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Potential Members of Stellar Kinematic Groups within 30 pc of the Sun
We analyze the kinematic histories of stars within 30 pc of the Sun, forwhich three-dimensional spatial coordinates and three-dimensionalvelocity vectors are available. From this sample, we extract members ofstellar kinematic groups (SKGs) in the following manner. First, weconsider in the three-dimensional velocity space centered on the localstandard of rest, a sphere with a radius of 8 km s-1centered on the mean velocity vector of a particular SKG. Around eachSKG velocity center, we have found a significant excess of starscompared to background field stars. For each candidate, in thethree-dimensional spatial coordinate space, its trajectory is tracedback in time by the age of the relevant SKG to obtain the estimateddistance from the SKG center at the time of the SKG's birth by theepicyclic approximation and harmonic vertical motion. It often happensthat a star is a candidate member of multiple SKGs. Then we rank thecandidacy to multiple SKGs based on the smallness of distanceseparations. In this manner, we have kinematically selected 238candidates. We further impose at least one of the following qualitativecriteria for being a member: spectral type A or B, variability, or EUVand X-ray emission. We have finally selected 137 candidate members ofSKGs out of a sample of 966 stars.
| Effect of magnetic activity saturation in chromospheric flux-flux relationships
We present a homogeneous study of chromospheric and coronal flux-fluxrelationships using a sample of 298 late-type dwarf active stars withspectral types F to M. The chromospheric lines were observedsimultaneously in each star to avoid spread as a result of long-termvariability. Unlike other works, we subtract the basal chromosphericcontribution in all the spectral lines studied. For the first time, wequantify the departure of dMe stars from the general relations. We showthat dK and dKe stars also deviate from the general trend. Studying theflux-colour diagrams, we demonstrate that the stars deviating from thegeneral relations are those with saturated X-ray emission and we showthat these stars also present saturation in the H? line. Usingseveral age spectral indicators, we show that these are younger starsthan those following the general relationships. The non-universality offlux-flux relationships found in this work should be taken into accountwhen converting between fluxes in different chromospheric activityindicators.
| A Photometric Variability Survey of Field K and M Dwarf Stars with HATNet
Using light curves from the HATNet survey for transiting extrasolarplanets we investigate the optical broadband photometric variability ofa sample of 27, 560 field K and M dwarfs selected by color and propermotion (V - K >~ 3.0, ? > 30 mas yr-1, plusadditional cuts in J - H versus H - KS and on the reducedproper motion). We search the light curves for periodic variations andfor large-amplitude, long-duration flare events. A total of 2120 starsexhibit potential variability, including 95 stars with eclipses and 60stars with flares. Based on a visual inspection of these light curvesand an automated blending classification, we select 1568 stars,including 78 eclipsing binaries (EBs), as secure variable stardetections that are not obvious blends. We estimate that a further ~26%of these stars may be blends with fainter variables, though most ofthese blends are likely to be among the hotter stars in our sample. Wefind that only 38 of the 1568 stars, including five of the EBs, havepreviously been identified as variables or are blended with previouslyidentified variables. One of the newly identified EBs is 1RXSJ154727.5+450803, a known P = 3.55 day, late M-dwarf SB2 system, forwhich we derive preliminary estimates for the component masses and radiiof M 1 = M 2 = 0.258 ± 0.008 Msun and R 1 = R 2 = 0.289 ±0.007 R sun. The radii of the component stars are larger thantheoretical expectations if the system is older than ~200 Myr. Themajority of the variables are heavily spotted BY Dra-type stars forwhich we determine rotation periods. Using this sample, we investigatethe relations between period, color, age, and activity measures,including optical flaring, for K and M dwarfs, finding that many of thewell-established relations for F, G, and K dwarfs continue into the Mdwarf regime. We find that the fraction of stars that is variable withpeak-to-peak amplitudes greater than 0.01 mag increases exponentiallywith the V - KS color such that approximately half of fielddwarfs in the solar neighborhood with M <~ 0.2 M sun arevariable at this level. Our data hint at a change in therotation-activity-age connection for stars with M <~ 0.25 Msun.
