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Late main-sequence evolution of lithium and beryllium
We examine the effects of the tachocline diffusion process on thesurface abundances of light elements in solar-like stars(M*=0.96-1.04 Msun). Acting during main sequenceevolution, the tachocline diffusion can account for the gradual decreasein lithium surface abundance while preserving beryllium, in agreementwith the most recent observational data for open cluster stars olderthan the Hyades ( ~ 600 Myr). We show that helioseismology andobservations of surface rotation demand a nearly solid-body rotation ofsolar analogs after ~1 Gyr. By then, these stars have become slowrotators and lost most of their initial angular momentum. We argue thatmixing due to angular momentum loss does not appear to be a viablemechanism to account for the observed abundances.Using the results of helioseismology and of the observations of solarlithium abundance, we calibrate the two parameters of the tachoclinemixing, the Brunt-Väisälä frequency and the tachoclinethickness. We then evolve stellar models starting at the Hyades age andcompare the results of 7Li and 9Be abundances tothe observations of M 67 ( ~ 4.5 Gyr). Finally, we investigate theeffects of slight differences in specific metal abundance ratios on thetachocline diffusion. Because of opacity effects, we find differences inthe amount of lithium depletion of ~ 0.5 dex for solar effectivetemperature and iron abundance at the age of M 67 that can partlyexplain the observed lithium spread in this cluster.
| 71 Tauri: Hyades Enigma Resolved?
71 Tauri (HD 28052; F0 IV-V) is an enigmatic object for two reasons: (1)it is the second brightest X-ray source in the Hyades, yet early F starsas a rule are not strong coronal emitters; and (2) it lies a magnitudeabove the cluster main sequence, but radial velocity studies and speckleimaging suggest that it is single. Recently, long-slit ultravioletspectra of the star, obtained with the Space Telescope ImagingSpectrograph (STIS), serendipitously have revealed the presence of astellar companion at a distance of 0.1" directly south of the primary.The companion is seen only in its far-UV chromospheric emission lines.The nature of this object cannot be determined from our STIS spectraalone, but its high emission levels are most readily explained if it isa close binary of coronally active dG/dK stars. The presence of thesecondary can account for the striking X-ray properties of 71 Tau butnot its unusual location in the cluster color-magnitude diagram. It isconceivable that the primary itself is a close double of nearly equalstars, making 71 Tau a possible quadruple system. The alternative-that71 Tau is ~150 Myr older than other members of the Hyades, approachingthe end of core hydrogen burning for a 2 Msolar star-wouldchallenge the presumed synchrony of star formation in the cluster.
| The Second Extreme Ultraviolet Explorer Right Angle Program Catalog
We present the detection of 235 extreme ultraviolet sources, of which169 are new detections, using the Extreme Ultraviolet Explorer's (EUVE)Right Angle Program (RAP) data. This catalog includes observations sincethe first EUVE RAP catalog (1994 January) and covers 17% of the sky. TheEUVE RAP uses the all-sky survey telescopes (also known as``scanners''), mounted at right angles to the Deep Survey andspectrometer instruments, to obtain photometric data in four wavelengthbands centered at ~100 Å (Lexan/B), ~200 Å (Al/Ti/C), ~400Å (Ti/Sb/Al), and ~550 Å (Sn/SiO). This allows the RAP toaccumulate data serendipitously during pointed spectroscopicobservations. The long exposure times possible with RAP observationsprovide much greater sensitivity than the all-sky survey. We presentEUVE source count rates and probable source identifications from theavailable catalogs and literature. The source distribution is similar toprevious extreme ultraviolet (EUV) catalogs with 2% early-type stars,45% late-type stars, 8% white dwarfs, 6% extragalactic, 24% with no firmclassification, and 15% with no optical identification. We also present36 detections of early-type stars that are probably the result ofnon-EUV radiation. We have detected stellar flares from approximately 12sources, including: EUVE J0008+208, M4 star G32-6 (EUVE J0016+198), anew source EUVE J0202+105, EUVE J0213+368, RS CVn V711 Tau (EUVEJ0336+005), BY Draconis type variable V837 Tau (EUVE J0336+259), the newK5 binary EUVE J0725-004, EUVE J1147+050, EUVE J1148-374, EUVE J1334-083(EQ Vir), EUVE J1438-432 (WT 486/487), EUVE J1808+297, and the M5.5estar G208-45 (EUVE J1953+444). We present sample light curves for thebrighter sources.
