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The inner region of the asteroid Main Belt: a spectroscopic and dynamic analysis
Aims.To better understand the dynamical and collisional evolution of theinner Main Belt, we perform a visible spectroscopic survey and constructdynamical maps of the region. Methods: .The survey was performedbetween March 2002 and August 2005, at diverse observatories. Thedynamical analysis was performed by the integration of 3131 masslessparticles homogeneously distributed in the region. Results: .Weobtained new taxonomic classification for 88 asteroids representing a13% increase in the sample of asteroids with know classification in theinner region of the Main Belt. The increase in the number of classifiedobjects further confirms the notion that the inner region can be dividedinto three compositional zones: the innermost, where asteroids of theS-group concentrate, the outermost, where the C-group peaks, andin-between, with the highest concentration of V-type. The dynamicalanalysis shows that the region is covered by a dense web of mean-motionand secular resonances which may play an important role in the dynamicaldiffusion of the asteroids.
| Spectroscopy of near-Earth asteroids
We present spectra and taxonomic classifications of 12 Near-EarthAsteroids (NEAs) and 2 inner Main Belt asteroids. The observations werecarried out with the ESO 3.5 m NTT and the Danish 1.54 m telescope at LaSilla, Chile. Eleven of the investigated NEAs belong to the S classwhile only one C-type has been identified. Two NEAs were observed atphase angles larger than 60° introducing significant phasereddening. In order to allow for comparisons between spectra ofasteroids observed at different phase angles we make attempts to correctfor this effect. However, it turned out that a uniform approach based onprevious measurements of phase reddening by means of observational datais not reasonable. For the NEAs we question the approach of taxonomicclassification in terms of subgroups, when the classification is basedon spectra obtained at large phase angles.
| 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.
| 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 Planet-Metallicity Correlation
We have recently carried out spectral synthesis modeling to determineTeff, logg, vsini, and [Fe/H] for 1040 FGK-type stars on theKeck, Lick, and Anglo-Australian Telescope planet search programs. Thisis the first time that a single, uniform spectroscopic analysis has beenmade for every star on a large Doppler planet search survey. We identifya subset of 850 stars that have Doppler observations sufficient todetect uniformly all planets with radial velocity semiamplitudes K>30m s-1 and orbital periods shorter than 4 yr. From this subsetof stars, we determine that fewer than 3% of stars with-0.5<[Fe/H]<0.0 have Doppler-detected planets. Above solarmetallicity, there is a smooth and rapid rise in the fraction of starswith planets. At [Fe/H]>+0.3 dex, 25% of observed stars have detectedgas giant planets. A power-law fit to these data relates the formationprobability for gas giant planets to the square of the number of metalatoms. High stellar metallicity also appears to be correlated with thepresence of multiple-planet systems and with the total detected planetmass. This data set was examined to better understand the origin of highmetallicity in stars with planets. None of the expected fossilsignatures of accretion are observed in stars with planets relative tothe general sample: (1) metallicity does not appear to increase as themass of the convective envelopes decreases, (2) subgiants with planetsdo not show dilution of metallicity, (3) no abundance variations for Na,Si, Ti, or Ni are found as a function of condensation temperature, and(4) no correlations between metallicity and orbital period oreccentricity could be identified. We conclude that stars with extrasolarplanets do not have an accretion signature that distinguishes them fromother stars; more likely, they are simply born in higher metallicitymolecular clouds.Based on observations obtained at Lick and Keck Observatories, operatedby the University of California, and the Anglo-Australian Observatories.
| Is Sedna another Triton?
