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Searching for stars closely encountering with the solar system
Based on a new version of the Hipparcos catalog and currently availableradial velocity data, we have searched for stars that either haveencountered or will encounter the solar neighborhood within less than 3pc in the time interval from ?2 Myr to +2 Myr. Nine new candidateswithin 30 pc of the Sun have been found. To construct the stellar orbitsrelative to the solar orbit, we have used the epicyclic approximation.We show that, given the errors in the observational data, theprobability that the well-known star HIP 89 825 (GL 710) encounteringwith the Sun most closely falls into the Oort cloud is 0.86 in the timeinterval 1.45 ± 0.06 Myr. This star also has a nonzeroprobability, 1 × 10?4, of falling into the regiond < 1000 AU, where its influence on Kuiper Belt objects becomespossible.
| The Geneva-Copenhagen survey of the solar neighbourhood. III. Improved distances, ages, and kinematics
Context: Ages, chemical compositions, velocity vectors, and Galacticorbits for stars in the solar neighbourhood are fundamental test datafor models of Galactic evolution. The Geneva-Copenhagen Survey of theSolar Neighbourhood (Nordström et al. 2004; GCS), amagnitude-complete, kinematically unbiased sample of 16 682 nearby F andG dwarfs, is the largest available sample with complete data for starswith ages spanning that of the disk. Aims: We aim to improve theaccuracy of the GCS data by implementing the recent revision of theHipparcos parallaxes. Methods: The new parallaxes yield improvedastrometric distances for 12 506 stars in the GCS. We also use theparallaxes to verify the distance calibration for uvby? photometryby Holmberg et al. (2007, A&A, 475, 519; GCS II). We add newselection criteria to exclude evolved cool stars giving unreliableresults and derive distances for 3580 stars with large parallax errorsor not observed by Hipparcos. We also check the GCS II scales of T_effand [Fe/H] and find no need for change. Results: Introducing thenew distances, we recompute MV for 16 086 stars, and U, V, W,and Galactic orbital parameters for the 13 520 stars that also haveradial-velocity measurements. We also recompute stellar ages from thePadova stellar evolution models used in GCS I-II, using the new valuesof M_V, and compare them with ages from the Yale-Yonsei andVictoria-Regina models. Finally, we compare the observed age-velocityrelation in W with three simulated disk heating scenarios to show thepotential of the data. Conclusions: With these revisions, thebasic data for the GCS stars should now be as reliable as is possiblewith existing techniques. Further improvement must await consolidationof the T_eff scale from angular diameters and fluxes, and the Gaiatrigonometric parallaxes. We discuss the conditions for improvingcomputed stellar ages from new input data, and for distinguishingdifferent disk heating scenarios from data sets of the size andprecision of the GCS.Full Table 1 is 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?J/A+A/501/941
| Structure and Evolution of Nearby Stars with Planets. II. Physical Properties of ~1000 Cool Stars from the SPOCS Catalog
We derive detailed theoretical models for 1074 nearby stars from theSPOCS (Spectroscopic Properties of Cool Stars) Catalog. The Californiaand Carnegie Planet Search has obtained high-quality (R~=70,000-90,000,S/N~=300-500) echelle spectra of over 1000 nearby stars taken with theHamilton spectrograph at Lick Observatory, the HIRES spectrograph atKeck, and UCLES at the Anglo Australian Observatory. A uniform analysisof the high-resolution spectra has yielded precise stellar parameters(Teff, logg, vsini, [M/H], and individual elementalabundances for Fe, Ni, Si, Na, and Ti), enabling systematic erroranalyses and accurate theoretical stellar modeling. We have created alarge database of theoretical stellar evolution tracks using the YaleStellar Evolution Code (YREC) to match the observed parameters of theSPOCS stars. Our very dense grids of evolutionary tracks eliminate theneed for interpolation between stellar evolutionary tracks and allowprecise determinations of physical stellar parameters (mass, age,radius, size and mass of the convective zone, surface gravity, etc.).Combining our stellar models with the observed stellar atmosphericparameters and uncertainties, we compute the likelihood for each set ofstellar model parameters separated by uniform time steps along thestellar evolutionary tracks. The computed likelihoods are used for aBayesian analysis to derive posterior probability distribution functionsfor the physical stellar parameters of interest. We provide a catalog ofphysical parameters for 1074 stars that are based on a uniform set ofhigh-quality spectral observations, a uniform spectral reductionprocedure, and a uniform set of stellar evolutionary models. We explorethis catalog for various possible correlations between stellar andplanetary properties, which may help constrain the formation anddynamical histories of other planetary systems.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| An activity catalogue of southern stars
We have acquired high-resolution echelle spectra of 225 F6-M5 type starsin the Southern hemisphere. The stars are targets or candidates to betargets for the Anglo-Australian Planet Search. CaII H& K line coreswere used to derive activity indices for all of these objects. Theindices were converted to the Mt. Wilson system of measurements andlogR'HK values determined. A number of these stars had nopreviously derived activity indices. In addition, we have also includedthe stars from Tinney et al. using our Mt. Wilson calibration. Theradial-velocity instability (also known as jitter) level was determinedfor all 21 planet-host stars in our data set. We find the jitter to beat a level considerably below the radial-velocity signatures in all butone of these systems. 19 stars from our sample were found to be active(logR'HK > -4.5) and thus have high levels of jitter.Radial-velocity analysis for planetary companions to these stars shouldproceed with caution.
