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Main-sequence magnetic CP stars: II. Physical parameters and chemical composition of the atmosphere
This paper continues a series of reviews dedicated to magnetic CP stars.The occurrence frequency of CP stars among B5 F0-type main-sequencestars is shown to be equal to about 15 20%. The problems ofidentification and classification of these objects are addressed. Weprefer the classification of Preston, which subdivides chemicallypeculiar stars into the following groups: Am, λ Boo, Ap/Bp,Hg-Mn, He-weak, and He-strong stars. The main characteristic features ofobjects of each group are briefly analyzed. The rotation velocities ofCP stars are shown to be about three times lower than those of normalstars of the same spectral types (except for λ Boo and He-strongobjects). The rotation periods of CP stars range from 0.5 to 100 days,however, there is also a small group of objects with especially long (upto several tens of years) variability periods. All kinds of peculiarstars can be found in visual binaries, with Am-and Hg-Mn-type starsoccurring mostly in short-period binaries with P < 10 days, and thebinary rate of these stars is close to normal. The percentage ofbinaries among magnetic stars (20%) is lower than among normal stars. Arather large fraction of CP1-and CP2-type stars was found to occur inyoung clusters (with ages smaller than 107 years).Photometric and spectral variability of peculiar stars of various typesis discussed, and it is shown that only objects possessing magneticfields exhibit light and spectral variations. The chemical compositionof the atmospheres of CP stars of various types is considered. Theabundances of various elements are usually determined by comparing theline profiles in the observed spectrum with those of the syntheticspectra computed for various model atmospheres. Different mechanisms areshown to contribute to chemical inhomogeneity at the star’ssurface, and the hypothesis of selective diffusion of atoms in a stableatmosphere is developed. Attention is also paid to the problems of thedetermination of local chemical composition including the stratificationof elements. Some of the coolest SrCrEu peculiar stars are found toexhibit fast light variations with periods ranging from 6 to 15 min.These variations are unassociated with rotation, but are due tononradial pulsations. The final part of the the review considers thefundamental parameters of CP stars. The effective temperatures,luminosities, radii, and masses of these objects are shown to agree withthe corresponding physical parameters of normal main-sequence stars ofthe same spectral types.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| Multiplicity among chemically peculiar stars. II. Cool magnetic Ap stars
We present new orbits for sixteen Ap spectroscopic binaries, four ofwhich might in fact be Am stars, and give their orbital elements. Fourof them are SB2 systems: HD 5550, HD 22128, HD 56495 and HD 98088. Thetwelve other stars are: HD 9996, HD 12288, HD 40711, HD 54908, HD 65339,HD 73709, HD 105680, HD 138426, HD 184471, HD 188854, HD 200405 and HD216533. Rough estimates of the individual masses of the components of HD65339 (53 Cam) are given, combining our radial velocities with theresults of speckle interferometry and with Hipparcos parallaxes.Considering the mass functions of 74 spectroscopic binaries from thiswork and from the literature, we conclude that the distribution of themass ratio is the same for cool Ap stars and for normal G dwarfs.Therefore, the only differences between binaries with normal stars andthose hosting an Ap star lie in the period distribution: except for thecase of HD 200405, all orbital periods are longer than (or equal to) 3days. A consequence of this peculiar distribution is a deficit of nulleccentricities. There is no indication that the secondary has a specialnature, like e.g. a white dwarf. Based on observations collected at theObservatoire de Haute-Provence (CNRS), France.Tables 1 to 3 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/394/151Appendix B is only available in electronic form athttp://www.edpsciences.org
| Radial velocities. Measurements of 2800 B2-F5 stars for HIPPARCOS
Radial velocities have been determined for a sample of 2930 B2-F5 stars,95% observed by the Hipparcos satellite in the north hemisphere and 80%without reliable radial velocity up to now. Observations were obtainedat the Observatoire de Haute Provence with a dispersion of 80Ä,mm(-1) with the aim of studying stellar and galactic dynamics.Radial velocities have been measured by correlation with templates ofthe same spectral class. The mean obtained precision is 3.0 km s(-1)with three observations. A new MK spectral classification is estimatedfor all stars. Based on observations made at the Haute ProvenceObservatory, France and on data from The Hipparcos Catalogue, ESA.Tables 4, 5 and 6 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr or viahttp://cdsweb.u-strasbg.fr/Abstract.htm
| The HR-diagram from HIPPARCOS data. Absolute magnitudes and kinematics of BP - AP stars
The HR-diagram of about 1000 Bp - Ap stars in the solar neighbourhoodhas been constructed using astrometric data from Hipparcos satellite aswell as photometric and radial velocity data. The LM method\cite{luri95,luri96} allows the use of proper motion and radial velocitydata in addition to the trigonometric parallaxes to obtain luminositycalibrations and improved distances estimates. Six types of Bp - Apstars have been examined: He-rich, He-weak, HgMn, Si, Si+ and SrCrEu.Most Bp - Ap stars lie on the main sequence occupying the whole width ofit (about 2 mag), just like normal stars in the same range of spectraltypes. Their kinematic behaviour is typical of thin disk stars youngerthan about 1 Gyr. A few stars found to be high above the galactic planeor to have a high velocity are briefly discussed. Based on data from theESA Hipparcos astrometry satellite and photometric data collected in theGeneva system at ESO, La Silla (Chile) and at Jungfraujoch andGornergrat Observatories (Switzerland). Tables 3 and 4 are onlyavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| CP2 stars as viewed by the UVBY H_beta system
The aim of this work is to study the capacity of the uvby H_βsystem for detecting the chemically peculiar (CP) stars based on theeffect that peculiar features in the flux distribution have on all theStromgren-Crawford indices. Our study focuses on the classical magneticpeculiar stars (CP2), though Am stars (CP1) are also included forcomparison with cool CP2 stars. Satisfactory results were obtained forhot CP2 stars: the definition of a new index p, which is a linearcombination of uvby H_β colours, allowed us to separate a highpercentage of hot CP2 stars from normal stars. According to this newindex, 60 new CP2 candidates are proposed. The working sample wasextracted from The General Catalogue of Ap and Am stars by \cite[Rensonet al. (1991)]{ren91}. Photometric observations to enlarge the sample ofCP2 stars with complete uvby H_β photometry were carried out. Theseobservations are also reported in the present paper. The new index p isalso used to correct the reddening of early CP2 stars computed as ifthey were normal stars. Tables 2, 3 and 7 are also available inelectronic form from CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html
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Osservazione e dati astrometrici
| Costellazione: | Unicorno |
| Ascensione retta: | 07h10m38.97s |
| Declinazione: | -01°50'34.4" |
| Magnitudine apparente: | 7.979 |
| Distanza: | 131.406 parsec |
| Moto proprio RA: | -37.2 |
| Moto proprio Dec: | -1.7 |
| B-T magnitude: | 8.336 |
| V-T magnitude: | 8.009 |
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