90377 Sedna is, so far, the largest and most distant trans-neptunianobject. It was observed at visible and near-infrared wavelengths usingsimultaneously two 8.2 m telescopes at the Very Large Telescope of theEuropean Southern Observatory. The spectrum of Sedna suggests thepresence on its surface of different ices (total abundance >50%). Itssurface composition is different from that determined for othertrans-neptunian objects, and apparently resembles that of Triton,particularly in terms of the possible presence of nitrogen and methaneices.
| The HARPS search for southern extra-solar planets. III. Three Saturn-mass planets around HD 93083, HD 101930 and HD 102117
We report on the detection of three Saturn-mass planets discovered withthe HARPS instrument. HD 93083 shows radial-velocity (RV) variationsbest explained by the presence of a companion of 0.37 MJuporbiting in 143.6 days. HD 101930 b has an orbital period of 70.5 daysand a minimum mass of 0.30 MJup. For HD 102117, we presentthe independent detection of a companion with m2 sin{i} =0.14 MJup and orbital period P = 20.7 days. This planet wasrecently detected by Tinney et al. (ApJ, submitted). Activity andbisector indicators exclude any significant RV perturbations of stellarorigin, reinforcing the planetary interpretation of the RV variations.The radial-velocity residuals around the Keplerian fits are 2.0, 1.8 and0.9 m s-1 respectively, showing the unprecedented RV accuracyachieved with HARPS. A sample of stable stars observed with HARPS isalso presented to illustrate the long-term precision of the instrument.All three stars are metal-rich, confirming the now well-establishedrelation between planet occurrence and metallicity. The new planets areall in the Saturn-mass range, orbiting at moderate distance from theirparent star, thereby occupying an area of the parameter space whichseems difficult to populate according to planet formation theories. Asystematic exploration of these regions will provide new constraints onformation scenarios in the near future.
| A study of Cybele asteroids
We have used the 3.5 m New Technology Telescope at ESO, La Silla,to obtain spectra of 18 asteroids belonging to the Cybele group. Oneadditional Cybele asteroid was observed with the ESO 3.6 m telescope.From the spectra we have derived spectral slopes and taxonomyclassifications. Our observations show that spectrally red D-typeCybeles tend to be smaller than more spectrally neutral P- and C-typeobjects from this group. Similar colour-diameter trends have previouslybeen reported for other outer belt low albedo asteroids (Hildas andTrojans). We discuss possible reasons for this trend. In particular,the observed dominance of red objects for small diameters is consistentwith a space weathering scenario, where irradiation of asteroidregoliths with solar wind plasma neutralizes their surface colours dueto carbonization of originally reddish organic components. Collisionaldisruption of such large greyish "aged" P-type objects would produce anumber of redder D-type fragments lacking mature regoliths. Inaddition, the observed colour-diameter trend may be due to compositionaldifferences between D-, P- and C-type asteroids. P- and C-types may belacking at small diameters, since their materials are less susceptibleto collisional break-up than spectrally red D-type material. Asimultaneous contribution of both factors (compositional differences andspace weathering) to the observed trend is possible as well.Observations were made at the European Southern Observatory (ESO) withthe NTT telescope under program 56.F-0355 and the 3.6 m telescope underprogram 62.S-0133.
| S3OS2: the visible spectroscopic survey of 820 asteroids
We present the results of a visible spectroscopic survey of 820asteroids carried on between November 1996 and September 2001 at the1.52 m telescope at ESO (La Silla). The instrumental set-up allowed anuseful spectral range of about 4900 Å<λ<9200 Å.The global spatial distribution of the observed asteroids covers quitewell all the region between 2.2 and 3.3 AU though some concentrationsare apparent. These are due to the fact that several sub-sets ofasteroids, such as families and groups, have been selected and studiedduring the development of the survey. The observed asteroids have beenclassified using the Tholen and the Bus taxonomies which, in general,agree quite well.
