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.
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The comparative accuracy of photographic observations of radio stars observed at the Engelhardt Astronomical Observatory
At the Engelhardt Astronomical Observatory (EAO), we observedphotographic positions of 113 Galactic Radio Sources (GRS) in the systemPPM catalogue (Rizvanov & Dautov 1998). Analysis of their accuracyis made by comparison with the Hipparcos catalogue (Perryman et al.1997) and astrometric catalogue of radio stars in the radio window fromthe article of Walter et al. (1991). Table 2 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?J/A+A/375/670
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Radio star catalogue observed in San Juan (RSSJ95)
Using the data observed in San Juan with the photoelectric AstrolabeMark II of the Beijing Astronomical Observatory from February, 1992 toMarch, 1997, the radio star catalogue in San Juan(RSSJ95) has beencompiled. There are 69 radio stars in this catalogue. The positions ofthe radio stars are for the epoch of observation and the equinox J2000.0and a system close to that of the system FK5. The mean precisions are+/-2.2 ms and +/-0.035'' in right ascensions and declinations,respectively. The magnitudes of stars are from 0.9 to 10.7. Thedeclinations are from -2fdg 5 to -60(deg) . The mean epoch is 1995.1.Finally, the comparison results between the Hipparcos catalogue andRSSJ95 are given.
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Evolved, single, slowly rotating ... but magnetically active. The G8-giant HR 1362 = EK Eridani revisited
We rediscuss the unusual case of the slowly rotating late-type giant HR1362, which exhibits a very unusual high level of magnetic activity. NewBVRI photometry from two robotic telescopes from 1991 through 1998together with previously published photometric data gives a very precisephotometric period of 306.9+/-0.4 days. With the aid of high-resolution(R=120,000) optical spectra and the Hipparcos parallax we redeterminethe absolute parameters of HR 1362 and find it to be a single G8IV-IIIstar of 14 L_sun and a mass of 1.85 M_sun with T_eff=5125 K, log g=3.25,and solar abundances. Lithium is not significantly different from solarand we obtain log n(Li)=1.14 from a detailed spectrum synthesisincluding both isotopes at 6708 Angstroms. Vsin i and macroturbulenceare determined from fits of disk-integrated models to the observed lineprofiles as well as their Fourier transforms and are 1.5+/-0.5 km s(-1)\ and ~5 km s(-1) , respectively. The minimum radius from vsin i andP_rot is only then in agreement with the spectral classification and thebolometric luminosity from the Hipparcos parallax if the inclination ofthe stellar rotation axis is nearly 90°. We concur with thearguments of Stȩpień (\cite{step}) that HR 1362 is anevolved Ap star, and therefore the magnetic field is possibly ofgalactic origin rather than dynamo generated.
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San Juan radio star catalogue and comparison with HIPPARCOS catalogue.
Not Available
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Rotational Velocities of Late-Type Stars
A calibration based on the results of Gray has been used to determineprojected rotational velocities for 133 bright stars with spectral typesof F, G, or K, most of which appear in {\it The Bright Star Catalogue}.The vast majority have {\it v} sin {\it i} $\leq$ 10 km s$^{-1}$ and,thus, are slow rotators. With the new calibration, projected rotationalvelocities have been determined for a sample of 111 late-type stars,most of which are chromospherically active. Some of the stars have hadtheir rotational velocities measured for the first time. (SECTION:Stars)
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The 73rd Name-List of Variable Stars
Not Available
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HDE 233517: Lithium and Excess Infrared Emission in Giant Stars
Recent studies have identified a small class of moderately rapidlyrotating, chromospherically active, single giants, some of which arelithium rich. We present evidence suggesting the peculiar K-type starHDE 233517 is one such object. Previously, HDE 233517 has been suggestedto be a young star, consistent with its large far-infrared excess andour log epsilon (Li) ~ 3.3. However, our high-resolution spectroscopicobservations show it is likely a single, post--main-sequence K2 giantwith v sin i = 15 km s-1 and modest Ca II H and K emission. The giantstatus of HDE 233517 is determined directly from luminosity-sensitiveline ratios and a lack of significant line wings, and is furthersupported by a large radial velocity (46.5 km s-1), small proper motion,and the presence of interstellar absorption features. Interpretation ofthe data in the context of a recent mass outflow model for giant starsproposed by de la Reza and coworkers indicates that HDE 233517 has thelargest mass-loss rate, ~3 x 10-7 Msolar yr-1, of any known luminosityclass III giant. We suggest that the processes causing rapid rotation,large lithium abundance, and infrared excess are triggered at the baseof the giant branch when the convection zone reaches the rapidlyrotating core of low-mass stars.
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Chromospherically Active Stars. XIV. A Rediscussion of the Properties and Evolutionary State of HD 181943
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....109.2821F&db_key=AST
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Radio continuum emission from stars: a catalogue update.
An updated version of my catalogue of radio stars is presented. Somestatistics and availability are discussed.
