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The Nainital-Cape Survey. III. A search for pulsational variability in chemically peculiar stars
Context: The Nainital-Cape survey is a dedicated research programme tosearch for and study the pulsational variability in chemically peculiarstars in the Northern Hemisphere. Aims: The aim of thesurvey is to search for such chemically peculiar stars that arepulsationally unstable. Methods: The observations of thesample stars were carried out in high-speed photometric mode using athree-channel fast photometer attached to the 1.04-m Sampurnanandtelescope at ARIES. Results: The new photometricobservations confirmed that the pulsational period of star HD 25515 is2.78-hrs. The repeated time-series observations of HD 113878 and HD118660 revealed that previously known frequencies are indeed present inthe new data sets. We have estimated the distances, absolute magnitudes,effective temperatures and luminosities of these stars. Their positionsin the H-R diagram indicate that HD 25515 and HD 118660 lie near themain-sequence while HD 113878 is an evolved star. We also present acatalogue of 61 stars classified as null results, along with thecorresponding 87 frequency spectra taken from 2002-2008. A statisticalanalysis of these null results shows, by comparison with past data, thatthe power of the noise in the light curves has slightly increased duringthe last few years.
| New magnetic chemically peculiar stars
Spectropolarimetric observations of 96 chemically peculiar (CP)main-sequence stars have been carried out at the 6-m telescope at theSpecial Astrophysical Observatory of the Russian Academy of Sciences(SAO RAS) with the aim of searching for the presence of stellar magneticfields. The stars selected for investigation were CP stars known to havestrong anomalies in the wavelength region of the continuum fluxdepression around λ 5200Å. This selection was conductedwith the aid of low-resolution spectral observations, made with the SAORAS 1-m telescope, and of published differential photometric data.Magnetic fields have been successfully detected in 72 stars of whichonly three stars were previously known to have magnetic fields. For twostars, the longitudinal component of the magnetic field Beexceeds 5 kG: HD178892 - 7.4 kG, and HD258686 - 6.7 kG. We failed toreliably detect the magnetic field in the other 24 CP stars. These starsare mostly fast rotators, a feature which hampers accurate measurementsof Be. It is demonstrated in this paper that selectingcandidate magnetic stars by considering their photometric indices Z orΔa, or alternatively, by inspecting low-resolution spectra aroundthe λ5200Å flux depression, considerably increases thedetection rate.This paper is based on data obtained at the 6-m telescope of the RussianAcademy of Sciences.E-mail: dkudr@sao.ru
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| On the detection of chemically peculiar stars using Δa photometry
We have summarized all Δ a measurements for galactic field stars(1474 objects) from the literature published over more than two decades.These measurements were, for the first time, compiled and homogeneouslyanalyzed. The Δ a intermediate band photometric system samples thedepth of the 5200 Å flux depression by comparing the flux at thecenter with the adjacent regions with bandwidths of 110 Å to 230Å. Because it was slightly modified over the last three decades,we checked for systematic trends for the different measurements butfound no correlations whatsoever. The Δ a photometric system ismost suitable to detecting magnetic chemically peculiar (CP) stars withhigh efficiency, but is also capable of detecting a small percentage ofnon-magnetic CP objects. Furthermore, the groups of (metal-weak)λ Bootis, as well as classical Be/shell stars, can besuccessfully investigated. In addition, we also analyzed the behaviourof supergiants (luminosity class I and II). On the basis of apparentnormal type objects, the correlation of the 3σ significance limitand the percentage of positive detection for all groups was derived. Wecompared the capability of the Δ a photometric system with theΔ (V1 - G) and Z indices of the Geneva 7-color system to detectpeculiar objects. Both photometric systems show the same efficiency forthe detection of CP and λ Bootis stars, while the indices in theGeneva system are even more efficient at detecting Be/shell objects. Onthe basis of this statistical analysis it is possible to derive theincidence of CP stars in galactic open cluster and extragalactic systemsincluding the former unknown bias of undetected objects. This isespecially important in order to make a sound statistical analysis ofthe correlation between the occurrence of these objects andastrophysical parameters such as the age, metallicity, and strength ofglobal, as well as local, magnetic fields.
| 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
| 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
| Statistics on the spectral classification of CP2 stars in the Southern Sky
A number of about 1500 spectroscopically classified CP2 stars in thesouthern sky (delta = -90 deg to -12 deg) was extracted from theMichigan Catalogue (Vols. I - IV). This sample was compared with theclassification from Bidelman & Mc Connell. We confirmed the spectralclassification with the known photometric peculiarity indices in theGeneva system and in the 3-filter Delta a system. 10 % of these starsshow discordance between their respective types from the Michigan andBidelman catalogues. Several objects were measured with a CCD in theDelta a system in spring 1995. Eight stars are peculiar in Delta a.Furthermore, we have investigated the galactic distribution of allprogramme stars. We conclude that the distribution resembles the one ofearly-type stars, where the hotter (= Silicon) stars are moreconcentrated towards the galactic plane than the cooler (= Strontium)objects.
| 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
| First CCD measurements in the {DELTA}a system for detecting CP2 stars.
This is the first time that CCD-photometry in the three filter {DELTA}asystem (Maitzen, 1976A&A....52..223M) was carried out after twodecades of classical photoelectric photometry. The aim is to extend thesuccessful search for chemically peculiar stars to more and distant openclusters as well as far galactic fields. In this paper we presentCCD-photometry for a sample of 25 field stars with publishedspectroscopic peculiarity types. 22 of them show discordance betweentheir Michigan catalogue types (non-peculiar) and the Bidelman &MacConnell (1973AJ.....78..678B; BC) peculiarity assignments. Eightstars are peculiar in {DELTA}a (five of them also in the Geneva index{DELTA}(V1-G)) thus supporting BC, mainly among their Silicon stardiscoveries. Considering cases where Silicon line enhancements wereinterpreted as peculiar instead as indicator of higher luminosity by BC,and the perfect detection of the three unambiguous peculiar stars, inaddition to the achievement of an accuracy of 0.003mags, we arejustified to conclude that the performance of our CCD-{DELTA}aphotometry perfectly matches the requirements of the conventionalphotometric technique and thus opens the way to observations of fainterstars.
| Objective-prism discoveries in the declination zone 0 deg to -20 deg
An inspection of 130 10-deg-prism plates taken for the University ofMichigan Southern Spectral Survey has yielded 154 new peculiar orotherwise interesting stars. The regions surveyed are mainly at fairlyhigh galactic latitudes; this fills a gap in previous work of this type.About three-quarters of the objects will eventually be reclassified byHouk in a systematic work on all of the Henry Draper Catalogue stars,but many of these are of sufficient interest to justify earlypublication.
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