Dusty Debris Disks as Signposts of Planets: Implications for Spitzer Space Telescope
Submillimeter and near-infrared images of cool dusty debris disks andrings suggest the existence of unseen planets. At dusty but nonimagedstars, semimajor axes of associated planets can be estimated from thedust temperature. For some young stars these semimajor axes are greaterthan 1" as seen from Earth. Such stars are excellent targets forsensitive near-infrared imaging searches for warm planets. To probe thefull extent of the dust and hence of potential planetary orbits, Spitzerobservations should include measurements with the 160 μm filter.
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Automated spectroscopic abundances of A and F-type stars using echelle spectrographs. II. Abundances of 140 A-F stars from ELODIE
Using the method presented in Erspamer & North (\cite{erspamer},hereafter Paper I), detailed abundances of 140 stars are presented. Theuncertainties characteristic of this method are presented and discussed.In particular, we show that for a S/N ratio higher than 200, the methodis applicable to stars with a rotational velocity as high as 200 kms-1. There is no correlation between abundances and Vsin i,except a spurious one for Sr, Sc and Na which we explain by the smallnumber of lines of these elements combined with a locally biasedcontinuum. Metallic giants (Hauck \cite{hauck}) show larger abundancesthan normal giants for at least 8 elements: Al, Ca, Ti, Cr, Mn, Fe, Niand Ba. The anticorrelation for Na, Mg, Si, Ca, Fe and Ni with Vsin isuggested by Varenne & Monier (\cite{varenne99}) is not confirmed.The predictions of the Montréal models (e.g. Richard et al.\cite{richard01}) are not fulfilled in general. However, a correlationbetween left [(Fe)/(H)right ] and log g is found for stars of 1.8 to 2.0M_sun. Various possible causes are discussed, but the physical realityof this correlation seems inescapable.Based on observations collected at the 1.93 m telescope at theObservatoire de Haute-Provence (St-Michel l'Observatoire, France) andCORALIE.Based on observations collected at the Swiss 1.2 m Leonard Eulertelescopes at the European Southern Observatory (La Silla, Chile).Tables 5 and 6 are 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/398/1121
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Ages of A-Type Vega-like Stars from uvbyβ Photometry
We have estimated the ages of a sample of A-type Vega-like stars byusing Strömgren uvbyβ photometric data and theoreticalevolutionary tracks. We find that 13% of these A stars have beenreported as Vega-like stars in the literature and that the ages of thissubset run the gamut from very young (50 Myr) to old (1 Gyr), with noobvious age difference compared to those of field A stars. We clearlyshow that the fractional IR luminosity decreases with the ages ofVega-like stars.
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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
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A search for circumstellar gas around normal A stars and Lambda Bootis stars
We have searched for interstellar or circumstellar absorption lines inthe center of Ca II K towards bright A-type stars that are mostly within80 pc of the Sun. Narrow absorption features are found in about 30 % ofthe 28 normal main-sequence A stars and 18 metal-deficient lambda Bootisstars studied. We have determined surface gravities and projectedrotational velocities. Most of the stars with detectable Ca K featureshave comparatively low gravities and high projected rotationalvelocities. This correlation with stellar properties implies that mostof the narrow absorption features are of circumstellar rather thaninterstellar origin. The preference of low gravity and rapid rotationfurthermore suggests that most of the gas shells around A stars developin the pre-main-sequence phase of evolution, and disappear largelybefore the star arrives at the ZAMS. Among the normal A stars studied,about 50 % are known to have dust disks. Unlike A stars withcircumstellar gas, these dusty stars do not prefer low log g and high vsin i. This results in an apparent lack of correlation between gas anddust, and indicates that normal A stars with gas shells and those withdust disks are not in the same evolutionary stage. We conjecture thatdust disks tend to develop after most of the gas has disappeared. Basedon observations collected at the European Southern Observatory, LaSilla, Chile
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Dusty and dust-free A stars
We present preliminary results of our search for circumstellarabsorption features in the Ca K lines based on high S/N observationsobtained with the ESO CAT/CES system.