| The Multiplicity of the Hyades and Its Implications for Binary Star Formation and Evolution
A 2.2 μm speckle imaging survey of 167 bright (K < 8.5 mag) Hyadesmembers reveals a total of 33 binaries with separations spanning 0.044"to 1.34" and magnitude differences as large as 5.5 mag. Of thesebinaries, 9 are new detections and an additional 20 are now spatiallyresolved spectroscopic binaries, providing a sample from which dynamicalmasses and distances can be obtained. The closest three systems,marginally resolved at Palomar Observatory, were reobserved with the 10m Keck Telescope in order to determine accurate binary star parameters.Combining the results of this survey with previous radial velocity,optical speckle, and direct-imaging Hyades surveys, the detectedmultiplicity of the sample is 98 singles, 59 binaries, and 10 triples. Astatistical analysis of this sample investigates a variety of multiplestar formation and evolution theories. Over the binary separation range0.1"-1.07" (5-50 AU), the sensitivity to companion stars is relativelyuniform, with = 4 mag, equivalent to a mass ratio = 0.23. Accounting for the inability to detect high fluxratio binaries results in an implied companion star fraction (CSF) of0.30 +/- 0.06 in this separation range. The Hyades CSF is intermediatebetween the values derived from observations of T Tauri stars (CSF_TTS =0.40 +/- 0.08) and solar neighborhood G dwarfs (CSF_SN = 0.14 +/- 0.03).This result allows for an evolution of the CSF from an initially highvalue for the pre-main sequence to that found for main-sequence stars.Within the Hyades, the CSF and the mass ratio distribution provideobservational tests of binary formation mechanisms. The CSF isindependent of the radial distance from the cluster center and theprimary star mass. The distribution of mass ratios is best fitted by apower law q^-1.3+/-0.3 and shows no dependence on the primary mass,binary separation, or radial distance from the cluster center. Overall,the Hyades data are consistent with scale-free fragmentation, butinconsistent with capture and disk-assisted capture in small clusters.Without testable predictions, scale-dependent fragmentation and diskfragmentation cannot be assessed with the Hyades data.
| On the X-ray emission from M-type giants
We have searched for X-ray emission from M-type giants and supergiantslisted in the Bright Star Catalogue (BSC) in the data of the ROSATall-sky survey (RASS). These stars lie to the far right of the X-raydividing line and are thus not expected to be X-ray sources. Any X-raydetection would therefore violate the common paradigm of X-ray darkM-type giants beyond the X-ray dividing line. We found 11 BSC M-typegiants and supergiants to coincide with RASS X-ray sources. While for 4stars the X-ray emission is very likely related to their cataclysmic orsymbiotic nature or can be attributed to a visual G-type companion, theother 7 stars are candidates for intrinsic X-ray emission. Of theseobjects, 3 have a rather large offset between optical and X-rayposition, so their proper identification with late-type giants is atleast questionable. For the remaining four stars, we obtained opticallow-dispersion spectra in order to search for emission lines indicativeof a possible symbiotic nature. None of these stars shows any brightemission lines, so they are probably quite normal M-type giants. Wediscuss possible origins of X-ray emission in these stars and theimportance of evolutionary aspects. Based on observations by the ROSATand Calar Alto Observatories
| Extreme Ultraviolet Explorer Right Angle Program observations of cool stars
The Extreme Ultraviolet Explorer (EUVE) Right Angle Program (RAP)obtains photometric data in four bands centered at 100 (Lexan/B), 200(Al/Ti/C), 400 (Ti/Sb/Al), and 550 (Sn/SiO) during pointed spectroscopicobservations. RAP observations are up to 20 times more sensitive thanthose in the EUVE all-sky survey. We present RAP observations of twodozen late-type stars. We derive surface fluxes from the Lexan/B andAl/Ti/C count rates and cataloged ROSAT Position Sensitive ProportionalCounter (PSPC) data. The EUVE surface fluxes are reasonably correlatedwith surface fluxes calculated from PSPC measurements. The timevariability of the sources has been examined. Most of the sources showno significant variability at the 99 percent confidence level. Flareswere detected from the K7 V star Melotte 25 VA 334, the K3 V star V834Tau (HD 29697), and the K3 + K8 Hyades binary BD +22669. The BD +22669count rate at the peak of the flare is a factor of 6 higher than thequiescent count rate, with a peak Lexan/B luminosity of 7.9 1029 ergs/s.The V834 Tau flare was detected in both Lexan/B and Al/Ti/C bands. Thepeak luminosity of the flare is 1.6 1029 and 8 1028 ergs/s for Lexan/Band Al/Ti/C, respectively.
