SKY-MAP.ORG
 首页 开始 To Survive in the Universe News@Sky 天文图片 收集 论坛 Blog New! 常见问题 新闻 登录

# ι Leo (Tsze Tseang)

### 图像

DSS Images   Other Images

### 相关文章

 Reduction of time-resolved space-based CCD photometry developed for MOST Fabry Imaging data*The MOST (Microvariability and Oscillations of Stars) satellite obtainsultraprecise photometry from space with high sampling rates and dutycycles. Astronomical photometry or imaging missions in low Earth orbits,like MOST, are especially sensitive to scattered light from Earthshine,and all these missions have a common need to extract target informationfrom voluminous data cubes. They consist of upwards of hundreds ofthousands of two-dimensional CCD frames (or subrasters) containing fromhundreds to millions of pixels each, where the target information,superposed on background and instrumental effects, is contained only ina subset of pixels (Fabry Images, defocused images, mini-spectra). Wedescribe a novel reduction technique for such data cubes: resolvinglinear correlations of target and background pixel intensities. Thisstep-wise multiple linear regression removes only those targetvariations which are also detected in the background. The advantage ofregression analysis versus background subtraction is the appropriatescaling, taking into account that the amount of contamination may differfrom pixel to pixel. The multivariate solution for all pairs oftarget/background pixels is minimally invasive of the raw photometrywhile being very effective in reducing contamination due to, e.g. straylight. The technique is tested and demonstrated with both simulatedoscillation signals and real MOST photometry. Asteroseismology and interferometry .Asteroseismology aims at constraining the stellar evolution theory, andallows to determine the age of stars together with other fundamentalparameters. We present recent results obtained by interferometry, andprospects for the future. The Asiago Database of Spectroscopic Databases (ADSD)Databases of observed stellar spectra are continuously being publishedand made publicly available, and the average number of stars perdatabase is increasing. This paper reviews the current status. TheAsiago Database of Spectroscopic Databases (ADSD) aims to provide acensus of publicly available libraries of observed stellar spectra, todocument their content and to homogenize their parameters for easierconsultation and access. Refereed journals, conference proceedings andpersonal web pages have been searched for libraries of a given minimumsize, properly documented and with data made publicly and directlyaccessible. A total of 294 databases (54 ultraviolet, 183 optical, 50infrared and 7 combined) have been found to match the selection criteriaand have been included in ADSD. They provide spectra of 16046 differentstars in electronic or printed formats. A card for each librarydescribes in a homogeneous way its aims, content, type of data, caveats,data download links, source paper, properties of included stars andmore. A dedicated web page allows direct access to ADSD, plans futureupdates, and provides interrogation tools to search all the librariesmatching given characteristics or including any given star. Can Life Develop in the Expanded Habitable Zones around Red Giant Stars?We present some new ideas about the possibility of life developingaround subgiant and red giant stars. Our study concerns the temporalevolution of the habitable zone. The distance between the star and thehabitable zone, as well as its width, increases with time as aconsequence of stellar evolution. The habitable zone moves outward afterthe star leaves the main sequence, sweeping a wider range of distancesfrom the star until the star reaches the tip of the asymptotic giantbranch. Currently there is no clear evidence as to when life actuallyformed on the Earth, but recent isotopic data suggest life existed atleast as early as 7×108 yr after the Earth was formed.Thus, if life could form and evolve over time intervals from5×108 to 109 yr, then there could behabitable planets with life around red giant stars. For a 1Msolar star at the first stages of its post-main-sequenceevolution, the temporal transit of the habitable zone is estimated to beseveral times 109 yr at 2 AU and around 108 yr at9 AU. Under these circumstances life could develop at distances in therange 2-9 AU in the environment of subgiant or giant stars, and in thefar distant future in the environment of our own solar system. After astar completes its first ascent along the red giant branch and the Heflash takes place, there is an additional stable period of quiescent Hecore burning during which there is another opportunity for life todevelop. For a 1 Msolar star there is an additional109 yr with a stable habitable zone in the region from 7 to22 AU. Space astronomy missions, such as proposed for the TerrestrialPlanet Finder (TPF) and Darwin, that focus on searches for signatures oflife on extrasolar planets, should also consider the environments ofsubgiants and red giant stars as potentially interesting sites forunderstanding the development of life. We performed a preliminaryevaluation of the difficulty of interferometric observations of planetsaround red giant stars compared to a main-sequence star environment. Weshow that pathfinder missions for TPF and Darwin, such as Eclipse andFKSI, have sufficient angular resolution and sensitivity to search forhabitable planets around some of the closest evolved stars of thesubgiant and red giant class. UVBLUE: A New High-Resolution Theoretical Library of Ultraviolet Stellar SpectraWe present an extended ultraviolet-blue (850-4700 Å) library oftheoretical stellar spectral energy distributions computed at highresolution, λ/Δλ=50,000. The UVBLUE grid, as wenamed the library, is based on LTE calculations carried out with ATLAS9and SYNTHE codes developed by R. L. Kurucz and consists of nearly 1800entries that cover a large volume of the parameter space. It spans arange in Teff from 3000 to 50,000 K, the surface gravityranges from logg=0.0 to 5.0 with Δlogg=0.5 dex, while sevenchemical compositions