Садржај
Слике
Уплоадјуј своје слике
DSS Images Other Images
Везани чланци
Tertiary companions to close spectroscopic binaries
We have surveyed a sample of 165 solar-type spectroscopic binaries (SB)with periods from 1 to 30 days for higher-order multiplicity. Asubsample of 62 targets were observed with the NACO adaptive opticssystem and 13 new physical tertiary companions were detected. Anadditional 12 new wide companions (5 still tentative) were found usingthe 2MASS all-sky survey. The binaries belong to 161 stellar systems; ofthese 64 are triple, 11 quadruple and 7 quintuple. After correction forincompleteness, the fraction of SBs with additional companions is foundto be 63% ± 5%. We find that this fraction is a strong functionof the SB period P, reaching 96% for P<3d and dropping to34% for P>12^d. Period distributions of SBs with and withouttertiaries are significantly different, but their mass ratiodistributions are identical. The statistical data on the multiplicity ofclose SBs presented in this paper indicates that the periods and massratios of SBs were established very early, but the periods of SB systemswith triples were further shortened by angular momentum exchange withcompanions.
| Speckle interferometry of nearby multiple stars. II.
This paper is a continuation of diffraction-limited speckleinterferometry of binary and multiple stars carried out at the 6-mtelescope of the Special Astrophysical Observatory in Zelenchuk. Theprogram has concentrated on nearby (π>10 mas) close binariesdiscovered or measured during the Hipparcos mission. Here, we present132 measurements of relative positions and magnitude differences for 99pairs and 8 measurements for 6 triple systems. 54 entries in the paperare new Hipparcos binaries. New triple systems with late-type dwarfcomponents, discovered in the course of observations, are HIP 8533 andHIP 25354.Based on data collected at the Special Astrophysical Observatory,Russia.{Tables 1-3 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?/A+A/422/627
| Speckle Observations of Binary Stars with the WIYN Telescope. IV. Differential Photometry
Five hundred seventy-six magnitude difference measures are presented for260 binary stars. These measures are derived from CCD-based speckleobservations taken at the WIYN 3.5 m telescope at Kitt Peak NationalObservatory during the period 1997-2000. Separations of the systemsrange from over 1" down to near the diffraction limit of the telescope.A study of multiple measures of the same targets indicates that themeasures have a typical uncertainty of better than 0.13 mag per 2 minuteobservation, and that multiple observations can be averaged to arrive atsmaller uncertainties. Results presented here are also compared, insofaras it is possible, with measures in the Hipparcos Catalogue and toprevious studies using adaptive optics. No major systematic errors wereidentified.The WIYN Observatory is a joint facility of the University ofWisconsin-Madison, Indiana University, Yale University, and the NationalOptical Astronomy Observatory.
| 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.
| Speckle Observations of Binary Stars with the WIYN Telescope. II. Relative Astrometry Measures during 1998-2000
Five hundred twelve relative astrometry measures are presented for 253double stars, including 53 double stars discovered by Hipparcos. In 15cases, relative astrometry is reported for the first time for newlyconfirmed pairs. In addition, 20 high-quality nondetections ofcompanions are reported for stars suspected of being nonsingle byHipparcos. Observations were taken using a fast-readout CCD camerasystem at the WIYN 3.5 m telescope at Kitt Peak, Arizona. In comparingthese measures with ephemeris predictions for binary stars with verywell known orbits, we find that the measurement precision is better than3 mas in separation and 1° in position angle per individualobservation. Measurement precision and detection capabilities are fullydiscussed, and confirmed orbital motion is reported in four cases of theHipparcos double star discoveries. The WIYN Observatory is a jointfacility of the University of Wisconsin-Madison, Indiana University,Yale University, and the National Optical Astronomy Observatory.
| Tidal Evolution of the Planetary System around HD 83443
Two planets with an orbital period ratio of approximately 10:1 have beendiscovered around the star HD 83443. The inner and more massive planet,HD 83443b, has the smallest semimajor axis among all currently knownexoplanets. Unlike other short-period exoplanets, it maintains asubstantial orbital eccentricity, e1=0.079+/-0.008, in spiteof efficient tidal damping. This is a consequence of its secularinteractions with HD 83443c, whose orbital eccentricitye2=0.42+/-0.06. Dissipation, associated with tides the starraises in the inner planet, removes energy but not angular momentum fromits orbit, while secular interactions transfer angular momentum but notenergy from the inner to the outer planet's orbit. The outward transferof angular momentum decreases the tidal decay rate of the inner planet'sorbital eccentricity while increasing that of the outer planet. Thealignment of the apsides of the planets' orbits is another consequenceof tidal and secular interactions. In this state the ratio of theirorbital eccentricities, e1/e2, depends on thesecular perturbations the planets exert on each other and on additionalperturbations that enhance the inner planet's precession rate. Tidal androtational distortions of the inner planet along with general relativityprovide the most important of these extra precessional perturbations,each of which acts to reduce e1/e2. Provided theplanets' orbits are coplanar, the observed eccentricity ratio uniquelyrelates sini andC≡(k2/k2J)(R1/RJ)5, where the tidal Love number, k2, andradius, R1, of the inner planet are scaled by their Jovianequivalents.
