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Magnetic fields of chemically peculiar stars. II: Magnetic fields and rotation of stars with strong and weak anomalies in the continuum energy distribution
We make a comparative analysis of magnetic fields and rotationparameters of magnetic CP stars with strong and weak anomalies in thespectral energy distribution. Stars with strong depressions in thecontinuum at 5200 Å are shown to have significantly strongerfields (the mean longitudinal component of the fields of these stars is< B e> = 1341 ± 98 G) compared to objects withweaker depressions (< B e> = 645 ± 58 G). Starswith stronger depressions are also found to occur more commonly amongslow rotators. Their rotation periods are, on the average, about 10 dayslong, three times longer than these of stars with weak depressions(about three days). This fact is indicative of a decrease of the degreeof anomality of the magnetic stars continuum spectrum with increasingrotational velocity. Yet another proof has been obtained suggesting thatslow rotation is one of the crucial factors contributing to thedevelopment of the phenomenon of magnetic chemically peculiar stars.Magnetic CP stars with weak depressions at 5200 Å are intermediateobjects between stars with strong depressions and normal A- and B-typestars both in terms of field strength and rotational velocity.
| Magnetic fields of chemically peculiar stars. I. The catalog of magnetic CP stars
This is the first paper of the series dedicated to the analysis of themagnetism of chemically peculiar (CP) stars of the upper Main Sequence.We use our own measurements and published data to compile a catalog ofmagnetic CP stars containing a total of 326 objects with confidentlydetected magnetic fields and 29 stars which are very likely to possessmagnetic field. We obtained the data on the magnetism of theoverwhelming majority of the stars solely based on the analysis oflongitudinal field component B e . The surface magneticfield, B s , has been measured for 49 objects. Our analysisshows that the number of magnetic CP stars decreases with increasingfield strength in accordance with exponential law, and stars with B e exceeding 5kG occur rarely (about 3% objects of ourlist).
| Magnetic field structure of slow CP-rotators: HD 9996 and HD 188041
This is the final paper on a study of the magnetic field structure of CPstars with long rotation periods. It is first demonstrated that theorientation and strength of the magnetic field have no effect on theirrotation velocity. The orientation of the dipole structures in slowmagnetic rotators is shown to be random, as it is in fast rotators. Thehypothesis that magnetic stars are slowed down under the influence ofthe magnetic field is called into question. The origin of CP stars isprobably related to their initial slow rotation.
| Magnetic-field dependence of chemical anomalies in CP stars
The dependence of the degree of anomaly of parameter Z of Genevaphotometry ( Z0 = Z CP ℒ Z norm.) on theaverage surface magnetic field Bs is analyzed. The Z0 value isproportional to the degree of anomaly of chemical composition. It wasfound that Bs → 0 corresponds Z0 → ‑0.010÷‑0.015, i.e., part of CP stars are virtually devoid of magneticfield, but exhibit chemical anomalies. This effect may be due toselection whereby only objects with strong chemical anomalies areclassified as CP stars, thereby producing a deficit of stars withrelatively weak anomalies. Moreover, CP stars have other sources ofstabilization of their atmospheres besides the magnetic field, e.g.,slow rotation. Formulas relating Z0 to Bs are derived.