are considered:[M/H]=-2.0,-1.5,-1.0,-0.5,+0.0,+0.3, and +0.5 dex. For its coverageacross the Hertzsprung-Russell diagram, this library is the mostcomprehensive one ever computed at high resolution in theshort-wavelength spectral range, and useful application can be foreseenfor both the study of single stars and in population synthesis models ofgalaxies and other stellar systems. We briefly discuss some relevantissues for a safe application of the theoretical output to ultravioletobservations, and a comparison of our LTE models with the non-LTE (NLTE)ones from the TLUSTY code is also carried out. NLTE spectra are found,on average, to be slightly redder'' compared to the LTE ones for thesame value of Teff, while a larger difference could bedetected for weak lines, which are nearly wiped out by the enhanced coreemission component in case of NLTE atmospheres. These effects seem to bemagnified at low metallicity (typically [M/H]<~-1). A match with aworking sample of 111 stars from the IUE atlas, with availableatmosphere parameters from the literature, shows that UVBLUE modelsprovide an accurate description of the main mid- and low-resolutionspectral features for stars along the whole sequence from the B to ~G5type. The comparison sensibly degrades for later spectral types, withsupergiant stars that are in general more poorly reproduced than dwarfs.As a possible explanation of this overall trend, we partly invoke theuncertainty in the input atmosphere parameters to compute thetheoretical spectra. In addition, one should also consider the importantcontamination of the IUE stellar sample, where the presence of binaryand variable stars certainly works in the sense of artificiallyworsening the match between theory and observations. Boron Depletion in F and G Dwarf Stars and the Beryllium-Boron CorrelationBoron provides a special probe below the stellar surface since itsurvives to greater depths than do Li and Be. To search for B depletionswe have observed B in 13 F and G dwarfs with large Be depletions; forcomparison we have also obtained spectra of five stars that areundepleted in Li and Be. We have used HST with STIS to obtain spectra ofthe B I resonance line at 2497 Å. The spectral resolution is30,000 or 114,000, and the median signal-to-noise ratio is 70pixel-1. New Be and Li spectra have been obtained at Keck Iwith HIRES of four of the five standard stars at ~48,000 resolution.Abundances have been determined by the spectrum synthesis method withMOOG. A comparison between the standard stars and those with severe Bedepletions shows a distinct difference in the B abundances between thetwo groups of 0.22 dex. We have discovered a correlation between the Beand B abundances. The slope between A(Be) and A(B)NLTE is0.22+/-0.05 [where A(element)=logN(element)/N(H)+12.00], which, asexpected, is shallower than the slope between A(Li) and A(Be) of 0.38.We have normalized the light-element abundances to account for theobservation that the initial abundances are somewhat lower in lowermetallicity stars by employing recently published empirical relationsbetween Be and [Fe/H] and between B and [Fe/H]. The correlation betweenthe normalized A(Be) and A(B)NLTE has a slope of 0.18+/-0.06.The star with the largest Be depletion, HR 107, a main-sequence Ba star,also has the largest B depletion, with the B abundance lower by a factorof 3.5 relative to the standard stars.Based on observations obtained with the NASA/ESA Hubble Space Telescopethrough the Space Telescope Science Institute, which is operated by theAssociation of Universities for Research in Astronomy, Inc., under NASAcontract NAS5-26555. Adaptive Optics Photometry and Astrometry of Binary StarsWe present astrometric and photometric measurements of 39 binary starsmade with the adaptive optics system on the 3.6 m AdvancedElectro-Optical System (AEOS) telescope, taken from 2002 November to2003 March. The binaries have separations ranging from 0.08" to 5.11"and differential magnitudes ranging from 0.096 to 7.9. Also, we includea list of observations of 23 known binaries that we were unable toresolve. In the process of these measurements, we discovered three newcompanions to two previously known binary stars. We also discuss theeffects of scintillation and anisoplanatism on measurements of binarystar photometry in adaptive optics images. Suggestions on how tominimize these effects are then given.Based on observations made at the Maui Space Surveillance Systemoperated by Detachment 15 of the US Air Force Research Laboratory'sDirected Energy Directorate. Lithium abundances of the local thin disc starsLithium abundances are presented for a sample of 181 nearby F and Gdwarfs with accurate Hipparcos parallaxes. The stars are on circularorbits about the Galactic centre and, hence, are identified as belongingto the thin disc. This sample is combined with two published surveys toprovide a catalogue of lithium abundances, metallicities ([Fe/H]),masses, and ages for 451 F-G dwarfs, almost all belonging to the thindisc. The lithium abundances are compared and contrasted with publishedlithium abundances for F and G stars in local open clusters. The fieldstars span a larger range in [Fe/H] than the clusters for which [Fe/H]~=0.0 +/- 0.2. The initial (i.e. interstellar) lithium abundance of thesolar neighbourhood, as derived from stars for which astration oflithium is believed to be unimportant, is traced from logɛ(Li) =2.2 at [Fe/H]=-1 to logɛ(Li) = 3.2 at +0.1. This form for theevolution is dependent on the assumption that astration of lithium isnegligible for the stars defining the relation. An argument is advancedthat this latter assumption may not be entirely correct, and, theevolution of lithium with [Fe/H] may be flatter than previouslysupposed. A sharp Hyades-like Li dip is not seen among the field starsand appears to be replaced by a large spread among lithium abundances ofstars more massive than the lower mass limit of the dip. Astration oflithium by stars of masses too low to participate in the Li dip isdiscussed. These stars show little to no spread in lithium abundance ata given [Fe/H] and mass. A near-infrared stellar spectral library: I. H-band spectra.This paper presents the H band near-infrared (NIR) spectral library of135 solar type stars covering spectral types O5-M3 and luminosityclasses I-V as per MK classification. The observations were carried outwith 1.2 meter Gurushikhar Infrared Telescope (GIRT), at Mt. Abu, Indiausing a NICMOS3 HgCdTe 256 x 256 NIR array based spectrometer. Thespectra have a moderate resolution of 1000 (about 16 A) at the H bandand have been continuum shape corrected to their respective effectivetemperatures. This library and the remaining ones in J and K bands oncereleased will serve as an important database for stellar populationsynthesis and other applications in conjunction with the newly formedlarge optical coude feed stellar spectral library of Valdes et al.