| The Hyades Binary 51 Tauri: Spectroscopic Detection of the Primary, the Distance to the Cluster, and the Mass-Luminosity Relation
51 Tauri has long been known as a double-lined spectroscopic binary(orbital period = 11 yr) with the peculiarity that only the velocitiesof the secondary component could be measured. We report here newspectroscopic observations of this system that have enabled us tomeasure velocities for the rapidly rotating primary using TODCOR, atwo-dimensional cross-correlation technique, and we have derived adouble-lined orbit. In addition, 51 Tau is a visual binary resolved byspeckle interferometry. By combining the astrometric and spectroscopicdata, we have obtained the first complete visual-spectroscopic solutionfor the system, from which we derive the orbital parallax ( pi orb =0."0179 +/- 0."0006) and the individual masses (MA = 1.80 +/- 0.13Mȯ and MB = 1.46 +/- 0.18 Mȯ). Based on this orbital parallax,we use relative proper motions for a representative sample of clustermembers to obtain a distance modulus for the cluster of m - M = 3.40 +/-0.07 (47.8 +/- 1.6 pc). We compare the empirical mass-luminosityrelation from all available direct mass determinations with recenttheoretical models, and we take advantage of the unusual opportunitythat we have absolute luminosities and colors to derive an age estimateof 600 Myr for the Hyades, by comparing with stellar evolution modelswithout any arbitrary adjustments.
| Optical and X-Ray Characteristics of Stars Detected in the Einstein Slew Survey
We detect X-rays for the first time from 63 cool (types AM) stars. Thesestars are part of the 229 total stellar X-ray sources identified to datein the Einstein Slew Survey (hereafter Slew). We also list new X-raydata on one A star that may have a corona, five OB stars, and reportdiscoveries of two new T Tauri stars and two new cataclysmic variables.The stellar content of the Slew high-latitude subset (currently 93%identified for |b_II_| > 20^deg^) is 26%. This agrees well with theEinstein Extended Medium Sensitivity Survey (EMSS) stellar sample, whichonly considered high latitudes. Because of the large solid angle coveredby the Slew, and its shallow limiting flux, the sample will better probethe bright end of the stellar X-ray luminosity function (L_X_ >10^30^ ergs s^-1^). Presently (based on the 221 Slew stars with knownspectral types), the sample is dominated by late-type systems (coolerthan F; 68%). These include dMe's, BY Dra, RS CVn, and FK Comae systems.Based on the limiting magnitudes of catalogs searched to date, the Slewis assessed to be complete for spectral types earlier than K. Hence, Kand M systems will be prominent in the ~50 as yet unidentified stars. Wehave embarked on an extensive program to (1) confirm the X-rayidentifications with the optical counterparts; (2) search for Ca II Hand K and Balmer line emission as activity signatures; and (3) searchfor supporting evidence of magnetic activity by measuring rotationalvelocities and relating them to X-ray luminosity level. Of 64 proposedcoronal systems observed to date, we have confirmed 44 active stars,while in the remaining 20 we have been unable to find definitiveactivity. We have confirmed an additional 19 active stars from stellardatabase searches, and reclassified nine systems as having nonstellaroptical counterparts from optical follow-up identification work andextragalactic database searches. We discuss notable new discoveries.From the sample of single active F7-MS Slew stars with measured ν sini-values, we find a strong (99.9% confidence level) linear correlationof X-ray luminosity with ν sin i and with stellar radius (R).However, L_X_ is uncorrelated with angular rotation speed at the 99%level. For the combined Slew and EMSS single star F7-MS sample, we findthe same 99.9% ν sin i-L_X_ and R-L_X_ correlations. The L_X_-νsin i relation for the combined sample appears to flatten with respectto the quadratic behavior seen for optically selected stellar samples atrotational velocities in excess of ~16 km s^-1^. For the unevolvedsubset of the Slew single star sample, we also find a correlationbetween L_X_ and Rossby number (R_0_; more than 99% confidence). Aleast-squares fit gives L_X_ ~ R_0_^-0.4^, which is similarly flatterthan the quadratic dependence seen in optical samples. Using the stellarsurface X-ray flux F_X_ versus B - V diagram, we interpret these resultsas saturation of the stellar surface by active regions at F_X_/F_bol_ ~10^-3^.