| Evolution of magnetic fields in stars across the upper main sequence: II. Observed distribution of the magnetic field geometry
We re-discuss the evolutionary state of upper main sequence magneticstars using a sample of Ap and Bp stars with accurate Hipparcosparallaxes and definitely determined longitudinal magnetic fields. Weconfirm our previous results obtained from the study of Ap and Bp starswith accurate measurements of the mean magnetic field modulus and meanquadratic magnetic fields that magnetic stars of mass {M}<3 M_ȯare concentrated towards the centre of the main-sequence band. Incontrast, stars with masses {M}>3 M_ȯ seem to be concentratedcloser to the ZAMS. The study of a few known members of nearby openclusters with accurate Hipparcos parallaxes confirms these conclusions.Stronger magnetic fields tend to be found in hotter, younger and moremassive stars, as well as in stars with shorter rotation periods. Thelongest rotation periods are found only in stars which spent alreadymore than 40% of their main sequence life, in the mass domain between1.8 and 3 M_ȯ and with log g values ranging from 3.80 to 4.13. Noevidence is found for any loss of angular momentum during themain-sequence life. The magnetic flux remains constant over the stellarlife time on the main sequence. An excess of stars with largeobliquities β is detected in both higher and lower mass stars. It isquite possible that the angle β becomes close to 0o inslower rotating stars of mass {M}>3 M_ȯ too, analog to thebehaviour of angles β in slowly rotating stars of {M}<3 M_ȯ.The obliquity angle distribution as inferred from the distribution ofr-values appears random at the time magnetic stars become observable onthe H-R diagram. After quite a short time spent on the main sequence,the obliquity angle β tends to reach values close to either90o or 0o for {M}<3 M_ȯ. The evolution ofthe obliquity angle β seems to be somewhat different for low andhigh mass stars. While we find a strong hint for an increase of βwith the elapsed time on the main sequence for stars with {M}>3M_ȯ, no similar trend is found for stars with {M}<3 M_ȯ.However, the predominance of high values of β at advanced ages inthese stars is notable. As the physics governing the processes takingplace in magnetised atmospheres remains poorly understood, magneticfield properties have to be considered in the framework of dynamo orfossil field theories.
| Main-sequence magnetic CP stars: II. Physical parameters and chemical composition of the atmosphere
This paper continues a series of reviews dedicated to magnetic CP stars.The occurrence frequency of CP stars among B5 F0-type main-sequencestars is shown to be equal to about 15 20%. The problems ofidentification and classification of these objects are addressed. Weprefer the classification of Preston, which subdivides chemicallypeculiar stars into the following groups: Am, λ Boo, Ap/Bp,Hg-Mn, He-weak, and He-strong stars. The main characteristic features ofobjects of each group are briefly analyzed. The rotation velocities ofCP stars are shown to be about three times lower than those of normalstars of the same spectral types (except for λ Boo and He-strongobjects). The rotation periods of CP stars range from 0.5 to 100 days,however, there is also a small group of objects with especially long (upto several tens of years) variability periods. All kinds of peculiarstars can be found in visual binaries, with Am-and Hg-Mn-type starsoccurring mostly in short-period binaries with P < 10 days, and thebinary rate of these stars is close to normal. The percentage ofbinaries among magnetic stars (20%) is lower than among normal stars. Arather large fraction of CP1-and CP2-type stars was found to occur inyoung clusters (with ages smaller than 107 years).Photometric and spectral variability of peculiar stars of various typesis discussed, and it is shown that only objects possessing magneticfields exhibit light and spectral variations. The chemical compositionof the atmospheres of CP stars of various types is considered. Theabundances of various elements are usually determined by comparing theline profiles in the observed spectrum with those of the syntheticspectra computed for various model atmospheres. Different mechanisms areshown to contribute to chemical inhomogeneity at the star’ssurface, and the hypothesis of selective diffusion of atoms in a stableatmosphere is developed. Attention is also paid to the problems of thedetermination of local chemical composition including the stratificationof elements. Some of the coolest SrCrEu peculiar stars are found toexhibit fast light variations with periods ranging from 6 to 15 min.These variations are unassociated with rotation, but are due tononradial pulsations. The final part of the the review considers thefundamental parameters of CP stars. The effective temperatures,luminosities, radii, and masses of these objects are shown to agree withthe corresponding physical parameters of normal main-sequence stars ofthe same spectral types.
| 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.