(2004). The complete H-Band library is available online at: http://vo.iucaa.ernet.in/~voi/NIR_Header.html The Indo-US Library of Coudé Feed Stellar SpectraWe have obtained spectra for 1273 stars using the 0.9 m coudéfeed telescope at Kitt Peak National Observatory. This telescope feedsthe coudé spectrograph of the 2.1 m telescope. The spectra havebeen obtained with the no. 5 camera of the coudé spectrograph anda Loral 3K×1K CCD. Two gratings have been used to provide spectralcoverage from 3460 to 9464 Å, at a resolution of ~1 Å FWHMand at an original dispersion of 0.44 Å pixel-1. For885 stars we have complete spectra over the entire 3460 to 9464 Åwavelength region (neglecting small gaps of less than 50 Å), andpartial spectral coverage for the remaining stars. The 1273 stars havebeen selected to provide broad coverage of the atmospheric parametersTeff, logg, and [Fe/H], as well as spectral type. The goal ofthe project is to provide a comprehensive library of stellar spectra foruse in the automated classification of stellar and galaxy spectra and ingalaxy population synthesis. In this paper we discuss thecharacteristics of the spectral library, viz., details of theobservations, data reduction procedures, and selection of stars. We alsopresent a few illustrations of the quality and information available inthe spectra. The first version of the complete spectral library is nowpublicly available from the National Optical Astronomy Observatory(NOAO) via ftp and http. Synthetic Lick Indices and Detection of α-enhanced Stars. II. F, G, and K Stars in the -1.0 < [Fe/H] < +0.50 RangeWe present an analysis of 402 F, G, and K solar neighborhood stars, withaccurate estimates of [Fe/H] in the range -1.0 to +0.5 dex, aimed at thedetection of α-enhanced stars and at the investigation of theirkinematical properties. The analysis is based on the comparison of 571sets of spectral indices in the Lick/IDS system, coming from fourdifferent observational data sets, with synthetic indices computed withsolar-scaled abundances and with α-element enhancement. We useselected combinations of indices to single out α-enhanced starswithout requiring previous knowledge of their main atmosphericparameters. By applying this approach to the total data set, we obtain alist of 60 bona fide α-enhanced stars and of 146 stars withsolar-scaled abundances. The properties of the detected α-enhancedand solar-scaled abundance stars with respect to their [Fe/H] values andkinematics are presented. A clear kinematic distinction betweensolar-scaled and α-enhanced stars was found, although a one-to-onecorrespondence to thin disk'' and thick disk'' components cannot besupported with the present data. Boron Benchmarks for the Galactic DiskSixteen Population I solar-type dwarfs have been selected to ascertainthe baseline B abundance in the Galactic disk for a range of a factor of4 in metallicity: from [Fe/H] of -0.5 to +0.1. All the stars selectedare undepleted in Be, which ensures that they have also retained theirfull initial abundance of B. Evaluation of the trend of B with Feprovides a means to study the evolution of B in the Galactic disk. Weobserved 16 bright stars around the B I 2497 Å line, using theSTIS echelle spectrograph on HST. New observations of Li and Be in somestars were made, and previous abundance studies of Li and Be in thesestars were reevaluated using revised parameters and a modified spectralsynthesis code for consistency with the B measurements. Abundances of Bwere calculated by spectrum synthesis with the revised MOOG code, whichaccounts for the increased opacity in the UV due to metals; the LTE Babundances were then corrected for non-LTE effects. Four additionalstars with undepleted Be have HST B observations, which increase oursample to 20. For these disk stars there is a shallow slope for B versusFe and Be versus Fe, such that as Fe increases by a factor of 4, B andBe increase by 1.7 times. The slope for BLTE versus Fe is0.31+/-0.09, for BNLTE versus Fe 0.40+/-0.12, and for Beversus Fe 0.38+/-0.14. We have estimated the effect of additional UVopacity from Mg and find that an increase of 0.3 dex in Mg results in ahigher B abundances by 0.1 dex for all the disk stars. Individual starsare not consistently above (or below) the mean in both B and Be,implying that the star-to-star differences are not due to variations inthe elemental content of the natal'' clouds. We find that the trend ofB abundance with [Fe/H] is consistent with the general trend observed inhalo stars. If we connect the halo and disk stars, then an increase inthe Fe abundance by 103 is accompanied by increases of 100times in B and 550 times in Be. However, fitting two separate relationsfor the disk and the halo stars results in a somewhat steeper slope forBe for the halo stars (1.08+/-0.07) relative to the disk stars(0.38+/-0.14). This is the case for B also in LTE, with Bhalo(0.90+/-0.07) versus Bdisk (0.32+/-0.12). However, the NLTE Babundance increases more slowly for halo stars than the Be abundancedoes; since this is not predicted by light-element synthesis ordepletion, we suggest that a full NLTE analysis would be preferable tomaking the (small) corrections to the LTE abundances. Some of the lowestmetallicity stars are thought to have only upper limits on the Babundance; if