| Chemical enrichment and star formation in the Milky Way disk. III. Chemodynamical constraints
In this paper, we investigate some chemokinematical properties of theMilky Way disk, by using a sample composed by 424 late-type dwarfs. Weshow that the velocity dispersion of a stellar group correlates with theage of this group, according to a law proportional to t0.26,where t is the age of the stellar group. The temporal evolution of thevertex deviation is considered in detail. It is shown that the vertexdeviation does not seem to depend strongly on the age of the stellargroup. Previous studies in the literature seem to not have found it dueto the use of statistical ages for stellar groups, rather thanindividual ages. The possibility to use the orbital parameters of a starto derive information about its birthplace is investigated, and we showthat the mean galactocentric radius is likely to be the most reliablestellar birthplace indicator. However, this information cannot bepresently used to derive radial evolutionary constraints, due to anintrinsic bias present in all samples constructed from nearby stars. Anextensive discussion of the secular and stochastic heating mechanismscommonly invoked to explain the age-velocity dispersion relation ispresented. We suggest that the age-velocity dispersion relation couldreflect the gradual decrease in the turbulent velocity dispersion fromwhich disk stars form, a suggestion originally made by Tinsley &Larson (\cite{tinsley}, ApJ, 221, 554) and supported by several morerecent disk evolution calculations. A test to distinguish between thetwo types of models using high-redshift galaxies is proposed.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/423/517
| 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.
| Statistical cataloging of archival data for luminosity class IV-V stars. II. The epoch 2001 [Fe/H] catalog
This 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 catalog
This 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
| Extrasolar planets around HD 196050, HD 216437 and HD 160691
We report precise Doppler measurements of the stars HD 216437, HD 196050and HD 160691 obtained with the Anglo-Australian Telescope using theUCLES spectrometer together with an iodine cell as part of theAnglo-Australian Planet Search. Our measurements reveal periodicKeplerian velocity variations that we interpret as evidence for planetsin orbit around these solar type stars. HD 216437 has a period of 1294+/- 250 d, a semi-amplitude of 38 +/- 3 m s-1 and aneccentricity of 0.33 +/- 0.09. The minimum (M sin i) mass of thecompanion is 2.1 +/- 0.3 MJUP and the semi-major axis is 2.4+/- 0.5 au. HD 196050 has a period of 1300 +/- 230 d, a semi-amplitudeof 49 +/- 8 m s-1 and an eccentricity of 0.19 +/- 0.09. Theminimum mass of the companion is 2.8 +/- 0.5 MJUP and thesemi-major axis is 2.4 +/- 0.5 au. We also report further observationsof the metal-rich planet bearing star HD 160691. Our new solutionconfirms the previously reported planet and shows a trend indicating asecond, longer-period companion. These discoveries add to the growingnumbers of mildly eccentric, long-period extrasolar planets aroundmetal-rich Sun-like stars.
| HIPPARCOS age-metallicity relation of the solar neighbourhood disc stars
We derive age-metallicity relations (AMRs) and orbital parameters forthe 1658 solar neighbourhood stars to which accurate distances aremeasured by the HIPPARCOS satellite. The sample stars comprise 1382 thindisc stars, 229 thick disc stars, and 47 halo stars according to theirorbital parameters. We find a considerable scatter for thin disc AMRalong the one-zone Galactic chemical evolution (GCE) model. Orbits andmetallicities of thin disc stars show now clear relation each other. Thescatter along the AMR exists even if the stars with the same orbits areselected. We examine simple extension of one-zone GCE models whichaccount for inhomogeneity in the effective yield and inhomogeneous starformation rate in the Galaxy. Both extensions of the one-zone GCE modelcannot account for the scatter in age - [Fe/H] - [Ca/Fe] relationsimultaneously. We conclude, therefore, that the scatter along the thindisc AMR is an essential feature in the formation and evolution of theGalaxy. The AMR for thick disc stars shows that the star formationterminated 8 Gyr ago in the thick disc. As already reported by Grattonet al. (\cite{Gratton_et.al.2000}) and Prochaska et al.(\cite{Prochaska_et.al.2000}), thick disc stars are more Ca-rich thanthin disc stars with the same [Fe/H]. We find that thick disc stars showa vertical abundance gradient. These three facts, the AMR, verticalgradient, and [Ca/Fe]-[Fe/H] relation, support monolithic collapseand/or accretion of satellite dwarf galaxies as likely thick discformation scenarios. Tables 2 and 3 are only 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/ cgi-bin/qcat?J/ A+A/394/927
| Carbon Monoxide in type II supernovae
Infrared spectra of two type II supernovae 6 months after explosion arepresented. The spectra exhibit a strong similarity to the observationsof SN 1987A and other type II SNe at comparable epochs. The continuumcan be fitted with a cool black body and the hydrogen lines haveemissivities that are approximately those of a Case B recombinationspectrum. The data extend far enough into the thermal region to detectemission by the first overtone of carbon monoxide. The molecularemission is modeled and compared with that in the spectra of SN 1987A.It is found that the flux in the CO first overtone is comparable to thatfound in SN 1987A. We argue that Carbon Monoxide forms in the ejecta ofall type II SNe during the first year after explosion. Based onobservations collected at the European Southern observatory, Chile intime allocated to proposals 62.H-0708 and 65.H.-0462.
