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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.
| FCAPT uvby Photometry of the mCP Stars HD 20629, HR 3724, 45 Leo, and HD 192678
The Four College Automated Photoelectric Telescope obtained differentialStrömgren uvby observations of the magnetic chemically peculiar(mCP) stars HD 20629, HR 3724, 45 Leo, and HD 192678. HD 20629, amoderately large amplitude variable, has a period of 2.9934 days.Analyses of this new photometry with published uvby values show that HR3724 and 45 Leo had periods of 33.984 and 1.44404 days, respectively,for at least 30 yr. New observations of HD 192678 refine the period ofthis small-amplitude variable to 6.4193 days.
| 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.
| The diagnosis of the mean quadratic magnetic field of Ap stars
Aims.We assess the validity of the method of determination of the meanquadratic field modulus and we explore its limits. Methods.Weanalyse high spectral resolution, high signal-to-noise spectra of a fewAp stars, and of a superficially normal main-sequence A star, recordedover a broad wavelength range with EMMI at the NTT.Results.Weintroduce a revised form of the regression equation describing thedependence of the second-order moment of the line profiles about theircentre, in natural light, on various parameters of the correspondingtransitions. We show that interpretation of the observed dependencesallows one to determine the mean quadratic magnetic field modulus of thestudied stars, and their v sin i. We explain why the contributions tothe quadratic field of the mean square magnetic field modulus and of themean square longitudinal field cannot in general be disentangled. Forthose stars of the sample that have resolved magnetically split lines,we show that the derived values of the quadratic field are mostlyconsistent with the values of the mean longitudinal magnetic field andof the mean magnetic field modulus at the observed phase. However thereare some hints that they may occasionally slightly underestimate theactual field. This suggests that the method is unlikely to yieldspurious field detections. In addition, we illustrate the importance forthis type of analyses of using, as far as possible, samples of lines ofa single ion, and to specify in the presentation of the results whichion was used.Conclusions.The results presented in this paper lendstrong support to the validity of the quadratic field diagnostic methodto obtain a realistic quantitative characterisation of the magneticfields Ap and related stars.
| 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.
| 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.
| 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
| 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.
| 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.
| 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.
| ICCD Speckle Observations of Binary Stars. XXIII. Measurements during 1982-1997 from Six Telescopes, with 14 New Orbits
We present 2017 observations of 1286 binary stars, observed by means ofspeckle interferometry using six telescopes over a 15 year period from1982 April to 1997 June. These measurements constitute the 23dinstallment in CHARA's speckle program at 2 to 4 m class telescopes andinclude the second major collection of measurements from the MountWilson 100 inch (2.5 m) Hooker Telescope. Orbital elements are alsopresented for 14 systems, seven of which have had no previouslypublished orbital analyses.
| An analysis of the Ap binary HD 81009
We present a detailed investigation of the orbit, componentcharacteristics and magnetic field of the single spectrum (SB1), visualAp binary HD 81009. By simultaneously modeling new and archival radialvelocity measurements and new and archival speckle interferometricmeasurements (obtained with the CHARA array) we obtain a unique model ofthe orbital geometry and constraints on the component masses of HD81009. Additional constraints provided by the Hipparcos parallax andcomponent magnitude difference and the optical spectral energydistribution allow us to determine a self-consistent solution for thebasic physical properties of the components. HD 81009 is a highlyeccentric (e=0.718), long-period (P_orb=29.3 y) binary composed of twomain sequence A-type stars. While its presence is required in order toexplain the astrometric and photometric observations, the coolersecondary component is never detected spectroscopically, and istherefore inferred to rotate somewhat more rapidly than the hottercomponent. The hotter primary component is identified as theslowly-rotating (P_rot=33fd 984) magnetic Ap star. We have modeled themagnetic field geometry of this star using new and archival longitudinalmagnetic field and mean magnetic field modulus observations. Therotational variations of the magnetic quantities are consistent with adecentered dipole surface magnetic field geometry with small magneticobliquity (beta < 20degr ). This is consistent with the observationof Landstreet & Mathys (2000), who report that nearly all magneticAp stars with periods longer than around 25 days exhibit beta <20degr, implying that their magnetic fields are approximately aligned withtheir rotational axes. Based on observations obtained at the EuropeanSouthern Observatory (La Silla, Chile), the Haute Provence and Pic duMidi Observtories (France), and the Las Campanas Observatory (Chile)
| 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.
| 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.
| 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
| Photometry from the HIPPARCOS Catalogue: Constant MCP Stars, Comparison and Check Stars
Photometry from the Hipparcos catalogue is used to verify the constancyof four magnetic CP stars, as well as the comparison and the check starsused for variability studies of normal and chemically peculiar B and Astars with the Four College Automated Photoelectric Telescope;variability in these stars can produce spurious results. A few of thecomparison stars are found to be variable and should be replaced forfuture differential photometric studies.
| 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 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
| Mass determination of astrometric binaries with Hipparcos. II. Selection of candidates and results
In a previous paper (\cite{Mar97}) we have shown that for double starswith orbital periods smaller than about 25 years, it was possible todetermine from the Hipparcos data, the mass ratio B of the components orthe difference between the mass and intensity ratios, beta -B, providedthe orbital elements of the relative orbit are available. From anextensive literature search we have selected 145 potential systems, ofwhich 46 yielded eventually a satisfactory solution. For eight systemswith the largest separations, the peculiarities of the natural directionassociated to the Hipparcos observations, the 'hippacentre', have beenfully exploited to derive the mass ratio of the components without anyadditional assumption. For the remaining 38, the derivation of the massratio was possible only by taking the magnitude difference between thetwo components from other sources. The parallax determinedsimultaneously, is then used to produce the individual masses of thecomponents. The astrophysical relevance of the results is discussed andwhen possible (17 systems) the masses are compared to ground-basedvalues.
| 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)
| Spectropolarimetry of magnetic stars. VI. Longitudinal field, crossover and quadratic field: New measurements
New determinations of the mean longitudinal magnetic field, of thecrossover, and of the mean quadratic magnetic field of Ap stars arepresented. They are based on spectra recorded simultaneously in bothcircular polarizations at ESO with the CASPEC spectrograph fed by the3.6 m telescope. This paper discusses 95 observations of 44 stars. Amajor result of this study is the discovery that HD 137509 has apredominantly quadrupolar magnetic field, a strucuture previously foundin only a couple of stars. Improvement or revision of the determinationof the rotation period has been achieved for 3 stars. The stars studiedin this work include 14 rapidly oscillating Ap stars (for 6 of which noprevious attempt to detect a magnetic field had ever been made) and 21Ap stars with spectral lines resolved into their magnetically splitcomponents when observed at high enough dispersion in unpolarized light(for 9 of these stars, no determination of the longitudinal field hadbeen performed before). The observations discussed in this paper havebeen performed between 1989 and 1994, a period during which CASPEC andits Zeeman analyzer have progressively undergone various configurationchanges. The results reported here demonstrate that the polarimetricperformance of the instrument has remained unaltered through thesemodifications. Thanks to the latter, the achieved resolving power wasincreased, which resulted in improved magnetic measurement accuracies.Based on observations collected at the European Southern Observatory (LaSilla, Chile; ESO programmes Nos. 47.7-045 and 49.7-029).
| 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.
| ICCD Speckle Observations of Binary Stars. XIII. Measurements During 1989- 1994 From the Cerro Tololo 4 M Telescope
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....111..936H&db_key=AST
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