that is the case, the NLTE B slope is steeper, nearing1.0. The abundance of B in the disk stars is observed to be a factor of~15+7-5 more than the abundance of Be in thesestars, a result consistent with the predictions of Galactic cosmic-ray(GCR) spallation, B/Be=15+/-5. The upper envelope for Li versus Feyields Li/B and Li/Be ratios that, when coupled with models andpredictions, indicate that 20%-45% of Li might be produced by GCRs.While there is no evidence to support the production of B by neutrinospallation, we cannot rule it out.Based on observations obtained with the NASA/ESA Hubble Space Telescope(HST) through the Space Telescope Science Institute, which is operatedby the Association of Universities for Research in Astronomy, Inc.,under NASA contract NAS5-26555. The Structure of the Local Interstellar Medium. II. Observations of D I, C II, N I, O I, Al II, and Si II toward Stars within 100 ParsecsModerate- and high-resolution measurements(λ/Δλ>~40,000) of interstellar resonance lines ofD I, C II, N I, O I, Al II, and Si II (hereafter called light ions) arepresented for all available observed targets located within 100 pc thatalso have high-resolution observations of interstellar Fe II or Mg II(heavy ions) lines. All spectra were obtained with the Goddard HighResolution Spectrograph or the Space Telescope Imaging Spectrographinstrument aboard the Hubble Space Telescope. Currently, there are 41sight lines to targets within 100 pc with observations that include aheavy ion at high resolution and at least one light ion at moderate orhigh resolution. We present new measurements of light ions along 33 ofthese sight lines and collect from the literature results for theremaining sight lines that have already been analyzed. For all of thenew observations we provide measurements of the central velocity,Doppler width parameter, and column density for each absorptioncomponent. We greatly increase the number of sight lines with usefullocal interstellar medium (LISM) absorption-line measurements of lightions by using knowledge of the kinematic structure along a line of sightobtained from high-resolution observations of intrinsically narrowabsorption lines, such as Fe II and Mg II. We successfully fit theabsorption lines with this technique, even with moderate-resolutionspectra. Because high-resolution observations of heavy ions are criticalfor understanding the kinematic structure of local absorbers along theline of sight, we include 18 new measurements of Fe II and Mg II in anAppendix. We present a statistical analysis of the LISM absorptionmeasurements, which provides an overview of some physicalcharacteristics of warm clouds in the LISM, including temperature andturbulent velocity. This complete collection and reduction of allavailable LISM absorption measurements provides an important databasefor studying the structure of nearby warm clouds, including ionization,abundances, and depletions. Subsequent papers will present models forthe morphology and physical properties of individual structures (clouds)in the LISM.Based on observations made with the NASA/ESA Hubble Space Telescope,obtained from the Data Archive at the Space Telescope Science Institute,which is operated by the Association of Universities for Research inAstronomy, Inc., under NASA contract NAS AR-09525.01A. Theseobservations are associated with program 9525. Nearby stars of the Galactic disk and halo. III.High-resolution spectroscopic observations of about 150 nearby stars orstar systems are presented and discussed. The study of these and another100 objects of the previous papers of this series implies that theGalaxy became reality 13 or 14 Gyr ago with the implementation of amassive, rotationally-supported population of thick-disk stars. The veryhigh star formation rate in that phase gave rise to a rapid metalenrichment and an expulsion of gas in supernovae-driven Galactic winds,but was followed by a star formation gap for no less than three billionyears at the Sun's galactocentric distance. In a second phase, then, thethin disk - our familiar Milky Way'' - came on stage. Nowadays ittraces the bright side of the Galaxy, but it is also embedded in a hugecoffin of dead thick-disk stars that account for a large amount ofbaryonic dark matter. As opposed to this, cold-dark-matter-dominatedcosmologies that suggest a more gradual hierarchical buildup throughmergers of minor structures, though popular, are a poor description forthe Milky Way Galaxy - and by inference many other spirals as well - if,as the sample implies, the fossil records of its long-lived stars do notstick to this paradigm. Apart from this general picture that emergeswith reference to the entire sample stars, a good deal of the presentwork is however also concerned with detailed discussions of manyindividual objects. Among the most interesting we mention the bluestraggler or merger candidates HD 165401 and HD 137763/HD 137778, thelikely accretion of a giant planet or brown dwarf on 59 Vir in itsrecent history, and HD 63433 that proves to be a young solar analog at\tau200 Myr. Likewise, the secondary to HR 4867, formerly suspectednon-single from the Hipparcos astrometry, is directly detectable in thehigh-resolution spectroscopic tracings, whereas the visual binary \chiCet is instead at least triple, and presumably even quadruple. Withrespect to the nearby young stars a complete account of the Ursa MajorAssociation is presented, and we provide as well plain evidence foranother, the Hercules-Lyra Association'', the likely existence ofwhich was only realized in recent years. On account of its rotation,chemistry, and age we do confirm that the Sun is very typical among itsG-type neighbors; as to its kinematics, it appears however not unlikelythat the Sun's known low peculiar space velocity could indeed be thecause for the weak paleontological record of mass extinctions and majorimpact events on our parent planet during the most recent Galactic planepassage of the solar system. Although the significance of thiscorrelation certainly remains a matter of debate for years to come, wepoint in this context