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On-line database of photometric observations of magnetic chemically peculiar stars
We present our extensive project of the On-line database ofphotometric observations of magnetic chemically peculiar stars tocollect published data of photometric observations of magneticchemically peculiar (mCP) stars in the optical and near IR regions. Nowthe nascent database contains more than 107 000 photometric measurementsof 102 mCP stars and will be continually supplemented with published ornew photometric data on these and about 150 additional mCP stars. Thisreport describes the structure and organization of the database.Moreover, for the all included data we estimated the error ofmeasurements and the effective amplitudes of the light curves.
| Evolutionary state of magnetic chemically peculiar stars
Context: .The photospheres of about 5-10% of the upper main sequencestars exhibit remarkable chemical anomalies. Many of these chemicallypeculiar (CP) stars have a global magnetic field, the origin of which isstill a matter of debate. Aims: .We present a comprehensivestatistical investigation of the evolution of magnetic CP stars, aimedat providing constraints to the theories that deal with the origin ofthe magnetic field in these stars. Methods: .We have collectedfrom the literature data for 150 magnetic CP stars with accurateHipparcos parallaxes. We have retrieved from the ESO archive 142 FORS1observations of circularly polarized spectra for 100 stars. From thesespectra we have measured the mean longitudinal magnetic field, anddiscovered 48 new magnetic CP stars (five of which belonging to the rareclass of rapidly oscillating Ap stars). We have determined effectivetemperature and luminosity, then mass and position in the H-R diagramfor a final sample of 194 magnetic CP stars. Results: .We foundthat magnetic stars with M > 3 ~M_ȯ are homogeneouslydistributed along the main sequence. Instead, there are statisticalindications that lower mass stars (especially those with M ≤2~M_ȯ) tend to concentrate in the centre of the main sequence band.We show that this inhomogeneous age distribution cannot be attributed tothe effects of random errors and small number statistics. Our datasuggest also that the surface magnetic flux of CP stars increases withstellar age and mass, and correlates with the rotation period. For starswith M > 3~M_ȯ, rotation periods decrease with age in a wayconsistent with the conservation of the angular momentum, while for lessmassive magnetic CP stars an angular momentum loss cannot be ruledout. Conclusions: .The mechanism that originates and sustains themagnetic field in the upper main sequence stars may be different in CPstars of different mass.
| A catalog of stellar magnetic rotational phase curves
Magnetized stars usually exhibit periodic variations of the effective(longitudinal) magnetic field Be caused by their rotation. Wepresent a catalog of magnetic rotational phase curves, Be vs.the rotational phase φ, and tables of their parameters for 136stars on the main sequence and above it. Phase curves were obtained bythe least squares fitting of sine wave or double wave functions to theavailable Be measurements, which were compiled from theexisting literature. Most of the catalogued objects are chemicallypeculiar A and B type stars (127 stars). For some stars we also improvedor determined periods of their rotation. We discuss the distribution ofparameters describing magnetic rotational phase curves in our sample.All tables and Appendix A are only available in electronic form athttp://www.edpsciences.org
| Spectral Classification of Stars in A Supplement to the Bright Star Catalogue
MK spectral types are given for about 584 stars in A Supplement to theBright Star Catalogue. These are compared with Hipparcos parallaxes tocheck the reliability of those classifications. The estimated errors are+/-1.2 subtypes, and 10% of the luminosity classes may be wrong.