| Lithium abundance in binaries of the Hyades open cluster.
We have derived accurate and homogeneous lithium abundances in 49 MainSequence binary systems belonging to the Hyades open cluster by using adeconvolution method to determine individual magnitudes and colors forthe primary and secondary components of the binary. The input parametersof the model are the observed Li equivalent width, the actual distanceto the binary, the integrated apparent magnitude and the integratedcolors of the binaries -BV(RI)_K_. We show that the general behavior isthe same in binaries and in single stars (Li is depleted faster in Kstars than in G stars and there is a deep dip for mid-F stars). However,there is a larger scatter in the abundances of binary systems than insingle stars. Moreover, in general, binary systems have anoverabundance, which is more conspicuous in close binaries. In fact,there is a cut-off period, which can be estimated as P_orb_~9d. Thisvalue is in excellent agreement with the theoretical prediction of Zahn(1994).
| Lithium in a Praesepe Short-Period Binary
We present spectroscopy of the 6707A Li I region of the short periodPraesepe binary KW 367. The double-lined nature of this object inferredfrom radial velocity data is confirmed. While blending complicates theanalysis, our estimated Li abundance for the primary isindistinguishable from that of other Praesepe stars of similar color.Given the likely presence of a tertiary companion, the unremarkable Liabundance can not be said to conflict with recent theory and supportingobservations which suggest short-period systems undergo reduced Lidepletion. Rather, our results support the contention that the binary'snear-critical or lower period alone is not sufficient to ensure reduceddepletion of Li. (SECTION: Stars)
| The Second Extreme-Ultraviolet Explorer Source Catalog
We present the second catalog of extreme-ultraviolet objects detected bythe Extreme-Ultraviolet Explorer. The data include (1) all-sky surveydetections from the initial 6 month scanner-survey phase, (2) additionalscanner detections made subsequently during specially programmedobservations designed to fill in low-exposure sky areas of the initialsurvey, (3) sources detected with deep-survey-telescope observationsalong the ecliptic, (4) objects detected by the scanner telescopesduring targeted spectroscopy observations, and ( 3) other observations.We adopt an innovative source detection method that separates the usuallikelihood function into two parts: an intensity diagnostic and aprofile diagnostic. These diagnostics allow each candidate detection tobe tested separately for both signal-to-noise ratio and conformance withthe known instrumental point-spread function. We discuss the dependenceof the false-alarm rate and the survey's completeness on the survey'ssensitivity threshold. We provide three lists of the EUV sourcesdetected: the all-sky survey detections, the deep-survey detections, andsources detected during other phases of the mission. Each list givespositions and intensities in each wave band. The total number of objectslisted is 734. For approximately 65% of these we also provide plausibleoptical, UV, radio, and/or X-ray identifications.
| Mixing by internal waves. II. Li and Be depletion rate in low mass main sequence.
