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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
| Rotational velocities of A-type stars. I. Measurement of v sin i in the southern hemisphere
Within the scope of a Key Programme determining fundamental parametersof stars observed by HIPPARCOS, spectra of 525 B8 to F2-type starsbrighter than V=8 have been collected at ESO. Fourier transforms ofseveral line profiles in the range 4200-4500 Å are used to derivev sin i from the frequency of the first zero. Statistical analysis ofthe sample indicates that measurement error is a function of v sin i andthis relative error of the rotational velocity is found to be about 6%on average. The results obtained are compared with data from theliterature. There is a systematic shift from standard values from\citet{Slk_75}, which are 10 to 12% lower than our findings. Comparisonswith other independent v sin i values tend to prove that those fromSlettebak et al. are underestimated. This effect is attributed to thepresence of binaries in the standard sample of Slettebak et al., and tothe model atmosphere they used. Based on observations made at theEuropean Southern Observatory (ESO), La Silla, Chile, in the frameworkof the Key Programme 5-004-43K. Table 4 is only available in electronicform at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.125.5)or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/381/105
| Tucana Association
Among star clusters, only the sparse Ursa Major nucleus is closer toEarth than the recently identified Tucana association. Based on newphotometric VRI magnitudes, we construct a color-magnitude diagramcomposed of likely and possible Tucana members. The implied age of theTucana association stars, <~40 Myr, is consistent with the agedetermined from a previous analysis by Stelzer & Neuhäuser ofthe X-ray luminosities of plausible association members. Based primarilyon space motions and X-ray fluxes, we identify potential new members ofthe Tucana association not considered in earlier studies. Torres andcoworkers recently identified a group of post-T Tauri stars, theHorologium association, which is located near the Tucana association inright ascension and declination. Because the Horologium stars have thesame space motions, age, distance from Earth, volume density, and rangeof spectral types as Tucana stars, we suggest that, rather than beingcharacterized as a separate group, it would be appropriate andeconomical to subsume the Horologium association stars into the Tucanastream.
| 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).
| Radial velocities of HIPPARCOS southern B8-F2 type stars
Radial velocities have been determined for a sample of B8-F2 type starsobserved by the Hipparcos satellite. Observations were obtained withinthe framework of an ESO key-program. Radial velocities have beenmeasured using a cross-correlation method, the templates being a grid ofsynthetic spectra. The obtained precision depends on effectivetemperature and projected rotational velocity of the star as well as ona possible asymmetry of the correlation peak generally due to secondarycomponents. New spectroscopic binaries have been detected from theseasymmetries and the variability of the measured radial velocity.Simulations of binary and triple systems have been performed. Forbinaries our results have been compared with Hipparcos binary data.Adding the variable radial velocities, the minimum binary fraction hasbeen found 60% for physical systems. Radial velocities have beendetermined for 581 B8-F2 stars, 159 being new. Taking into accountpublished radial velocities, 39% south A-type stars with V magnitudelower than 7.5 have a radial velocity. Based on observations obtained atthe European Southern Observatory (ESO, La Silla, Chile) and on datafrom the ESA Hipparcos astrometry satellite.}\fnmsep \thanks{Tables 7, 8and 9 are only available in electronic form at the CDS via anonymous ftpto cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| 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.
| An extensive Delta a-photometric survey of southern B and A type bright stars
Photoelectric photometry of 803 southern BS objects in the Deltaa-system as detection tool for magnetic chemically peculiar (=CP2) starshas been carried out and compared to published spectral types. Thestatistical yield of such objects detected by both techniques ispractically the same. We show that there are several factors whichcontaminate the search for these stars, but this contamination is onlyof the order of 10% in both techniques. We find a smooth transition fromnormal to peculiar stars. Our sample exhibits the largest fraction ofCP2 stars at their bluest colour interval, i.e. 10% of all stars in thecolour range -0.19 <= B-V < -0.10 or -0.10 <= b-y < -0.05.No peculiar stars based on the Delta a-criterion were found at bluercolours. Towards the red side the fraction of CP2 stars drops to about3% for positive values of B-V or b-y with red limits roughlycorresponding to normal stars of spectral type A5. The photometricbehaviour of other peculiar stars: Am, HgMn, delta Del, lambda Boo, Heabnormal stars, as well as Be/shell stars and supergiants shows someslight, but definite deviations from normal stars. Spectroscopic andvisual binaries are not distinguished from normal stars in their Delta abehaviour. The results of this work justify larger statistical work(e.g. in open clusters) employing more time-saving photometric methods(CCD). \newpage Based on observations obtained at the European SouthernObservatory, La Silla, Chile. This research has made use of the Simbaddatabase, operated at CDS, Strasbourg, France. Table 2 is only availablein electronic form via anonymous ftp 130.79.128.5 orhttp://cdsweb.u-strasbg.fr/Abstract.html