to the principal importance of the thick disk fora complete census with respect to the local surface and volumedensities. Other important effects that can be ascribed to this darkstellar population comprise (i) the observed plateau in the shape of theluminosity function of the local FGK stars, (ii) a small thoughsystematic effect on the basic solar motion, (iii) a reassessment of theterm asymmetrical drift velocity'' for the remainder (i.e. the thindisk) of the stellar objects, (iv) its ability to account for the bulkof the recently discovered high-velocity blue white dwarfs, (v) itsmajor contribution to the Sun's 220 km s-1 rotationalvelocity around the Galactic center, and (vi) the significant flatteningthat it imposes on the Milky Way's rotation curve. Finally we note ahigh multiplicity fraction in the small but volume-complete local sampleof stars of this ancient population. This in turn is highly suggestivefor a star formation scenario wherein the few existing single stellarobjects might only arise from either late mergers or the dynamicalejection of former triple or higher level star systems. The Geneva-Copenhagen survey of the Solar neighbourhood. Ages, metallicities, and kinematic properties of 14 000 F and G dwarfsWe present and discuss new determinations of metallicity, rotation, age,kinematics, and Galactic orbits for a complete, magnitude-limited, andkinematically unbiased sample of 16 682 nearby F and G dwarf stars. Our63 000 new, accurate radial-velocity observations for nearly 13 500stars allow identification of most of the binary stars in the sampleand, together with published uvbyβ photometry, Hipparcosparallaxes, Tycho-2 proper motions, and a few earlier radial velocities,complete the kinematic information for 14 139 stars. These high-qualityvelocity data are supplemented by effective temperatures andmetallicities newly derived from recent and/or revised calibrations. Theremaining stars either lack Hipparcos data or have fast rotation. Amajor effort has been devoted to the determination of new isochrone agesfor all stars for which this is possible. Particular attention has beengiven to a realistic treatment of statistical biases and errorestimates, as standard techniques tend to underestimate these effectsand introduce spurious features in the age distributions. Our ages agreewell with those by Edvardsson et al. (\cite{edv93}), despite severalastrophysical and computational improvements since then. We demonstrate,however, how strong observational and theoretical biases cause thedistribution of the observed ages to be very different from that of thetrue age distribution of the sample. Among the many basic relations ofthe Galactic disk that can be reinvestigated from the data presentedhere, we revisit the metallicity distribution of the G dwarfs and theage-metallicity, age-velocity, and metallicity-velocity relations of theSolar neighbourhood. Our first results confirm the lack of metal-poor Gdwarfs relative to closed-box model predictions (the G dwarfproblem''), the existence of radial metallicity gradients in the disk,the small change in mean metallicity of the thin disk since itsformation and the substantial scatter in metallicity at all ages, andthe continuing kinematic heating of the thin disk with an efficiencyconsistent with that expected for a combination of spiral arms and giantmolecular clouds. Distinct features in the distribution of the Vcomponent of the space motion are extended in age and metallicity,corresponding to the effects of stochastic spiral waves rather thanclassical moving groups, and may complicate the identification ofthick-disk stars from kinematic criteria. More advanced analyses of thisrich material will require careful simulations of the selection criteriafor the sample and the distribution of observational errors.Based on observations made with the Danish 1.5-m telescope at ESO, LaSilla, Chile, and with the Swiss 1-m telescope at Observatoire deHaute-Provence, France.Complete Tables 1 and 2 are only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/418/989 Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 Parsecs: The Northern Sample. I.We have embarked on a project, under the aegis of the Nearby Stars(NStars)/Space Interferometry Mission Preparatory Science Program, toobtain spectra, spectral types, and, where feasible, basic physicalparameters for the 3600 dwarf and giant stars earlier than M0 within 40pc of the Sun. In this paper, we report on the results of this projectfor the first 664 stars in the northern hemisphere. These resultsinclude precise, homogeneous spectral types, basic physical parameters(including the effective temperature, surface gravity, and overallmetallicity [M/H]), and measures of the chromospheric activity of ourprogram stars. Observed and derived data presented in this paper arealso available on the project's Web site. Stellar Kinematic Groups. II. A Reexamination of the Membership, Activity, and Age of the Ursa Major GroupUtilizing Hipparcos parallaxes, original radial velocities and recentliterature values, new Ca II H and K emission measurements,literature-based abundance estimates, and updated photometry (includingrecent resolved measurements of close doubles), we revisit the UrsaMajor moving group membership status of some 220 stars to produce afinal clean list of nearly 60 assured members, based on kinematic andphotometric criteria. Scatter in the velocity dispersions and H-Rdiagram is correlated with trial activity-based membership assignments,indicating the usefulness of criteria based on photometric andchromospheric emission to examine membership. Closer inspection,however, shows that activity is considerably more robust at excludingmembership, failing to do so only for <=15% of objects, perhapsconsiderably less. Our UMa members demonstrate nonzero vertex deviationin the Bottlinger diagram, behavior seen in older and recent studies ofnearby young disk stars and perhaps related to Galactic spiralstructure. Comparison of isochrones and our final UMa group membersindicates an age of 500+/-100 Myr, some 200 Myr older than thecanonically