In this paper we present the results of lithium and beryllium abundancesas a function of spectral type provided by the internal wave diffusioncoefficient presented by Montalban (1994). The (Li,T_eff_) curves forHyades and Praesepe clusters obtained after adding the pre-main sequenceburning (D'Antona & Mazzitelli 1994) fit satisfactorily the mostrecent observational data. The Be abundance is also in good agreementwith observational estimations.
| EUVE Right Angle Program Observations of Late-Type Stars
The EUVE Right Angle Program (RAP) obtains photometric data in fourbands centered at ~ 100 Angstroms (Lexan/B), ~ 200 Angstroms (Al/Ti/C),~ 400 Angstroms (Ti/Sb/Al), and ~ 550 Angstroms (Sn/SiO). RAPobservations are up to 20 times more sensitive than the all-sky survey.We present RAP observations of the late-type stars: BD+03 301, BD+05300, HR 1262, BD+23 635, BD+22 669, Melotte 25 VA 334, Melotte 25 1366,Melotte 25 59, Melotte 25 65, theta (1) Tau, V834 Tau, GJ 2037, BD-211074, GJ 205, RE J0532-030, GJ 9287A, HT Vir, BD+46 1944, Proxima Cen,alpha Cen A/B, HR 6094, CPD-48 10901, and HR 8883. We derive fluxes andemission measures from Lexan/B and Al/Ti/C count rates. The timevariability of the sources has been examined. Most of the sources showno significant variability at the 99% confidence level. Flares weredetected from the K3V star V834 Tau (HD 29697) and the K0 star BD+22669. The BD+22 669 count rate at the peak of the flare is a factor of 10higher than the quiescent count rate with a peak Lexan/B luminosity of7.9 x 10(29) erg s(-1) . The V834 Tau flare was detected in both Lexan/Band Al/Ti/C bands. The peak luminosity of the flare is 1.6 x 10(29) ergs(-1) and 8 x 10(28) ergs s(-1) for Lexan/B and Al/Ti/C, respectively.This is a factor of 4.3 higher than the quiescent luminosity in Lexan/B,and a factor of 4.6 in Al/Ti/C\@. This work is supported by NASAcontract NAS5-29298.
| 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.
| Lithium in Short-Period Tidally Locked Binaries: A Test of Rotationally Induced Mixing
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...453..819R&db_key=AST
| ROSAT All-Sky Survey Observations of the Hyades Cluster
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...448..683S&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.
| The Henry Draper Extension Charts: A catalogue of accurate positions, proper motions, magnitudes and spectral types of 86933 stars
The Henry Draper Extension Charts (HDEC), published in the form offinding charts, provide spectral classification for some 87000 starsmostly between 10th and 11th magnitude. This data, being highlyvaluable, as yet was practically unusable for modern computer-basedastronomy. An earlier pilot project (Roeser et al. 1991) demonstrated apossibility to convert this into a star catalogue, using measurements ofcartesian coordinates of stars on the charts and positions of theAstrographic Catalogue (AC) for subsequent identification. We presenthere a final HDEC catalogue comprising accurate positions, propermotions, magnitudes and spectral classes for 86933 stars of the HenryDraper Extension Charts.
| Radio continuum emission from stars: a catalogue update.
An updated version of my catalogue of radio stars is presented. Somestatistics and availability are discussed.
| Lithium depletion in late-type stars through wind-driven mixing
Not Available
| A case study of the quadruple system XI Ursae Majoris: Its activity and lithium depletion
The quadruple system Xi Ursae Majoris (xi UMa) is an interesting testcase for the numerous problems encountered when studying theevolutionary status, chromospheric activity and lithium depletion ofsolar-type stars. We have carried out a detailed analysis of the majorcomponents A and B of xi UMa from high resolution, high signal-to-noiseCFHT spectra. We determine accurate temperatures for each of theprincipal components, neither disturbed by their invisible, much lessmassive companion, and find that the two differ in temperature by 300 K,one being somewhat hotter than the Sun, the other cooler. The metalabundances derived from iron and a few other elements are identical forthe two stars, and the system is moderately metal-deficient, by factorof two with respect to the Sun. We concur with previous studies thatlithium is fairly abundant in A whereas it is below detection in B: wemeasured log N(Li) = 2.33 in A and place a more stringent upper limitlog N(Li) less than 0.8 for B. We discuss this unusual combination oflithium abundances and the position of the stars in theHertzsprung-Russell (HR) diagram in the light of the complex binarynature of the two components, and of current theories of stellarevolution and of lithium depletion. We suggest that B has kept a highlevel of activity because its rotation is tidally locked with theorbital motion, and that it has therefore lost about ten times morematter than a single star of the same mass, which explains its stronglithium depletion.
