Rotational velocities of A-type stars. III. Velocity distributions
Aims.A sample of v sin i of B9 to F2-type main sequence single stars hasbeen built from highly homogeneous {v sin i} parameters determined for alarge sample cleansed of objects presenting the Am and Ap phenomenon aswell as of all known binaries. The aim is to study the distributions ofrotational velocities in the mass range of A-type stars for normalsingle objects. Methods: .Robust statistical methods are used torectify the {v sin i} distributions for the projection effect and theerror distribution. The equatorial velocity distributions are obtainedfor about 1100 stars divided in six groups defined by the spectral type,under the assumption of randomly orientated rotational axes.Results: .We show that late B and early A-type main-sequence stars havegenuine bimodal distributions of true equatorial rotational velocitiesprobably due to angular momentum loss and redistribution that the starunderwent before reaching the main sequence. A striking lack of slowrotators is noticed among intermediate and late A-type stars.Full Table [see full text] is only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/463/671 Appendices areonly available in electronic form at http://www.aanda.org
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CCD Speckle Observations of Binary Stars from the Southern Hemisphere. IV. Measures during 2001
We present 549 observations of 181 primarily southern binary stars. Ofthese, 32 are high-quality nondetections, meaning that, if binary, thesystem had a separation below the diffraction limit at the time of theobservation, and relative astrometry is presented for the remaining 517observations. In addition, a magnitude difference measure is reported in312 cases in which the observation was judged to be of sufficientquality to have little decorrelation of the speckle pattern of thesecondary relative to the primary star. These data were obtained fromspeckle observations taken at the Lowell-Tololo 0.6 m telescope at CerroTololo Inter-American Observatory using a fast-readout CCD detectorduring 2001 November. Results from an astrometric measurement precisionstudy indicate that the measures have typical uncertainties of12.2+/-1.4 mas in separation and 1.28d+/-0.21d in position angle withlittle systematic error. The magnitude differences presented show goodagreement with values in the Hipparcos catalog where comparisons can bemade. Their uncertainties are also characterized; they show a typicalvalue of 0.18 mag per 2 minute observation. Four systems of particularinterest are discussed.
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Speckle Interferometry of Southern Double Stars. III. Measures from the Cesco Observatory, 1994-1996
Position angle and separation measures of 482 primarily southern binarystars are presented. These were obtained from speckle observations takenat the Carlos U. Cesco Observatory, El Leoncito, Argentina, using amultianode microchannel array detector during the period 1994 July to1996 July. When comparing our measures to the ephemeris predictions inthe case of objects with well-determined orbits, we find that ourmeasures have a precision of approximately 13 mas per observation inseparation and 0.75d/ρ in position angle, where ρ is theseparation in arcseconds. We briefly discuss the photometric propertiesof the data and highlight four southern binaries of particular interestthat emerge from the list presented.
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Rotation- and temperature-dependence of stellar latitudinal differential rotation
More than 600 high resolution spectra of stars with spectral type F andlater were obtained in order to search for signatures of differentialrotation in line profiles. In 147 stars the rotation law could bemeasured, with 28 of them found to be differentially rotating.Comparison to rotation laws in stars of spectral type A reveals thatdifferential rotation sets in at the convection boundary in theHR-diagram; no star that is significantly hotter than the convectionboundary exhibits the signatures of differential rotation. Four lateA-/early F-type stars close to the convection boundary and at v sin{i}≈ 100 km s-1 show extraordinarily strong absolute shear atshort rotation periods around one day. It is suggested that this is dueto their small convection zone depth and that it is connected to anarrow range in surface velocity; the four stars are very similar inTeff and v sin{i}. Detection frequencies of differentialrotation α = ΔΩ/Ω > 0 were analyzed in starswith varying temperature and rotation velocity. Measurable differentialrotation is more frequent in late-type stars and slow rotators. Thestrength of absolute shear, ΔΩ, and differential rotationα are examined as functions of the stellar effective temperatureand rotation period. The highest values of ΔΩ are found atrotation periods between two and three days. In slower rotators, thestrongest absolute shear at a given rotation rateΔΩmax is given approximately byΔΩmax ∝ P-1, i.e.,αmax ≈ const. In faster rotators, bothαmax and ΔΩmax diminish lessrapidly. A comparison with differential rotation measurements in starsof later spectral type shows that F-stars exhibit stronger shear thancooler stars do and the upper boundary in absolute shear ΔΩwith temperature is consistent with the temperature-scaling law found inDoppler Imaging measurements.