| A high-resolution spectroscopic survey of late-type stars: chromospheric activity, rotation, kinematics, and age
Aims: We present a compilation of spectroscopic data from asurvey of 144 chromospherically active young stars in the solarneighborhood, which may be used to investigate different aspects of itsformation and evolution in terms of kinematics and stellar formationhistory. The data have already been used by us in several studies. Withthis paper, we make all these data accessible to the scientificcommunity for future studies on different topics. Methods: Weperformed spectroscopic observations with echelle spectrographs to coverthe entirety of the optical spectral range simultaneously. Standard datareduction was performed with the IRAF echelle package. We applied thespectral subtraction technique to reveal chromospheric emission in thestars of the sample. The equivalent width of chromospheric emissionlines was measured in the subtracted spectra and then converted tofluxes using equivalent width-flux relationships. Radial and rotationalvelocities were determined by the cross-correlation technique.Kinematics, equivalent widths of the lithium line ?6707.8 Åand spectral types were also determined. Results: A catalog ofspectroscopic data is compiled: radial and rotational velocities, spacemotion, equivalent widths of optical chromospheric activity indicatorsfrom Ca II H & K to the calcium infrared triplet and the lithiumline in ?6708 Å. Fluxes in the chromospheric emission linesand R'_HK are also determined for each observation of a star in thesample. We used these data to investigate the emission levels of ourstars. The study of the H? emission line revealed two differentpopulations of chromospheric emitters in the sample, clearly separatedin the logFH?/Fbol - (V-J) diagram. Thedichotomy may be associated with the age of the stars.Based on observations made with the 2.2 m telescope of theGerman-Spanish Astronomical Centre, Calar Alto (Almería, Spain),operated jointly by the Max-Planck-Institute for Astronomy, Heidelberg,and the Spanish National Commission for Astronomy; the Nordic OpticalTelescope (NOT), operated on the island of La Palma jointly by Denmark,Finland, Iceland, Norway and Sweden, in the Spanish Observatorio delRoque de Los Muchachos of the Instituto de Astrofísica deCanarias; the Isaac Newton Telescope (INT) operated on the island of LaPalma by the Isaac Newton Group in the Spanish Observatorio del Roque deLos Muchachos of the Instituto de Astrofísica de Canarias; withthe Italian Telescopio Nazionale Galileo (TNG) operated on the island ofLa Palma by the Centro Galileo Galilei of the INAF (Istituto Nazionaledi Astrofisica) at the Spanish Observatorio del Roque de Los Muchachosof the Instituto de Astrofísica de Canarias; and with theHobby-Eberly Telescope (HET) operated by McDonald Observatory on behalfof The University of Texas at Austin, the Pennsylvania State University,Stanford University, Ludwig-Maximilians-Universität München,and Georg-August-Universität Göttingen. This research has madeuse of the SIMBAD database and VizieR catalog access tool, operated atCDS, Strasbourg, France.Tables A.1-A.4 and reduced spectra are alsoavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/514/A97
| The main sequence from F to K stars of the solar neighbourhood in SDSS colours
For an understanding of Galactic stellar populations in the SDSS filtersystem well defined stellar samples are needed. The nearby stars providea complete stellar sample representative for the thin disc population.We compare the filter transformations of different authors applied tothe main sequence stars from F to K dwarfs to SDSS filter system anddiscuss the properties of the main sequence. The location of the meanmain sequence in colour-magnitude diagrams is very sensitive tosystematic differences in the filter transformation. A comparison withfiducial sequences of star clusters observed in g', r', and i' show goodagreement. Theoretical isochrones from Padua and from Dartmouth havestill some problems, especially in the (r-i) colours.