| Catalogue of averaged stellar effective magnetic fields. I. Chemically peculiar A and B type stars
This paper presents the catalogue and the method of determination ofaveraged quadratic effective magnetic fields < B_e > for 596 mainsequence and giant stars. The catalogue is based on measurements of thestellar effective (or mean longitudinal) magnetic field strengths B_e,which were compiled from the existing literature.We analysed the properties of 352 chemically peculiar A and B stars inthe catalogue, including Am, ApSi, He-weak, He-rich, HgMn, ApSrCrEu, andall ApSr type stars. We have found that the number distribution of allchemically peculiar (CP) stars vs. averaged magnetic field strength isdescribed by a decreasing exponential function. Relations of this typehold also for stars of all the analysed subclasses of chemicalpeculiarity. The exponential form of the above distribution function canbreak down below about 100 G, the latter value representingapproximately the resolution of our analysis for A type stars.Table A.1 and its references are only available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/407/631 and Tables 3 to 9are only available in electronic form at http://www.edpsciences.org
| Some Comments on the Magnetic Braking of CP Stars
The low rotation velocities of magnetic CP stars are discussed.Arguments against the involvement of the magnetic field in the loss ofangular momentum are given: (1) the fields are not strong enough inyoung stars in the stage of evolution prior to the main sequence; (2)there is no significant statistical correlation between the magneticfield strength and the rotation period of CP stars; (3) stars with shortperiods have the highest fields; (4) a substantial number of stars withvery low magnetic fields (B e P>25 days, which form 12% of the total,probably lie at the edge of the velocity distribution for low massstars. All of these properties conflict with the hypothesis of magneticbraking of CP stars.
| 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 Naini Tal - Cape survey for pulsations in chemically peculiar A-type stars. I. Methods and preliminary results
A new survey for pulsating, chemically peculiar A- and F-type stars inthe northern hemisphere has been initiated using the 1-m telescope atUttar Pradesh State Observatory in Naini Tal. The survey is primarilystructured to reveal high-overtone pulsations in chemically peculiar A-Fstars, but it is also revealing low-overtone delta Scuti-type pulsationsin stars with peculiar colours. This paper describes the scope andmethods of the survey. Preliminary observations of 28 candidate starsare presented and the discovery of three new pulsators, HD 12098, HD13038 and HD 13079, is announced. Null results for the remaining 25stars are also discussed.
| Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The 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
| High-precision magnetic field measurements of Ap and Bp stars
In this paper we describe a new approach for measuring the meanlongitudinal magnetic field and net linear polarization of Ap and Bpstars. As was demonstrated by Wade et al., least-squares deconvolution(LSD; Donati et al.) provides a powerful technique for detecting weakStokes V, Q and U Zeeman signatures in stellar spectral lines. Thesesignatures have the potential to apply strong new constraints to modelsof stellar magnetic field structure. Here we point out two importantuses of LSD Stokes profiles. First, they can provide very precisedeterminations of the mean longitudinal magnetic field. In particular,this method allows one frequently to obtain 1σ error bars betterthan 50G, and smaller than 20G in some cases. This method is applicableto both broad- and sharp-lined stars, with both weak and strong magneticfields, and effectively redefines the quality standard of longitudinalfield determinations. Secondly, LSD profiles can in some cases provide ameasure of the net linear polarization, a quantity analogous to thebroad-band linear polarization recently used to derive detailed magneticfield models for a few stars (e.g. Leroy et al.). In this paper wereport new high-precision measurements of the longitudinal fields of 14magnetic Ap/Bp stars, as well as net linear polarization measurementsfor four of these stars, derived from LSD profiles.
