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.
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Hβ photometry of southern CP2 stars: is the uvbybeta luminosity calibration also valid for peculiar stars?
We present Hβ photometry of 233 southern CP2 stars (covering themagnetic Ap stars according to the definition by Preston 1974) brighterthan V < 8.5 mag from the list of Bidelman & MacConnell (1973).Absolute magnitudes derived from this photometry together with alreadyexisting uvby photometry is confronted with Hipparcos results availablefor a common subset of 152 stars. In order to compare peculiar withnormal stars, we identified a sample of 1147 normal B to F-type starsusing their published uvbybeta and Hipparcos data. For our analysis wedivide both samples into three temperature as well as two Hipparcosparallax accuracy groups. The error distribution of both samples provedto be statistically comparable. As a result the absolute magnitudes forthe B-type CP2 stars show up to be significantly too bright by anaverage of 0.5 mag using the actual photometric calibration. On theother hand, the photometric absolute magnitudes for cool A to F-type CP2stars are up to three magnitudes fainter as compared to Hipparcos. Basedon observations at ESO-La Silla and with the Hipparcos satellite
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On the HIPPARCOS photometry of chemically peculiar B, A, and F stars
The Hipparcos photometry of the Chemically Peculiar main sequence B, A,and F stars is examined for variability. Some non-magnetic CP stars,Mercury-Manganese and metallic-line stars, which according to canonicalwisdom should not be variable, may be variable and are identified forfurther study. Some potentially important magnetic CP stars are noted.Tables 1, 2, and 3 are available only in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
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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
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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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The observed periods of AP and BP stars
A catalogue of all the periods up to now proposed for the variations ofCP2, CP3, and CP4 stars is presented. The main identifiers (HD and HR),the proper name, the variable-star name, and the spectral type andpeculiarity are given for each star as far as the coordinates at 2000.0and the visual magnitude. The nature of the observed variations (light,spectrum, magnetic field, etc.) is presented in a codified way. Thecatalogue is arranged in three tables: the bulk of the data, i.e. thosereferring to CP2, CP3, and CP4 stars, are given in Table 1, while thedata concerning He-strong stars are given in Table 2 and those foreclipsing or ellipsoidal variables are collected in Table 3. Notes arealso provided at the end of each table, mainly about duplicities. Thecatalogue contains data on 364 CP stars and is updated to 1996, October31. This research has made use of the SIMBAD database, operated at CDS,Strasbourg, France.
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The Cousins VRI System: A Consistency Test of Equatorial and Southern Standard Stars
Abstract image available at:http://adsabs.harvard.edu/abs/1996AJ....111.1338T
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The Cape rapidly oscillating AP star survey - III. Null results of searches for high-overtone pulsation.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1994MNRAS.271..129M&db_key=AST
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A new list of effective temperatures of chemically peculiar stars. II.
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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First supplement to the catalog of observed periods of AP stars
Supplementary data on the periods of Ap stars with references arepresented; 58 new stars are introduced for which periodic variabilityhas been discovered since 1983. For some of these stars periodicity wasknown before 1983 but they were not reported in the previous catalog.Recently attributed variable star names are also reported.
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Instrumental effects and the Stroemgren photometric system
The extent to which the use of different photometers can affect resultson stellar color indices was investigated by simultaneously observing asample of widely different stars with several uvby photometric systemsavailable at the ESO, La Silla, Chile. In one instance, the ESO 50-cmtelescope and the four-channel photometer at the Danish 50-cm telescopewere used simultaneously. The reductions were performed separately oneach data set, using a linear color transformation procedure. Theresults agree with theoretical investigations which showed thatsubstantial errors can arise from the nonconformity of passbands. It isemphasized that it is necessary to use separate color transformationsfor various stellar types and classes and for different interstellarreddenings.
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Photometric variability of southern CP stars
The photometric behavior of eight southern CP stars with relativelylarge amplitudes of variation is analyzed. Periods of variation andparameters of the light curves are obtained by least-squares fitting. Awide variety is found in the periods and in the shapes of the lightcurves, confirming the lack of correlation between these parameters andthe amplitudes.
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Evidence of decay of the magnetic fields of AP stars
Data obtained in the Geneva photometric system (Rufener, 1981) andappropriate calibrations of this system in terms of surface magneticfield and gravity are used to provide, on the basis of 708 field andcluster Ap stars, observational evidence that these stars undergo decayof their magnetic field on an evolutionary timescale. Justifications aregiven for the application of a photometric gravity calibration topeculiar stars. The dependence of the photometrically estimated surfacemagnetic field on gravity is found to differ markedly from availabletheoretical calculations. HgMn stars are found to show the same trend,strengthening the impression that they might be slightly magnetic.He-weak stars do not.
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Photoelectric photometry of peculiar and related stars. II Delta-a-photometry of 339 southern Ap-stars
Delta-a system photometry of the sample of Ap stars from Bidelman andMcConnell's (1973) catalogue is discussed. Comparing delta-ameasurements in four marginally different systems, slight modificationsof the delta-a photometric system are found to be uncritical except forthe wavelength of the depression filter g2. The reddening-free index isvery efficient for silicon and chromium stars, and the spectroscopicdetection probability for these stars decreases with decreasingtemperature. Comparison of delta-a results with the Geneva index delta(V1-G) confirms that the latter's efficiency in recognizing peculiaritydrops strongly from hot to cool Ap stars. A decrease of delta-a towardsthe hot Ap stars is found using the a vs. (u-b) diagram, implying thatb-v is an unsuitable temperature indicator for such stars. The lowaverage intrinsic variability of the delta-a in the sample, whencompared with the small variation of integrated surface magnetic fieldsin case of dipole configuration, implies that the wavelength 5200feature correlates with the surface magnetic field strength.
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UBV photometry of E region standard stars of intermediate brightness
Photometry data are given for 335 stars in the nine E regions.Observations were made using a photometer and filters on the 47 cmreflector at Cape Town. The stellar dispersions are summarized. Data arepresented in tabular form.
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Photometric properties of AP stars in the Geneva system
An examination of the properties in some photometric diagrams of morethan 600 Ap stars measured in the Geneva photometric system confirm thatthe Balmer discontinuity is smaller than for normal stars, along withthe link between a proposed peculiarity parameter and both rotationalvelocity and effective magnetic field. It is shown that the peculiarityparameter is sensitive to interstellar reddening, and it is foundthrough examination of the standard deviations for visual magnitudesthat cool CP 2 stars without Eu peculiarity have the greatestamplitudes. Rapid rotators have a mild peculiarity, while positivecorrelation exists for Si and SrCr stars.
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Photometric standard stars for the UBV and (RI)KC systems.
Not Available
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Fainter Standards for VRI Photometry in the E Regions
Not Available
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Photoelectric observations of peculiar A and related stars. I - Stromgren photometry of 341 AP stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1979A&AS...36..477V&db_key=AST
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Standard magnitudes in the E regions.
Not Available
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