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# 67 Cnc (67 Cancri)

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 Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statisticsThe 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 A-shell stars in the Geneva systemAmong the various kinds of A stars having a peculiar spectrum, we findthe A-shell stars. Many questions are still open concerning these stars,including their evolutionary status. In the present study we have useddata from the Hipparcos catalogue to examine this point. We have foundthat the majority of A-shell stars are well above the main sequence. Nodifferences could be established between A-shell stars in luminosityclasses III and I and those in luminosity class V as regardsvariability, duplicity, or the importance of the shell feature. AE and A type shell starsWe present and discuss the observations of 14 Ae and A type shell starsin the visual, the Hα region and the near infrared. At least 57%of these stars are spectrum variables. The Paschen lines are formed in aregion which has the characterics of giant stars. We find that thesystems lie one magnitude above the main sequence and that a largepercentage belong to double and triple systems. The Angular Momentum of Main Sequence Stars and Its Relation to Stellar ActivityRotational 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) Hot Inner Disks that Appear and Disappear around Rapidly Rotating A-Type DwarfsAt any one time, approximately one-quarter of the most rapidly rotatingnormal A-type dwarfs (V sin i >= 200 km s-1) show shell lines of TiII in the near-ultraviolet. Our observations during 22 years show thatthe lines appear and disappear on timescales of decades but do notdisplay significant changes within 1 year. This implies that they arenot remnants of the star formation but rather are probably caused bysporadic mass-loss events. A working hypothesis is that all A-type starsthat are rotating near their limits have these shells, but for onlyone-quarter of the time. Because these lines do not appear in stars withsmaller sin i, the shells must be disks. These are hot inner disks thatmay or may not be related to the cool outer disks seen by Smith andTerrile around beta Pic or through infrared excesses around Vega andother A-type dwarfs. The similar, limited line widths indicate that thedisks are ~7 R* above the stellar surfaces. Polarisation in A-type stars with circumstellar shells.We present the results of optical linear polarisation measurements ofabout 30 A-type stars that are known to be either Ae/A shell stars orhave shown anomalous emission in the infrared. Compared with the generalpopulation of A-type stars, stars of this group are found to havepolarisation that is also anomalous and is suggested to be circumstellarin origin. The Relation between Rotational Velocities and Spectral Peculiarities among A-Type StarsAbstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJS...99..135A&db_key=AST 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. Radial velocity studies of A-type shell stars.We have measured radial velocities for a sample of A-type shell stars.We examine the results for the H I, Ti II and Ca II shell lines andcompared them with the radial velocities derived for the underlyingstars. We found that the A-type shell stars reproduce on a smaller scalethe phenomena observed in B-type shell stars. 49 Camelopardalis: an uncommon magnetic starWe have discovered that the magnetic variable 49 Cam displays aremarkable linear polarization, with periodic variations larger thanthose of other Ap stars. The time variation of the Stokes parameters hasbeen established with good accuracy for the standard B band andadditional measurements in the U and V bands already give some insightinto the spectral variation of the polarization. 49 Cam is expected tobe closer than about 50 pc and its polarization, like that of mostneighboring stars, suffers little contamination from the interstellarpolarization. The hypothetical presence of continum polarization due toa circumstellar shell seems unlikely, given both the spectral dependenceof the polarization and the negative result of our polarimetry bearingon several A-shell stars. Therefore, we think that the polarization of49 Cam has to be understood, as for the other Ap stars, as the result ofmagnetic intensification in spectral lines. The interpretation of thepolarization variation is much easier if one knows the magnetic phasederived from the classical longitudinal magnetic field measurements. Thespecific shape of the linear polarization diagram makes it difficult tointerpret our observations in the customary framework of the obliquerotating