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The Frequency of Mid-Infrared Excess Sources in Galactic Surveys
We have identified 230 Tycho-2 Spectral Catalog stars that exhibit 8μm mid-IR extraphotospheric excesses in the MSX and Spitzer GLIMPSEsurveys. Of these, 183 are either OB stars earlier than B8 in which theexcess plausibly arises from a thermal bremsstrahlung component orevolved stars in which the excess may be explained by an atmosphericdust component. The remaining 47 stars have spectral classifications B8or later and appear to be main-sequence or late pre-main-sequenceobjects harboring circumstellar disks. Six of the 47 stars exhibitmultiple signatures characteristic of pre-main-sequence circumstellardisks, including emission lines, near-IR K-band excesses, and X-rayemission. Approximately one-third of the remaining 41 sources haveemission lines suggesting relative youth. We modeled the excesses in 26stars having two or more measurements in excess of the expectedphotospheres as single-component blackbodies. We determine probable disktemperatures and fractional IR luminosities in the range 191K
| Nearby Debris Disk Systems with High Fractional Luminosity Reconsidered
By searching the IRAS and ISO databases, we compiled a list of 60 debrisdisks that exhibit the highest fractional luminosity values(fd>10-4) in the vicinity of the Sun (d<120pc). Eleven out of these 60 systems are new discoveries. Special carewas taken to exclude bogus disks from the sample. We computed thefractional luminosity values using available IRAS, ISO, and Spitzer dataand analyzed the Galactic space velocities of the objects. The resultsrevealed that stars with disks of high fractional luminosity oftenbelong to young stellar kinematic groups, providing an opportunity toobtain improved age estimates for these systems. We found thatpractically all disks with fd>5×10-4 areyounger than 100 Myr. The distribution of the disks in the fractionalluminosity versus age diagram indicates that (1) the number of oldsystems with high fd is lower than was claimed before, (2)there exist many relatively young disks of moderate fractionalluminosity, and (3) comparing the observations with a currenttheoretical model of debris disk evolution, a general good agreementcould be found.
| CO emission from discs around isolated HAeBe and Vega-excess stars
We describe results from a survey for J = 3-2 12CO emissionfrom visible stars classified as having an infrared excess. The line isclearly detected in 21 objects, and significant molecular gas(>=10-3 Jupiter masses) is found to be common in targetswith infrared excesses >=0.01 (>=56 per cent of objects), but rarefor those with smaller excesses (~10 per cent of objects).A simple geometrical argument based on the infrared excess implies thatdisc opening angles are typically >=12° for objects with detectedCO; within this angle, the disc is optically thick to stellar radiationand shields the CO from photodissociation. Two or three CO discs have anunusually low infrared excess (<=0.01), implying the shielding discis physically very thin (<=1°).Around 50 per cent of the detected line profiles are double-peaked,while many of the rest have significantly broadened lines, attributed todiscs in Keplerian rotation. Simple model fits to the line profilesindicate outer radii in the range 30-300 au, larger than found throughfitting continuum SEDs, but similar to the sizes of debris discs aroundmain-sequence stars. As many as five have outer radii smaller than theSolar System (50 au), with a further four showing evidence of gas in thedisc at radii smaller than 20 au. The outer disc radius is independentof the stellar spectral type (from K through to B9), but there isevidence of a correlation between radius and total dust mass. Also themean disc size appears to decrease with time: discs around stars of age3-7 Myr have a mean radius ~210 au, whereas discs of age 7-20 Myr are afactor of three smaller. This shows that a significant mass of gas (atleast 2 M⊕) exists beyond the region of planetformation for up to ~7 Myr, and may remain for a further ~10Myr withinthis region.The only bona fide debris disc with detected CO is HD9672; this shows adouble-peaked CO profile and is the most compact gas disc observed, witha modelled outer radius of 17 au. In the case of HD141569, detailedmodelling of the line profile indicates gas may lie in two rings, withradii of 90 and 250 au, similar to the dust structure seen in scatteredlight and the mid-infrared. In both AB Aur and HD163296 we also findthat the sizes of the molecular disc and the dust scattering disc aresimilar; this suggests that the molecular gas and small dust grains areclosely co-located.