| Magnetic field model for slowly rotating CP-stars. γEqu= HD201601
A magnetic field model is constructed for the extremely slow rotatorγEqu based on measurements of its magnetic field over many yearsand using the “magnetic charge” method. An analysis ofγEqu and of all the data accumulated up to the present on themagnetic field parameters of chemically peculiar stars leads to someinteresting conclusions, of which the main ones are: the fact that theaxis of rotation and the dipole axis are not parallel in γEqu andthe other slowly rotating magnetic stars which we have studiedpreviously is one of the signs that the braking of CP stars does notinvolve the participation of the magnetic field as they evolve “tothe main sequence.” The axes of the magnetic field dipole in slowrotators are oriented arbitrarily with respect to their axes ofrotation. The substantial photometric activity of these CP stars alsoargues against these axes being close. The well-known absence ofsufficiently strong magnetic fields in the Ae/Be Herbig stars alsopresents difficulties for the hypothesis of “magneticbraking” in the “pre-main sequence” stages ofevolution. The inverse relation between the average surface magneticfield Bs and the rotation period P is yet another fact in conflict withthe idea that the magnetic field is involved in the braking of CP stars.We believe that angular momentum loss involving the magnetic field canhardly have taken place during evolution immediately prior “to themain sequence,” rather the slow rotation of CP stars most likelyoriginates from protostellar clouds with low angular momentum. Some ofthe slowly rotating stars have a central dipole magnetic fieldconfiguration, while others have a displaced dipole configuration, wherethe displacement can be toward the positive or the negative magneticpole.
| Magnetic field models for HD 116458 and HD 126515
We have modeled the magnetic fields of the slowly rotating stars HD116458 and HD 126515 using the “magnetic charge” technique.HD 116458 has a small angle between its rotation axis and dipole axis(β = 12°), whereas this angle is large for HD 126515 (β =86°). Both stars can be described with a decentered-dipole model,with the respective displacements being r = 0.07 and r = 0.24 in unitsof the stellar radius. The decentered-dipole model is able tosatisfactorily explain the phase relations for the effective field, Be(P), and the mean surface field, B s(P), for both stars, along with thefact that the B e(P) phase relation for HD 126515 is anharmonic. Wediscuss the role of systematic measurement errors possibly resultingfrom instrumental or methodical effects in one or both of the phaserelations. The displacement of the dipole probably reflects realasymmetry of the stellar field structure, and is not due to measurementerrors. Using both phase relations, B e(P) and B s(P), in the modelingconsiderably reduces the influence of the nonuniform distribution ofchemical elements on the stellar surface.
| Model of the Magnetic Field of HD 187474
A model is constructed for the magnetic field of the star HD 187474,which has a very long axial rotation period P = 2345d. It turns out thatthe structure of the magnetic field is best described by a model of adisplaced (Δα = 0.1) dipole inclined to the axis of rotationby an angle β = 24°. The star is inclined to the line of sightby an angle i = 86°. Because of the displaced dipole the magnitudeof the magnetic field differs at the poles: Bp = +6300 and 11600 G. AMercator map of the distribution of the magnetic field over the surfaceis obtained. The 7 slowly rotating CP stars studied thus far have anaverage angle β = 62°, which equals the average value for arandom orientation of dipoles.
| 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 effect of the surface distribution of elements on measuring the magnetic field of chemically peculiar stars. The case of the roAp star HD 24712
A non-homogeneous distribution over the stellar surface of the chemicalelements and the presence of a large-scale magnetic field are invoked inorder to explain the periodic line strength, photometric and magneticvariability of magnetic chemically peculiar stars. In such a framework,the variability period is identical to the rotational period. Inmagnetic chemically peculiar stars, the so-called effective magneticfield Heff, the average over the visible stellar disk of thelongitudinal field component weighted by the local line strength, isroutinely measured from Stokes I and V profiles of selected spectrallines. In spite of evidence that the distribution of the variouschemical elements over the stellar surface can be inhomogeneous anddifferent from element to element, Heff values obtained fromlines of different elements are often statistically combined to improvethe accuracy of effective field measurements. Similarly, mean high S/Nprofiles are obtained from the profiles of lines of different elements.We have established, by means of R = 115 000 circular spectropolarimetryof the magnetic chemically peculiar star HD 24712 in the 4700-7000Å range, the dependence of the measurements of Heff onthe atomic weight of 24 elements (from carbon to erbium, if possible atdifferent ionisation states). At all 3 rotational phases considered,Heff values derived from different elements can differ by upto 800 G. We find an overall increase in Heff with atomicnumber and a maximum near Z=60. The behaviour of sodium is quitesingular inasmuch as it always exhibits a negative value of the field,peaking at -0.39 kG when the rare earths give Heff = 1.2 kG.Under the assumption of a dipolar field, we conclude that the elementsgiving the largest values of Heff are concentrated near thepositive polar region and that the other elements are more homogeneouslydistributed over the stellar surface or concentrated in belts around themagnetic equator. Sodium seems to be localised in the negative magnetichemisphere only. This picture is corroborated by the equivalent widthvariability of the lines: up to iron, equivalent widths changesout-of-phase with respect to the Heff variability; elementsheavier than iron present equivalent widths that are variable in-phase.We do not find any relation between the respective amplitudes of theequivalent width variations and the atomic numbers of the elements. Foriron, the observed equivalent width variability does not seem to besimply related to any non-homogeneous distribution over the stellarsurface. We conclude that measurements originating from differentelements cannot in general be combined to improve the precision ofHeff measurements. Indeed, any modelling attempt based on theperiodic variations in Heff is subject to the risk that thesampling of the magnetic field over the stellar surface by the lines ofa given chemical element is uneven or incomplete.In memory of Horace Babcock.
