Contents
Images
Upload your image
DSS Images Other Images
Related articles
Roche tomography of cataclysmic variables - III. Star-spots on AE Aqr
We present a Roche tomography reconstruction of the secondary star inthe cataclysmic variable AE Aqr. The tomogram reveals several surfaceinhomogeneities that are due to the presence of large, cool star-spots.In addition to a number of lower latitude spots, the maps also show thepresence of a large, high-latitude spot similar to that seen in Dopplerimages of rapidly rotating isolated stars, and a relative paucity ofspots at a latitude of 40°. In total, we estimate that some 18 percent of the Northern hemisphere of AE Aqr is spotted.We have also applied the entropy landscape technique to determineaccurate parameters for the binary system. We obtain optimal massesM1 = 0.74Msolar, M2 =0.50Msolar, a systemic velocity γ = -63kms-1and an orbital inclination i = 66°.Given that this is the first study to successfully image star-spots onthe secondary star in a cataclysmic variable, we discuss the role thatfurther studies of this kind may play in our understanding of thesebinaries.
| Spectroscopic Properties of Cool Stars (SPOCS). I. 1040 F, G, and K Dwarfs from Keck, Lick, and AAT Planet Search Programs
We present a uniform catalog of stellar properties for 1040 nearby F, G,and K stars that have been observed by the Keck, Lick, and AAT planetsearch programs. Fitting observed echelle spectra with synthetic spectrayielded effective temperature, surface gravity, metallicity, projectedrotational velocity, and abundances of the elements Na, Si, Ti, Fe, andNi, for every star in the catalog. Combining V-band photometry andHipparcos parallaxes with a bolometric correction based on thespectroscopic results yielded stellar luminosity, radius, and mass.Interpolating Yonsei-Yale isochrones to the luminosity, effectivetemperature, metallicity, and α-element enhancement of each staryielded a theoretical mass, radius, gravity, and age range for moststars in the catalog. Automated tools provide uniform results and makeanalysis of such a large sample practical. Our analysis method differsfrom traditional abundance analyses in that we fit the observed spectrumdirectly, rather than trying to match equivalent widths, and wedetermine effective temperature and surface gravity from the spectrumitself, rather than adopting values based on measured photometry orparallax. As part of our analysis, we determined a new relationshipbetween macroturbulence and effective temperature on the main sequence.Detailed error analysis revealed small systematic offsets with respectto the Sun and spurious abundance trends as a function of effectivetemperature that would be inobvious in smaller samples. We attempted toremove these errors by applying empirical corrections, achieving aprecision per spectrum of 44 K in effective temperature, 0.03 dex inmetallicity, 0.06 dex in the logarithm of gravity, and 0.5 kms-1 in projected rotational velocity. Comparisons withprevious studies show only small discrepancies. Our spectroscopicallydetermined masses have a median fractional precision of 15%, but theyare systematically 10% higher than masses obtained by interpolatingisochrones. Our spectroscopic radii have a median fractional precisionof 3%. Our ages from isochrones have a precision that variesdramatically with location in the Hertzsprung-Russell diagram. We planto extend the catalog by applying our automated analysis technique toother large stellar samples.
| The Planet-Metallicity Correlation
We have recently carried out spectral synthesis modeling to determineTeff, logg, vsini, and [Fe/H] for 1040 FGK-type stars on theKeck, Lick, and Anglo-Australian Telescope planet search programs. Thisis the first time that a single, uniform spectroscopic analysis has beenmade for every star on a large Doppler planet search survey. We identifya subset of 850 stars that have Doppler observations sufficient todetect uniformly all planets with radial velocity semiamplitudes K>30m s-1 and orbital periods shorter than 4 yr. From this subsetof stars, we determine that fewer than 3% of stars with-0.5<[Fe/H]<0.0 have Doppler-detected planets. Above solarmetallicity, there is a smooth and rapid rise in the fraction of starswith planets. At [Fe/H]>+0.3 dex, 25% of observed stars have detectedgas giant planets. A power-law fit to these data relates the formationprobability for gas giant planets to the square of the number of metalatoms. High stellar metallicity also appears to be correlated with thepresence of multiple-planet systems and with the total detected planetmass. This data set was examined to better understand the origin of highmetallicity in stars with planets. None of the expected fossilsignatures of accretion are observed in stars with planets relative tothe general sample: (1) metallicity does not appear to increase as themass of the convective envelopes decreases, (2) subgiants with planetsdo not show dilution of metallicity, (3) no abundance variations for Na,Si, Ti, or Ni are found as a function of condensation temperature, and(4) no correlations between metallicity and orbital period oreccentricity could be identified. We conclude that stars with extrasolarplanets do not have an accretion signature that distinguishes them fromother stars; more likely, they are simply born in higher metallicitymolecular clouds.Based on observations obtained at Lick and Keck Observatories, operatedby the University of California, and the Anglo-Australian Observatories.