| The effect of activity on stellar temperatures and radii
Context: Recent analyses of low-mass eclipsing binary stars haveunveiled a significant disagreement between the observations andpredictions of stellar structure models. Results show that theoreticalmodels underestimate the radii and overestimate the effectivetemperatures of low-mass stars but yield luminosities that accord withobservations. A hypothesis based upon the effects of stellar activitywas put forward to explain the discrepancies. Aims: In this paper westudy the existence of the same trend in single active stars and providea consistent scenario to explain systematic differences between activeand inactive stars in the H-R diagram reported earlier. Methods: Theanalysis is done using single field stars of spectral types late-K and Mand computing their bolometric magnitudes and temperatures throughinfrared colours and spectral indices. The properties of the stars insamples of active and inactive stars are compared statistically toreveal systematic differences. Results: After accounting for a numberof possible bias effects, active stars are shown to be cooler thaninactive stars of similar luminosity therefore implying a larger radiusas well, in proportions that are in excellent agreement with those foundfrom eclipsing binaries. Conclusions: The present results generalisethe existence of strong radius and temperature dependences on stellaractivity to the entire population of low-mass stars, regardless of theirmembership in close binary systems.Tables 1 and 2 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/478/507
| New Distant Companions to Known Nearby Stars. II. Faint Companions of Hipparcos Stars and the Frequency of Wide Binary Systems
We perform a search for faint, common proper motion companions ofHipparcos stars using the recently published Lépine-Shara ProperMotion-North catalog of stars with proper motionμ>0.15'' yr-1. Our survey uncovers a totalof 521 systems with angular separations3''<Δθ<1500'', with 15 triplesand 1 quadruple. Our new list of wide systems with Hipparcos primariesincludes 130 systems identified here for the first time, including 44 inwhich the secondary star has V>15.0. Our census is statisticallycomplete for secondaries with angular separations20''<Δθ<300'' and apparentmagnitudes V<19.0. Overall, we find that at least 9.5% of nearby(d<100 pc) Hipparcos stars have distant stellar companions withprojected orbital separations s>1000 AU. We observe that thedistribution in orbital separations is consistent with Öpik's law,f(s)ds~s-1ds, only up to a separation s~4000 AU, beyond whichit follows a more steeply decreasing power law f(s)ds~s-ldswith l=1.6+/-0.1. We also find that the luminosity function of thesecondaries is significantly different from that of the single stars'field population, showing a relative deficiency in low-luminosity(8
| Multicolour CCD measurements of visual double and multiple stars. III
Context: Recent CCD observations were performed in the period 1998-2004for a large sample of visual double and multiple stars selected from theHipparcos Catalogue and/or from the Gliese Catalogue of Nearby Stars. Aims: Accurate astrometric and photometric data allowing us tocharacterise the individual components are provided. These data arecompared to Hipparcos data or to data from an older epoch to assess thenature of the observed systems. Methods: We simultaneously apply aMoffat-Lorentz profile with a similar shape to all detected componentsand adjust the profile parameters from which we obtain the relativeastrometric position (epoch, position angle, angular separation) as wellas differential multi-colour photometry (filters (B)VRI). Results: Wethus acquired recent data for 71 visual systems of which 6 are orbitalbinaries, 27 are nearby, and 30 are multiple systems. In three of thesecases, the systems remained unresolved. 23 new components were detectedand measured. Two new visual double stars of intermediate separationwere also found. The estimated accuracies in relative position are0.04° and 0.01 arcsec respectively, while those in differentialphotometry are of the order of 0.01-0.02 mag in general. Conclusions:.The nature of the association of 55 systems is evaluated. New basicbinary properties are derived for 20 bound systems. Component coloursand masses are provided for two orbital binaries.Based on observations collected at the National AstronomicalObservatory, Rozhen, and the Astronomical Observatory, Belogradchik,both operated by the Institute of Astronomy, Bulgarian Academy ofSciences. Also based on data obtained by the Hipparcos astrometrysatellite. Appendix A is only available in electronic form athttp://www.aanda.org Tables 4-6 are only 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/464/641
| A Catalog of Northern Stars with Annual Proper Motions Larger than 0.15" (LSPM-NORTH Catalog)