| 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
| A statistical analysis of the magnetic structure of CP stars
We present the results of a statistical study of the magnetic structureof upper main sequence chemically peculiar stars. We have modelled asample of 34 stars, assuming that the magnetic morphology is describedby the superposition of a dipole and a quadrupole field, arbitrarilyoriented. In order to interpret the modelling results, we haveintroduced a novel set of angles that provides one with a convenient wayto represent the mutual orientation of the quadrupolar component, thedipolar component, and the rotation axis. Some of our results aresimilar to what has already been found in previous studies, e.g., thatthe inclination of the dipole axis to the rotation axis is usually largefor short-period stars and small for long-period ones - see Landstreet& Mathys (\cite{Landstreet2000}). We also found that forshort-period stars (approximately P<10 days) the plane containing thetwo unit vectors that characterise the quadrupole is almost coincidentwith the plane containing the stellar rotation axis and the dipole axis.Long-period stars seem to be preferentially characterised by aquadrupole orientation such that the planes just mentioned areperpendicular. There is also some loose indication of a continuoustransition between the two classes of stars with increasing rotationalperiod.
| 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
| Magnetic AP Stars in the Hertzsprung-Russell Diagram
The evolutionary state of magnetic Ap stars is rediscussed using therecently released Hipparcos data. The distribution of the magnetic Apstars of mass below 3 Msolar in the H-R diagram differs fromthat of the normal stars in the same temperature range at a high levelof significance. Magnetic stars are concentrated toward the center ofthe main-sequence band. This is shown in two forms of the H-R diagram:one where logL is plotted against logTeff and a version moredirectly tied to the observed quantities, showing the astrometry-basedluminosity (Arenou & Luri) against the (B2-G)0 index ofGeneva photometry. In particular, it is found that magnetic fieldsappear only in stars that have already completed at least approximately30% of their main-sequence lifetime. No clear picture emerges as to thepossible evolution of the magnetic field across the main sequence. Hintsof some (loose) relations between magnetic field strength and otherstellar parameters are found: stars with shorter periods tend to havestronger fields, as do higher temperature and higher mass stars. Amarginal trend of the magnetic flux to be lower in more slowly rotatingstars may possibly be seen as suggesting a dynamo origin for the field.No correlation between the rotation period and the fraction of themain-sequence lifetime completed is observed, indicating that the slowrotation in these stars must already have been achieved before theybecame observably magnetic. Based on data from the ESA Hipparcossatellite and on observations collected at the European SouthernObservatory (La Silla, Chile; ESO programs Nos. 43.7-004, 44.7-012,49.7-030, 50.7-067, 51.7-041, 52.7-063, 53.7-028, 54.E-0416, and55.E-0751), at the Observatoire de Haute-Provence (Saint-Michell'Observatoire, France), at Kitt Peak National Observatory, and at theCanada-France-Hawaii Telescope.