| Lithium in a short-period tidally locked binary of M67: Implications for stellar evolution, Galactic Lithium evolution, and cosmology
In open clusters, late-F stars exhibit a Li maximum (the Li 'peak'region) at lower abundance with age, which could be due either tostellar depletion or Galactic Li enrichment (or some other cause). Wehave observed a short-period tidally locked binary (SPTLB) on the Lipeak region in the old cluster M67 to distinguish between alternatives.SPTLBs which synchronized in the early pre-main sequence would avoid therotational mixing which, according to Yale models, may be responsiblefor depleting Li with age in open cluster dwarfs. We find that bothcomponents of the M67 SPTLB have a Li abundance lying about a factor of2 or more above any other M67 single star and about a factor of 3 ormore above the mean Li peak region abundance in M67. Our results suggestthat the initial Li abundance in M67 is at least as high asapproximately 3.0 = 12 + log (NLi/NH). Our highM67 SPTLB Li abundance and those in other clusters support thecombination of Zahn's tidal circularization and the Yale rotationalmixing theories and may indicate that the halo Li plateau (analogous tothe cluster Li peak region) abundance has been depleted from a higherprimordial value. Implications are discussed.
| Rotation and lithium depletion in late-type binaries
Late-type stars possess two firmly established properties: both theirrotation speed and their lithium abundance decrease with age. Quitenaturally, it has been suggested that the lithium depletion is relatedwith the loss of angular momentum. Such a causal link may just bepostulated in the evolutionary calculations, and the free parameterscalibrated with the observations (Endal & Sofia 1978; Pinsonneaultet al. 1989). But it can also be justified on theoretical reasons, withthe meridian circulation playing the major role in the transport ofmatter and angular momentum (Zahn 1992a). In the present paper, we seekan observational confirmation of this link in the behavior of closebinaries. In addition to the torque exerted on them by the stellar wind,which is responsible for the spin-down of single stars, binary starsexperience a tidal torque, which tends to synchronize their rotationwith the orbital motion. As a result, they exchange lesser amounts ofangular momentum than single stars of the same mass and age, andtherefore they should retain more of their original lithium. Based onthe current tidal theory (Zahn 1989), we calculate the dynamicalevolution of close binaries, and infer from it the differences inlithium abundance one should expect between them and single stars.Underdepletion should occur in systems which were tidally locked on theZAMS, i.e. for orbital periods below =~8 days for solar-type stars ofPopulation I, and 6 days for halo stars. Our theoretical predictions arein good agreement with the latest available data (Soderblom et al. 1993;Thorburn et al. 1993; Spite et al. 1994), and we take this as a prooffor the existence of a physical link between the depletion of lithiumand the loss of angular momentum. We conclude that the abundance oflithium measured in old disk and halo stars by Spite & Spite (1982)is less than the original one, and cannot be taken as such to constrainthe models of the primordial nucleosynthesis. Another implication isthat magnetic torquing has played little role in the radiative interiorof late-type stars, and that the core of these stars is probablyrotating faster than their surface.
| Low-Mass Stars in the Hyades
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993MNRAS.265..785R&db_key=AST
| The low mass Hyades and the evaporation of clusters
The 135 single stars and 85 binary systems, redder than R-I = +0.34 magand brighter than V = 17 mag, between alpha = 3.75 h and 5.0 h and delta= +5 deg and + 25 deg show a luminosity function that differsconsiderably from that of the general field stars within 20 pc of theSun. The ratio of double star components to single cluster membersincreases markedly with decreasing luminosity. Forty-three single starsand 16 binary systems that are members of the Hyades supercluster within20 pc of the Sun show the same luminosity function as the field stars inthat region. Fifty percent of the cluster members and 40 percent of thesupercluster members are components of binary stars. The equivalentwidths of H-alpha appear to support a range of ages (approximately 8 to16 x 108 yr) for the cluster stars and demonstrate that theoldest objects are in the supercluster. A list of cluster members, whichmay include the end of the stable main sequence, but for which accurate(R-I) photometry is not available, is included. The half-dozen knownparallax stars of the faintest luminosity contain at least onesupercluster member, TVLM 868-110639, which is probably beyond thestable, nuclear burning main sequence as a 'transitional' or 'brown'dwarf.
