Statistical Constraints for Astrometric Binaries with Nonlinear Motion
Useful constraints on the orbits and mass ratios of astrometric binariesin the Hipparcos catalog are derived from the measured proper motiondifferences of Hipparcos and Tycho-2 (Δμ), accelerations ofproper motions (μ˙), and second derivatives of proper motions(μ̈). It is shown how, in some cases, statistical bounds can beestimated for the masses of the secondary components. Two catalogs ofastrometric binaries are generated, one of binaries with significantproper motion differences and the other of binaries with significantaccelerations of their proper motions. Mathematical relations betweenthe astrometric observables Δμ, μ˙, and μ̈ andthe orbital elements are derived in the appendices. We find a remarkabledifference between the distribution of spectral types of stars withlarge accelerations but small proper motion differences and that ofstars with large proper motion differences but insignificantaccelerations. The spectral type distribution for the former sample ofbinaries is the same as the general distribution of all stars in theHipparcos catalog, whereas the latter sample is clearly dominated bysolar-type stars, with an obvious dearth of blue stars. We point outthat the latter set includes mostly binaries with long periods (longerthan about 6 yr).
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Rotational velocities of A-type stars in the northern hemisphere. II. Measurement of v sin i
This work is the second part of the set of measurements of v sin i forA-type stars, begun by Royer et al. (\cite{Ror_02a}). Spectra of 249 B8to F2-type stars brighter than V=7 have been collected at Observatoirede Haute-Provence (OHP). Fourier transforms of several line profiles inthe range 4200-4600 Å are used to derive v sin i from thefrequency of the first zero. Statistical analysis of the sampleindicates that measurement error mainly depends on v sin i and thisrelative error of the rotational velocity is found to be about 5% onaverage. The systematic shift with respect to standard values fromSlettebak et al. (\cite{Slk_75}), previously found in the first paper,is here confirmed. Comparisons with data from the literature agree withour findings: v sin i values from Slettebak et al. are underestimatedand the relation between both scales follows a linear law ensuremath vsin inew = 1.03 v sin iold+7.7. Finally, thesedata are combined with those from the previous paper (Royer et al.\cite{Ror_02a}), together with the catalogue of Abt & Morrell(\cite{AbtMol95}). The resulting sample includes some 2150 stars withhomogenized rotational velocities. Based on observations made atObservatoire de Haute Provence (CNRS), France. Tables \ref{results} and\ref{merging} are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.125.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/393/897
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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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X-ray emission from A0-F6 spectral type stars
We use the ROSAT public data archive to study the X-ray emission of asample of supposedly single A0-F6 spectral type stars from the BrightStar Catalogue. We detected X-ray emission from 19 A- and 33 F-typestars. However, our results are not sufficient to associate withcertainty the X-ray emission to the A-type stars themselves, since theusual argument that it may originate from a binary companion cannot beexcluded. A spectral analysis was conducted for 14 sources (3 A and 11F), finding that for 12 of them a two temperature thermal plasma modelis needed to reproduce the observed spectra. The two temperatures arecentered at 0.13 and 0.54 keV, respectively. The values found for thehigher temperature are lower than that ones of X-ray selected singlelate-type stars. The X-ray luminosities are in the range LX ~10(28}-10({30)) erg s(-1) , with a distribution similar to that ofactive late-type stars. No correlation is found between LXand B-V color, V sin i and Lbol, while a positive correlationis found between the X-ray luminosity and the hardness ratio.