| Groundbased investigation of asteroid 9969 Braille, target of the spacecraft mission Deep Space 1
Asteroid 9969 Braille (1992 KD) was encountered on July 29, 1999 by theDeep Space 1 mission, the first of NASA's New Millennium Program,launched on October 24 1998. The data obtained by the space mission seemto indicate a composition of the object similar to that of Vesta. Tocomplete the information obtained in the infrared region by the DeepSpace 1 mission we have performed a visible spectroscopic andphotometric investigation of the asteroid respectively with the 1.5 mtelescope and the NTT of ESO, La Silla. The spectrum was obtained in thespectral range 4500-8200 Å and, for the photometry, BVRI filterswere used. In this paper we report the results of the analysis of thedata obtained indicating that, on the basis of our visible data, thecomposition of the asteroid may range from V-type to Q-type, but weobserve also a strong similarity to the H-type ordinary chondrites.Based on observations carried out at the European Southern Observatory(ESO) of La Silla, Chile, programs N.62S-0173 and N.62S-0305A.
| Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The 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
| Sixth Catalogue of Fundamental Stars (FK6). Part III. Additional fundamental stars with direct solutions
The FK6 is a suitable combination of the results of the HIPPARCOSastrometry satellite with ground-based data, measured over a longinterval of time and summarized mainly in the FK5. Part III of the FK6(abbreviated FK6(III)) contains additional fundamental stars with directsolutions. Such direct solutions are appropriate for single stars or forobjects which can be treated like single stars. Part III of the FK6contains in total 3272 stars. Their ground-based data stem from thebright extension of the FK5 (735 stars), from the catalogue of remainingSup stars (RSup, 732 stars), and from the faint extension of the FK5(1805 stars). From the 3272 stars in Part III, we have selected 1928objects as "astrometrically excellent stars", since their instantaneousproper motions and their mean (time-averaged) ones do not differsignificantly. Hence most of the astrometrically excellent stars arewell-behaving "single-star candidates" with good astrometric data. Thesestars are most suited for high-precision astrometry. On the other hand,354 of the stars in Part III are Δμ binaries in the sense ofWielen et al. (1999). Many of them are newly discovered probablebinaries with no other hitherto known indication of binarity. The FK6gives, besides the classical "single-star mode" solutions (SI mode),other solutions which take into account the fact that hidden astrometricbinaries among "apparently single-stars" introduce sizable "cosmicerrors" into the quasi-instantaneously measured HIPPARCOS proper motionsand positions. The FK6 gives, in addition to the SI mode, the "long-termprediction (LTP) mode" and the "short-term prediction (STP) mode". TheseLTP and STP modes are on average the most precise solutions forapparently single stars, depending on the epoch difference with respectto the HIPPARCOS epoch of about 1991. The typical mean error of anFK6(III) proper motion in the single-star mode is 0.59 mas/year. This isa factor of 1.34 better than the typical HIPPARCOS errors for thesestars of 0.79 mas/year. In the long-term prediction mode, in whichcosmic errors are taken into account, the FK6(III) proper motions have atypical mean error of 0.93 mas/year, which is by a factor of about 2better than the corresponding error for the HIPPARCOS values of 1.83mas/year (cosmic errors included).