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Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
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First signatures of strong differential rotation in A-type stars
We reanalyzed high quality spectra of 158 stars of spectral types A0-F1and v sin{i} values between 60 and 150 km s-1. Using a leastsquares deconvolution technique we extracted high S/N broadeningprofiles and determined the loci of the Fourier transform zerosq1 and q2 where the S/N-ratio was high enough. For78 stars q2 could be determined and the ratioq2/q1 was used as a shape parameter sensitive tosolar-like differential rotation (the equatorial velocity is faster thanthe near polar velocities). Seventy-four of the 78 stars have values ofq2/q1 consistent with solid body rotation; in fourof the 78 cases, values of q2/q1 are notconsistent with rigid rotation. Although these stars may be binaries,none of their profiles shows any signatures of a companion. The Fouriertransforms do not indicate any distortions and the broadening profilescan be considered due to single objects. One of these candidates may bean extremely rapid rotator seen pole-on, but for the other three starsof spectral types as early as A6, differential rotation seems to be themost plausible explanation for the peculiar profiles.
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First signatures of strong differential rotation in A-type stars
We reanalyzed high quality spectra of 158 stars of spectral types A0-F1and v \sini between 60 and 150 km s-1. Using a Least SquaresDeconvolution technique we extracted high S/N broadening profiles anddetermined the loci of the Fourier transform zeros q1 andq2 where the S/N-ratio was high enough. The values of v \siniwere redetermined and found to be consistent with the values derived by\cite{Royer02a}. For 78 stars q2 could be determined and theratio q2/q1 was used as a shape parametersensitive for solar-like differential rotation (Equator faster thanPole). 74 of the 78 stars have values of q2/q1consistent with solid body rotation; in four of the 78 cases, values ofq2/q1 are not consistent with rigid rotation.Although these stars may be binaries, none of the profiles showssignatures of a companion. The Fourier transforms do not indicate anydistortions and the broadening profiles can be considered due to singleobjects. One of those candidates may be an extremely rapid rotator seenpole-on, but for the other three stars of spectral types as early as A6,differential rotation seems to be the most plausible explanation for thepeculiar profiles.Based on observations collected at the European Southern Observatory, LaSilla.
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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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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
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A New Association of Post-T Tauri Stars near the Sun
Observing ROSAT sources in an area 20°×25° centered at thehigh-latitude (b=-59°) active star ER Eri, we found evidences for anearby association, that we call the Horologium association (HorA),formed by at least 10 very young stars, some of them being bona fidepost-T Tauri stars. We suggest other six stars as possible members ofthis proposed association. We examine several requirements thatcharacterize a young stellar association. Although no one of them,isolated, gives an undisputed prove of the existence of the HorA, alltogether practically create a strong evidence for it. In fact, the Liline intensities are between those of the older classical T Tauri starsand the ones of the Local Association stars. The space velocitycomponents of the HorA relative to the Sun (U=-9.5+/-1.0, V=-20.9+/-1.1,W=-2.1+/-1.9) are not far from those of the Local Association, so thatit could be one of its last episodes of star formation. In this regionof the sky there are some hotter and non-X-ray active stars, withsimilar space velocities, that could be the massive members of the HorA,among them, the nearby Be star Achernar. The maximum of the massdistribution function of its probable members is around 0.7-0.9Msolar. We estimate its distance as ~60 pc and its size as~50 pc. If spherical, this size would be larger than the surveyed area,and many other members could have been missed. ER Eri itself was foundto be not a member, but a background RS CVn-like system. We alsoobserved three control regions, two at northern and southern Galacticlatitudes and a third one in the known TW Hya association (TWA), and theproperties and distribution of their young stars strengthen the realityof the HorA. Contrary to the TWA, the only known binaries in the HorAare two very wide systems. The HorA is much more isolated from cloudsand older (~30 Myr) than the TWA and could give some clues about thelifetime of the disks around T Tauri stars. Actually, none of theproposed members is an IRAS source indicating an advanced stage of theevolution of their primitive accreting disks. Based on observations madeunder the Observatório Nacional-ESO agreement for the jointoperation of the 1.52 m ESO telescope and at the Observatório doPico dos Dias, operated by MCT/Laboratório Nacional deAstrofísica, Brazil
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Two-colour photometry for 9473 components of close Hipparcos double and multiple stars
Using observations obtained with the Tycho instrument of the ESAHipparcos satellite, a two-colour photometry is produced for componentsof more than 7 000 Hipparcos double and multiple stars with angularseparations 0.1 to 2.5 arcsec. We publish 9473 components of 5173systems with separations above 0.3 arcsec. The majority of them did nothave Tycho photometry in the Hipparcos catalogue. The magnitudes arederived in the Tycho B_T and V_T passbands, similar to the Johnsonpassbands. Photometrically resolved components of the binaries withstatistically significant trigonometric parallaxes can be put on an HRdiagram, the majority of them for the first time. Based on observationsmade with the ESA Hipparcos satellite.
