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uvby FCAPT photometry of the mCP stars HD 32633, θ Aur, 49 Cam, and 3 Hya
Differential Strömgren uvby observations from the Four CollegeAutomated Photoelectric Telescope are presented for the magneticChemically Peculiar (mCP) stars HD 32633, θ Aur, 49 Cam, and 3Hya. We find for over 30 years, these four stars with stable opticalregion light curves have had constant periods of 6.4300, 3.61868,4.28679, and 11.305 days, respectively.
| 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
| The spectroscopic signature of roAp stars
To reliably determine the spectroscopic signature of rapidly oscillatingchemically peculiar (roAp) stars it is also necessary to investigate asample of non pulsating chemically peculiar (noAp) as well as presumably``normal'' stars. We describe in this study the sample ofspectroscopically investigated stars and comment on the techniques usedfor the analysis. In particular we discuss ionization disequilibria ofrare earths in roAp stars that distinguish them from noAp stars. In thelight of the recently discovered pulsation of β CrB we seearguments that all magnetic CP2 stars up to a transition temperature ofabout 8100 K may be pulsating.Based on observations obtained at the European Southern Observatory (LaSilla, Chile), the Canadian-French-Hawaii telescope, the South AfricaAstronomical Observatory, The Crimean Astrophysical Observatory and onnumerous SIMBAD interrogations.
| 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.
| Spatial Distribution of Magnetic CP Stars
The spatial distribution of magnetic CP stars is studied using thecatalog of CP stars compiled by the Special Astrophysical Observatory ofthe Russian Academy of Sciences. It is shown that the overwhelmingmajority of these objects are at distances closer than 500 pc from thesun. The axes of rotation and the magnetic axes of the field CP starsare distributed randomly, while a preferential orientation of themagnetic axes in certain directions is seen for stars that are membersof open clusters. The closeness of the magnetic models for CP stars thatare members of clusters may be evidence that there is a general factorwhich influences the origin of magnetic fields in stars. The magneticfield of the galaxy may be such a factor.
| 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
| On the Periods of the Magnetic CP Stars
An HR diagram annotated to show several ranges of photometericallydetermined periods has been constructed for the magnetic CP stars whoseperiods have been determined by the author and his collaborators. Thedistribution of periods reflects both the initial conditions as well asthe subsequent stellar histories. Since the stellar magnetic field doesnot penetrate the convective core, eventually a shear zone near thecore-radiative envelope boundary may develop which produces turbulenceand modifies the field. Many, but not all, of the most rapidly rotatingmCP stars are close to the ZAMS and some of the least rapidly rotatingmCP stars are the furthest from the ZAMS.
| 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
| Rotational velocities of A-type stars in the northern hemisphere. II. Measurement of v sin i
This work is the second part of the set of measurements of v sin i forA-type stars, begun by Royer et al. (\cite{Ror_02a}). Spectra of 249 B8to F2-type stars brighter than V=7 have been collected at Observatoirede Haute-Provence (OHP). Fourier transforms of several line profiles inthe range 4200-4600 Å are used to derive v sin i from thefrequency of the first zero. Statistical analysis of the sampleindicates that measurement error mainly depends on v sin i and thisrelative error of the rotational velocity is found to be about 5% onaverage. The systematic shift with respect to standard values fromSlettebak et al. (\cite{Slk_75}), previously found in the first paper,is here confirmed. Comparisons with data from the literature agree withour findings: v sin i values from Slettebak et al. are underestimatedand the relation between both scales follows a linear law ensuremath vsin inew = 1.03 v sin iold+7.7. Finally, thesedata are combined with those from the previous paper (Royer et al.\cite{Ror_02a}), together with the catalogue of Abt & Morrell(\cite{AbtMol95}). The resulting sample includes some 2150 stars withhomogenized rotational velocities. Based on observations made atObservatoire de Haute Provence (CNRS), France. Tables \ref{results} and\ref{merging} are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.125.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/393/897
| On the excitation mechanism in roAp stars
We investigate a model for the excitation of high-order oscillations inroAp stars. In this model we assume that the strong concentration ofmagnetic field about the magnetic poles is enough to suppressconvection. Thus the model considered is composed of two polar regions,in which convection is presumed to be suppressed totally, and anequatorial region, where the convection is unaffected. This model isgenerated by building pairs of locally spherically symmetricalequilibria to represent the polar and equatorial regions of the star,which are patched together below the base of the convection zone.Gravitational settling of heavy elements is taken into account bychoosing appropriate chemical composition profiles for both the polarand equatorial regions. Our results indicate that the composite model isunstable against axisymmetric non-radial high-order modes of pulsationthat are aligned with the magnetic poles. The oscillations are excitedby the κ mechanism acting principally in the hydrogen ionizationzones of the polar regions. The effect of the lateral inhomogeneity onthe second frequency differences is also investigated; we find that theperturbation to them by the inhomogeneity is of the same order as thesecond differences themselves, thereby hindering potential attempts touse such differences to identify the degrees of the modes in astraightforward way.
