV system and the first four filters of the Wingeight-color narrowband near-IR system. Of the 22 variables observed, TiOabsorption was detected in eight, and 10 variables displayedhydrogen-line emission at some phase. Spectral classifications wereassigned relative to the MK process. Color excesses were determined forthose variables for which spectroscopic and photometric data wereobtained within a few days of each other. The spectra obtained at aresolution of 2.5 A were fitted with synthetic spectra to determine thestellar atmospheric parameters. The range in metallicity among thevariables was found to be quite extensive, -0.3 to -0.7, and may reflecta mixture of stellar populations or masses.
| CA II H and K measurements made at Mount Wilson Observatory, 1966-1983
Summaries are presented of the photoelectric measurements of stellar CaII H and K line intensity made at Mount Wilson Observatory during theyears 1966-1983. These results are derived from 65,263 individualobservations of 1296 stars. For each star, for each observing season,the maximum, minimum, mean, and variation of the instrumental H and Kindex 'S' are given, as well as a measurement of the accuracy ofobservation. A total of 3110 seasonal summaries are reported. Factorswhich affect the ability to detect stellar activity variations andaccurately measure their amplitudes, such as the accuracy of the H and Kmeasurements and scattered light contamination, are discussed. Relationsare given which facilitate intercomparison of 'S' values with residualintensities derived from ordinary spectrophotometry, and for convertingmeasurements to absolute fluxes.
| Close binaries observed polarimetrically
Not Available
| High-resolution spectroscopic survey of 671 GK giants. I - Stellar atmosphere parameters and abundances
A high-resolution spectroscopic survey of 671 G and K field giants isdescribed. Broad-band Johnson colors have been calibrated againstrecent, accurate effective temperature, T(eff), measurements for starsin the range 3900-6000 K. A table of polynomial coefficients for 10color-T(eff) relations is presented. Stellar atmosphere parameters,including T(eff), log g, Fe/H, and microturbulent velocity, are computedfor each star, using the high-resolution spectra and various publishedphotometric catalogs. For each star, elemental abundances for a varietyof species have been computed using a LTE spectrum synthesis program andthe adopted atmosphere parameters.
| A search for lithium-rich giant stars
Lithium abundances or upper limits have been determined for 644 brightG-K giant stars selected from the DDO photometric catalog. Two of thesegiants possess surface lithium abundances approaching the 'cosmic' valueof the interstellar medium and young main-sequence stars, and eight moregiants have Li contents far in excess of standard predictions. At leastsome of these Li-rich giants are shown to be evolved to the stage ofhaving convectively mixed envelopes, either from the direct evidence oflow surface carbon isotope ratios, or from the indirect evidence oftheir H-R diagram positions. Suggestions are given for the uniqueconditions that might have allowed these stars to produce or accrete newlithium for their surface layers, or simply to preserve from destructiontheir initial lithium contents. The lithium abundance of the remainingstars demonstrates that giants only very rarely meet the expectations ofstandard first dredge-up theories; the average extra Li destructionrequired is about 1.5 dex. The evolutionary states of these giants andtheir average masses are discussed briefly, and the Li distribution ofthe giants is compared to predictions of Galactic chemical evolution.
| Stellar integrated fluxes in the wavelength range 380 NM - 900 NM derived from Johnson 13-colour photometry
Petford et al. (1988) have reported measured integrated fluxes for 216stars with a wide spread of spectral type and luminosity, and mentionedthat a cubic-spline integration over the relevant Johnson 13-colormagnitudes, converted to fluxes using Johnson's calibration, is inexcellent agreement with those measurements. In this paper a list of thefluxes derived in this way, corrected for a small dependence on B-V, isgiven for all the 1215 stars in Johnson's 1975 catalog with completeentries.
| Energy Distribution in the Stellar Spectra of Different Spectral Types and Luminosities - Part Five - Normal Stars
Not Available
| Spectroscopy and abundances of 88 K giants in Baade's Window
Spectroscopic and photometric observations of 122 stars in the Baade'sWindow region of the Galactic bulge (and of 63 K giant comparison starsin the Galactic disk and globular clusters), obtained using anintensified Reticon detector and a 600-line/mm 5000-A-blazed grating inthe Cassegrain spectrograph (spectral resolution 5 A) of the 2.5-mDuPont telescope at Las Campagnas Observatory during 1980-1984, arereported. The sample selection criteria and data-analysis techniques areexplained, and the data (including line strengths for 34 features andderived abundances for 88 K giants) are presented in extensive tablesand graphs and discussed in detail. It is concluded that the metalabundances in the nuclear-bulge strong-lined giants are significantlygreater than those of the metal-rich giants in the solar neighborhood.
| DDO, Cousins R-I, and photomultiplier scanner data for an analysis of very strong lined K giants
New DDO photometry and photomultiplier scanner data on a number ofsuper-metal-rich K giants are presented. The data provide information onblanketing, feature strengths, and stellar temperatures. Some of thescanner data are transformed to the Cousins R-I system and given withpreviously published measurements using this system.
| The 'Alternative X' question - What causes the strong molecular bands and damping lines in very strong lined (super-metal-rich) stars?
Absorption features in nearby, very strong lined (VSL) G and K stars areconsidered. Narrow-band blanketing is measured as well as broad-bandblanketing and the strong absorption features of CN, Ca I, CH, Mg I, andNa I. Data for Fe I and Ca II are analyzed for dwarfs. With theexception of CH in giants and Ca II in dwarfs, all the featuresconsidered are enhanced in typical VSL stars. The possibility that someVSL stars are super-metal-rich and the rest are explained by one or moreAlternatives X is examined.
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