| Astrometric radial velocities. III. Hipparcos measurements of nearby star clusters and associations
Radial motions of stars in nearby moving clusters are determined fromaccurate proper motions and trigonometric parallaxes, without any use ofspectroscopy. Assuming that cluster members share the same velocityvector (apart from a random dispersion), we apply a maximum-likelihoodmethod on astrometric data from Hipparcos to compute radial and spacevelocities (and their dispersions) in the Ursa Major, Hyades, ComaBerenices, Pleiades, and Praesepe clusters, and for theScorpius-Centaurus, alpha Persei, and ``HIP 98321'' associations. Theradial motion of the Hyades cluster is determined to within 0.4 kms-1 (standard error), and that of its individual stars towithin 0.6 km s-1. For other clusters, Hipparcos data yieldastrometric radial velocities with typical accuracies of a few kms-1. A comparison of these astrometric values withspectroscopic radial velocities in the literature shows a good generalagreement and, in the case of the best-determined Hyades cluster, alsopermits searches for subtle astrophysical differences, such as evidencefor enhanced convective blueshifts of F-dwarf spectra, and decreasedgravitational redshifts in giants. Similar comparisons for the ScorpiusOB2 complex indicate some expansion of its associations, albeit slowerthan expected from their ages. As a by-product from the radial-velocitysolutions, kinematically improved parallaxes for individual stars areobtained, enabling Hertzsprung-Russell diagrams with unprecedentedaccuracy in luminosity. For the Hyades (parallax accuracy 0.3 mas), itsmain sequence resembles a thin line, possibly with wiggles in it.Although this main sequence has underpopulated regions at certaincolours (previously suggested to be ``Böhm-Vitense gaps''), suchare not visible for other clusters, and are probably spurious. Futurespace astrometry missions carry a great potential for absoluteradial-velocity determinations, insensitive to the complexities ofstellar spectra. Based on observations by the ESA Hipparcos satellite.Extended versions of Tables \ref{tab1} and \ref{tab2} are available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.125.8) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/381/446
| A Hipparcos study of the Hyades open cluster. Improved colour-absolute magnitude and Hertzsprung-Russell diagrams
Hipparcos parallaxes fix distances to individual stars in the Hyadescluster with an accuracy of ~ 6 percent. We use the Hipparcos propermotions, which have a larger relative precision than the trigonometricparallaxes, to derive ~ 3 times more precise distance estimates, byassuming that all members share the same space motion. An investigationof the available kinematic data confirms that the Hyades velocity fielddoes not contain significant structure in the form of rotation and/orshear, but is fully consistent with a common space motion plus a(one-dimensional) internal velocity dispersion of ~ 0.30 kms-1. The improved parallaxes as a set are statisticallyconsistent with the Hipparcos parallaxes. The maximum expectedsystematic error in the proper motion-based parallaxes for stars in theouter regions of the cluster (i.e., beyond ~ 2 tidal radii ~ 20 pc) isla 0.30 mas. The new parallaxes confirm that the Hipparcos measurementsare correlated on small angular scales, consistent with the limitsspecified in the Hipparcos Catalogue, though with significantly smaller``amplitudes'' than claimed by Narayanan & Gould. We use the Tycho-2long time-baseline astrometric catalogue to derive a set of independentproper motion-based parallaxes for the Hipparcos members. The newparallaxes provide a uniquely sharp view of the three-dimensionalstructure of the Hyades. The colour-absolute magnitude diagram of thecluster based on the new parallaxes shows a well-defined main sequencewith two ``gaps''/``turn-offs''. These features provide the first directobservational support of Böhm-Vitense's prediction that (the onsetof) surface convection in stars significantly affects their (B-V)colours. We present and discuss the theoretical Hertzsprung-Russelldiagram (log L versus log T_eff) for an objectively defined set of 88high-fidelity members of the cluster as well as the delta Scuti startheta 2 Tau, the giants delta 1, theta1, epsilon , and gamma Tau, and the white dwarfs V471 Tau andHD 27483 (all of which are also members). The precision with which thenew parallaxes place individual Hyades in the Hertzsprung-Russelldiagram is limited by (systematic) uncertainties related to thetransformations from observed colours and absolute magnitudes toeffective temperatures and luminosities. The new parallaxes providestringent constraints on the calibration of such transformations whencombined with detailed theoretical stellar evolutionary modelling,tailored to the chemical composition and age of the Hyades, over thelarge stellar mass range of the cluster probed by Hipparcos.