| On the Variability of G0-G9 Stars
We investigate the Hipparcos Satellite photometry of G0-G9 stars. Mostare not particularly variable over the 3 year observing period, but maybe over a longer time. Stars for which further study is desirable areidentified.
| G0-G5V Stars and the Sun in the uveeby System
The color indices of the Sun in the u vby system are calculated usingthe spectral energy distribution of Lockwood, Tug, and White. Thisallows errors in the absolute calibration to be excluded from thecalculated color indices. The normal position of the Sun on the(v-b)-(b-y) and (v-y)-(b-y) color-color diagrams for early G starstestifies to the absence of any significant peculiarities in the Suncompared to other stars of similar spectral type. These diagrams canprovide a useful tool in searches for candidate solar analogues amongfaint stars.
| The infrared triplet lines of ionized calcium as a diagnostic tool for F, G, K-type stellar atmospheres
LTE calculations of the profiles of the infrared triplet lines ofionized calcium in the spectrum of F, G and K stars are described indetail with explicit quantitative consideration of their perturbation byhydrogen Paschen lines. The results of such calculations obtained withfive different solar model atmospheres are discussed. The sensitivity ofthe profiles to changes in basic stellar atmospheric parameters isillustrated. The flux in the center of the lambda 8542 Ä line isrelated empirically to the Mount-Wilson chromospheric activity indicatorR'HK. The predictive power of observations of the infraredtriplet lines is then summed up.
| Spectroscopic comparison of aqueous altered asteroids with CM2 carbonaceous chondrite meteorites
In the last year we have started a spectroscopic investigation ofasteroids located in the region of the main-belt between about 2.2 and3.6 AU. The aim of this work is to study the aqueous alteration processwhich acted in that zone, dominated by low albedo C-type asteroids, andto compare the spectra of these hydrous objects with those of CM2carbonaceous chondrite meteorites. In fact, the spectra of thesemeteorites reveal features probably due to aqueous altered materials ontheir surfaces. The study of the aqueous alteration process can giveimportant information on the chemical and thermal evolution of theearliest Solar System. More that 65% of the investigated objects haverevealed features suggesting the presence of hydrous materials. Thecomparison of the spectra of the hydrated asteroids obtained to datewith those of several CM2 carbonaceous chondrite meteorites seems toindicate that aqueous altered asteroids could be the parents of CM2meteorites. The data have been obtained during several observationalruns at the Asiago Observatory with the 1.8 m telescope and atESO-LaSilla with the 1.5 m telescope. Based on observations carried outat the European Southern Observatory (ESO), La Silla, Chile, and at theAsiago Observatory, Italy.
| 4979 Otawara: flyby target of the Rosetta mission
An international observing campaign was organized to determine thephysical and chemical characteristics of asteroid 4979 Otawara, which isthe first target of the Rosetta mission (flyby on July 10, 2006).Knowledge of the physical parameters of the flyby targets is requiredfor both refinement of the design of the spacecraft and the instrumentpayload, and optimization of the mission trajectory and scenarios. Wepresent the results of observations obtained from December, 1998 throughMarch, 1999. The spectral classification of 4979 Otawara could be eithera pyroxene and/or olivine-rich S-type asteroid or a V-type asteroid, amember of the Vesta dynamical family. Further observations are needed inorder to discriminate between the two spectral types. The synodicrotation period of Otawara is Psyn = 2.707 +/- 0.005 hr. Thelower limit for the axial ratio of the enveloping ellipsoid is a/b >=1.3. The circular effective radius is 2.0 or 1.3 km in the case of anS-type or a V-type asteroid, respectively. A lower limit on its densityis obtained: rho min >= 1.9 g cm-3 if we assumethat Otawara is an aggregate or rubble pile object. However, if Otawarais a single solid body, no constraint can be set on its density. 4979Otawara is a small, fast rotating asteroid (FRA) and hence, will be aparticularly interesting target to be studied from a spacecraft, sinceno fast rotator has been visited yet. partly based on observationscarried out at the European Southern Observatory (ESO) of La Silla,Chile, and at Steward Observatory, University of Arizona, Tucson, AZUSA.