| 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
| Submillimetre observations and modelling of Vega-type stars
We present new submillimetre observations of Vega-excess stars, andconsistent modelling for all known Vega-excess stars with submillimetredata. Our analysis uses dust grain models with realistic opticalproperties, with the aim of determining physical parameters of theunresolved discs from just their spectral energy distributions (SEDs).For the resolved targets, we find that different objects require verydifferent dust grain properties in order to fit the image data and SEDsimultaneously. Fomalhaut and Vega require solid dust grains, while HR4796 and HD 141569 can only be fitted using porous grains. The olderstars tend to have grains which are less porous than the younger stars,which may indicate that collisions in the discs have reprocessed theinitially fluffy grains into a more solid form. ɛ Eri appears to bedeficient in small dust grains compared with our best-fitting model.This may show that it is important to include all the factors that causethe size distribution to depart from a simple power law for grains closeto the radiation pressure blow-out limit. Alternatively, thisdiscrepancy may be due to some external influence on the disc (e.g. aplanet).When the model is applied to the unresolved targets, an estimate of thedisc size can be made. However, the large diversity in dust compositionfor the resolved discs means that we cannot make a reliable assumptionas to the composition of the grains in an unresolved disc, and there iscorresponding uncertainty in the disc size. In addition, the poor fitfor ɛ Eri shows that the model cannot always account for the SEDeven if the disc size is known. These two factors mean that it may notbe possible to determine the size of a disc without actually resolvingit.
| A search for debris discs around stars with giant planets
Eight nearby stars with known giant planets have been searched forthermal emission in the submillimetre arising from dust debris. The nullresults imply quantities of dust typically less than 0.02 Earth massesper star. Conversely, literature data for 20 Sun-like stars with debrisdiscs show that <= 5 per cent have gas giants inside a fewastronomical units - but the dust distribution suggests that nearly allhave more distant planets. The lack of overlap in these systems - i.e.few stars possess both inner planets and a disc - indicates that thesephenomena either are not connected or are mutually exclusive. Comparisonwith an evolutionary model shows that debris masses are predicted to below by the stellar ages of 2-8 Gyr (unless the colliding parent bodiesare quite distant, located beyond 100-200 au), but it remains to beexplained why stars that do have debris should preferentially only havedistant planets. A simple idea is proposed that could produce theselargely different systems, invoking a difference in the primordial discmass. Large masses promote fast gas giant growth and inwards migration,whereas small masses imply slow evolution, low-mass gas giants andoutwards migration that increases the collision rate of Kuiper Belt-likeobjects. This explanation neglects other sources of diversity betweendiscs (such as density and planetesimal composition and orbits), but itdoes have the merit of matching the observational results.
| 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.
| Discovery of an Extremely Red Object in the Field of HD 155826
We have discovered an extremely red object, LSF 1, located 7" southwest(P.A. 217°) of the bright spectroscopic binary system HD 155826.Originally reported by IRAS as one source detected at 12-60 μm, andfound as a single 6-25 μm source of similar flux in the MidcourseSpace Experiment Galactic plane survey, two bright point sources werefound in arcsecond resolution infrared images obtained with the MIRLINcamera at the Infrared Telescope Facility and confirmed by the LongWavelength Spectrometer camera on Keck I. While HD 155826 itself waseasily detected in all the broadband and narrowband filters from 0.9 to12 μm that we used, the new counterpart, LSF 1, is only visible at 10μm. In Gunn z, J, H, and K', the upper limit to the new object'smagnitude is ~14. The detection of the new bright IR source explains theconfusing [K]-[N] IRAS colors that originally implied that HD 155826 wasa possible Vega-like system. The ``anomalous long-wavelength emission''is found to arise entirely from the new source. Without mid-IR extensionor excess long-wavelength emission, HD 155826 should no longer beclassified as a Vega-like system. We suspect LSF 1 to be either a highlyreddened carbon star or a Class II YSO, with no association with thehigh proper motion HD 155826 system.
| Mid-Infrared Imaging of Candidate Vega-like Systems
We have conducted deep mid-infrared imaging of a relatively nearbysample of candidate Vega-like stars using the OSCIR instrument on theCerro Tololo Inter-American Observatory 4 m and Keck II 10 m telescopes.Our discovery of a spatially resolved disk around HR 4796A has alreadybeen reported in 1998 by Jayawardhana et al. Here we present imagingobservations of the other members of the sample, including the discoverythat only the primary in the HD 35187 binary system appears to harbor asubstantial circumstellar disk and the possible detection of extendeddisk emission around 49 Ceti. We derive global properties of the dustdisks, place constraints on their sizes, and discuss several interestingcases in detail. Although our targets are believed to be main-sequencestars, we note that several have large infrared excesses compared withprototype Vega-like systems and may therefore be somewhat younger. Thedisk size constraints we derive, in many cases, imply emission fromrelatively large (>~10 μm) particles at mid-infrared wavelengths.