dipole. Modifications of this model are necessary. One canreproduce fairly well the variations of the polarization of 49 Cam ifthe magnetic signal is not symmetrical with respect to the magnetic axisand has some peculiarities in the polar regions. The problem is not tofind a magnetic solution but rather that there are too many possiblesolutions. While we cannot claim that we have already found a firm modelfor 49 Cam, there are serious guidelines for progress of theinterpretation. In any case, it is clear that this star is one of themost peculiar objects among the 40 Ap stars considered in ourinvestigation. Radial-velocity measurements. V - Ground support of the HIPPARCOS satellite observation programThe paper presents data on 1070 radial velocity measurements of starsdistributed in 39 fields measuring 4 deg x 4 deg. The PPO series ofFehrenbach et al. (1987) and Duflot et al. (1990) is continued using theFehrenbach objective prism method. UBV photometry of stars whose positions are accurately known. VIResults are presented from UBV photometric observations of 1000 stars ofthe Bright Star Catalogue and the faint extension of the FK5.Observations were carried out between July 1987 and December 1990 withthe 40-cm Cassegrain telescope of the Kvistaberg Observatory. Anomalous infrared emitters among A-type starsSpectroscopic observations of a sample of 26 stars have been analyzed inthe blue and near-IR to find out if anomalous IR emitters (AIEs) have aspectral signature. It is found that many, but not all, such starsexhibit shell characteristics. Analysis of available IRAS photometricobservations of A-type stars shows that the detection of circumstellarfeatures depends strongly on the number of IR bands at which the objectwas observed. Out of the 707 stars observed by IRAS, 41 AIEs, or 5.7percent, are found. Among nonsupergiant AIEs, 23 percent show shellfeatures. The true percentage of AIEs among A-type stars is estimated tobe 1.5 percent in a volume-corrected sample. A list of 24 stars whichwere apparently not previously detected as AIEs is given. AE and A-type shell stars in the near infraredSpectroscopic observations in the near-infrared of a number of Ae and Ashell stars are presented. It is shown that shells can be detectedthrough the enhancement of the lambda 7773 line and through otherspectroscopic criteria. Search for Beta Pictoris-like starThe results are reported of a systematic search for Beta Pic-like stars,undertaken at ESO, CFHT and OHP. The candidate stars, either IRAS excessstars or shell stars, are investigated by means of high resolutionspectroscopy in the Ca II and Na I lines, which in the case of Beta Pic,are very peculiar. The observations are presented and it is shown thatamong the selected stars, few do show spectral similarities with BetaPic. Some interesting cases, HR10, HR2174, HR9043 and HR6519 arediscussed. A survey of AE and A-type shell stars in the photographic regionA total of 28 northern Ae and A-type shell stars were observed in thephotographic spectral region. A regular pattern of line behavior withspectral type was found, which in part prolongs the behavior of Be starstoward cooler stars, although a discontinuity seems present around A0. Asurvey of other data concerning colors, rotation, variability, etc., isalso presented. Photometrically the stars simulate the behavior ofhigher-luminosity objects. A large proportion of shells seems to bevariable. The attempt to detect new shell stars among 13 stars known tobe rapid rotators with normal spectra failed, however. The H-alpha line in AE and A shell starsThe H-alpha profiles of a sample of 20 Ae and A shell stars areanalyzed. In the earlier types, emission features are present; in themiddle A-types only absorption cores are seen; and in the late A-typesthe H-alpha profiles are normal both in the profiles and the equivalentwidths. In this latter group the shell features visible in the360-480-nm region are unrelated to H-alpha. Because of the short timeinterval covered, some few cases of variability are found. The Postdam compilation of data on photometric variability of AP magnetic stars.Not Available 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. Catalogue of early-type stars measured in a narrow-band photometric systemA compilation of the photoelectric measurements in the Barbier-Morguleffsystem is presented. The catalogue includes data for 773 stars ofspectral type 08 to F6. 706 stars have been measured at least twice. Rotation and shell spectra among A-type dwarfs.Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1973ApJ...182..809A&db_key=AST 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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