The LSPM catalog is a comprehensive list of 61,977 stars north of theJ2000 celestial equator that have proper motions larger than 0.15"yr-1 (local-background-stars frame). The catalog has beengenerated primarily as a result of our systematic search for high propermotion stars in the Digitized Sky Surveys using our SUPERBLINK software.At brighter magnitudes, the catalog incorporates stars and data from theTycho-2 Catalogue and also, to a lesser extent, from the All-SkyCompiled Catalogue of 2.5 million stars. The LSPM catalog considerablyexpands over the old Luyten (Luyten Half-Second [LHS] and New LuytenTwo-Tenths [NLTT]) catalogs, superseding them for northern declinations.Positions are given with an accuracy of <~100 mas at the 2000.0epoch, and absolute proper motions are given with an accuracy of ~8 masyr-1. Corrections to the local-background-stars propermotions have been calculated, and absolute proper motions in theextragalactic frame are given. Whenever available, we also give opticalBT and VT magnitudes (from Tycho-2, ASCC-2.5),photographic BJ, RF, and IN magnitudes(from USNO-B1 catalog), and infrared J, H, and Ks magnitudes(from 2MASS). We also provide an estimated V magnitude and V-J color fornearly all catalog entries, useful for initial classification of thestars. The catalog is estimated to be over 99% complete at high Galacticlatitudes (|b|>15deg) and over 90% complete at lowGalactic latitudes (|b|>15deg), down to a magnitudeV=19.0, and has a limiting magnitude V=21.0. All the northern starslisted in the LHS and NLTT catalogs have been reidentified, and theirpositions, proper motions, and magnitudes reevaluated. The catalog alsolists a large number of completely new objects, which promise to expandvery significantly the census of red dwarfs, subdwarfs, and white dwarfsin the vicinity of the Sun.Based on data mining of the Digitized Sky Surveys (DSSs), developed andoperated by the Catalogs and Surveys Branch of the Space TelescopeScience Institute (STScI), Baltimore.Developed with support from the National Science Foundation (NSF), aspart of the NASA/NSF NStars program.
| Hipparcos red stars in the HpV_T2 and V I_C systems
For Hipparcos M, S, and C spectral type stars, we provide calibratedinstantaneous (epoch) Cousins V - I color indices using newly derivedHpV_T2 photometry. Three new sets of ground-based Cousins V I data havebeen obtained for more than 170 carbon and red M giants. These datasetsin combination with the published sources of V I photometry served toobtain the calibration curves linking Hipparcos/Tycho Hp-V_T2 with theCousins V - I index. In total, 321 carbon stars and 4464 M- and S-typestars have new V - I indices. The standard error of the mean V - I isabout 0.1 mag or better down to Hp~9 although it deteriorates rapidly atfainter magnitudes. These V - I indices can be used to verify thepublished Hipparcos V - I color indices. Thus, we have identified ahandful of new cases where, instead of the real target, a random fieldstar has been observed. A considerable fraction of the DMSA/C and DMSA/Vsolutions for red stars appear not to be warranted. Most likely suchspurious solutions may originate from usage of a heavily biased color inthe astrometric processing.Based on observations from the Hipparcos astrometric satellite operatedby the European Space Agency (ESA 1997).}\fnmsep\thanks{Table 7 is onlyavailable 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/qcat?J/A+A/397/997
| Late-type members of young stellar kinematic groups - I. Single stars
This is the first paper of a series aimed at studying the properties oflate-type members of young stellar kinematic groups. We concentrate ourstudy on classical young moving groups such as the Local Association(Pleiades moving group, 20-150Myr), IC 2391 supercluster (35Myr), UrsaMajor group (Sirius supercluster, 300Myr), and Hyades supercluster(600Myr), as well as on recently identified groups such as the Castormoving group (200Myr). In this paper we compile a preliminary list ofsingle late-type possible members of some of these young stellarkinematic groups. Stars are selected from previously established membersof stellar kinematic groups based on photometric and kinematicproperties as well as from candidates based on other criteria such astheir level of chromospheric activity, rotation rate and lithiumabundance. Precise measurements of proper motions and parallaxes takenfrom the Hipparcos Catalogue, as well as from the Tycho-2 Catalogue, andpublished radial velocity measurements are used to calculate theGalactic space motions (U, V, W) and to apply Eggen's kinematic criteriain order to determine the membership of the selected stars to thedifferent groups. Additional criteria using age-dating methods forlate-type stars will be applied in forthcoming papers of this series. Afurther study of the list of stars compiled here could lead to a betterunderstanding of the chromospheric activity and their age evolution, aswell as of the star formation history in the solar neighbourhood. Inaddition, these stars are also potential search targets for directimaging detection of substellar companions.
