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The Correlation of Lithium and Beryllium in F and G Field and Cluster Dwarf Stars
Although Li has been extensively observed in main-sequence field andcluster stars, there are relatively fewer observations of Be. We haveobtained Keck HIRES spectra of 36 late F and early G dwarfs in order tostudy the Li-Be correlation we found previously in the temperatureregime of 5900-6650 K. The sample size for this temperature range withdetectable and (usually) depleted Li and Be is now 88, including Li andBe abundances in both cluster and field stars. Therefore we can nowinvestigate the influence of other parameters such as age, temperature,and metallicity on the correlation. The Be spectra at 3130 Å weretaken over six nights from 1999 November to 2002 January and have aspectral resolution of ~48,000 and a median signal-to-noise ratio (S/N)of 108 pixel-1. We obtained Li spectra of 22 stars with theUniversity of Hawaii 88 inch (2.2 m) telescope and coudéspectrograph with a spectral resolution of ~70,000 and a median S/N of110 pixel-1. We have redetermined the effective temperaturesfor all the stars and adopted other parameters from published data orempirical relations. The abundances of both Li and Be in the stars weobserved were determined from spectrum synthesis with MOOG 2002. Thepreviously observed Li equivalent widths for some of our Be stars wereused with the new temperatures and MOOG 2002 in the ``blends'' mode. Forthe 46 field stars from this and earlier studies we find a linearrelation between A(Li) and A(Be) with a slope of 0.375+/-0.036. Over theTeff range 5900-6650 K, we find the modest scatter about theBe-Li relation to be significantly correlated with Teff andperhaps also [Fe/H]. Dividing the sample into two temperature regimes of6300-6650 K (corresponding to the cool side of the Li-Be dip) and5900-6300 K (corresponding to the Li ``plateau'') reveals possible smalldifferences in the slopes for the two groups, 0.404+/-0.034 and0.365+/-0.049, respectively. When we include the cluster stars (Hyades,Pleiades, Praesepe, UMa Group, and Coma), the slope for the fulltemperature range (88 stars) is essentially the same, at 0.382+/-0.030,as for the field stars alone. For the hotter temperature group of 35Li-Be dip stars in the field and in clusters the slope is higher, at0.433+/-0.036, while for the cooler star group (54 stars) the slope is0.337+/-0.031, different by more than 1 σ. This small differencein the slope is predicted by the theory of rotationally induced mixing.The four stars with [Fe/H] less than -0.4 are all below the best-fitrelation, i.e., there is more Be depletion at a given A(Li) or less Beab initio. The youngest stars, i.e., Pleiades, have less depletion ofboth Li and Be. This too is predicted by rotationally induced slowmixing. Combining the Be results from both field and cluster stars, wefind that there are stars with undepleted Be, i.e., near the meteoriticvalues of 1.42 dex, at all temperatures from 5500 to 6800 K. Depletionsof Be of up to and even exceeding 2 orders of magnitude are commonbetween 6000 and 6700 K.
| The Geneva-Copenhagen survey of the Solar neighbourhood. Ages, metallicities, and kinematic properties of 14 000 F and G dwarfs
We 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. Our63 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
| X-ray/optical observations of stars with shallow convection zones (A8-G2 V)
We present Walraven photometry and ROSAT All-Sky Survey data for asample of 173 bright main-sequence stars with spectral types between A8Vand G2V\@. These observations are part of a study of the onset ofmagnetic surface activity along the main sequence. Values for theeffective temperature, surface gravity and interstellar reddening havebeen obtained from a comparison of the observed Walraven colours withtheoretical values. These parameters have been used to derive accurateX-ray\ surface flux densities.
| Photometric surveys of suspected small-amplitude red variables. 3: an AAVSO photometric photometry survey
We have carried out a survey of the photometric (V) variability of 61'known' or suspected small-amplitude red variables, mostly M giants.Approximately two-thirds appear to be variable; several suspectedvariable comparison stars have also been identified. The incidence andaverage amplitude of variability increase rapidly from spectral type M0III to M6 III.
| Visual multiples. VIII - 1000 MK types
A total of 1000 new classifications are given for stars brighter than B= 8.0 mag in the Aitken double star catalog. The classificationssupplement 865 classifications obtained in 1981 and 1984. Among thenewly discovered stars are 12 new Ap stars, eight Lambda Bootis stars,one Ba II star, and 60 Am stars. A detailed list of the newclassifications is given.
| Close visual binaries. I - MK classifications
Each component of 170 close visual binaries has been classified with newprocedures for controlling contamination problems. These classificationsare presented and are shown to be on the MK system. Two sources of areascanner UBV photometry were compared in order to establish homogeneousphotometric as well as spectroscopic data. From a consideration ofsystematic errors in the V magnitude difference (Delta V) betweencomponents the photometry of Hurly and Warner (1983) is to be preferred.Absolute magnitudes for each binary are derived from Delta V via atested MK - M(v) map.
| Close visual binaries. II - Quantitative test of isochrones
Homogeneous and accurate color-magnitude data are available from Paper Ifor each component of 56 close visual binaries, 30 with evolvedcomponents. The 21 binaries with main-sequence primaries are comparedwith new Yale isochrones to determine the appropriate isochronecomposition: Y = 0.25, Z = 0.04. Explanations are given for eightbinaries found to be inconsistent with this isochrone. Some of theremaining binaries suggest a decrease by 0.5 in the mixing lengthparameter for the reddest main-sequence stars, and either a smallerdecrease or mass loss in the subgiant and giant phase of evolution. Ingeneral, the mean apparent age difference between binary components (0.0+ or - 0.1 Gyr) shows stellar evolution to be well modeled by the newYale isochrones.
| Area Scanner Observations of Close Visual Double Stars - Part Two - Results for 153 Southern Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1983MNRAS.202..761H&db_key=AST
| Combined-light UBV Photometry of 103 Bright Southern Visual Doubles
Not Available
| Photovisual differences in magnitudes of 331 mainly southern double stars
Not Available
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הכנס מאמר חדש
לינקים קשורים
הכנס לינק חדש
משמש של הקבוצה הבאה
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | פסל |
| התרוממות ימנית: | 23h44m28.90s |
| סירוב: | -26°14'47.0" |
| גודל גלוי: | 6.17 |
| מרחק: | 68.027 פארסק |
| תנועה נכונה: | -35.1 |
| תנועה נכונה: | -27.9 |
| B-T magnitude: | 6.791 |
| V-T magnitude: | 6.282 |
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