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EF Chamaeleontis: Warm Dust Orbiting a Nearby 10 Myr Old Star
Most Vega-like stars have far-infrared excess (60 μm or longward inIRAS, ISO, or Spitzer MIPS bands) and contain cold dust (<~150 K)analogous to the Sun's Kuiper Belt region. However, dust in a regionmore akin to our asteroid belt and thus relevant to the terrestrialplanet building process is warm and produces excess emission inmid-infrared wavelengths. By cross-correlating Hipparcos dwarfs with theMSX catalog, we found that EF Cha, a member of the recently identified,~10 Myr old, ``Cha-Near'' moving group, possesses prominent mid-infraredexcess. N-band spectroscopy reveals a strong emission featurecharacterized by a mixture of small, warm, amorphous, and possiblycrystalline silicate grains. Survival time of warm dust grains aroundthis A9 star is <~105 yr, much less than the age of thestar. Thus, grains in this extrasolar terrestrial planetary zone must beof a ``second generation'' and not a remnant of primordial dust and aresuggestive of substantial planet formation activity. Such secondgeneration warm excess occurs around ~13% of the early-type stars innearby young stellar associations.
| Thermal lines of methanol towards bipolar outflows
Not Available
| Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 pc-The Southern Sample
We are obtaining spectra, spectral types, and basic physical parametersfor the nearly 3600 dwarf and giant stars earlier than M0 in theHipparcos catalog within 40 pc of the Sun. Here we report on resultsfor 1676 stars in the southern hemisphere observed at Cerro TololoInter-American Observatory and Steward Observatory. These resultsinclude new, precise, homogeneous spectral types, basic physicalparameters (including the effective temperature, surface gravity, andmetallicity [M/H]), and measures of the chromospheric activity of ourprogram stars. We include notes on astrophysically interesting stars inthis sample, the metallicity distribution of the solar neighborhood, anda table of solar analogs. We also demonstrate that the bimodal nature ofthe distribution of the chromospheric activity parameterlogR'HK depends strongly on the metallicity, andwe explore the nature of the ``low-metallicity'' chromosphericallyactive K-type dwarfs.
| 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.
| 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
| 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
| 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
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| Ca II H and K Filter Photometry on the UVBY System. II. The Catalog of Observations
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....109.2828T&db_key=AST
| 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
| Four-colour UVBY and H-beta photometry of all stars earlier than G0 and brighter than MPG of about 10.7 M in Selected Area 203 towards the Chamaeleon-Musca dark clouds
Results are presented of Stromgren uvby(beta) photometry for 213 starsearlier than G0 and brigher than mpg of about 10.7 m inSelected Area 203. The observed area lies close to the geometric centerof the Chamaeleon-Musca dark clouds complex. The results yield V, (b-y),m1, c1, and beta on the standard systems, withoverall rms errors for one observation of one star of 0.010, 0.004,0.007, 0.009, and 0.011, respectively.
| BVRI photometry of the Gliese Catalogue stars
Photoelectri BVRI photometry on the Cousins (Kron-Cape) system has beenobtained for many of the southern faint stars in the Gliese Catalog(1969). This extends the work of Cousins (1980) and provides a uniformset of data for the nearby stars. Several red dwarfs are noted, whichwere used to define the red end of the Cousins system.
| Secondary standards for H-beta photometry in the Southern Hemisphere (second series).
Not Available
| The unidentified infrared bands and space observations with ISO
Well-defined emission bands superimposed over a continuum extend fromthe visible to infrared spectrum exhibited by a large number ofastronomical infrared sources in their spectra between 3 and 12 micronare the subject of the study. Emphasis is placed on candidate materialsconsidered to be the carriers for such unidentified infrared bands, andon open problems associated with these carriers. It is pointed out thatsuch problems might be clarified with the help of high spectral- andspatial-resolution satellite observations provided by the Infrared SpaceObservatory (ISO) mission.
| Near-infrared spectroscopic observations of young stellar objects
The paper presents medium-resolution observations of the Br-gamma andBr-alpha emission lines for 20 premain-sequence stars, most of which arelow-luminosity objects. In 10 of these, strong Br-gamma emission hasbeen detected, whose intensity exceeds that expected from the value inCase B recombination with Lyman continuum radiation from the stars. Theline ratio suggests that these lines are emitted from optically thickregions. For low-luminosity stars these lines are considered to comefrom neutral and dense circumstellar regions.
| The infrared emission bands. III - Southern IRAS sources
Airborne 5-8-micron spectra of southern IRAS sources are presented whichdisplay the strong PAH emission features. The sources studied includethose in a previous paper (Cohen et al, 1986) and NGC 6302, HR 4049, andCPD -56 deg 8032. A good correlation is found between the intensityratio of the 7.7-micron feature relative to the FIR dust continuum andnebular C/O ratio, supporting a carbonaceous carrier for these emissionfeatures. In addition, a weak PAH band is detected near 5.2 microns inseveral sources.
| UBV (RI)c standard stars in the E- and F-regions and in the Magellanic Clouds - a revised catalogue.