quoted UMa age. Our UMa kinematic/photometric members' meanchromospheric emission levels, rotational velocities, and scattertherein are indistinguishable from values in the Hyades and smaller thanthose evinced by members of the younger Pleiades and M34 clusters,suggesting these characteristics decline rapidly with age over 200-500Myr. None of our UMa members demonstrate inordinately low absolutevalues of chromospheric emission, but several may show residual fluxes afactor of >=2 below a Hyades-defined lower envelope. If one defines aMaunder-like minimum in a relative sense, then the UMa results maysuggest that solar-type stars spend 10% of their entire main-sequencelives in periods of precipitously low activity, which is consistent withestimates from older field stars. As related asides, we note six evolvedstars (among our UMa nonmembers) with distinctive kinematics that liealong a 2 Gyr isochrone and appear to be late-type counterparts to diskF stars defining intermediate-age star streams in previous studies,identify a small number of potentially very young but isolated fieldstars, note that active stars (whether UMa members or not) in our samplelie very close to the solar composition zero-age main sequence, unlikeHipparcos-based positions in the H-R diagram of Pleiades dwarfs, andargue that some extant transformations of activity indices are notadequate for cool dwarfs, for which Ca II infrared triplet emissionseems to be a better proxy than Hα-based values for Ca II H and Kindices. Lithium and rotation in F and G dwarfs and subgiantsLithium abundances have been determined in 127 F and G Pop I stars basedon new measurements of the equivalent width of the lambda 6707 ÅLi I line from their high resolution CCD spectra. Distances and absolutemagnitudes of these stars have been obtained from the HipparcosCatalogue and their masses and ages derived, enabling us to investigatethe behaviour of lithium as a function of these parameters. Based ontheir location on the HR diagram superposed on theoretical evolutionarytracks, the sample of the stars has been chosen to ensure that they havemore or less completed their Li depletion on the main sequence. A largespread in the Li abundances is found at any given effective temperatureespecially in the already spun down late F and early G stars. Thisspread persists even if the Li-dip'' stars that have evolved from themain sequence temperature interval 6500-6800 K are excluded. Stars inthe mass range up to 2 M/Msun when divided into threemetallicity groups show a linear correlation between Li abundance andmass, albeit with a large dispersion around it which is not fullyaccounted for by age either. The large depletions and the observedspread in Li are in contrast to the predictions of the standard stellarmodel calculations and suggest that they are aided by non-standardprocesses depending upon variables besides mass, age and metallicity.The present study was undertaken to examine, in particular, the effectsof rotation on the depletion of Li. No one-to-one correlation is foundbetween the Li abundance and the present projected rotational velocity.Instead the observed abundances seem to be dictated by the rotationalhistory of the star. However, it is noted that even this interpretationis subject to the inherent limitation in the measurement of the observedLi EQW for large rotational velocities.Table 1 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/409/251 Catalogue of averaged stellar effective magnetic fields. I. Chemically peculiar A and B type starsThis paper presents the catalogue and the method of determination ofaveraged quadratic effective magnetic fields < B_e > for 596 mainsequence and giant stars. The catalogue is based on measurements of thestellar effective (or mean longitudinal) magnetic field strengths B_e,which were compiled from the existing literature.We analysed the properties of 352 chemically peculiar A and B stars inthe catalogue, including Am, ApSi, He-weak, He-rich, HgMn, ApSrCrEu, andall ApSr type stars. We have found that the number distribution of allchemically peculiar (CP) stars vs. averaged magnetic field strength isdescribed by a decreasing exponential function. Relations of this typehold also for stars of all the analysed subclasses of chemicalpeculiarity. The exponential form of the above distribution function canbreak down below about 100 G, the latter value representingapproximately the resolution of our analysis for A type stars.Table A.1 and its references 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/407/631 and Tables 3 to 9are only available in electronic form at http://www.edpsciences.org On the link between rotation, chromospheric activity and Li abundance in subgiant starsThe connection rotation-CaII emission flux-lithium abundance is analyzedfor a sample of bona fide subgiant stars, with evolutionary statusdetermined from HIPPARCOS trigonometric parallax measurements and fromthe Toulouse-Geneva code. The distribution of rotation and CaII emissionflux as a function of effective temperature shows a discontinuitylocated around the same spectral type, F8IV. Blueward of this spectraltype, subgiants have a large spread of values of rotation and CaII flux,whereas stars redward of F8IV show essentially low rotation and low CaIIflux. The strength of these declines depends on stellar mass. Theabundance of lithium also shows a sudden decrease. For subgiants withmass lower than about 1.2 Msun the decrease is located laterthan that in rotation and CaII flux, whereas for masses higher than 1.2Msun the decrease in lithium abundance is located around thespectral type F8IV. The discrepancy between the location of thediscontinuities of rotation and CaII emission flux and log n(Li) forstars with masses lower than 1.2 Msun seems to reflect thesensitivity of these phenomena to the mass of the convective envelope.The drop in rotation, which results mostly from a magnetic braking,requires an increase in the mass of the convective envelope less thanthat required for the decrease in log n(Li). The location of thediscontinuity in log n(Li) for stars with