| A Study of Rare Earth Elements in the Atmospheres of Chemically Peculiar Stars. Pr III and Nd III Lines
We determine the abundances of Pr and Nd in the atmospheres of magneticand non-magnetic chemically peculiar stars from the lines of rare earthelements in the first and second ionization states. The computations forthe magnetic stars take into account the influence of the magnetic fieldon line formation. We studied the influence of errors in thestellar-atmosphere parameters and the atomic parameters of the spectrallines on the accuracy of abundance determinations. Within the derivedaccuracy, ionization equilibrium is satisfied in the atmospheres ofnon-pulsating magnetic and non-magnetic stars (so that abundancesderived separately from lines of first and second ions agree). For allthe pulsating magnetic (roAp) stars studied, the abundances derived fromlines of second ions are 1.0 to 1.7 dex higher than those derived fromfirst ions. The violation of ionization equilibrium in the atmospheresof pulsating stars is probably due to, first, considerable enrichment ofPr and Nd in the uppermost atmospheric layers, and second, a higherlocation for the layer of enhanced elemental abundance in roAp starsthan in non-pulsating stars. Two objects from the list of non-pulsatingmagnetic stars, HD 62140 and HD 115708, exhibit anomalies of their Prand Nd lines characteristic of roAp stars. The differences in the rareearth anomalies for the pulsating and non-pulsating peculiar stars canbe used as a selection criterion for candidate roAp stars.
| Are Stellar Rotational Axes Distributed Randomly?
Stellar line widths yield values of Vsini, but the equatorial rotationalvelocities, V, cannot be determined for individual stars withoutknowledge of their inclinations, i, relative to the lines of sight. Forlarge numbers of stars we usually assume random orientations ofrotational axes to derive mean values of V, but we wonder whether thatassumption is valid. Individual inclinations can be derived only inspecial cases, such as for eclipsing binaries where they are close to90° or for chromospherically active late-type dwarfs or spotted(e.g., Ap) stars where we have independent information about therotational periods. We consider recent data on 102 Ap stars for whichCatalano & Renson compiled rotational periods from the literatureand Abt & Morrell (primarily) obtained measures of Vsini. We findthat the rotational axes are oriented randomly within the measuringerrors. We searched for possible dependence of the inclinations onGalactic latitude or longitude, and found no dependence.
| 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.
| Rapidly oscillating Ap stars versus non-oscillating Ap stars
The positions in the HR diagram and the kinematic characteristics ofrapidly oscillating and non-oscillating chemically peculiar stars areobtained using new Hipparcos proper motions and parallaxes, and our ownradial velocity measurements. We find that rapidly oscillating stars, asa group, are (-0.47 +/- 0.34) mag above the zero-age main sequence(ZAMS), while the non-oscillating stars are (-1.20 +/- 0.65) mag abovethe ZAMS and so appear slightly more evolved on average. From thecomparison of the kinematical characteristics, we conclude that bothgroups are very similar. The results of radial velocity measurementsindicate that there is a real deficiency of binaries among rapidlyoscillating stars. Presently, no such star is known to be aspectroscopic binary.