Not Available
| UBV(RI)c photometry of some standard sequences in the Harvard F regions and in the Magellanic Clouds
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1988MNRAS.231.1047M&db_key=AST
| Combined Interferometer and Single Dish Maps of Dark Clouds
Not Available
| Bipolar flows, molecular gas disks, and the collapse and accretion of rotating interstellar clouds
The collapse of rotating interstellar clouds may lead naturally to theformation of flattened molecular gas disks embedded in an extended cloudconducive to the collimation of even an isotropic stellar wind into abipolar flow. Rigorous numerical models of the collapse and accretion ofrotating, axisymmetric, isothermal interstellar clouds are used toverify this hypothesis, for a variety of possible initial clouds. Thecalculations are relevant for highly evolved clouds containingpre-main-sequence (rather than protostellar) objects. The modelsdemonstrate that in general, rotating interstellar clouds collapse toform a central protostellar core surrounded by a flattened molecular gasdisk, perpendicular to an evacuated, bipolar region of remarkable extentand narrowness. An isotropic stellar wind should flow outwardpreferentially through the previously evacuated bipolar holes.
| Mass loss from very young massive stars
The physics of mass loss from very young massive stars is reviewed, andmass-loss rates are determined for several objects on the basis ofpublished observational data. The observational evidence for mass lossof 0.0001-0.001 solar mass/yr with velocity 10-60 km/s, dynamicaltimescale 1000-100,000 yr, and kinetic energy (1-100) x 10 to the 38th Wfrom these objects is chracterized; techniques for estimating mass-lossrates from H recombination lines, CO line profiles maser data, andIR-continuum observations are described; rates for molecular outflowsand ionized winds are presented in tabels; and theoretical modelsdeveloped to explain the mechanism driving bipolar mass loss areexamined critically. It is found that neither radiation pressure on dustgrins nor the ionized winds can drive the molecular outflow. The modelsconsidered most probable are those involving production of holes byoriginal spherical stellar winds (Canto, 1980, rotationally drivenmagnetic pressure (Draine, 1983), and infall from an accretion disk(Torbett, 1984).
| Lithium abundances of southern F, G, and K dwarfs
Observations are reported of the lithium feature (6708 A) in some brightsouthern stars, most of which are F, G, or K dwarfs. Three of thesestars have been suggested as belonging to the Ursa Major Group. Two ofthese three have the large Li abundance and strong Ca II H and Kemission expected of such young stars. The third potential Ursa MajorGroup member has little Li, but is also not a true kinematic member. Nostars were found with abnormal (Li-6)/(Li-7) ratios, in accord withother recent analyses. Thus it appears that all stars have (Li-6)/(Li-7)near the solar/terrestrial value of 0.08.
| Predicted infrared brightness of stars within 25 parsecs of the sun
Procedures are given for transforming selected optical data intoinfrared flux densities or irradiances. The results provide R, T(eff)blackbody approximations for about 2000 of the stars in Woolley et al.'sCatalog of Stars (1970) within 25 pc of the sun, and additional whitedwarfs, with infrared flux densities predicted for them at ninewavelengths from 2.2 to 101 microns including the Infrared AstronomySatellite bands.
| DDO Observations of Southern Stars
Not Available
| The chemical evolution of the solar neighborhood. I - A bias-free reduction technique and data sample
The possible ways of measuring the age-metallicity relation for thegalactic disk in the neighborhood of the sun are discussed. It is shownthat the use of a field star sample chosen on the basis of effectivetemperature introduces a bias which results in a monotonic increase inthe metal abundance of the disk with time. However, if theage-metallicity relation for the disk can be shown to satisfy certaincriteria, the bias introduced in such a sample can be neglected: thegalactic disk apparently satisfies the criteria. It is concluded that asample analyzed through the use of uvby and H(beta) photometry inconjunction with a self-consistent set of theoretical isochronesprovides the least biased, most accurate estimate of the age-metallicityrelation for the disk.
| Prediction of spectral classification from photometric observations - Application of the UVBY beta photometry and the MK spectra classification. II - General case
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1980A&A....85...93M&db_key=AST
| Prediction of spectral classification from photometric observations-application to the UVBY beta photometry and the MK spectral classification. I - Prediction assuming a luminosity class
An algorithm based on multiple stepwise and isotonic regressions isdeveloped for the prediction of spectral classification from photometricdata. The prediction assumes a luminosity class with reference touvbybeta photometry and the MK spectral classification. The precisionattained is about 90 percent and 80 percent probability of being withinone spectral subtype respectively for luminosity groups I and V and forluminosity groups III and IV. A list of stars for which discrepanciesappear between photometry and spectral classification is given.
| VRI photometry of nearby stars.
Not Available
| Three-dimensional motion of dwarf stars and RR Lyrae variables
A collection of 220 high-velocity dwarfs, 532 low-velocity dwarfs, and114 RR Lyrae variables is given in tables with calculations ofkinematical quantities in a three-dimensional model of galactic space. Ametal indicator, Delta-S, for RR Lyrae variables is transformed into theultraviolet excess, delta (0.6), which is utilized for a statisticalstudy of kinematics under the same metallicity classification. It isfound that the primordial Galaxy contracted by a factor of at least 20in the radial direction as compared to at least 50 in the Z direction.
| Detection of errors in spectral classification by cluster analysis
Cluster analysis methods are applied to the photometric catalogue ofuvby-beta measurements by Hauck and Lindemann (1973) and point out 249stars the spectral type of which should be reconsidered or thephotometric indices of which should be redetermined.
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משמש של הקבוצה הבאה
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | זבוב |
| התרוממות ימנית: | 11h42m14.92s |
| סירוב: | -75°13'38.3" |
| גודל גלוי: | 6.475 |
| מרחק: | 34.388 פארסק |
| תנועה נכונה: | 43.4 |
| תנועה נכונה: | -5.8 |
| B-T magnitude: | 7.097 |
| V-T magnitude: | 6.527 |
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