| Spectropolarimetric measurements of magnetic Ap and Bp stars in all four Stokes parameters
In this paper we begin an exploration of the potential of spectral lineZeeman linear and circular polarization signatures for reconstructingthe surface magnetic field topologies of magnetic Ap and Bp stars. Wepresent our first observational results, which include the very firsthigh-quality measurements of stellar Zeeman spectral line linearpolarization ever obtained. Using the new MuSiCoS spectropolarimeter atthe Pic du Midi Observatory, over 360 spectra were obtained, in circularor linear polarization, of 14 magnetic Ap/Bp stars and six calibrationobjects. Zeeman circular polarization signatures are detected in mostsingle lines in essentially all spectra of magnetic Ap stars, withtypical relative amplitudes of a few per cent. Linear polarizationZeeman signatures are unambiguously detected in individual strong,magnetically sensitive lines in outstanding spectra of five objects.However, linear polarization is generally not detected in individualstrong lines in our much more common moderate signal-to-noise ratio(S/N) spectra, and is essentially never detected in weak lines. In orderto overcome the limitations imposed by the S/N ratio and the inherentweakness of linear polarization Zeeman signatures, we exploit theinformation contained in the many lines in our spectra by using theleast-squares deconvolution (LSD) technique. Using LSD, mean linearpolarization signatures are consistently detected within the spectrallines of 10 of our 14 programme stars. These mean linear polarizationsignatures are very weak, with typical amplitudes 10-20 times smallerthan those of the associated mean circular polarization signatures. For11 stars full or partial rotational phase coverage has been obtained inthe Stokes I and V or the Stokes I, V, Q and U parameters. Therotational modulation of the LSD mean signatures is reported for theseobjects. Measurements of the longitudinal field and net linearpolarization obtained from these LSD profiles show they are consistentwith existing comparable data, and provide constraints on magnetic fieldmodels which are at least as powerful as any other data presentlyavailable. To illustrate the new information available from these datasets, we compare for four stars the observed Stokes profiles with thosepredicted by magnetic field models published previously in theliterature. Important and sometimes striking differences between theobserved and computed profiles indicate that the Zeeman signaturespresented here contain important new information about the structure ofthe magnetic fields of Ap and Bp stars capable of showing thelimitations of the best magnetic field models currently available.
| 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
| 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
| Modelling of magnetic fields of CP stars. I. A diagnostic method for dipole and quadrupole fields from Stokes I and V observations
This paper is the first of a series aimed at developing and applying anew modelling technique for magnetic fields of chemically peculiar (CP)stars. Newly introduced observational techniques provided us evidencethat the ``oblique rotator model'' with a simple dipolar field is notsufficient to describe the magnetic morphology of CP stars, and that theproblem of inverting data must be approached within a more sophisticatedframework. In this paper we consider the configuration produced by thesuperposition of a dipole and a quadrupole, and we study in detail thebehaviour of some observational quantities related to the magneticfield, i.e. the ``mean longitudinal field'', the ``crossover'' and the``mean square field'', which are obtained from Stokes I and Vobservations. We illustrate the diagnostic content of the combinedanalysis of these three kinds of measurement, and we discuss someintrinsic limitations of the method. We present an algorithm forinverting the data, which has been tested against numerical simulations.We examine the possibility of recovering the stellar magneticconfiguration from real measurements, by taking into account theproblems related to the observational errors.
| 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
| Effective temperatures of AP stars
A new method of determination of the effective temperatures of Ap starsis proposed. The method is based on the fact that the slopes of theenergy distribution in the Balmer continuum near the Balmer jump for``normal" main sequence stars and chemically peculiar stars with thesame Teff are identical. The effective temperaturecalibration is based on a sample of main sequence stars with well knowntemperatures (\cite[Sokolov 1995]{sokolov}). It is shown that theeffective temperatures of Ap stars are derived by this method in goodagreement with those derived by the infrared flux method and by themethod of \cite[Stepien & Dominiczak (1989)]{stepien}. On the otherhand, the comparison of obtained Teff with Teffderived from the color index (B2-G) of Geneva photometry shows a largescatter of the points, nevertheless there are no systematicaldifferences between two sets of the data.
| Delta a and Stroemgren photometry of stars in the Renson-catalogue of AP and AM stars
We have observed 131 stars of \cite[Renson's (1991)]{re91} catalogue ofAp and Am stars both in the Stroemgren & Maitzen's (1976) Delta asystem as a contribution to the photometric studies of the lambda 5200broad band flux depression feature in chemically peculiar stars. Withfew exceptions the probability grouping of Renson for membership in theCP2 group of peculiar stars is nicely reflected by peculiar values ofDelta a. Comparison with already available Delta a values yieldsslightly larger values due to a minor shift in the filter g_1 samplingthe depression. As found by \cite[Maitzen & Vogt (1983)]{ma83} theGeneva system peculiarity parameters correlate well with Delta a. Thisstudy demonstrates the advantageous performance of a photoelectricphotometer with a rapidly rotating filter wheel moving in a stop and gomode. Tables 3 and 4 are also available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| 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.
| Evolutionary estimates for 10 magnetic AP stars calculated from their rigid rotator geometries.