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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
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Speckle Interferometry of Southern Double Stars.I.First Results of the Yale-San Juan Speckle Interferometry Program
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....111.1681H&db_key=AST
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Secondary UVBY standards in the Harvard E-regions
Photoelectric uvby photometry for 201 stars which are already UBV (RI)cstandards is presented. The photoelectric data are closely tied to theCousins uvby standards and the stars should be suitable for use asfainter (7-11 mag) secondary standards.
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Micrometric measurements of visual binaries (5th list)
The data resulting from 596 micrometric measurements of 152 binaries areset forth which represent observations taken on the GPO astrograph(described by Scardia, 1990). The traditional declination method is usedto track star position, and some of the measurements are related toprevious work by the author (1990). The data given include O-Cmeasurements corresponding to the Worley and Heintz catalogue (1984) andother relevant data.
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Secondary standards for H-beta photometry in the Southern Hemisphere (second series).
Not Available
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Secondary standards for H-beta photometry in the E regions.
Not Available
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UBV (RI)c standard stars in the E- and F-regions and in the Magellanic Clouds - a revised catalogue.
Not Available
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Secondary standards for the Stromgren UVBY system
Observations of 158 E region stars have been made in the Stromgrensystem, using the 46-cm reflector at Cape Town. They are mostly brighterthan eighth magnitude and are intended for use as secondary standardsfor the four-color system. The E region relative zero points are definedwith a precision of + or - 0.001 mag, and the internal standard errorsof the colors life between + or - 0.001 and + or - 0.002 mag.
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Differential population synthesis of early-type galaxies. I - Spectrophotometric atlas of synthesis standard spectra
Continuous spectrophotometry has been obtained for 200 objects at aresolution of 10-17 A over the wavelength region 3600-10,000 A.Kron-Cousins BVRI colors are computed from the spectra and compared withpublished photoelectric photometry. The (V - R)C color index is used togroup the individual observations to form synthesis standard spectra for48 common spectral types. The standard groups include a solar abundancesequence of most spectral types and luminosity classes, metal-rich andmetal weak G - K giant-branch sequences, and horizontal-branch giants.The variations with color, luminosity, and metallicity of severalprominent line strengths are discussed. The spectral atlas is availableas a FITS magnetic tape.
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Micrometric measurements of southern double stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1983A&AS...53..177A&db_key=AST
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Photometric standard stars for the UBV and (RI)KC systems.
Not Available
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Measures of southern visual double stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1977PASP...89..588H&db_key=AST
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VRI standards in the E regions
Not Available
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Standard Stars for VRI Photometry with S25 Response Photocathodes [Errata: 1974MNSSA..33....1C]
Not Available
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Three New Bright Eclipsing Binaries
Not Available
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Lichtelektrische UBV-Photometrie von Standardsternen und in vier Sternfeldern am Äquator
Not Available
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Standard magnitudes in the E regions.
Not Available
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INHABITED SKY
