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מאמרים קשורים
Stratification of Methane Ice on Eris' Surface
We present new photometric and spectroscopic data of the dwarf planetEris obtained on 2006 October and 2007 December with the Very LargeTelescopes at ESO, Chile. We use three different instruments (FORS,ISAAC, and SINFONI) covering the 0.4-2.4 μm wavelength range. We showthat N2 ice is not directly detected, but the wavelengthpositions of the bands of CH4 measured on the completewavelength range seem to indicate that, as already suggested by Brown etal. and Licandro et al., a part of CH4 ice is diluted inN2. Spectral modeling using the Hapke theory reveals that asegregation of small and large particles of methane ice could exist onthe surface. The presence of water ice and nitrogen is not completelyexcluded even if the respective absorption bands of these ices have notbeen directly detected. We present in this paper our methods todetermine the wavelength shifts of the methane bands and the chemicalcomposition from spectral modeling.These observations are part of the large programme 178.C-0036.
| Visible spectroscopy of the new ESO large program on trans-Neptunian objects and Centaurs. Part 1
Aims. A second large observational program was started to improve ourknowledge of the physical properties of Centaurs and trans-Neptunianobjects, TNOs. The program is being executed in the facilities at theCerro Paranal of the European Southern Observatory, ESO, in Chile. Methods: Visible spectroscopy was carried out using FORS1 at the UT2 ofthe VLT telescope. We computed the spectral slope, S, for each object,and we searched for the possible existence of weak absorption features.We compared our data with those from the literature. Results: Wepresent spectra for 21 objects, 7 of them with no previously reportedspectra. Our sample includes 5 Centaurs, 5 resonant objects, 8 classicalTNOs, 2 detached objects, and 1 scattered disk object. There aresignificant differences between the distribution of spectral slopes forCentaurs and classical TNOs. The data presented here generally agreewith previous published data. One exception is 60 558 Echeclus, whosespectral slope is considerably smaller than previous measurements.Another interesting object is 47 932 (2000 GN{171}), which does not showevidence of a proposed feature at 0.7 μm. Most of the spectra arelinear and featureless; however, the well-known bands of solid methaneare detected in 136 199 Eris spectra and some weak features are detectedfor a few other objects. The most interesting case is that of 2003AZ{84}, which has a feature at about 0.65 μm, maybe due to aqueousalteration.Based on observations at the VLT Observatory Cerro Paranal of EuropeanSouthern Observatory, ESO, Chile, in the framework of program178.C-0036.
| The N2K Consortium. VII. Atmospheric Parameters of 1907 Metal-rich Stars: Finding Planet-Search Targets
We report high-precision atmospheric parameters for 1907 stars in theN2K low-resolution spectroscopic survey, designed to identify metal-richFGK dwarfs likely to harbor detectable planets. Of these stars, 284 arein the ideal temperature range for planet searches,Teff<=6000 K, and have a 10% or greater probability ofhosting planets based on their metallicities. The stars in thelow-resolution spectroscopic survey should eventually yield >60 newplanets, including 8-9 hot Jupiters. Short-period planets have alreadybeen discovered orbiting the survey targets HIP 14810 and HD 149143.
| Effective temperature scale and bolometric corrections from 2MASS photometry
We present a method to determine effective temperatures, angularsemi-diameters and bolometric corrections for population I and II FGKtype stars based on V and 2MASS IR photometry. Accurate calibration isaccomplished by using a sample of solar analogues, whose averagetemperature is assumed to be equal to the solar effective temperature of5777 K. By taking into account all possible sources of error we estimateassociated uncertainties to better than 1% in effective temperature andin the range 1.0-2.5% in angular semi-diameter for unreddened stars.Comparison of our new temperatures with other determinations extractedfrom the literature indicates, in general, remarkably good agreement.These results suggest that the effective temperaure scale of FGK starsis currently established with an accuracy better than 0.5%-1%. Theapplication of the method to a sample of 10 999 dwarfs in the Hipparcoscatalogue allows us to define temperature and bolometric correction (Kband) calibrations as a function of (V-K), [m/H] and log g. Bolometriccorrections in the V and K bands as a function of T_eff, [m/H] and log gare also given. We provide effective temperatures, angularsemi-diameters, radii and bolometric corrections in the V and K bandsfor the 10 999 FGK stars in our sample with the correspondinguncertainties.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| 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
| Improved Astrometry and Photometry for the Luyten Catalog. II. Faint Stars and the Revised Catalog
We complete construction of a catalog containing improved astrometry andnew optical/infrared photometry for the vast majority of NLTT starslying in the overlap of regions covered by POSS I and by the secondincremental Two Micron All Sky Survey (2MASS) release, approximately 44%of the sky. The epoch 2000 positions are typically accurate to 130 mas,the proper motions to 5.5 mas yr-1, and the V-J colors to0.25 mag. Relative proper motions of binary components are measured to 3mas yr-1. The false-identification rate is ~1% for11<~V<~18 and substantially less at brighter magnitudes. Theseimprovements permit the construction of a reduced proper-motion diagramthat, for the first time, allows one to classify NLTT stars intomain-sequence (MS) stars, subdwarfs (SDs), and white dwarfs (WDs). We inturn use this diagram to analyze the properties of both our catalog andthe NLTT catalog on which it is based. In sharp contrast to popularbelief, we find that NLTT incompleteness in the plane is almostcompletely concentrated in MS stars, and that SDs and WDs are detectedalmost uniformly over the sky δ>-33deg. Our catalogwill therefore provide a powerful tool to probe these populationsstatistically, as well as to reliably identify individual SDs and WDs.
| Lightcurves of selected minor planets.
We present 81 photometric lightcurves of 36 minor planets observed inthe V and B bands at the ESO 50 cm telescope at La Silla (Chile). Theseasteroids were selected preferentially in order to improve theirecliptic longitude coverage in view of pole determinations andlightcurve inversions. We also give some first photometric observationsand/or rotational period for several asteroids.
| 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
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| קבוצת-כוכבים: | לויתן |
| התרוממות ימנית: | 00h32m50.10s |
| סירוב: | -13°15'27.5" |
| גודל גלוי: | 8.727 |
| מרחק: | 73.368 פארסק |
| תנועה נכונה: | 169.8 |
| תנועה נכונה: | -40 |
| B-T magnitude: | 9.562 |
| V-T magnitude: | 8.796 |
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