| Chromospheric Ca II Emission in Nearby F, G, K, and M Stars
We present chromospheric Ca II H and K activity measurements, rotationperiods, and ages for ~1200 F, G, K, and M type main-sequence stars from~18,000 archival spectra taken at Keck and Lick Observatories as a partof the California and Carnegie Planet Search Project. We have calibratedour chromospheric S-values against the Mount Wilson chromosphericactivity data. From these measurements we have calculated medianactivity levels and derived R'HK, stellar ages,and rotation periods from general parameterizations for 1228 stars,~1000 of which have no previously published S-values. We also presentprecise time series of activity measurements for these stars.Based on observations obtained at Lick Observatory, which is operated bythe University of California, and on observations obtained at the W. M.Keck Observatory, which is operated jointly by the University ofCalifornia and the California Institute of Technology. The KeckObservatory was made possible by the generous financial support of theW. M. Keck Foundation.
| 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.
| Statistical cataloging of archival data for luminosity class IV-V stars. II. The epoch 2001 [Fe/H] catalog
This paper describes the derivation of an updated statistical catalog ofmetallicities. The stars for which those metallicities apply are ofspectral types F, G, and K, and are on or near the main sequence. Theinput data for the catalog are values of [Fe/H] published before 2002February and derived from lines of weak and moderate strength. Theanalyses used to derive the data have been based on one-dimensional LTEmodel atmospheres. Initial adjustments which are applied to the datainclude corrections to a uniform temperature scale which is given in acompanion paper (see Taylor \cite{t02}). After correction, the data aresubjected to a statistical analysis. For each of 941 stars considered,the results of that analysis include a mean value of [Fe/H], an rmserror, an associated number of degrees of freedom, and one or moreidentification numbers for source papers. The catalog of these resultssupersedes an earlier version given by Taylor (\cite{t94b}).Catalog is only available in electronic form at the CDS via anonymousftp cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/398/731
| Statistical cataloging of archival data for luminosity class IV-V stars. I. The epoch 2001 temperature catalog
This paper is one of a pair in which temperatures and metallicitycatalogs for class IV-V stars are considered. The temperature catalogdescribed here is derived from a calibration based on stellar angulardiameters. If published calibrations of this kind are compared by usingcolor-index transformations, temperature-dependent differences among thecalibrations are commonly found. However, such differences are minimizedif attention is restricted to calibrations based on Johnson V-K. Acalibration of this sort from Di Benedetto (\cite{dib98}) is thereforetested and adopted. That calibration is then applied to spectroscopicand photometric data, with the latter predominating. Cousins R-Iphotometry receives special attention because of its high precision andlow metallicity sensitivity. Testing of temperatures derived from thecalibration suggests that their accuracy and precision are satisfactory,though further testing will be warranted as new results appear. Thesetemperatures appear in the catalog as values of theta equiv5040/T(effective). Most of these entries are accompanied by measured orderived values of Cousins R-I. Entries are given for 951 stars.Catalog is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/398/721
| The radii and spectra of the nearest stars
We discuss direct measurements of the radii of 36 stars located closerthan 25 parsecs to the Sun. We present the data on 307 radii and 326spectral types and luminosity classes for the nearest stars locatedinside the sphere with a radius of 10 parsecs.
| 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.