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Candidate Main-Sequence Stars with Debris Disks: A New Sample of Vega-like Sources
Vega-like sources are main-sequence stars that exhibit IR fluxes inexcess of expectations for stellar photospheres, most likely due toreradiation of stellar emission intercepted by orbiting dust grains. Wehave identified a large sample of main-sequence stars with possibleexcess IR radiation by cross-correlating the Michigan Catalog ofTwo-dimensional Spectral Types for the HD Stars with the IRAS FaintSource Survey Catalog. Some 60 of these Vega-like sources were not foundduring previous surveys of the IRAS database, the majority of whichemployed the lower sensitivity Point Source Catalog. Here, we providedetails of our search strategy, together with a preliminary examinationof the full sample of Vega-like sources.
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The surface composition of Beta Pictoris.
We present an element-by-element analysis of the surface composition ofβ Pic (A5V) based on high-resolution broad-band optical spectra.The abundances (relative to H) of C, Ca, Ti, Cr, Fe, Sr, and Ba aresolar. Obviously β Pic does not show the "λ-Boo phenomenon"- the metal deficiency of certain cool A-type stars attributed toaccreting circumstellar matter.
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A microwave survey of southern early-type stars
A multi-epoch survey with the Parkes telescope of a completedistance-limited sample of 57 stars earlier than F6 has detectedpossible 8.4-GHz emission from 16 stars. Single-epoch partial synthesisobservations with the Australia Telescope Compact Array (ATCA) at 4.8GHz on 27 stars from the same sample (including the possible Parkesdetections) found no emission at the stellar positions above a fluxdensity limit of 1.2-1.9 mJy, but the maps show that the Parkesdetections are not merely the results of confusion of sources within theParkes beam. Three early F stars with UV and/or X-ray emission wereobserved simultaneously at 4.8 and 8.4 GHz in 12-h syntheses with the6-element ATCA. Two of these stars were from the above sample and thethird was the supergiant Alpha Carinae. We detected only alphaCar withflux densities of 300+/-65 and 140+/-65 muJy at 4.8 and 8.6 GHz(S~nu^-1.3+/-1.3). We discuss the legitimacy of the Parkes 3-6sigmadetections and show that, although none has been detected by synthesisobservations, there is no compelling reason for rejecting them on theinternal evidence. The power emitted by the supergiant alphaCar issimilar to that of the 16 possible Parkes detections, although itsactivity index is orders of magnitude lower. We show that this emissioncannot be thermal bremsstrahlung from the 10^7.2-K corona of the starbut is probably synchrotron emission from a magnetically maintainedcorona.
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Pre-Main-Sequence Stars in the Pleiades Supercluster
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....110.1749E&db_key=AST
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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
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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.
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High-resolution spectroscopy of λ Bootis stars and `dusty' normal A stars: circumstellar gas, rotation, and accretion.
We present results of a high-S/N search for circumstellar Ca K lines intwo classes of A stars: (i) metal-deficient stars of the λBootistype whose surface anomalies are believed to be due to accretion ofdepleted gas, and (ii) stars known to possess circumstellar dust disks,including Vega and βPictoris. We derive T_eff_ and logg and combinemodel-atmosphere analysis with spectrum synthesis to determine projectedrotational velocities, calcium abundances, and the motion ofcircumstellar gas with respect to the star. Narrow components in Ca Kare present in five of the eleven λBoo stars studied. Thisexceptional high incidence suggests that the λBoo phenomenon isrelated to the presence of circumstellar gas. Specific topics discussed(Sect. 6) include: (1) a connection between rotation, the presence ofdetectable amounts of CS gas, and metal deficiency, (2) Vega andβPic as suspected λBoo stars, (3) λBoo stars asprobable pre-main-sequence objects, and (4) episodes of massiveaccretion in βPic and in the λBoo star HR4881.
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Newly identified main-sequence A stars with circumstellar dust
The IRAS Faint Source Survey data base and the ADDSCAN/SCANPI softwareare used to search for systems with circumstellar dust in two samples:all of the 62 A stars in Woolley's catalog, which lie near the mainsequence and are typically within 25 pc of the sun, and all A stars inthe Bright Star Catalogue with mV in the range 4-5 and v sin i not lessthan 100 km/s. In the first sample, 11 nearby A stars having (12)-(25)and (25)-(60) colors consistent with circumstellar dust are found. Theanalysis of the second sample demonstrates that the use of the FSS database increases the likelihood of identifying A stars with circumstellardust fainter than mV = 4. Three more new dusty systems are found in thissample. Beta Pictoris (A5 IV-V) is the only star within 25 pc of the sunthat displays IR colors indicative of both warm and cool dust. It isinferred from the absence of cool dust in the vast majority of thesystems that the dust disks of these stars are much less extended thanthat seen around Beta Pictoris.