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The Angular Momentum of Main Sequence Stars and Its Relation to Stellar Activity
Rotational velocities are reported for intermediate-mass main sequencestars it the field. The measurements are based on new, high S/N CCDspectra from the Coudé Feed Telescope of the Kitt Peak NationalObservatory. We analyze these rotation rates for a dependence on bothmass and age. We compare the average rotation speeds of the field starswith mean velocities for young stars in Orion, the Alpha Persei cluster,the Pleiades, and the Hyades. The average rotation speeds of stars moremassive than $\sim1.6$ \msun\experience little or no change during theevolutionary lifetimes of these stars on the zero age main sequence orwithin the main sequence band. Less massive stars in the range betwee n1.6\msun\ and 1.3\msun\ also show little decline in mean rotation ratewhile they are on the main sequence, and at most a factor of 2 decreasein velocity as they evolve off the main sequence. The {\it e}-foldingtime for the loss of angular momentum b y the latter group of stars isat least 1--2 billion years. This inferred characteristic time scale forspindown is far longer than the established rotational braking time forsolar-type stars with masses below $\sim1.3$ \msun. We conclude from acomparison of the trends in rotation with trends in chromospheric andcoronal activity that the overall decline in mean rotation speed alongthe main sequence, from $\sim2$ \msun\ down to $\sim1.3$ \msun, isimposed during the pre-main sequence phase of evolution, and that thispattern changes little thereafter while the star resides on the mainsequence. The magnetic activity implicated in the rotational spindown ofthe Sun and of similar stars during their main sequence lifetimes mus ttherefore play only a minor role in determining the rotation rates ofthe intermediate mass stars, either because a solar-like dynamo is weakor absent, or else the geometry of the magnetic field is appreciablyless effective in removing angular momentu m from these stars. (SECTION:Stars)
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The Relation between Rotational Velocities and Spectral Peculiarities among A-Type Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJS...99..135A&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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Interstellar polarization at high galactic latitudes from distant stars. 2: First results for Z less than or equal to 600 PC
We present the first results from our Crimean-Tuorla program forpolarimetry of distant stars at high galactic latitudes. The availableobservations reveal a clear increase in the interstellar linearpolarization of A and F stars, up to Z approximately equals 600 pc whereone reaches PV approximately equals 0.25%. This means anaverage AB greater than or equal to 0.11 mag over thenorthern polar cap for the diffuse component of the interstellarextinction that we are probing. There is no clear indication in the datathat the asymptotic level of PV has been reached, and withfuture observations above Z = 600 pc we shall investigate this question.The trend found is in agreement with the stellar reddening analysis byTeerikorpi (1990). The directions of the plane of vibration are inagreement with Markkanen's (1979) analysis of closer (Z less than 200pc) stars in his 'Area II'. Outside of this area we define two sectors Band C which encompass the Local Spiral Arm and had little stars inprevious investigations. Here the polarization vectors deviate stronglyfrom those in Markkanen's Area II, where one is probably looking at aninterarm region, close to the edge of the Local Spiral Arm. Ourmeasurements indicate for B and C average polarization vectorsconsistent with the direction l approximately equals 110 deg obtained byother authors for the magnetic field in the Local Spiral Arm using therotation measure method.
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Accretion from Circumstellar Discs and the Lambda-Bootis Phenomenon
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1994MNRAS.269..209K&db_key=AST
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Catalogue of Lambda Bootis Candidates
Not Available
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Third preliminary catalogue of stars observed with the photoelectric astrolabe of the Beijing Astronomical Observatory.
Not Available
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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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Two-colour diagrams for differentially rotating stars
Not Available
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Further Studies of A-Stars and F-Stars in the Region of the North Galactic Pole - Part Four - a Catalogue of Uvbyr Photometry and Derived Quantities
Not Available
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Further Studies of A-Stars and F-Stars in the Region of the North Galactic Pole - Part Three - a Catalogue of Star Names and Positions
Not Available
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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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Spectral classification of the bright F stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1976PASP...88...95C&db_key=AST
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Interstellar reddening near the north galactic pole
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972PASP...84..497F&db_key=AST
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Rotation of evolving A and F stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972A&A....18..428D&db_key=AST
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The Motions of the A Stars at the North Galactic Pole
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1969PASP...81..741E&db_key=AST
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The galactic force law K(z
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1969AJ.....74..139P&db_key=AST
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Interstellar gas dynamics and the motions of young stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1968MNRAS.140..287D&db_key=AST
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Polarimetric Observations of Nearby Stars in the Directions of the Galactic Poles and the Galactic Plane
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1968ApJ...151..907A&db_key=AST
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Radial Velocities of A-Type Stars Near the North Galactic Pole
Not Available
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Three-colour photometry of early-type stars near the galactic poles
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1963MNRAS.127...83W&db_key=AST
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Spectral Classification of 533 B8-A2 Stars and the Mean Absolute Magnitude of a0 V Stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1959ApJ...130..159O&db_key=AST
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Positions et Mouvements propres de 357 Etoiles de Repère de la Zone + 16° à + 18° pour l'époque et l'équinoxe 1950,0
Not Available
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INHABITED SKY