| The ISO-SWS post-helium atlas of near-infrared stellar spectra
We present an atlas of near-infrared spectra (2.36 mu m-4.1 mu m) of ~300 stars at moderate resolution (lambda /delta lambda ~ 1500-2000). Thespectra were recorded using the Short-Wavelength Spectrometer aboard theInfrared Space Observatory (ISO-SWS). The bulk of the observations wereperformed during a dedicated observation campaign after the liquidhelium depletion of the ISO satellite, the so-called post-heliumprogramme. This programme was aimed at extending the MK-classificationto the near-infrared. Therefore the programme covers a large range ofspectral types and luminosity classes. The 2.36 mu m-4.05 mu m region isa valuable spectral probe for both hot and cool stars. H I lines(Bracket, Pfund and Humphreys series), He I and He II lines, atomiclines and molecular lines (CO, H2O, NH, OH, SiO, HCN,C2H2, ...) are sensitive to temperature, gravityand/or the nature of the outer layers of the stellar atmosphere(outflows, hot circumstellar discs, etc.). Another objective of theprogramme was to construct a homogeneous dataset of near-infraredstellar spectra that can be used for population synthesis studies ofgalaxies. At near-infrared wavelengths these objects emit the integratedlight of all stars in the system. In this paper we present the datasetof post-helium spectra completed with observations obtained during thenominal operations of the ISO-SWS. We discuss the calibration of the SWSdata obtained after the liquid helium boil-off and the data reduction.We also give a first qualitative overview of how the spectral featuresin this wavelength range change with spectral type. The dataset isscrutinised in two papers on the quantitative classification ofnear-infrared spectra of early-type stars ({Lenorzer} et al.\cite{lenorzer:2002a}) and late-type stars (Vandenbussche et al., inprep). Based on observations with ISO, an ESA project with instrumentsfunded by ESA Members States (especially the PI countries France,Germany, the Netherlands and the United Kingdom) and with theparticipation of ISAS and NASA. The full atlas is available inelectronic form at www.edpsciences.org Table 1 is only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?/A+A/390/1033
| Planetary Companions to HD 12661, HD 92788, and HD 38529 and Variations in Keplerian Residuals of Extrasolar Planets
Precision Doppler observations at the Lick and Keck observatories haverevealed Keplerian velocity variations in the stars HD 12661, HD 92788,and HD 38529. HD 12661 (G6 V) has an orbital period of 252.7+/-2.7 days,velocity semiamplitude K=88.4+/-2.0 m s-1, and orbitaleccentricity e=0.23+/-0.024. Adopting a stellar mass of 1.07Msolar, we infer a companion mass of Msini=2.79 MJand a semimajor axis of a=0.79 AU. HD 92788 (G5 V) has an orbital periodof 326.7+/-3.2 days, velocity semiamplitude K=99.9+/-2.4, and orbitaleccentricity e=0.30+/-0.06. The adopted stellar mass of 1.06Msolar yields a companion mass of Msini=3.34 MJand a semimajor axis of a=0.95 AU. HD 38529 (G4 IV) has an orbitalperiod of 14.3+/-0.8 days, velocity semiamplitude K=53.8+/-2.0 ms-1, and eccentricity e=0.27+/-0.03. The stellar mass of 1.4Msolar sets Msini=0.77 MJ, with a semimajor axisof a=0.13 AU for this companion. In addition to the 14.3 dayperiodicity, the velocity residuals for HD 38529 show curvature over thethree years of observations. Based on a measurement of Ca II H and Kemission, all three stars are chromospherically inactive. Based on bothspectral synthesis modeling and narrowband photometry, HD 12661, HD92788, and HD 38529 all appear to be metal-rich stars, reinforcing thecorrelation of high metallicity in the host stars of gas giantextrasolar planets. We examine the velocity residuals to the Keplerianfits for a subsample of 12 planet-bearing stars that have been observedlonger than two years at the Lick Observatory. Five of the 12 (UpsAndromedae, τ Boo, 55 Cnc, HD 217107, and HD 38529) exhibit coherentvariations in the residual velocities that are consistent withadditional companions. Except for Upsilon Andromedae, the source of thevelocity variation remains speculative pending completion of one fullorbit. GJ 876 exhibits residual velocities with high rms scatter (24 ms-1), lacking identifiable coherence. The residual velocitiesfor six of the 12 stars (51 Peg, 70 Vir, 16 Cyg B, ρ CrB, 47 UMa,and HD 195019) exhibit rms velocity scatter of ~7 m s-1,consistent with errors. The residual velocity trends suggest that knownplanet-bearing stars appear to harbor a distant (>3 AU) detectablecompanion more often than other stars in our planet survey. Based onobservations obtained at the Lick Observatory, which is operated by theUniversity of California, and on observations obtained at the W. M. KeckObservatory, which is operated jointly by the University of Californiaand the California Institute of Technology.