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Chromospheric activity in G and K giants: the spectroscopic data base
I present high-resolution CCD spectra of CaII H and K emission lines of59 evolved stars of spectral type G and K and luminosity Class III,III-IV, and IV. This includes active stars like RS CVn binaries but alsoactive and inactive single stars. Most of the objects were observed forthe first time and several were discovered to be chromosphericallyactive. Spectra for ten stars of luminosity Class V are also given.
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Chromospheric activity in G and K giants and their rotation-activity relation
We obtained high-resolution CCD spectra of Ca II H and K emission linesof 59 evolved stars of spectral type G and K and luminosity class III,III-IV, and IV. Our sample includes active stars like RS CVn binariesbut also active and inactive single stars. Whenever possible wedetermine absolute emission line surface fluxes and use them,supplemented by previously published fluxes from high-resolutionspectra, to quantify the rotation-activity relation for evolved stars.We find that the Ca II surface fluxes from evolved stars scale linearlywith stellar rotational velocity and that the flux from the cooler starsdepends stronger upon rotation than the flux from the hotter stars, inagreement with previous findings for main-sequence stars. However, largescatter indicates that rotational velocity might not be the onlyrelevant parameter. We also present some evidence for the existence of a'basal' flux for evolved stars that scales approximately with the eightpower of the effective surface temperature.
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HR 1362: The Evolved 53 Camelopardalis
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993ApJ...416..368S&db_key=AST
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The 71st Name-List of Variable Stars
Not Available
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HD 181943: an Active Single Subgiant with Lithium
Not Available
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An astrometric catalogue of radio stars
The first part is presented of a radio star catalog encompassing 186objects whose selection was guided by the priority criteria of theHipparchos Input Catalogue Consortium. Since these criteria are wellsuited to the need for linkage of ground-based optical systems to radioreference frames, this first selection is also considered a suitablebase for the catalog. Seventeen categories of stellar parameters arefurnished for each of the stars, including optical and radio positions,optical and radio parallax, radial velocity, type of variability, andoptical structure.
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Photometry of 50 suspected variable stars
Fifty stars have been chosen as suspected variable stars and analyzedfor variability. A large portion of this sample are stars that areeither proved active chromosphere stars or are candidates for suchactivity. The photometric data base consists of differential Vmeasurements of the Vanderbilt 16 inch (41 cm) automatic photoelectrictelescope and 25 observers at 26 observatories worldwide. Publishedphotometric data have also been utilized, with proper adjustments madeto ensure that all magnitudes are differential. Searches for photometricperiod, amplitudes, and times of minimum light showed 68 percent of thesample to be photometrically variable with periods found for 34. Twostars were deemed norvariable for the period of observation. Conclusivestatements could not be made concerning the photometric variability ofthe 14 remaining stars.
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HR 1362 - A test case for stellar dynamo theories
An analysis of 11 yr of photometry of HR 1362 = EK Eri has shown awell-established photometric period of 335 days. This confirms anearlier period determination of about 310 days from 3 yr of APT data andis consistent with a new v sin i determination of 2 + or - 2 km/s.Recent Ca II H and K observations show moderately strong H and Kemission lines at a flux level of log F prime (K) of about 6.5 ergs sqm/s. If the photometric period is interpreted as the rotation period,this surface flux is more than one order of magnitude larger than whatcan be expected from empirical activity versus rotation relationships.The spectrum and the U-B and B-V colors are consistent with a single G8III-IV spectral classification, while the V-R and V-I values indicate asmall color excess, typical of chromospherically active stars.
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Optical positions of radiostars.
Precise optical positions, relative to either the Perth 70 or the AGK3Rcatalogs, are presented for 38 radiostars which have been proposed ascandidates for the Hipparcos observing list. The observations wereobtained with the 70/100/210 cm Maksutov Astrograph at the EstacionAstronomica de Cerro El Roble. The precision levels are shown to beabout 0.2 arcsec in both coordinates.
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Stellar radio luminosity and stellar rotation
Two measurements of the microwave surface brightness of 63 activechromospheric stars, one related to surface flux and one related to fluxratio, are correlated with rotational parameters. Although both methodsare found to provide similar results, the surface flux method accountsfor more of the variance in the regression. The consistency of theobserved surface brightnesses of the sun and three BY-Dra-type flarestars with the present rotational relationships is considered.
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A relation between radio luminosity and rotation for late-type stars
A relation is found between peak radio luminosities measured at 8 GHzand the rotational velocity of 51 late-type F, G, and K stars (includingthe sun). The sample includes both single stars and active components ofclose binary systems, with equatorial surface velocities ranging from 1to 100 km/s. A gyrosynchrotron source model originally developed toexplain solar microwave bursts could explain the relation. The mainparameter depending on rotation rate is the filling factor, i.e., thefraction of the stellar surface and corona occupied by intense magneticfields. As the rotation speed increases, the scale size of the coronalstructures emitting microwave gyrosynchrotron radiation increases, andthere is a corresponding increase in the area of the surface covered byintense starspot magnetic fields. However, the peak magnetic field ofthe starspots probably does not increase significantly above observedsunspot values.