| Metallicity effects on the chromospheric activity-age relation for late-type dwarfs
We show that there is a relationship between the age excess, defined asthe difference between the stellar isochrone and chromospheric ages, andthe metallicity as measured by the index [Fe/H] for late-type dwarfs.The chromospheric age tends to be lower than the isochrone age formetal-poor stars, and the opposite occurs for metal-rich objects. Wesuggest that this could be an effect of neglecting the metallicitydependence of the calibrated chromospheric emission-age relation. Wepropose a correction to account for this dependence. We also investigatethe metallicity distributions of these stars, and show that there aredistinct trends according to the chromospheric activity level. Inactivestars have a metallicity distribution which resembles the metallicitydistribution of solar neighbourhood stars, while active stars appear tobe concentrated in an activity strip on the logR'_HKx[Fe/H] diagram. Weprovide some explanations for these trends, and show that thechromospheric emission-age relation probably has different slopes on thetwo sides of the Vaughan-Preston gap.
| Far-Ultraviolet Continuum of G-Type Stars: A Signature of the Temperature Minimum Region
The main results of a program of systematic comparison between observedand computed UV spectral energy distributions of field G-type stars areillustrated. We constructed the UV observed energy distributions for 53G stars, starting from the IUE Uniform Low Dispersion Archive (ULDA) andcomputed the corresponding theoretical fluxes by using the atmosphericparameters from the Catalogue of [Fe/H] Determinations (1996 edition)and a Kurucz grid of model fluxes. From the comparison betweenobservations and classical models, a UV excess shortward of 2000 Åis evident for all the program stars. The UV continuum in the region1600-2000 Å can be described by synthetic fluxes computed fromsemiempirical models based on the temperature minimum concept. Valuesfor the T_min/T_eff ratio on the order of 0.80 are suitable for theinterpretation of the observed fluxes. The residual discrepanciesshortward of 1600 Å are suggested to be effects of thechromosphere, on the basis of a comparison with the Maltby et al.semiempirical model of the Sun.
| A Multiplicity Survey of Chromospherically Active and Inactive Stars
Surveys of three samples of solar-type stars, segregated bychromospheric emission level, were made to determine their multiplicityfractions and to investigate the evolution of multiplicity with age. Intotal, 245 stars were searched for companions with DeltaV <= 3.0 andseparations of 0.035" to 1.08" using optical speckle interferometry. Byincorporating the visual micrometer survey for duplicity of theLamontHussey Observatory, the angular coverage was extended to 5.0" withno change in the DeltaV limit. This magnitude difference allows massratios of 0.63 and larger to be detected throughout a search region of2-127 AU for the stars observed. The 84 primaries observed in thechromospherically active sample are presumably part of a youngpopulation and are found to have a multiplicity fraction of 17.9% +/-4.6%. The sample of 118 inactive, presumably older, primaries wereselected and observed using identical methods and are found to have amultiplicity fraction of only 8.5% +/- 2.7%. Given the known linkbetween chromospheric activity and age, these results tentatively implya decreasing stellar multiplicity fraction from 1 to 4 Gyr, theapproximate ages of the two samples. Finally, only two of the 14 veryactive primaries observed were found to have a companion meeting thesurvey detection parameters. In this case, many of the systems areeither very young, or close, RS CVn type multiples that are unresolvableusing the techniques employed here.