| Catalogue and bibliography of the UV Cet-type flare stars and related objects in the solar vicinity
This new catalogue of flare stars includes 463 objects. It containsastrometric, spectral and photometric data as well as information on theinfrared, radio and X-ray properties and general stellar parameters.From the total reference list of about 3400 articles, partial listsselected by objects, authors, key words and by any pairs of thesecriteria can be obtained Tables 1, 2 and 3 are only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html.
| The ROSAT all-sky survey catalogue of the nearby stars
We present X-ray data for all entries of the Third Catalogue of NearbyStars \cite[(Gliese & Jahreiss 1991)]{gli91} that have been detectedas X-ray sources in the ROSAT all-sky survey. The catalogue contains1252 entries yielding an average detection rate of 32.9 percent. Inaddition to count rates, source detection parameters, hardness ratios,and X-ray fluxes we also list X-ray luminosities derived from Hipparcosparallaxes. Catalogue also available at CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| The 74th Special Name-list of Variable Stars
We present the Name-list introducing GCVS names for 3153 variable starsdiscovered by the Hipparcos mission.
| The Galactic Orbits of Nearby UV Ceti Stars
The galactic orbits of 93 UV Ceti stars of the solar neighborhood havebeen numerically integrated. The UV Ceti stars studied are those of theworking list for which Poveda et al. (1996a) determined kinematicproperties and ages. All stars are contained within 25 pc of the Sun(π ≥ 0.04''), and values for their distances, proper motions andradial velocities are available for them (Gliese & Jahreiss 1991).The galactic potential model of Allen & Santillán (1991) wasused, and the orbits were integrated for times similar to the age of theold disk. The galactic orbital parameters are obtained. The orbits areall regular, and the values found for the orbital parameters are similarto those characteristic of the classic young thin disk. The verticalscale height found for the whole sample is 115 pc. However, the orbitalparameters found for the 7 objects with extreme kinematiccharacteristics recognized in Poveda et al. are markedly different fromthose of the rest of the flare stars; in particular, their orbitaleccentricities are larger than 0.3. The vertical scale height of thesample excluding the anomalous objects is just 103 pc. Consequently, wepropose that the anomalous objects belong to the thick disk, which maybe characterized by either e≥ 0.3 or | zmax | > 400 pc.
| An H-alpha survey of neglected Vyssotsky Catalog stars
Consideration is given to a significant number of Vyssotsky K- andM-dwarfs that have either no published radial velocity (71 stars), or avelocity based on a single measure (22), or with an uncertaintly greaterthan 5 km/s (19). An 'in flare' observation of Vys 250A compared to itsquiescent state, and an example of the double-lined phase of Vys 250Bare illustrated. Mean values from the observations are given in tabularform.
| The Palomar/MSU Nearby Star Spectroscopic Survey.II.The Southern M Dwarfs and Investigation of Magnetic Activity
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....112.2799H&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.
| The Palomar/MSU Nearby-Star Spectroscopic Survey. I. The Northern M Dwarfs -Bandstrengths and Kinematics
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....110.1838R&db_key=AST
| The ROSAT Wide Field Camera all-sky survey of extreme-ultraviolet sources - II. The 2RE Source Catalogue
During 1990-1991 the Wide Field Camera (WFC) on the ROSAT satelliteperformed the first all-sky survey at EUV wavelengths. The survey wasconducted in two `colours' using broad-band filters to define wavebandscovering the ranges 60-140 A and 112-200 A. It was fully imaging, witheffective spatial resolution of about 3 arcmin FWHM, and point sourcelocation accuracy of typically better than 1 arcmin. From an initialanalysis, Pounds et al. published the WFC Bright Source Catalogue (BSC)of 383 sources. In this paper we report results from reprocessing of thecomplete survey database; the resulting list of sources is the `2RE'Catalogue. It contains 479 sources, of which 387 are detected in bothsurvey wavebands, a significant advance on the BSC (80 per cent versus60 per cent). Improvements over the original BSC include: (i) betterrejection of poor aspect periods, and smaller random errors in theaspect reconstruction; (ii) improved background screening; (iii)improved methods for source detection; (iv) inclusion of atime-variability test for each source; (v) more extensive investigationof the survey sensitivity. We define the catalogue selection criteria,and present the catalogue contents in terms of tables and sky maps. Wealso discuss the sky coverage, source number-flux relations, opticalidentifications and source variability.