| Simulating observable comets. III. Real stellar perturbers of the Oort cloud and their output
Context: .This is the third of a series of papers on simulating themechanisms acting currently on the Oort cloud and producing the observedlong-period comets.Aims.In this paper we investigate the influence ofcurrent stellar perturbers on the Oort cloud of comets under thesimultaneous galactic disk tide. We also analyse the past motion of theobserved long-period comets under the same dynamical model to verify thewidely used definition of dynamically new comets. Methods.The action ofnearby stars and the galactic disk tide on the Oort cloud was simulated.The original orbital elements of all 386 long-period comets of qualityclasses 1 and 2 were calculated, and their motion was followednumerically for one orbital revolution into the past, down to theprevious perihelion. We also simulated the output of the close futurepass of GJ 710 through the Oort cloud. Results.The simulated flux of theobservable comets resulting from the current stellar and galacticperturbations, as well as the distribution of perihelion direction, wasobtained. The same data are presented for the future passage of GJ 710.A detailed description is given of the past evolution of aphelion andperihelion distances of the observed long-period comets. Conclusions. Weobtained no fingerprints of the stellar perturbations in the simulatedflux and its directional structure. The mechanisms producing observablecomets are highly dominated by galactic disk tide because all currentstellar perturbers are too weak. Also the effect of the close passage ofthe star GJ 710 is very difficult to recognise on the background of theGalactic-driven observable comets. For the observed comets we found only45 to be really dynamically "new" according to our definition based onthe previous perihelion distance value.
| Spectroscopic Properties of Cool Stars (SPOCS). I. 1040 F, G, and K Dwarfs from Keck, Lick, and AAT Planet Search Programs
We present a uniform catalog of stellar properties for 1040 nearby F, G,and K stars that have been observed by the Keck, Lick, and AAT planetsearch programs. Fitting observed echelle spectra with synthetic spectrayielded effective temperature, surface gravity, metallicity, projectedrotational velocity, and abundances of the elements Na, Si, Ti, Fe, andNi, for every star in the catalog. Combining V-band photometry andHipparcos parallaxes with a bolometric correction based on thespectroscopic results yielded stellar luminosity, radius, and mass.Interpolating Yonsei-Yale isochrones to the luminosity, effectivetemperature, metallicity, and α-element enhancement of each staryielded a theoretical mass, radius, gravity, and age range for moststars in the catalog. Automated tools provide uniform results and makeanalysis of such a large sample practical. Our analysis method differsfrom traditional abundance analyses in that we fit the observed spectrumdirectly, rather than trying to match equivalent widths, and wedetermine effective temperature and surface gravity from the spectrumitself, rather than adopting values based on measured photometry orparallax. As part of our analysis, we determined a new relationshipbetween macroturbulence and effective temperature on the main sequence.Detailed error analysis revealed small systematic offsets with respectto the Sun and spurious abundance trends as a function of effectivetemperature that would be inobvious in smaller samples. We attempted toremove these errors by applying empirical corrections, achieving aprecision per spectrum of 44 K in effective temperature, 0.03 dex inmetallicity, 0.06 dex in the logarithm of gravity, and 0.5 kms-1 in projected rotational velocity. Comparisons withprevious studies show only small discrepancies. Our spectroscopicallydetermined masses have a median fractional precision of 15%, but theyare systematically 10% higher than masses obtained by interpolatingisochrones. Our spectroscopic radii have a median fractional precisionof 3%. Our ages from isochrones have a precision that variesdramatically with location in the Hertzsprung-Russell diagram. We planto extend the catalog by applying our automated analysis technique toother large stellar samples.
| 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
| Stroemgren photometry of F- and G-type stars brighter than V = 9.6. I. UVBY photometry
Within the framework of a large photometric observing program, designedto investigate the Galaxy's structure and evolution, Hβ photometryis being made for about 9000 stars. As a by-product, supplementary uvbyphotometry has been made. The results are presented in a cataloguecontaining 6924 uvby observations of 6190 stars, all south ofδ=+38deg. The overall internal rms errors of one observation(transformed to the standard system) of a program star in the interval6.5
| Broad-band photometry of selected southern ultraviolet-bright stars.
Not Available
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משמש של הקבוצה הבאה
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | כלב גדול |
| התרוממות ימנית: | 06h22m57.67s |
| סירוב: | -24°33'21.7" |
| גודל גלוי: | 7.368 |
| מרחק: | 29.394 פארסק |
| תנועה נכונה: | -4 |
| תנועה נכונה: | 5.5 |
| B-T magnitude: | 8.199 |
| V-T magnitude: | 7.437 |
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