| 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
| Six New Planets from the Keck Precision Velocity Survey
We report results of a search for planets around 530 main-sequence starsusing the Keck HIRES spectrometer, which has provided Doppler precisionof 3 m s-1 during the past 3 yr. We report six new strongplanet candidates having complete Keplerian orbits, with periods rangingfrom 24 days to 3 yr. These are HD 10697, HD 37124, HD 134987, HD177830, HD 192263, and HD 222582. We also provide updated orbitalparameters for the previously announced planets around HD 187123, HD195019, HD 201277, and HD 217107. Four of the six newly discoveredplanets have minimum Msini masses less than 2 MJUP, while theremaining two have Msini~5 MJUP. The distribution ofplanetary masses continues to exhibit a rise toward lower masses. Theorbital eccentricities of the new planets range from 0.12 to 0.71, whichalso continues the ubiquity of high eccentricities. All 17 knownextrasolar planets orbiting beyond 0.2 AU have eccentricities greaterthan ~0.1. The current limiting Doppler precision of the Keck Dopplersurvey is 3 m s-1 per observation as determined fromobservations of both stable stars and residuals to Keplerian fits. Basedon observations obtained at the W. M. Keck Observatory, which isoperated jointly by the University of California and the CaliforniaInstitute of Technology. Keck Telescope time comes from both NASA andthe University of California.
| Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions
The FK6 is a suitable combination of the results of the HIPPARCOSastrometry satellite with ground-based data, measured over more than twocenturies and summarized in the FK5. Part I of the FK6 (abbreviatedFK6(I)) contains 878 basic fundamental stars with direct solutions. Suchdirect solutions are appropriate for single stars or for objects whichcan be treated like single stars. From the 878 stars in Part I, we haveselected 340 objects as "astrometrically excellent stars", since theirinstantaneous proper motions and mean (time-averaged) ones do not differsignificantly. Hence most of the astrometrically excellent stars arewell-behaving "single-star candidates" with good astrometric data. Thesestars are most suited for high-precision astrometry. On the other hand,199 of the stars in Part I are Δμ binaries in the sense ofWielen et al. (1999). Many of them are newly discovered probablebinaries with no other hitherto known indication of binarity. The FK6gives, besides the classical "single-star mode" solutions (SI mode),other solutions which take into account the fact that hidden astrometricbinaries among "apparently single-stars" introduce sizable "cosmicerrors" into the quasi-instantaneously measured HIPPARCOS proper motionsand positions. The FK6 gives in addition to the SI mode the "long-termprediction (LTP) mode" and the "short-term prediction (STP) mode". TheseLTP and STP modes are on average the most precise solutions forapparently single stars, depending on the epoch difference with respectto the HIPPARCOS epoch of about 1991. The typical mean error of anFK6(I) proper motion in the single-star mode is 0.35 mas/year. This isabout a factor of two better than the typical HIPPARCOS errors for thesestars of 0.67 mas/year. In the long-term prediction mode, in whichcosmic errors are taken into account, the FK6(I) proper motions have atypical mean error of 0.50 mas/year, which is by a factor of more than 4better than the corresponding error for the HIPPARCOS values of 2.21mas/year (cosmic errors included).