masses higher than 1.2Msun, in the same region of the discontinuities in rotationand CaII emission flux, may also be explained by the behavior of thedeepening of the convective envelope. The more massive the star is, theearlier is the increase of the convective envelope. In contrast to therelationship between rotation and CaII flux, which is fairly linear, therelationship between lithium abundance and rotation shows no cleartendency toward linear behavior. Similarly, no clear linear trend isobserved in the relationship between lithium abundance and CaII flux. Inspite of these facts, subgiants with high lithium content also have highrotation and high CaII emission flux. STELIB: A library of stellar spectra at R ~ 2000We present STELIB, a new spectroscopic stellar library, available athttp://webast.ast.obs-mip.fr/stelib. STELIB consists of an homogeneouslibrary of 249 stellar spectra in the visible range (3200 to 9500Å), with an intermediate spectral resolution (la 3 Å) andsampling (1 Å). This library includes stars of various spectraltypes and luminosity classes, spanning a relatively wide range inmetallicity. The spectral resolution, wavelength and spectral typecoverage of this library represents a substantial improvement overprevious libraries used in population synthesis models. The overallabsolute photometric uncertainty is 3%.Based on observations collected with the Jacobus Kaptein Telescope,(owned and operated jointly by the Particle Physics and AstronomyResearch Council of the UK, The Nederlandse Organisatie voorWetenschappelijk Onderzoek of The Netherlands and the Instituto deAstrofísica de Canarias of Spain and located in the SpanishObservatorio del Roque de Los Muchachos on La Palma which is operated bythe Instituto de AstrofÃ­sica de Canarias), the 2.3 mtelescope of the Australian National University at Siding Spring,Australia, and the VLT-UT1 Antu Telescope (ESO).Tables \ref{cat1} to \ref{cat6} and \ref{antab1} to A.7 are onlyavailable in electronic form at http://www.edpsciences.org. The StellarLibrary STELIB library is also available at the CDS, via anonymous ftpto cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/402/433 Selection criteria for targets of asteroseismic campaignsVarious dedicated satellite projects are underway or in advanced stagesof planning to perform high-precision, long duration time seriesphotometry of stars, with the purpose of using the frequencies ofstellar oscillations to put new constraints on the internal structure ofstars. It is known (cf. \cite{Bro+94}) that the effectiveness ofoscillation frequencies in constraining stellar model parameters issignificantly higher if classical parameters such as effectivetemperature and luminosity are known with high precision. In order tooptimize asteroseismic campaigns it is therefore useful to selecttargets from among candidates for which good spectroscopic andastrometric data already exists. This paper presents selection criteria,as well as redeterminations of stellar luminosity and reddening forstars satisfying these criteria. Statistical cataloging of archival data for luminosity class IV-V stars. II. The epoch 2001 [Fe/H] catalogThis paper describes the derivation of an updated statistical catalog ofmetallicities. The stars for which those metallicities apply are ofspectral types F, G, and K, and are on or near the main sequence. Theinput data for the catalog are values of [Fe/H] published before 2002February and derived from lines of weak and moderate strength. Theanalyses used to derive the data have been based on one-dimensional LTEmodel atmospheres. Initial adjustments which are applied to the datainclude corrections to a uniform temperature scale which is given in acompanion paper (see Taylor \cite{t02}). After correction, the data aresubjected to a statistical analysis. For each of 941 stars considered,the results of that analysis include a mean value of [Fe/H], an rmserror, an associated number of degrees of freedom, and one or moreidentification numbers for source papers. The catalog of these resultssupersedes an earlier version given by Taylor (\cite{t94b}).Catalog is only available in electronic form at the CDS via anonymousftp cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/398/731 Statistical cataloging of archival data for luminosity class IV-V stars. I. The epoch 2001 temperature catalogThis paper is one of a pair in which temperatures and metallicitycatalogs for class IV-V stars are considered. The temperature catalogdescribed here is derived from a calibration based on stellar angulardiameters. If published calibrations of this kind are compared by usingcolor-index transformations, temperature-dependent differences among thecalibrations are commonly found. However, such differences are minimizedif attention is restricted to calibrations based on Johnson V-K. Acalibration of this sort from Di Benedetto (\cite{dib98}) is thereforetested and adopted. That calibration is then applied to spectroscopicand photometric data, with the latter predominating. Cousins R-Iphotometry receives special attention because of its high precision andlow metallicity sensitivity. Testing of temperatures derived from thecalibration suggests that their accuracy and precision are satisfactory,though further testing will be warranted as new results appear. Thesetemperatures appear in the catalog as values of theta equiv5040/T(effective). Most of these entries are accompanied by measured orderived values of Cousins R-I. Entries are given for 951 stars.Catalog is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/398/721 Rotation and differential rotation in field F- and G-type starsWe present a detailed study of rotation and differential rotationanalyzing high resolution high S/N spectra of 142 F-, G- and earlyK-type field stars. Using Least Squares Deconvolution we obtainbroadening profiles for our sample stars and use the Fourier transformmethod to determine projected rotational velocities v sin i.Distributions of rotational velocities and periods are studied in theHR-diagram. For a subsample of 32 stars of spectral type F0-G0 we