| Spectropolarimetric measurements of the mean longitudinal magnetic field of chemically peculiar stars. On the light, spectral and magnetic variability
We have equipped the spectrograph of the Catania AstrophysicalObservatory with a polarimetric module which gives simultaneouscircularly right and left polarised radiation spectra. This facility hasbeen used to perform time-resolved spectropolarimetric (Stokes V)measurements of the mean longitudinal (effective) magnetic field forseven chemically peculiar stars. Since this class of stars ischaracterised by a periodically variable magnetic field, the monitoringof the Stokes V parameter is a fundamental step to recover the magneticfield topology. To better define the variation of the effective magneticfield, we have combined our observations with data from the literature.Variability periods given in the literature have been verified usingHipparcos photometric data and, if necessary, we have re-determinedthem. From Hipparcos absolute magnitudes, we have determined the stellarradii and then, on the hypothesis of a rigid rotator, the inclination ofthe rotational axes with respect to the line of sight. On the hypothesisthat the magnetic field presents a dominant dipolar component (that is,where the Stokes Q and U parameters are not necessary to recover themagnetic configuration) we have determined the angle between therotational and dipole axes and the polar strength of the magnetic field.Chemically peculiar stars show periodic anti-phase light variationsshort-ward and long-ward of a constant wavelength, the null wavelength.We have performed numerical computations of the expected fluxdistribution for metal-enhanced atmospheres with different effectivetemperature and gravity. From the behaviour of the null wavelength, weconfirm the importance of the non-homogeneous distribution of elementson the stellar surface as origin of the light variability. However toexplain the photometric variability of some stars, we suggest that theflux distribution is also influenced by the contribution of the magneticfield to the hydrostatic equilibrium. Based on observations collected atthe Catania Astrophysical Observatory, Italy
| 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
| A search for rapid oscillations in chemically peculiar A-type stars
In 1995 we initiated a Northern Hemisphere survey for rapidlyoscillating Ap stars. This paper presents the results including one newroAp star (HD 122970), the confirmation of rapid oscillations of HD99563 and apparent null results for other stars. Using Hipparcos data astatistical analysis of the absolute magnitudes and galacticdistributions of all known roAp and noAp stars (also taken from theliterature) was made. A systematic trend for most of the program starsin a M_{ V} vs. beta (index of the Strömgren uvbybeta system)diagram was detected leading to the conclusion that beta issystematically influenced by the chemical peculiarity and/or magneticfield. Three roAp stars are outside the delta Scuti instability stripwhich implies that the driving mechanism of the two classes of pulsatingstar is different. This is also suggested by new pulsation models. Nostatistical difference between the galactic distribution of roAp andnoAp stars was found.
| Central Asian Network (CAN) - the history and present status
No abstract submitted
| 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
| 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.
| 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.
| 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
| Stromgren UVBY Photometry of the Magnetic Chemically Peculiar Stars HR 1643, theta Aur, 49 Cam, and HR 3724
Differential Stromgren uvby photometric observations from the FourCollege Automated Photoelectric Telescope of four magnetic ChemicallyPeculiar stars are used to refine rotational periods and to define theshapes of the light curves. HR 1643 (P = 2.73475 d) shows large in phasevariability in all four magnitudes. Theta Aur (P = 3.6188 d) exhibitslarge amplitude variations with two components contributing to theminima. For 49 Cam (P = 4.28679 d), we probably are observing both polarregions and much of the surface. The values for HR 3724 (P = 33.984 d)confirm Wolff's result that the main variability is in v. (SECTION:Stars)
| 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).
| A kinematical study of rapidly oscillating AP stars.
A kinematical study of rapidly oscillating Ap (roAp) stars and of asample of apparently similar Ap stars that show no pulsation isperformed, with a view to investigating possible differences between thetwo groups. The mean absolute magnitudes of the stars of both samples,derived through the mean parallax method, are at most marginallydifferent. From the consideration of the velocity ellipsoid parametersand of the mean orbital elements characterizing their motion in theGalaxy, the roAp stars appear significantly older than theirnon-pulsating counterparts.
| 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.
| The Relation between Rotational Velocities and Spectral Peculiarities among A-Type Stars
Abstract 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.
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| קבוצת-כוכבים: | ג'ירף |
| התרוממות ימנית: | 07h46m27.40s |
| סירוב: | +62°49'50.0" |
| גודל גלוי: | 6.49 |
| מרחק: | 81.169 פארסק |
| תנועה נכונה: | -37.2 |
| תנועה נכונה: | -61.4 |
| B-T magnitude: | 6.812 |
| V-T magnitude: | 6.495 |
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