| 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
| An Extremely Red Object in the Field of HD 155826
We have discovered an extremely red object located 7 arcsec southwest(P.A. 233 deg) of the bright binary system HD 155826. Originallyreported by IRAS as one source detected at 12-100 μ m, within theerror ellipse of HD 155826, two bright point sources were found ininfrared images obtained with the NSFCAM and MIRLIN cameras at the IRTFand confirmed by the LWS camera on Keck I. HD 155826 is easily detectedin the NSFCAM z, J, H, and K images, but there is no apparentcounterpart for the new source down to mag ~14th at Gunn z, J, nor is anobject found in the Aladin sky catalogue. The detection of the second,bright red source explains the confusing K-(IRAS 12μ m) colorsoriginally assigned to HD 155826 as a possible Vega-like system. While7" corresponds to 140 AU at the distance of HD 155826, as the field iswithin 12 deg. of the Galactic center and ≈7' from the Galacticplane, it is very possible that the two sources are associated byconfusion only. >From the lack of an optical counterpart and thebright mid-IR flux, we suspect the object to be either a highly reddenedcarbon star with a thick shell or an embedded protostar. Our next majorstep will be to distinguish between these two possibilities by measuringthe 5-20μ m SED with medium to high spectral resolution to search forthe strong 8-10μ m absorption due to SiC found in extreme carbonstars.
| Photometric Examination of Possible Sub-Stellar Companions of HD155826 and HD68456
A low-mass stellar and substellar companion search program has beencompleted using the Near-Infrared Camera and Multi-Object Spectrometer(NICMOS) Camera 2 coronagraph aboard the Hubble Space Telescope (HST).Coronagraphic observations of seven targets were obtained with theF165M, F171M, F180M, and F207M filters. Of the seven IR-excess starsobserved, two ( HD155826 and HD68456 ) were found to have potentialcompanions within 4" from the parent star. We report photometricmeasurements of the suspected companions and compare their photometry toGliese 229B. Support for this work was provided by NASA through grantnumber G0-07385.03-96A from the Space Telescope Science Institute(STScI).
| HD 155826
IAUC 7465 available at Central Bureau for Astronomical Telegrams.
| Visual binary orbits and masses POST HIPPARCOS
The parallaxes from Hipparcos are an important ingredient to derive moreaccurate masses for known orbital binaries, but in order to exploit theparallaxes fully, the orbital elements have to be known to similarprecision. The present work gives improved orbital elements for some 205systems by combining the Hipparcos astrometry with existing ground-basedobservations. The new solutions avoid the linearity constraints andomissions in the Hipparcos Catalog by using the intermediate TransitData which can be combined with ground-based observations in arbitarilycomplex orbital models. The new orbital elements and parallaxes give newmass-sum values together with realistic total error-estimates. To getindividual masses at least for main-sequence systems, the mass-ratioshave been generally estimated from theoretical isochrones and observedmagnitude-differences. For some 25 short-period systems, however, trueastrometric mass-ratios have been determined through the observedorbital curvature in the 3-year Hipparcos observation interval. Thefinal result is an observed `mass-luminosity relation' which falls closeto theoretical expectation, but with `outliers' due to undetectedmultiplicity or to composition- and age-effects in the nonuniformnear-star sample. Based in part on observations collected with the ESAHipparcos astrometry satellite. Tables~ 1, 3, 4 and 6 are also availablein electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr~(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| 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.
| Infrared excesses in A-type stars
Not Available
| Optical, infrared and millimetre-wave properties of Vega-like systems.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996MNRAS.279..915S&db_key=AST
| ICCD Speckle Observations of Binary Stars. XIII. Measurements During 1989- 1994 From the Cerro Tololo 4 M Telescope
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....111..936H&db_key=AST
| A Survey of Ca II H and K Chromospheric Emission in Southern Solar-Type Stars
More than 800 southern stars within 50 pc have been observed forchromospheric emission in the cores of the Ca II H and K lines. Most ofthe sample targets were chosen to be G dwarfs on the basis of colors andspectral types. The bimodal distribution in stellar activity first notedin a sample of northern stars by Vaughan and Preston in 1980 isconfirmed, and the percentage of active stars, about 30%, is remarkablyconsistent between the northern and southern surveys. This is especiallycompelling given that we have used an entirely different instrumentalsetup and stellar sample than used in the previous study. Comparisons tothe Sun, a relatively inactive star, show that most nearby solar-typestars have a similar activity level, and presumably a similar age. Weidentify two additional subsamples of stars -- a very active group, anda very inactive group. The very active group may be made up of youngstars near the Sun, accounting for only a few percent of the sample, andappears to be less than ~0.1 Gyr old. Included in this high-activitytail of the distribution, however, is a subset of very close binaries ofthe RS CVn or W UMa types. The remaining members of this population maybe undetected close binaries or very young single stars. The veryinactive group of stars, contributting ~5%--10% to the total sample, maybe those caught in a Maunder Minimum type phase. If the observations ofthe survey stars are considered to be a sequence of snapshots of the Sunduring its life, we might expect that the Sun will spend about 10% ofthe remainder of its main sequence life in a Maunder Minimum phase.
| 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.