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A microwave survey of southern active stars
The results of a survey of 153 active-chromosphere stars made with theParkes 64-m telescope at 5.0/8.4 GHz from 1981 to 1987 are reported.Microwave emission was detected from 70 stars on at least one occasion,with the highest detection rate of 68 percent from the RS CVn group. TheCa II stars and Algol-type binaries yielded detection rates of 44 and 30percent, respectively. The maximum powers emitted by the stars at5.0/8.4 GHz ranged over five orders of magnitude, with a median of 2.5 x10 to the 10th W/Hz. The maximum brightness temperatures had a smallerrange of three orders of magnitude, with a median of 3.6 x 10 to the 9thK.
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UBV(RI)c photometry for CaII emission stars. I - Observations at Sutherland
Extensive photometry in the UBV(RI)c system is given for 55 stars withstrong Ca II H and K emission. The UBV observations were made relativeto the standard stars of Lloyd Evans et al. (1983) while the (RI)cobservations were made relative to E-region standards over greaterangular distances. The data are plotted in phase diagrams.
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Radial velocities of calcium emission stars. I - Observations at Sutherland
Radial velocities are presented for 53 bright late-type stars withemission in the H and K lines of Ca II, which is indicative of a highlevel of chromospheric activity. Most of the stars are spectroscopicbinaries, for which orbital elements are presented.
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UBV photometry of ten southern hemisphere active-chromosphere stars
High-precision UBV photometry of ten southern hemisphereactive-chromosphere stars with strong Ca II H and K and/or H-alphaemission has been obtained. Eight of these stars showed variabilityduring June 1985. Complete or partial light curves are presented for thestars, and these data, as well as mean V magnitudes and colors, arecompared with the results of other investigators. In a number of cases,significant changes in photometric amplitude are found, which may serveto track the formation and evolution of active regions on these stars.
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A survey of chromospherically active stars
Photometric and/or spectroscopic observations have been obtained of 52late-type stars which are suspected or known to be chromosphericallyactive. Although not all types of observations were obtained for eachstar, these observations include all-sky BVRI Johnson photometry,ultraviolet spectrograms, low-dispersion blue-wavelength spectrograms,and high-dispersion red-wavelength spectrograms. From the spectroscopicobservations v sin i's, radial velocities, and the appearance of the CaII H and K emission lines have been determined as well as the H-alphaline. The photometric observations indicate that chromosphericallyactive stars have V - R and V - I color excesses. Such excesses willaffect the surface fluxes determined with the surface brightness-colorrelationship. On the other hand all-sky BVRI photometry appears to be anexcellent way to identify chromospherically active stars. A small groupof moderately rapidly rotating, possibly single G8-K2 giants has beenfound. These stars have very modest chromospheric activity and so arenot FK comae stars. A number of other unusual chromospherically activestars are identified.
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Radio emission from RS CVn binaries. I - VLA survey and period-radio luminosity relationship
A VLA survey of radio emission from 36 close binary stellar systems withRS CVn properties is reported. Eight new sources were detected. Asummary of all published reports of radio emission from RS CVn systemsis presented. There appears to be a correlation between maximum radioluminosity and rotational period, with a tentative functional form L(R)varies as P to the (-0.7) power. Rapid rotators (periods approximately 2days) may be underluminous compared with the extrapolated trend fromlonger-period systems. The luminosity-period correlation probablyresults from a dynamo mechanism which produces strong magnetic fieldsand, in turn, enhances the nonthermal radio emission. The decrease inradio luminosity at short periods may be caused by a saturation ofenergy deposition in the chromosphere, possibly because the surface ofthe active star has become covered with spotted regions.
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An H-alpha survey of southern hemisphere active chromosphere stars
Because of the variety of extraordinary phenomena exhibited by activechromosphere objects, discovery of new, bright surface-active stars isof considerable importance. Ca II emission is a well-known signature ofchromospheric activity, serving even as one of the points of definitionof the class of RS CVn binary stars. In connection with the presentinvestigation, spectroscopic observations of 27 Ca II emission starshave been conducted. The observations make it possible to identifyunambiguously the most chromospherically active stars in the sample. Byobserving the H-alpha line, rather than H and K, it is possible todistinguish nine of these stars which are likely to be observationaltargets as interesting as the extremely surface active objects V711 Tauor FK Com. Of the 27 stars surveyed, two (HD 86005, HD 204128) showedH-alpha as an emission feature above continuum, with estimatedequivalent width 1-2 A.
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Local photometric standards for CaII emission stars
UBV data are given for 108 stars which are suitable local standards for52 stars with strong Ca2 emissions. An additional eight stars wererejected as possible standards because of suspected variability.
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