| 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.
| ICCD Speckle Observations of Binary Stars. XXIII. Measurements during 1982-1997 from Six Telescopes, with 14 New Orbits
We present 2017 observations of 1286 binary stars, observed by means ofspeckle interferometry using six telescopes over a 15 year period from1982 April to 1997 June. These measurements constitute the 23dinstallment in CHARA's speckle program at 2 to 4 m class telescopes andinclude the second major collection of measurements from the MountWilson 100 inch (2.5 m) Hooker Telescope. Orbital elements are alsopresented for 14 systems, seven of which have had no previouslypublished orbital analyses.
| X-Ray Observations of Two Intermediate-Age Open Clusters: NGC 1039 and NGC 3532
Soft X-ray images of the intermediate-age (~250 Myr) NGC 1039 and NGC3532 open star clusters have been acquired with the ROSAT HighResolution Imager, resulting in the detection of 75 sources above a 3σ detection level of LX~=2.5×1029 ergss-1. Roughly half the sources detected in both images havelikely optical counterparts from earlier ground-based surveys. Theremainder are either prospective cluster members orforeground/background stars, which can be decided only throughadditional photometry, spectroscopy, and proper-motion studies. There issome indication (at the 98% confidence level) that solar-type stars inboth clusters, and in the similarly aged NGC 6475 cluster, may lack theextreme rotation and activity levels shown by those in the much youngerPleiades and α Persei clusters, but a detailed assessment of thecoronal X-ray properties of these clusters must await more sensitiveobservations in the future. If confirmed, this finding could help torule out the possibility that stellar dynamo activity and rotationalbraking are controlled by a rapidly spinning central core as stars passthrough this phase of evolution from the Pleiades stage to thatrepresented by the Hyades.
| Secular Evolution of Hierarchical Triple Star Systems
We derive octupole-level secular perturbation equations for hierarchicaltriple systems, using classical Hamiltonian perturbation techniques. Ourequations describe the secular evolution of the orbital eccentricitiesand inclinations over timescales that are long compared to the orbitalperiods. By extending previous work done to leading (quadrupole) orderto octupole level (i.e., including terms of order α3,where α≡a1/a2<1 is the ratio ofsemimajor axes), we obtain expressions that are applicable to a muchwider range of parameters. In particular, our results can be applied tohigh-inclination as well as coplanar systems, and our expressions arevalid for almost all mass ratios for which the system is in a stablehierarchical configuration. In contrast, the standard quadrupole-leveltheory of Kozai gives a vanishing result in the limit of zero relativeinclination. The classical planetary perturbation theory, while valid toall orders in α, applies only to orbits of low-mass objectsorbiting a common central mass, with low eccentricities and low relativeinclinations. For triple systems containing a close inner binary, wealso discuss the possible interaction between the classical Newtonianperturbations and the general relativistic precession of the innerorbit. In some cases we show that this interaction can lead toresonances and a significant increase in the maximum amplitude ofeccentricity perturbations. We establish the validity of our analyticexpressions by providing detailed comparisons with the results of directnumerical integrations of the three-body problem obtained for a largenumber of representative cases. In addition, we show that ourexpressions reduce correctly to previously published analytic resultsobtained in various limiting regimes. We also discuss applications ofthe theory in the context of several observed triple systems of currentinterest, including the millisecond pulsar PSR B1620-26 in M4, the giantplanet in 16 Cygni, and the protostellar binary TMR-1.
| 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 74th Special Name-list of Variable Stars
We present the Name-list introducing GCVS names for 3153 variable starsdiscovered by the Hipparcos mission.
| 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.