I present estimates of the evolutionary states (effective temperatures,masses, radii, luminosities and ages) of 10 magnetic Ap stars, andsubsequent constraints on the evolution of magnetic fields in theseobjects. Using rotational axis inclinations (sin i) reported by Leroy etal. (1996A&A...311..513L), combined with apparent rotationalvelocities (vsin i) and rotational periods (P_rot_) obtained from avariety of sources, the radii of these stars have been calculatedassuming rigid rotation. From the positions of these objects in theradius-effective temperature (log(R/Rsun_)-log(T_eff_)) planeI obtain their evolutionary states using the model evolutionarycalculations by Schaller et al. (1992A&AS...96..269S). The stars inthis study span the entire width of the main sequence, showing notendancy to cluster near the ZAMS or the TAMS. In this respect theseresults are consistent with the conclusion of North(1993IAUCo.138..577N) (who reports that the Ap (CP2) stars appear to bedistributed uniformly along the width of the main sequence) andinconsistent with that of Hubrig & Mathys (1994AN....315..343H) (whosuggest that the magnetic Ap stars may be near the end of their mainsequence life). When the magnetic field strengths of these stars aregraphed versus the fraction of main sequence evolution completed, nocorrelation is evident. However, it is of interest to note that strongmagnetic fields do exist in Ap stars at all evolutionary states (fromthe ZAMS to the TAMS), and that more than 70% of the stars discussed inthis paper have polar magnetic field strengths between 3 and 6kG. Asimilar graph of the magnetic axis obliquity angle β of each starversus age shows that intermediate values of β exist for stars asold as 10^9^yr. This indicates that, if β does evolve towardasymptotic values as suggested by Mestel et al. (1981MNRAS.195..979M),the timescale for this evolution is quite long, at least for stars with~5kG surface magnetic fields and rotational periods near 10 days.
| A magnetic model for the AP star HD 192678.
We present a magnetic model for the A2pCr star HD 192678 based uponmodeling of new and previously published longitudinal magnetic fieldmeasurements, surface field measurements, broadband linear polarimetryand unpolarized high-resolution spectra. The limitations of theclassical dipole oblique rotator model are clearly detectable in thecase of HD 192678. An oblique rotating dipole is not capable ofsimultaneously reproducing the surface field variations and thebroadband linear polarization variations. Line profile variations of theFe II λ6149.2 Zeeman doublet may be consistent with a dipolefield whose pole-to-equator modulus ratio has been decreased by about20%. However, this is uncertain since it relies critically on the amountof microturbulence present, about which we have little information.Excess broadening of Fe II λ6149.2 is apparent which appears tobe neither rotational nor microturbulent in origin, and may beindicative of small photospheric regions of high field strength. Ourmagnetic model for HD 192678 consists of an oblique rotating dipole withmodified field line inclinations. The polar field strength of the dipoleis 6.8+/-0.2kG, with i=173+/-5deg and β=120+/-7deg. This modelcontains a region of open field lines near the magnetic equator, arecurring feature in magnetic models of a number of Ap stars (Leroy etal. 1995b).
| Linear polarimetry of AP stars. VI. A modified dipolar model consistent with the observations.