| Magnetic models of slowly rotating magnetic Ap stars: aligned magnetic and rotation axes
As a result of major surveys carried out during the past decade byMathys and collaborators, we now have measurements with full phasecoverage of several magnetic field moments, including the meanlongitudinal field B_l, the mean field modulus B_s, and in most casesthe mean quadratic field B_mq and mean crossover field B_xover, for asample of 24 chemically peculiar magnetic (Ap) stars. This represents anincrease of a factor of order five in the stellar sample with data ofthis quality, compared to the situation a decade ago. We exploit thisdataset to derive general and statistical properties of the stars in thesample, as follows. First, we fit the available field momentobservations assuming a simple, axisymmetric multipole magnetic fieldexpansion (with dipole, quadrupole, and octupole components) over eachstellar surface. We show that this representation, though not exact,gives an adequate description of the available data for all the stars inthis sample, although the fit parameters are in many cases not unique.We find that many of the stars require an important quadrupole and/oroctupole field component to satisfy the observations, and that some(usually small) deviations from our assumed axisymmetric fielddistributions are certainly present. We examine the inclination i (0<= i <= 90o) of the rotation axis to the line of sightand the obliquity beta (0 <= beta <= 90o) of themagnetic field with respect to the rotation axis, and show that thestars with periods of the order of a month or longer have systematicallysmall values of beta : slowly rotating magnetic stars generally havetheir magnetic and rotation axes aligned to within about 20o,unlike the short period magnetic Ap stars, in which beta is usuallylarge. This is a qualitatively new result, and one which is veryimportant for efforts to understand the evolution of magnetic fields andangular momentum in the magnetic Ap stars.
| Magnetic field geometries of two slowly rotating Ap/Bp stars: HD 12288 and HD 14437
In this paper we report magnetic field models and basic physicalparameters for the slowly rotating Ap/Bp stars HD 12288 and HD 14437.Using new and previously published mean longitudinal magnetic field,mean magnetic field modulus, and hipparcos photometric measurements, wehave inferred the rotational periods of both stars (HD 12288:P_rot=34.9d +/- 0.2d HD 14437:P_rot=26.87d +/- 0.02d). From the magneticmeasurements we have determined the best-fit decentred magnetic dipoleconfigurations. For HD 12288, we find that the field geometry isconsistent with a centred dipole, while for HD 14437 a large decentringparameter (a=0.23 R_*) is inferred. Both stars show one angle in theambiguous (i,beta ) couplet which is smaller than about 20degr . This isconsistent with the observation of Landstreet & Mathys (2000), whopoint out that almost all magnetic Ap stars with periods longer thanabout 30 days exhibit magnetic fields aligned with their rotationalaxis.
| 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
| 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
| 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.
| A catalogue of [Fe/H] determinations: 1996 edition
A fifth Edition of the Catalogue of [Fe/H] determinations is presentedherewith. It contains 5946 determinations for 3247 stars, including 751stars in 84 associations, clusters or galaxies. The literature iscomplete up to December 1995. The 700 bibliographical referencescorrespond to [Fe/H] determinations obtained from high resolutionspectroscopic observations and detailed analyses, most of them carriedout with the help of model-atmospheres. The Catalogue is made up ofthree formatted files: File 1: field stars, File 2: stars in galacticassociations and clusters, and stars in SMC, LMC, M33, File 3: numberedlist of bibliographical references The three files are only available inelectronic form at the Centre de Donnees Stellaires in Strasbourg, viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5), or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| The mean magnetic field modulus of AP stars
We present new measurements of the mean magnetic field modulus of asample of Ap stars with spectral lines resolved into magnetically splitcomponents. We report the discovery of 16 new stars having thisproperty. This brings the total number of such stars known to 42. Wehave performed more than 750 measurements of the mean field modulus of40 of these 42 stars, between May 1988 and August 1995. The best of themhave an estimated accuracy of 25 - 30 G. The availability of such alarge number of measurements allows us to discuss for the first time thedistribution of the field modulus intensities. A most intriguing resultis the apparent existence of a sharp cutoff at the low end of thisdistribution, since no star with a field modulus (averaged over therotation period) smaller than 