derivethe amount of differential rotation in terms of alpha = (Omega_Equator- Omega_Pole )/Omega_Equator . We find evidence for differentialrotation in ten of the 32 stars. Differential rotation seems to be morecommon in slower rotators, but deviations from rigid rotation are alsofound in some fast rotators. We search for correlations betweendifferential rotation and parameters relevant for stellar activity andshow indications against strong differential rotation in very activestars. We derive values of Delta P and Delta Omega , which support aperiod dependence of differential rotation. Derived lap times 2pi /DeltaOmega are of the order of 20 d and contradict the assumption thatconstant lap times of the order of the solar one ( ~ 130 d) are therule in stars that are thought to harbour magnetic dynamos.Based on observations collected at the European Southern Observatory, LaSilla.Tables 3 and A1 are only available at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.125.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/398/647 A highly sensitive search for magnetic fields in B, A and F starsCircular spectropolarimetric observations of 74 stars were obtained inan attempt to detect magnetic fields via the longitudinal Zeeman effectin their spectral lines. The sample observed includes 22 normal B, A andF stars, four emission-line B and A stars, 25 Am stars, 10 HgMn stars,two lambda Boo stars and 11 magnetic Ap stars. Using the Least-SquaresDeconvolution multi-line analysis approach (Donati et al.\cite{donati97etal}), high precision Stokes I and V mean signatures wereextracted from each spectrum. We find absolutely no evidence formagnetic fields in the normal, Am and HgMn stars, with upper limits onlongitudinal field measurements usually considerably smaller than anypreviously obtained for these objects. We conclude that if any magneticfields exist in the photospheres of these stars, these fields are notordered as in the magnetic Ap stars, nor do they resemble the fields ofactive late-type stars. We also detect for the first time a field in theA2pSr star HD 108945 and make new precise measurements of longitudinalfields in five previously known magnetic Ap stars, but do not detectfields in five other stars classified as Ap SrCrEu. We also report newresults for several binary systems, including a new vsin i for therapidly rotating secondary of the Am-delta Del SB2 HD 110951. Based onobservations obtained using the MuSiCoS spectropolarimeter on theBernard Lyot telescope, l'Observatoire du Pic du Midi, France. Beryllium in F and G Field Dwarfs from High-Resolution Canada-France-Hawaii Telescope SpectraIt is important to add observations of Be to the huge arsenal of Liobservations in order to identify the mechanisms operating in stellarinteriors that alter the surface composition of the light elements.Beryllium is more resistant to destruction than is Li, so information onthe abundances of both Li and Be reveals more information on theinternal processes than either element does alone. We have madeobservations of Be II at 3131 Å in 46 solar-type stars from theCanada-France-Hawaii Telescope with high spectral resolution and highsignal-to-noise ratios (S/N). Our Li I 6707 Å data for 39 of thesestars come from our high-resolution, high-S/N observations with theUniversity of Hawaii 88 inch (2.2 m) telescope and coudéspectrograph and Keck I High Resolution Echelle Spectrometer and, forsix stars, from the literature. Most of the stars in our sample are Fand G dwarfs with Teff between 6100 and 6600 K and with[Fe/H] between -0.6 and +0.2. The abundances of Be have been determinedthrough spectrum synthesis, while Li has been analyzed as a blend tofind the Li abundance. We find a large range in both Li and Be in thesestars; for Be it is at least 2.5 dex and for Li at least 3 dex. However,there is an excellent correlation between Li and Be, as discovered byDeliyannis et al. from a smaller sample. We find that in the range ofTeff of 5850 K (near the Li peak'' in open clusters) to6680 K (at the bottom of the Li `gap'' as defined by the Hyades), Liand Be appear to be depleted together. The slope of this remarkablelogarithmic relation is 0.36: as Li is reduced by a factor of 10, Be isreduced by only 2.2 times. There is some scant evidence for a change inthe slope between the cooler stars and the hotter stars such that thecooler stars deplete more Li relative to Be than the hotter stars. Theseresults are well matched by models that incorporate rotationally inducedslow mixing of the stellar surface material with the deeper layers ofthe star. Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statisticsThe Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521 On the Variability of F1-F9 Luminosity Class III-V StarsHipparcos Satellite photometry of F1-F9 luminosity class III-V starsindicates that most are not particularly variable. A few stars for whichfurther study is desirable are identified. Two-colour photometry for 9473 components of close Hipparcos double and multiple starsUsing observations obtained with the Tycho instrument of the ESAHipparcos satellite, a two-colour photometry is produced for componentsof more than 7 000 Hipparcos double and multiple stars with angularseparations 0.1 to 2.5 arcsec. We publish 9473 components of 5173systems with separations above 0.3 arcsec. The majority of them did nothave Tycho photometry in the Hipparcos catalogue. The magnitudes arederived in the Tycho B_T and V_T passbands, similar to the Johnsonpassbands. Photometrically resolved components of the binaries withstatistically significant trigonometric parallaxes can be put on an HRdiagram, the majority of them for the first time. Based on observationsmade with the ESA Hipparcos satellite.

• - 没有找到链接 -

### 下列团体成员

#### 观测天体数据

 星座: 獅子座 右阿森松: 11h23m55.50s 赤纬: +10Â°31'45.0" 视星: 3.94 距离: 24.237 天文距离 右阿森松适当运动: 152.5 赤纬适当运动: -65.2 B-T magnitude: 4.484 V-T magnitude: 4.056

 适当名称 Tsze Tseang   (Edit) Bayer ι Leo Flamsteed 78 Leo HD 1989 HD 99028 TYCHO-2 2000 TYC 858-1221-1 USNO-A2.0 USNO-A2 0975-06715452 BSC 1991 HR 4399 HIP HIP 55642 → 要求更多目录从vizier