| Lithium in the Hyades. I - New observations
Results are presented of new observations, carried out at Li 6707 A, on68 main-sequence members of the Hyades cluster with spectral typesranging from late F to and early K, and their surface lithium abundanceLi/H is related to their mass, age, and initial composition. It is foundthat, for the sample as a whole, the observed distribution of lithiumabundances is inconsistent with the hypothesis of a unique relationshipbetween lithium abundance and mass. Moreover, is strong observationalevidence for main-sequence lithium depletion when the data are comparedwith observations in younger clusters, even for masses that are notpredicted to experience such depletion in standard stellar models.
| First results from ROSAT all-sky survey observations of the Hyades cluster
We present preliminary ROSAT all-sky survey results for the Hyadescluster. We detected 108 Hyades cluster members as X-ray sources withL(y) greater than about 3 x 10 exp 28 ergs/s. A number of short-period,chromospherically active binary systems and the giants Theta1 Tau andGamma Tau are among the most X-ray-luminous objects in the cluster. Thesecond brightest X-ray source, HR 1394 = 71 Tau = VB 141, is along-period lunar occultation binary. Seven cluster members were alsoseen in the Wide Field Camera EUV all-sky survey. Among the starsdetected in both X-rays and EUV is the Hyades white dwarf EG 37 (= VR16), confirming an earlier serendipitous EXOSAT detection. We alsoreport the first X-ray detection of the Hyades K0 giant Epsilon Tau, atroughly the survey limit. This new result establishes all four Hyadesgiants as X-ray emitters, although with an about 50:1 range in L(x). Acomparison of Einstein and ROSAT data for three of the giants suggeststhat long-term X-ray variability, perhaps due to activity cycles, may bepartly responsible for the wide dispersion in L(x).
| The Einstein Slew Survey
A catalog of 819 sources detected in the Einstein IPC Slew Survey of theX-ray sky is presented; 313 of the sources were not previously known asX-ray sources. Typical count rates are 0.1 IPC count/s, roughlyequivalent to a flux of 3 x 10 exp -12 ergs/sq cm s. The sources havepositional uncertainties of 1.2 arcmin (90 percent confidence) radius,based on a subset of 452 sources identified with previously knownpointlike X-ray sources (i.e., extent less than 3 arcmin).Identifications based on a number of existing catalogs of X-ray andoptical objects are proposed for 637 of the sources, 78 percent of thesurvey (within a 3-arcmin error radius) including 133 identifications ofnew X-ray sources. A public identification data base for the Slew Surveysources will be maintained at CfA, and contributions to this data baseare invited.
| Spectroscopic binaries - 15th complementary catalog
Published observational data on the orbital characteristics of 436spectroscopic binaries, covering the period 1982-1986, are compiled intables. The data sources and the organization of the catalog are brieflydiscussed, and notes are provided for each item.
| A radial-velocity survey of the Hyades
Photoelectric radial-velocity measurements, obtained with external erroras small as 0.1 km/s using the 200-inch Hale telescope at PalomarObservatory during the period 1971-1986, are reported for over 400candidate members (with V magnitude between 6 and 14) of the Hyadescluster. The history of Hyades observations is recalled; the Palomarinstrumentation and observing program are described; the data-reductionand standardization procedures are discussed in detail; and the data arepresented in extensive tables and graphs. About 200 of the stars areclassified as cluster members, including 60 spectroscopic binaries.
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Наблюдательные данные и астрометрия
| Созвездие: | Телец |
| Прямое восхождение: | 04h18m10.79s |
| Склонение: | +23°17'04.7" |
| Видимая звёздная величина: | 9.453 |
| Собственное движение RA: | 91.6 |
| Собственное движение Dec: | -39 |
| B-T magnitude: | 10.621 |
| V-T magnitude: | 9.55 |
Каталоги и обозначения:
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