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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.
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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.
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The late A-type stars - Refined MK classification, confrontation with Stromgren photometry, and the effects of rotation
The MK spectral classification for late A-type stars is refined and theeffects of rotation of spectral classification and uvby(beta) photometryfor these stars are examined. It is found that, for A3 stars, the4417/4481 A wavelength ratio produces results that are inconsistent withthe Stark broadening of the H lines. It is suggested that this ratio isnot useful as a luminosity criterion at any spectral type.Self-consistent sequences of narrow- and broadline standards areestablished. The results of the refined classification system arecompared with Stromgren photometry, showing a set of low-v sin i A-typestars with anomalously large delta(c1) indices for theirluminosity types. It is proposed that these stars are rapid rotatorsseen at fairly low inclination angles.
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A photometric survey of the bright southern Be stars
Repeated UBV photometric measurements were made of the 86 bright Bestars south of declination -20 deg, and a network of comparison starswas set up. From a statistical study of the differential photometry itwas found that short- or intermediate-term variability seems to beoccurring in about half of the Be stars, and to be more evident in thestars of earlier spectral type. It was also possible to identify 11individual short- or intermediate-term variables. Four of these (all ofearly B spectral type) appear to exhibit significant variability on atime-scale of a day or less. More intensive observations of one of thesestars, 28 Omega CMA, indicate short-term variations consistent with thepublished spectroscopic period of 1.37 day.
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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.
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Lists of photometric AM candidates
The Geneva photometric m parameter (Nicolet and Cramer, 1982) is used inorder to select Am photometric candidates from the Rufener (1981)catalogue. Two lists are given, the first containing field stars and thesecond cluster stars. According to the photometric criteria thediffusion process probably responsible for the Am phenomenon takes placerather quickly as Am candidates are present in young clusters. It isconfirmed that the phenomenon is enhanced by low rotational velocity andhigh metallicity. The age seems to slightly affect the Am phenomenon.
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On the search for transition zone lines in late A type stars
Observations of the 1400-1800 A region in late A type stars arepresented, which were obtained using the IUE satellite at low and highresolution. The calibrated energy distribution is derived and presents alarge variation with wavelength in the spectral range due to Si Iphotoionization discontinuities. Emission lines formed in the transitionregion do not appear, although upper limits on the emission in theselines are established. A schematic model is proposed for the outerlayers in A type stars, which suggests that the chromosphere in solartype stars is likely absent in A stars, while the NLTE photosphere couldbe immediately connected to the transition region, joining the upperphotosphere to the corona. In addition, the amount of matter in thetransition zone is found to be small.
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VRI photometry of nearby stars.
Not Available
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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.
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Absolute luminosity calibration of Stroemgren's 'late group'
A statistical parallax method based on the principle of maximumlikelihood is used to calibrate absolute luminosities for samples ofcooler stars constituting the 'late group' defined by Stromgren (1966).The samples examined include 415 stars of all luminosity classes and asubset comprising 86 main-sequence stars. Linear calibration relationsinvolving the Stromgren beta, (b-y), and bracketted c1 indices arederived which yield mean absolute magnitudes with an accuracy of 0.09magnitude for the overall sample and 0.13 magnitude for themain-sequence subsample. Several second-order relations are considered,and the results are compared with Crawford's (1975) calibrations as wellas with mean absolute magnitudes obtained from trigonometric parallaxes.The possible effect of interstellar absorption on the calibrationrelations is also investigated.
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Luminosity and velocity distribution of high-luminosity stars near the sun. II. The young disk giants
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1973PASP...85..379E&db_key=AST
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Four-colour and H BET photometry of some bright southern stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972MNRAS.159..165S&db_key=AST
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Intermediate-band photometry of RR LYR variables. I. Definition and characteristics of the system.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1971MNRAS.154...79J&db_key=AST
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K-Line Photometry of Southern a Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1971ApJS...23..421H&db_key=AST
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Moving Pairs among the A-Type Stars Within 20 PC
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1968ApJ...152..895V&db_key=AST
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Moving Pairs among the A-Type Stars within 20 PC
Not Available
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INHABITED SKY