| The Lick Planet Search: Detectability and Mass Thresholds
We present an analysis of 11 yr of precision radial velocitymeasurements of 76 nearby solar-type stars from the Lick radial velocitysurvey. For each star, we report on variability, periodicity, andlong-term velocity trends. Our sample of stars contains eight knowncompanions with mass (Mpsini) less than 8 Jupiter masses(MJ), six of which were discovered at Lick. For the remainingstars, we place upper limits on the companion mass as a function oforbital period. For most stars, we can exclude companions with velocityamplitude K>~20 m s-1 at the 99% level, orMpsini>~0.7MJ(a/AU)1/2 for orbitalradii a<~5 AU. We examine the implications of our results for theobserved distribution of mass and orbital radius of companions. We showthat the combination of intrinsic stellar variability and measurementerrors most likely explains why all confirmed companions so far haveK>~40 m s-1. The finite duration of the observationslimits detection of Jupiter-mass companions to a<~3 AU. Thus itremains possible that the majority of solar-type stars harborJupiter-mass companions much like our own, and if so these companionsshould be detectable in a few years. It is striking that more massivecompanions with Mpsini>3MJ are rare at orbitalradii 4-6 AU; we could have detected such objects in ~90% of stars, yetfound none. The observed companions show a ``piling-up'' toward smallorbital radii, and there is a paucity of confirmed and candidatecompanions with orbital radii between ~0.2 and ~1 AU. The small numberof confirmed companions means that we are not able to rule out selectioneffects as the cause of these features. We show that the traditionalmethod for detecting periodicities, the Lomb-Scargle periodogram, failsto account for statistical fluctuations in the mean of a sampledsinusoid, making it nonrobust when the number of observations is small,the sampling is uneven, or for periods comparable to or greater than theduration of the observations. We adopt a ``floating-mean'' periodogram,in which the zero point of the sinusoid is allowed to vary during thefit. We discuss in detail the normalization of the periodogram and theprobability distribution of periodogram powers. We stress that the threedifferent prescriptions in the literature for normalizing theperiodogram are statistically equivalent and that it is not possible towrite a simple analytic form for the false alarm probability, makingMonte Carlo methods essential.
| The Tokyo PMC catalog 90-93: Catalog of positions of 6649 stars observed in 1990 through 1993 with Tokyo photoelectric meridian circle
The sixth annual catalog of the Tokyo Photoelectric Meridian Circle(PMC) is presented for 6649 stars which were observed at least two timesin January 1990 through March 1993. The mean positions of the starsobserved are given in the catalog at the corresponding mean epochs ofobservations of individual stars. The coordinates of the catalog arebased on the FK5 system, and referred to the equinox and equator ofJ2000.0. The mean local deviations of the observed positions from theFK5 catalog positions are constructed for the basic FK5 stars to comparewith those of the Tokyo PMC Catalog 89 and preliminary Hipparcos resultsof H30.
| Metallicities and kinematics of G and K dwarfs
We have used accurate, spectroscopically determined abundances for G andK dwarfs of Morell, Kallander & Butcher and Morell to derive aphotometric abundance index for G and K dwarfs. Broad-band Cousins R-Iphotometry is used to estimate effective temperature and the Geneva b_1colour to estimate line blanketing in the blue and hence abundance.Abundances can be derived in the range -2.0<[Fe/H]<0.5 for G0 toK3 dwarfs, with a scatter in [Fe/H] of 0.2 dex. We apply the method to asample of Gliese catalogue G and K dwarfs, and examine the metallicityand kinematic properties of the stars. The stars show thewell-established observational features of the disc, thick disc and haloin the solar neighbourhood. We find that the distribution of local Kdwarf metallicity is quite similar to that of local G dwarfs, indicatingthat there is a `K dwarf' as well as a G dwarf problem.
| Discrete Classification with Principal Component Analysis: Discrimination of Giant and Dwarf Spectra in K Stars
We demonstrate the use of a variant of Principal Component Analysis(PCA) for discrimination problems in astronomy. This variant of PCA isshown to provide the best linear discrimination between data classes. Asa test case, we present the problem of discrimination between K giantand K dwarf stars from intermediate resolution spectra near the Mg `b'feature. The discrimination procedure is trained on a set of 24 standardK giants and 24 standard K dwarfs, and then used to perform giant -dwarf classification on a sample of ~ 1500 field K stars of unknownluminosity class which were initially classified visually. For thehighest S/N spectra, the automated classification agrees very well (atthe 90 - 95% level) with the visual classification. Most importantly,however, the automated method is found to classify stars in a repeatablefashion, and, according to numerical experiments, is very robust tosignal to noise (S/N) degradation.
| Reality Tests of Superclusters in the Young Disk Population
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....110.2862E&db_key=AST
| Ca II H and K Filter Photometry on the UVBY System. II. The Catalog of Observations
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....109.2828T&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.