While some Ap variables display a linear polarization variation verysimilar to that computed for a pure magnetic dipole, several Ap starsshow conspicuous peculiarities which must be interpreted in terms ofdepartures from the standard, oblique rotator model (we have shownpreviously that abundances anomalies are not sufficient to explain oddpolarization diagrams). We have designed an inversion method, based on aresidues minimization process, which allows us to build the map of themagnetic peculiarities at the surface of non-dipolar stars. As thelinear polarization is but weakly sensitive to the variations of thefield modulus, we interpret the polarization anomalies in terms ofinclination changes of the lines of force within their meridian plane.Keeping the magnetic equator as a plane of symmetry, we show that it issufficient to assume slightly expanded lines of force, over some partsof the magnetic equator, to explain most peculiar polarization curves(Figs. 2 to 7). Such regions, where the lines of force expand outwards,seem to occur preferentially in the vicinity of the rotation poles forthose stars having a β angle not far from 90deg. In the case ofβ CrB, which was studied previously in detail (Leroy, 1995), thisregion nearly coincides with the equatorial patch of enhanced fieldstrength, which must be postulated to explain the surface fieldmeasurements. The present study, which also provides unambiguousdeterminations of the i and β angles for 15 stars, marks theprovisional end of our investigation based on broadband linearpolarization measurements. We expect that similar measurements, having agood spectral resolution, will be available soon: they will yield moresevere observational constraints enabling a more detailed modeling work.However, we think that the series of articles which ends with thepresent paper has demonstrated the great value of linear polarizationdata and may have opened fruitful research tracks bearing on themagnetic structure of Ap stars.
| Linear polarimetry of AP stars. V. A general catalogue of measurements.
A systematic program of broadband linear polarimetry, bearing on 55 Apstars, has been developed during the 4 last years, at the Pic du MidiObservatory. While separate data have been already published, we presentin this paper a complete catalogue of our observational material,including more than 400 measurements. We complement these data withanother 100 measurements, obtained previously by other authors, so as toget a synthetic view of the phenomenon. Most of the observations havebeen dedicated to a small number (15) of stars, which show conspicuouschanges of the linear polarization, so that it is possible to knowaccurately the time variation of the Stokes parameters: we expect thatthese new data will really improve our knowledge of the magneticconfiguration, after a proper analysis which is currently beingdeveloped. For the other 40 stars, the polarization is either too small,or strongly contaminated by the interstellar polarization, so thatbroadband polarimetry is not very effective. Anyway, this firstsystematic investigation on the linear polarization of Ap stars will bea useful starting point for future measurements which should be madewith higher spectral resolution. Finally, our measurements have providednew determinations of the rotation period for several stars.
| Linear polarimetry of AP stars. IV. The influence of deviations from a pure dipolar model.
In the previous papers of this series we have described a newobservational program of broadband linear polarimetry aimed at Ap stars.At the same time, we have established a canonical model, based on theoblique rotator geometry, which describes successfully the main featuresof the observed polarization: in some cases the linear polarizationdata, combined with the classical circular polarization measurements,allow one to determine the characteristic parameters which define theoblique dipolar rotator. However, we have also observed polarizationdiagrams that depart clearly from those predicted by the canonicalmodel, which means that it is not always possible to rely on a puredipolar model (nor on a combination of a dipole plus a linear quadrupoleparallel to the dipole). Although an interpretation of the polarizationpeculiarities in terms of magnetic `anomalies' (i.e. deviations from thedipolar configuration) is quite natural, one must also take into accountthe possible influence of local abundance inhomogeneities. Therefore, wehave first studied the sensitivity of the polarized signal (which isknown to be due to the differential saturation of Zeeman components inspectral lines) to a variation of the metallic absorption spectrum. Thenwe have examined how a local enhancement (or reduction) of thepolarization produced by a dipolar magnetic field affects the Fourierspectrum of the observed polarization signal. Finally, we have designedan inversion program making possible the recovery - under certainrestrictions - of the spatial modulations of the polarization generatedby a dipole, which are necessary to explain `odd' polarimetric data.This program has been applied to the data gathered from three stars (49Cam, β CrB, HD 71866). As far as the last star is concerned, noneof the spatial modulations considered was able to reproduce theobservations. On the contrary, good solutions are found for the othertwo. However, if one interprets the variations of the polarization asthe result of abundance variations, which must correspond to amodulation of the absorption spectrum, a contradiction arises,especially for β CrB, because the observed spectral variability ofthese stars is too small to account for our computed maps. Therefore,non-canonical polarization diagrams must essentially be interpreted interms of magnetic anomalies, not of abundance anomalies: in other words,the peculiarities of the polarization diagrams are likely to resultmainly from departures of the magnetic configuration from the puredipolar configuration.