| Statistical studies of visual double and multiple stars. II. A catalogue of nearby wide binary and multiple systems.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1994RMxAA..28...43P&db_key=AST
| ROSAT Extreme Ultraviolet / EUV Luminosity Functions of Nearby Late Type Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1994MNRAS.267..840H&db_key=AST
| The Kinematics of Active Late Type Stars Observed by the ROSAT Wide-Field Camera
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993MNRAS.264..106J&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.
| Photometry of dwarf K and M stars
An observational program using UBVRI photometry is presented for 688stars from among the dwarf K and M stars already found spectroscopicallyby Vyssotsky (1958). Of these, 211 have not been observedphotometrically. These observations were obtained over a period ofseveral years at the Kitt Peak National Observatory using a GaAsphotomultiplier with an 0.9 m reflector. Based on night-to-nightvariations in the measures of individual stars, the internal errors maybe estimated to be roughly 0.01 mag for the colors and 0.015 for the Vmagnitudes. The photometric parallaxes reported for each star werecomputed in the manner discussed by Weis (1986).
| An optical Atlas of ROSAT Wide Field Camera EUV sources
The ROSAT Wide Field Camera has been detecting EUV sources since itslaunch in June 1990. A preliminary list of 384 bright sources has beensupplied by the Wide Field Camera team to the EUVE Guest ObserverCenter, and to the astronomical community. We have extracted 5.4 x 5.4arcmin images of all 384 WFC sources from the Space Telescope ScienceInstitute digitized sky archives. These images are presented asmosaicked finder charts for observers trying either to identify WFCsources or to characterize known sources.
| The ROSAT Wide Field Camera all-sky survey of extreme-ultraviolet sources. I - The Bright Source Catalogue
First comprehensive results from an initial processing of the ROSAT WideField Camera all-sky survey for cosmic sources of extreme-ultravioletradiation are presented. The reduction of the survey data has yielded acatalog of 383 relatively bright EUV sources, forming the WFC BrightSource Catalogue. Details of the EUV source positions and count ratesare given, as are optical identifications where known. It is found thatthe log N-log S distributions are unusually flat for the white dwarfstars, but almost Euclidean for the nearby main-sequence late-typestars. The sky distribution of identified white dwarfs is highlynonuniform, suggesting gross variations in the opacity of theinterstellar medium within about 100 pc.
| Catalogue of Variable or Suspected Stars Nearby the Sun
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1990A&AS...85..971P&db_key=AST
| H-alpha photometry of dwarf K and M stars - Chromospheric activity
H-alpha photometry of 118 K and M dwarfs are presented, with H-alphaequivalent width measures accurate to about 0.05 A. The data arecombined with the spectroscopic surveys of Stauffer and Hartmann (1986)and Fleming et al. (1988) to study the main features of thechromospheric activity versus mass relation for low-mass stars. An upperbound to the H-alpha equivalent width is found to be a function of themass relation (R-I). H-alpha luminosities and surface fluxes arecalculated for active stars, showing that both quantities generallydecline with R-I. The upper bound to the fraction of a star's bolometricluminosity, however, is independent of R-I. The results suggest that thechromospheres of most dMe stars with R-I less than 1.1 are in anactivity-saturated state. Also, H-alpha variability, probably due toflares, is detected in several stars.
| UBV photometry of stars whose positions are accurately known. IV
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1987A&AS...68..211O&db_key=AST
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| Сазвежђа: | Рак |
| Ректацензија: | 08h08m56.39s |
| Deклинација: | +32°49'11.4" |
| Apparent магнитуда: | 9.993 |
| Даљина: | 20.721 parsecs |
| Proper motion RA: | -42.1 |
| Proper motion Dec: | -189.3 |
| B-T magnitude: | 11.649 |
| V-T magnitude: | 10.13 |
Каталог и designations:
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