| The Hyades: distance, structure, dynamics, and age
{We use absolute trigonometric parallaxes from the Hipparcos Catalogueto determine individual distances to members of the Hyades cluster, fromwhich the 3-dimensional structure of the cluster can be derived.Inertially-referenced proper motions are used to rediscuss distancedeterminations based on convergent-point analyses. A combination ofparallaxes and proper motions from Hipparcos, and radial velocities fromground-based observations, are used to determine the position andvelocity components of candidate members with respect to the clustercentre, providing new information on cluster membership: 13 newcandidate members within 20 pc of the cluster centre have beenidentified. Farther from the cluster centre there is a gradual mergingbetween certain cluster members and field stars, both spatially andkinematically. Within the cluster, the kinematical structure is fullyconsistent with parallel space motion of the component stars with aninternal velocity dispersion of about 0.3 km s(-1) . The spatialstructure and mass segregation are consistent with N-body simulationresults, without the need to invoke expansion, contraction, rotation, orother significant perturbations of the cluster. The quality of theindividual distance determinations permits the cluster zero-age mainsequence to be accurately modelled. The helium abundance for the clusteris determined to be Y =3D 0.26+/-0.02 which, combined with isochronemodelling including convective overshooting, yields a cluster age of625+/-50 Myr. The distance to the observed centre of mass (a conceptmeaningful only in the restricted context of the cluster memberscontained in the Hipparcos Catalogue) is 46.34+/-0.27 pc, correspondingto a distance modulus m-M=3D3.33+/-0.01 mag for the objects within 10 pcof the cluster centre (roughly corresponding to the tidal radius). Thisdistance modulus is close to, but significantly better determined than,that derived from recent high-precision radial velocity studies,somewhat larger than that indicated by recent ground-based trigonometricparallax determinations, and smaller than those found from recentstudies of the cluster convergent point. These discrepancies areinvestigated and explained. } Based on observations made with the ESAHipparcos astrometry satellite. Table~2 is also available in electronicform at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)or via http://cdsweb.u-strasbg.fr/Abstract.html
| 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 ROSAT All-Sky Survey of Active Binary Coronae. III. Quiescent Coronal Properties for the BY Draconis--Type Binaries
We present X-ray observations of 35 active late-type BY Draconis dwarfbinary systems and 28 evolved binary systems, similar in nature to theRS Canum Venaticorum systems, obtained with the Position SensitiveProportional Counter (PSPC) during the ROSAT All-Sky Survey phase of themission. Of this sample, 52 targets were detected in exposures ofroughly 600 s or less. When these new data are combined with the earlierresults from Dempsey et al. (1993b), this survey represents the largestsample of active binary systems observed to date at any wavelength,including X-rays. We expand our investigation of how coronal properties(e.g., surface flux, luminosity, etc.) correlate with stellar parameters(e.g., rotation period, color, etc.) and confirm the conclusions ofDempsey et al. (1993b). Rotation period provides the best correlationwith X-ray surface flux with F_{{X}}~P^{-0.59+/-0.10}_{{rot}} for theentire sample. We find no evidence for a "basal" or nonmagnetic X-rayflux component. We model the low-resolution pulse-height spectra for 12systems with two-temperature thermal plasmas. The derived temperaturesfor the BY Dra systems are identical to those previously derived foractive evolved giants and subgiants in close binaries (Dempsey et al.1993c). We also show that the dependence of temperature and emissionmeasures on rotation period is the same for the dwarf, subgiant, andgiant binaries.
| The X-ray evidence that the 51 Peg companion is a planet
51 Pegasi is a nearby G2--3 V star which is similar to the Sun. Mayor& Queloz (1995) [Natur, 378, 355] have recently found that 51 Peghas sinusoidal radial velocity variations with a period of 4.2 days andamplitude of 59 m/s. The radial velocity, if due to orbital motionaround the system center-of-mass, implies a minimum companion mass of0.47 Jupiter masses, which results from the assumption that theinclination angle of the system is 90 deg from the line of sight.However, because the inclination angle is not directly measured thereremains an uncertainty in the companion mass. In the limit of anear-zero inclination angle the companion could even be a late-typedwarf star. We argue that the low measured X-ray luminosity of the 51Peg system supports the conclusion that the companion is a planet,independent of any assumption about the inclination angle. If 51 Pegwere a binary stellar system with a 4-day orbital period its X-rayemission would be in marked contrast with ALL known binary stellarsystems with similar orbital periods. When compared to the distributionof binary star X-ray luminosities, a system with the 51 Peg X-rayluminosity have an occurrence probability of only 1.7 times 10^-6. Thelow X-ray luminosity also confirms that 51 Peg is a slow rotator basedupon the correlation between X-ray emission and rotational velocity. Wediscuss the lack of synchronization between the 51 Peg orbital androtational periods and calculate model-dependent upper limits on thecompanion mass which also indicate that it is a planet.
| 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 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
|
Додај нови чланак
Линкови у сродству са темом
Додај нови линк
Чланови следећих група \:
|
Посматрања и Астрометриски подаци
| Сазвежђа: | Бик |
| Ректацензија: | 04h11m56.22s |
| Deклинација: | +23°38'10.7" |
| Apparent магнитуда: | 9.444 |
| Даљина: | 36.751 parsecs |
| Proper motion RA: | 143.1 |
| Proper motion Dec: | -56 |
| B-T magnitude: | 10.77 |
| V-T magnitude: | 9.554 |
Каталог и designations:
|