| Optical Polarization of 1000 Stars Within 50-PARSECS from the Sun
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&AS..101..551L&db_key=AST
| The importance of surface inhomogeneities for K and M dwarf chromospheric fluxes
We present published and archived spectroscopic and spectrophotometricdata of H-alpha, Ca II, Mg II, and X-rays for a large sample of K and Mdwarfs. The data set points to the importance that surfaceinhomogeneities have in the flux luminosity diagrams in these late-typedwarfs, irrespective of whether the Balmer lines are in emission orabsorption. Although supporting the fact that cooler stars exhibitincreasing levels of surface activity, evident through an increasingincidence of Balmer emission, surface inhomogeneities, or variations inthe local temperature and density structure, at the chromospheric level,dominate the total Ca II and Mg II fluxes. We show that the flux-fluxand luminosity-luminosity relations indicate differing extents ofinhomogeneity from the chromosphere through to the corona. A goodcorrelation between Ca II and Mg II fluxes indicates that they areformed in overlapping regions of the chromosphere, so that thecontribution of surface inhomogeneities is not evident from thisparticular flux-flux diagram. In the region of the upper chromospherethrough to the transition and corona, the correlation between Ly-alphaand X-ray fluxes indicates regions with similar levels of arealinhomogeneity. This appears to be uncorrelated with that at thechromospheric level.
| Santiago Fundamental Catalogue - A catalogue of 1105 FK5 stars (equinox J2000.0)
The positions in right ascension and declination of 1105 FK5 stars,observed with a Meridian Circle during the period 1979 to 1991, aregiven. The average mean square error of a position, for the wholecatalog, is +/- 0.009 s in right ascension and +/- 0.10 arcsec indeclination. The mean epoch of the catalog is 1983.148.
| Ca II H and K filter photometry on the UVBY system. I - The standard system
A fifth filter (fwhm = 90 A) centered on Ca II H and K has beendeveloped for use with the standard uvby system. The filter, called Ca,is designed primarily for applications to metal-poor dwarfs and redgiants, regions where the uvby metallicity index, m(l), loses somesensitivity. An index, hk, is defined by replacing v in m(l) by Ca. Theeffects of interstellar extinction on the index are modeled anddemonstrated to be modest and relatively insensitive to spectral type.Observations of V, (b-y), and hk for 163 primary standards are detailedand transformed to the standard V and (b-y) system. A qualitativeanalysis using only the primary standards indicates that hk is moresensitive than m(l) over the regions of interest by about a factor of 3.
| Photographic astrometry of binary and proper-motion stars. VI
Results are reported from observations of 85 parallax stars, obtained onphotographic plates on over 5000 nights using the Sproul refractor atSwarthmore College Observatory. The trigonometric parallaxes determinedfrom the plates are presented in tables and briefly characterized. Alsoprovided are the calculated mass ratios for 13 binary stars in thesample.
| H-alpha absolute chromospheric fluxes in G and K dwarfs and subgiants
High resolution, high S/N H-alpha observations for a sample of 85 dwarfsand subgiants of spectral type F8 to K5 are presented. A calibrationprocedure to convert the observed equivalent widths to absolute fluxesat the stellar surface is developed and these fluxes are compared withthose obtained in the Ca II K line are compared. Within the observedrange of spectral types there is some evidence that the ratio of H-alphato Ca II K line fluxes increases toward cooler stars, suggesting thatthis effect, which is prominent in M dwarfs, is already significant forK stars. For G and early K stars the H-alpha flux is found to increasewith increasing activity more slowly than the Ca II K flux, givingflux-flux relationships that are similar to those observed for solarplages. It is also found that all subgiants in the sample have very lowH-alpha fluxes, typically lower than for dwarfs of the same spectraltype. The survey clearly shows that the H-alpha line, although being auseful diagnostic of stellar chromospheres, and easily accessible tomodern solid-state detectors, is not particularly suitable for anaccurate determination of absolute chromospheric fluxes.
| Physical data of the fundamental stars.
Not Available
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
| Constellation: | Verseau |
| Right ascension: | 21h58m55.00s |
| Declination: | -04°22'23.0" |
| Apparent magnitude: | 6.22 |
| Distance: | 36.01 parsecs |
| Proper motion RA: | -2.1 |
| Proper motion Dec: | -253.6 |
| B-T magnitude: | 7.517 |
| V-T magnitude: | 6.342 |
Catalogs and designations:
|