| Linear polarimetry of AP stars. 3: A diagnostic method for the magnetic structure of rotating stars
A method for the diagnostic of magnetic fields in Ap stars is presented.It is based on the joint interpretation of traditional circularpolarization observations (giving Bl, the longitudinalmagnetic field averaged over the stellar surface) and of broadbandlinear polarization observations. The method consists in a numerical,best-fit algorithm which takes into account the possibility ofdescribing the time variation of broadband linear polarization by meansof analytical expressions. The algorithm has been checked againstnumerical simulations and has shown to be reliable especially for thedetermination of the magnetic configuration of the star. Twoapplications have been considered for the stars HD 24712 and HD 71866 byinterpreting new broadband linear polarization observations togetherwith circular polarization data available in the literature.
| Radio continuum emission from stars: a catalogue update.
An updated version of my catalogue of radio stars is presented. Somestatistics and availability are discussed.
| Catalogue of CP stars with references to short time scale variability
A catalogue was compiled which contains all references in the literaturesince 1962 related to variations of CP stars on time scales shorter thanthe rotation period. The role of this catalogue lies in the unbiasedlisting of all available references, and not in a critical evaluation.
| Detection of calcium abundance stratification in AP stars
Very recent observational and theoretical studies have shown that anabundance stratification of chemical elements seems to be present in theatmosphere of the Ap SrCrEu star 53 Cam. This is fundamental for ourunderstanding of the structure and the stability of the stellaratmosphere of magnetic stars. In contrast with previous work from theauthor which were devoted to an intensive study of 53 Cam, the purposeof the present paper is to investigate abundance stratification in asmaple of 28 Ap stars, mainly of the SrCrEu type. From the analysis ofthe well-known peculiar profile of the Ca II K line these objects andfrom a differential analysis using the Ca II H line, we obtain that alarge Ca abundance stratification seems to be present in all the Apstars with Teff less than 9000 K. For hotter objects, themethod used in this paper does not permit to conclude. This analysissupports strongly the conclusions from the diffusion model and gives newconstraints on hydrodynamical processes in the photosphere of Ap stars.It constitutes the first evidence for a symmetric abundancestratification of Ca in a large sample of magnetic stars.
| A new list of effective temperatures of chemically peculiar stars. II.
Not Available
| Spectrophotometry of Peculiar B-Stars and A-Stars - Part Nineteen - Variability of the Magnetic Cp-Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&AS..101..393A&db_key=AST
| Linear polarimetry of AP stars. II - New observations with a reappraisal of former ones
We have presented, in a previous paper, a canonical model which helpsone to understand the intrinsic linear polarization measured in thelight of magnetic Ap stars. This linear polarization, which provides atracer of the magnetic field component perpendicular to the line ofsight, can be observed in broad spectral regions, and it has beenactually observed in several stars. Such measurements can provide usefulinformation on the magnetism of Ap stars only when they sample correctlythe whole rotation period of the object under study. Up to now, thiscondition had been fulfilled only in the case of HD 65339; in othercases, a more limited amount of data was available. Adding our newobservations has enabled a first detailed analysis of HD 137909, HD 71866 and HD 115708; in particular, we can decide which of the angle i(between the line of sight and the rotation axis) and beta (between therotation axis and the magnetic axis) is larger. Altogether, this papercontains a general review on all existing measurements and acomprehensive investigation on the linear polarization of four Ap starsbased on previous observations and on our new measurements. Thecomparison of this observational material with the previouslyestablished model shows the capabilities and the limits of this methodof study of Ap stars.
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