| Kinematics and Metallicity of Stars in the Solar Region
Several samples of nearby stars with the most accurate astrometric andphotometric parameters are searched for clues to their evolutionaryhistory. The main samples are (1) the main-sequence stars with b - ybetween 0.29 and 0.59 mag (F3 to K1) in the Yale parallax catalog, (2) agroup of high-velocity subgiants studied spectroscopically by Ryan &Lambert, and (3) high-velocity main-sequence stars in the extensiveinvestigation by Norris, Bessel, & Pickles. The major conclusionsare as follows: (1) The oldest stars (halo), t >= 10-12 Gyr, haveV-velocities (in the direction of Galactic rotation and referred to theSun) in the range from about -50 to -800 km s^-1 and have aheavy-element abundance [Fe/H] of less than about -0.8 dex. The agerange of these objects depends on our knowledge of globular clusterages, but if age is correlated with V-velocity, the youngest may be M22and M28 (V ~ -50 km s^-1) and the oldest NGC 3201 (V ~ -500 km s^-1) andassorted field stars. (2) The old disk population covers the large agerange from about 2 Gyr (Hyades, NGC 752) to 10 or 12 Gyr (Arcturusgroup, 47 Tuc), but the lag (V) velocity is restricted to less thanabout 120 km s^-1 and [Fe/H] >= -0.8 or -0.9 dex. The [Fe/H] ~ -0.8dex division between halo and old disk, near t ~ 10-12 Gyr, is marked bya change in the character of the CN index (C_m) and of the blanketingparameter K of the DDO photometry. (3) The young disk population, t <2 Gyr, is confined exclusively to a well-defined area of the (U, V)velocity plane. The age separating young and old disk stars is also thatseparating giant evolution of the Hyades (near main-sequence luminosity)and M67 (degenerate helium cores and a large luminosity rise) kinds. Thetwo disk populations are also separated by such indexes as the g-indexof Geveva photometry. There appears to be no obvious need to invokeexogeneous influences to understand the motion and heavy-elementabundance distributions of the best-observed stars near the Sun.Individual stars of special interest include the parallax star HD 55575,which may be an equal-component binary, and the high-velocity star HD220127, with a well-determined space velocity near 1000 km s^-1.
| Determination of the temperatures of selected ISO flux calibration stars using the Infrared Flux Method
Effective temperatures for 420 stars with spectral types between A0 andK3, and luminosity classes between II and V, selected for a fluxcalibration of the Infrared Space Observatory, ISO, have been determinedusing the Infrared Flux Method (IRFM). The determinations are based onnarrow and wide band photometric data obtained for this purpose, andtake into account previously published narrow-band measures oftemperature. Regression coefficients are given for relations between thedetermined temperatures and the photometric parameters (B2-V1), (b-y)and (B-V), corrected for interstellar extinction through use ofHipparcos parallaxes. A correction for the effect of metallicity on thedetermination of integrated flux is proposed. The importance of aknowledge of metallicity in the representation of derived temperaturesfor Class V, IV and III stars by empirical functions is discussed andformulae given. An estimate is given for the probable error of eachtemperature determination. Based on data from the ESA HipparcosAstrometry Satellite.
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Группы:
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Наблюдательные данные и астрометрия
| Созвездие: | Корма |
| Прямое восхождение: | 06h20m06.10s |
| Склонение: | -48°44'28.0" |
| Видимая звёздная величина: | 6.6 |
| Расстояние: | 25.694 парсек |
| Собственное движение RA: | 234.4 |
| Собственное движение Dec: | -266.6 |
| B-T magnitude: | 7.41 |
| V-T magnitude: | 6.683 |
Каталоги и обозначения:
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INHABITED SKY