2.8 kG has been found in this study. Formore than one third of the studied stars, enough field determinationswell distributed throughout the stellar rotation cycle have beenachieved to allow us to characterize at least to some extent thevariations of the field modulus. These variations are oftensignificantly anharmonic, and it is not unusual for their extrema not tocoincide in phase with the extrema of the longitudinal field (for thefew stars for which enough data exist about the latter). This, togetherwith considerations on the distribution of the relative amplitude ofvariation of the studied stars, supports the recently emerging evidencefor markedly non-dipolar geometry and fine structure of the magneticfields of most Ap stars. New or improved determinations of the rotationperiods of 9 Ap stars have been achieved from the analysis of thevariations of their mean magnetic field modulus. Tentative values of theperiod have been derived for 5 additional stars, and lower limits havebeen established for 10 stars. The shortest definite rotation period ofan Ap star with magnetically resolved lines is 3.4 deg, while thosestars that rotate slowest appear to have periods in excess of 70 or 75years. As a result of this study, the number of known Ap stars withrotation periods longer than 30 days is almost doubled. We brieflyrediscuss the slow-rotation tail of the period distribution of Ap stars.This study also yielded the discovery of radial velocity variations in 8stars. There seems to be a deficiency of binaries with short orbitalperiods among Ap stars with magnetically resolved lines. Based onobservations collected at the European Southern Observatory (La Silla,Chile; ESO programmes Nos. 43.7-004, 44.7-012, 49.7-030, 50.7-067,51.7-041, 52.7-063, 53.7-028, 54.E-0416, and 55.E-0751), at theObservatoire de Haute-Provence (Saint-Michel-l'Observatoire, France), atKitt Peak National Observatory, and at the Canada-France-HawaiiTelescope. Tables 2, 3, and 4 are also available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html.
| 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.
| 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
| A catalogue of Fe/H determinations - 1991 edition
A revised version of the catalog of Fe/H determinations published by G.Cayrel et al. (1985) is presented. The catalog contains 3252 Fe/Hdeterminations for 1676 stars. The literature is complete up to December1990. The catalog includes only Fe/H determinations obtained from highresolution spectroscopic observations based on detailed spectroscopicanalyses, most of them carried out with model atmospheres. The catalogcontains a good number of Fe/H determinations for stars from open andglobular clusters and for some supergiants in the Magellanic Clouds.
| AP stars with resolved magnetically split lines
New high-resolution spectroscopic observations of Ap stars with resolvedmagnetically split spectral lines are presented. Six new such stars havebeen discovered: HD 2453, HD 9996, HD 18078, HD 50169, HD 137949, and HD192678. This raises the total number of known Ap stars with resolvedmagnetically split lines to 21. The spectral line profiles observed intwo more stars, HD 111133 and HD 147010, are strongly affected by themagnetic field, but they are not fully resolved, due to nonnegligiblerotational Doppler effect. Observations of fairly sharp-lined Ap starswhose lines are unresolved are also presented. The relative differencebetween the equivalent widths of the Fe II lines 6147.7 A and 6149.2 Ais shown to increase with the mean magnetic field modulus. The existenceof a simple, unambiguous correlation between the mean magnetic fieldmodulus and the index Z of Geneva photometry, which had previously beenadvocated, is not confirmed. At most, stars with large negative valuesof Z may be more prone to have strong magnetic fields, but the evidencefor this is not statistically strong.
| The third spectrum of praseodymium in magnetic AP stars
The identification of Pr III lines in the red spectrum of magnetic Apstars, whose great strength contrasts with the weakness of the secondspectrum of Pr in upper main-sequence, chemically peculiar stars, ispresently reported. This identification is judged to be a critical steptoward a knowledge of the abundance systematics of the lanthanides inchemically peculiar stars, as well as toward characterization of thechemical fractionation processes which they undergo.
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Membre dels grups següents:
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Dades d'Observació i Astrometria
| Constel·lació: | Cassiopeia |
| Ascensió Recta: | 02h03m30.51s |
| Declinació: | +69°34'56.3" |
| Magnitud Aparent: | 7.739 |
| Distancia: | 230.947 parsecs |
| Moviment propi RA: | 9.5 |
| Moviment propi Dec: | -2.1 |
| B-T magnitude: | 7.867 |
| V-T magnitude: | 7.75 |
Catàlegs i designacions:
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