| ICCD speckle observations of binary stars. VIII - Measurements during 1989-1991 from the Cerro Tololo 4 M telescope
One-thousand eighty-eight observations of 947 binary star systems,observed by means of speckle interferometry with the 4 m telescope onCerro Tololo, are presented. These measurements, made during the period1989-1991, comprise the second installment of results stemming from theexpansion of our speckle program to the southern hemisphere.
| A narrow-band search for extraterrestrial intelligence (SETI) using the interstellar contact channel hypothesis
A search is reported for narrow spectral line emission from 176 targets(including 166 stars and seven globular clusers) at the hypothesized'interstellar communications channel' frequency of 4.462336275 GHz (= pitimes the neutral hydrogen line at 1.42 GHz) using the Parkes Radiotelescope. The frequency was Doppler corrected for the solar barycenter,target barycenter, and cosmic microwave background (CMB) referenceframes. If a 'Galactic club' of extraterrestrial civilizations exists,then the null results, down to a 3 sigma limit of 2 Jy (6 Jy in CMBframe), set an upper limit of 10 exp 8 yr on the lifetime of suchcivilizations.
| On winds and X-rays of O-type stars
The dependence between stellar wind parameters and their X-ray fluxes isstudied. Bolometric corrections are examined as a function oftemperature, and a bolometric luminosity scale is proposed for theO-type stars. New mass-loss rates and terminal velocities of 40well-known, bright single stars or binaries are measured, and theLyman-alpha profile is modeled for the stars to determine the amount ofX-ray-absorbing hydrogen. The mass-loss rates found for the latestO-type stars are significantly smaller than expected from the power-lawdependences known for brighter, hot stars. The mass-loss rates forbinary system do not differ significantly from those of single stars. Adependence is found between the wind energy of the single stars and theX-ray luminosity, and it is suggested that this dependence is at leastpartially responsible for the proportionality between L(x) and L(bol).The X-ray fluxes from the close binaries behave in qualitative agreementwith predictions from simple theories of colliding stellar winds.
| Walraven photometry of nearby southern OB associations
Homogeneous Walraven (VBLUW) photometry is presented for 5260 stars inthe regions of five nearby southern OB associations: Scorpio Centaurus(Sco OB2), Orion OB1, Canis Major OB1, Monoceros OB1, and Scutum OB2.Derived V and (B - V) in the Johnson system are included.
| 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.
| ICCD speckle observations of binary stars. V - Measurements during 1988-1989 from the Kitt Peak and the Cerro Tololo 4 M telescopes
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1990AJ.....99..965M&db_key=AST
| Cool circumstellar matter around nearby main-sequence stars
Stars are presented which have characteristics similar to Vega and othermain-sequence stars with cool dust disks, based on the IRAS Point SourceCatalog fluxes. The objects are selected to have a 60-micron/100-micronratio similar to Vega, Beta Pic, Alpha PsA, and Epsilon Eri, and theyare also required to show evidence of extension in the IRAS WorkingSurvey Database. The fluxes are modeled using a blackbody energydistribution. The temperatures derived range from 50 to 650 K. Thediameters of the dust disks observed by IRAS are estimated.
| Speckle interferometric measurements of binary stars. IV
Speckle interferometric observations of interferometric binaries, closevisual double stars, and nearby stars suspected to be binaries have beenobtained with the 3.6-meter Canada-France-Hawaii telescope. As a part ofthis program, the stars Gl 616.2 and Gl 831 are clearly resolved as abinary for the first time, and Gl 793.1 appears to be marginallyresolved. Gl 747.2 and Gl 866 are confirmed as double stars.
| On the (B-V) colors of the bright stars
The possible causes of the dispersion of (B-V) colors of nearby stars inthe Bright Star Catalog are investigated. The distribution of (B-V)colors is presented for the entire range of spectral classes.Explanations for the dispersion in terms of a nonuniform distribution ofinterstellar absorbing material and a variability of metallicity areaddressed. A new statistical model for reddening by interstellar dustclouds is developed. It is concluded that extinction by nonuniforminterstellar matter is an important contribution to the reddening ofnearby stars, and that a part of the dispersion of (B-V) colors of Kand, possibly, M giants may be due to some unidentified variableproperty of those stars.
| Large and kinematically unbiased samples of G and K type stars. I - The dwarfs
Four-color, H-beta, and (R,I) photometry for the little-evolvedmain-sequence stars from the Bright Star Catalogue, South Galactic Pole,Griffin (1971), and Moore-Paddock-Wayman (Moore and Paddock 1950, andWayman 1960) samples are analyzed. The luminosity and heavy-elementabundances for these stars are calculated in terms of the Hyadessupercluster, the Wolf 630 group, the Sirius supercluster, and theKapteyn star group. The data reveal the presence of a metal-abundancedependent discontinuity near M(v) = +7 mag in the photometric parametersof dwarfs. The distributions of the abundances and the space motions ofthe sample stars are discussed.
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