| Convection, Thermal Bifurcation, and the Colors of A Stars
Broadband ultraviolet photometry from the TD-1 satellite andlow-dispersion spectra from the short wavelength camera of IUE have beenused to investigate a long-standing proposal of Bohm-Vitense that thenormal main-sequence A and early-F stars may divide into two differenttemperature sequences: (1) a high-temperature branch (and plateau)comprised of slowly rotating convective stars, and (2) a low-temperaturebranch populated by rapidly rotating radiative stars. We find noevidence from either data set to support such a claim, or to confirm theexistence of an "A-star gap" in the B-V color range 0.22 <= B-V <=0.28 due to the sudden onset of convection. We do observe, nonetheless,a large scatter in the 1800--2000 A colors of the A--F stars, whichamounts to ~0.65 mag at a given B-V color index. The scatter is notcaused by interstellar or circumstellar reddening. A convincing case canalso be made against binarity and intrinsic variability due topulsations of delta Sct origin. We find no correlation with establishedchromospheric and coronal proxies of convection, and thus nodemonstrable link to the possible onset of convection among the A--Fstars. The scatter is not instrumental. Approximately 0.4 mag of thescatter is shown to arise from individual differences in surface gravityas well as a moderate spread (factor of ~3) in heavy metal abundance andUV line blanketing. A dispersion of ~0.25 mag remains, which has noclear and obvious explanation. The most likely cause, we believe, is aresidual imprecision in our correction for the spread in metalabundances. However, the existing data do not rule out possiblecontributions from intrinsic stellar variability or from differential UVline blanketing effects owing to a dispersion in microturbulentvelocity.
| The X-Ray Light Curve of the Very Luminous Supernova SN 1978K in NGC 1313
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJ...456..187S&db_key=AST
| The X-Ray Emission of A-Type Stars
From X-ray images in the ROSAT public archives, we determine soft X-rayfluxes, or flux upper limits, for 74 A-type stars, which have beenobserved during deep integrations with the PSPC. Nine supposedly single,late A stars (0.20 < B-V < 0.35) are found to coincide with X-raysources. The X-ray luminosities we infer for these stars range fromlevels comparable to the Active Sun, at log L_x ~27.6, to much brighteremission levels similar to those observed for active late-type binarysystems, near log L_x ~30.1. Another 10 sources are identified withearly A stars (0.0 < B-V < 0.2). Five of these are confirmeddouble stars, the rest are ostensibly single. The maximum luminosity wedetect in the early A stars, log L_x = 30.1, is 3.5 orders of magnitudebrighter than the X-ray upper limits for the nondetected stars.Additional study, including radial velocity monitoring and/or opticalinterferometry, will be needed to determine whether the putativelysingle X-ray emitting stars are in fact single, or whether theiremission is produced entirely or in part by unknown or unresolved binarycompanions. The level of X-ray emission associated with chemicallynormal, single A stars thus far appears to be uncorrelated with anyobvious stellar property, including the rotation rate, which is known togreatly influence the dynamo activity and the X-ray emission levels oflower mass stars. (SECTION: Stars)
| 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.
| Improved Mean Positions and Proper Motions for the 995 FK4 Sup Stars not Included in the FK5 Extension
Not Available
| An Einstein Observatory X-ray survey of main-sequence stars with shallow convection zones
The results of an X-ray survey of bright late A and early F stars on themain B-V sequence between 0.1 and 0.5 are presented. All the stars wereobserved with the Einstein Observatory for a period of at least 500seconds. The survey results show significantly larger X-ray luminositiesfor the sample binaries than for the single stars. It is suggested thatthe difference is due to the presence of multiple X-ray sources inbinaries. It is shown that the X-ray luminosities for single starsincrease rapidly with increasing color, and that the relation Lx/Lbol isequal to about 10 to the -7th does not hold for A stars. No correlationwas found between X-ray luminosity and projected equatorial rotationvelocity. It is argued on the basis of the observations that X-rayemission in the sample stars originated from coronae. The availableobservational evidence supporting this view is discussed.
| 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
| 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.
| Four-colour and H BET photometry of some bright southern stars- II.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972MNRAS.160..155S&db_key=AST
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Pozíciós és asztrometriai adatok
| Csillagkép: | Háló |
| Rektaszcenzió: | 03h17m59.00s |
| Deklináció: | -66°55'37.0" |
| Vizuális fényesség: | 6.05 |
| Távolság: | 58.005 parszek |
| RA sajátmozgás: | 57.4 |
| Dec sajátmozgás: | 12.7 |
| B-T magnitude: | 6.203 |
| V-T magnitude: | 6.041 |
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