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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.
| HD 65949: the highest known mercury excess of any CP star?
ESO spectra of HD 65949 show it to be unlike any of the well-known typeswithin its temperature range ≈13 600 K. It is neither a silicon, nora mercury-manganese star, though it has a huge Hg II line atλ3984. We estimate log (Hg/H) + 12.0 ≈ 7.4. This is higherthan any published stellar mercury abundance. HD 65949 is a member of anearby open cluster, NGC 2516, which is only slightly older than thePleiades, and has been of recent interest because of its numerous X-rayemission stars, including HD 65949 itself, or a close companion. Alongitudinal magnetic field of the order of -290 Gauss at the 4.7σlevel was very recently diagnosed from accurate circularspectropolarimetric observations with FORS 1 at the VLT. The spectrallines are sharp, allowing a thorough identification study. Secondspectra of Ti, Cr, and Fe are rich. Mn II is well identified but notunusually strong. Numerous lines of S II and P II are found, but not GaII. The resonance lines of Sr II are strong. While many Y II lines areidentified, and Nb II is very likely present, no Zr II lines were found.Xe II is well identified. Strong absorptions from the third spectra ofthe lanthanides Pr, Nd, and Ho are present, but lines from the secondspectra of lanthanides are extremely weak or absent. Among lines fromthe heavier elements, those of Pt II are clearly present, and theheaviest isotope, 198Pt, is indicated. The uncommon spectrumof Re II is certain, while Os II and Te II are highly probable. Severalof the noted anomalies are unusual for a star as hot as HD 65949.
| 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.
| Line Identification of the Si Star HD 87240
Line identifications are presented for the peculiar Apstar HD7240(δ = - 59° 51' 00.1'') in the spectral region λλ3710-5520. This object is a member of the southern open cluster NGC114.Comparison of this object with other field silicon stars shows that itshares many of their line anomalies.
| 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
| Core-polarization effects in doubly ionized cerium (Ce III) for transitions of astrophysical interest
The importance of core-polarization effects on oscillator strengthdetermination in Ce III is emphasized. The inclusion of these effects inrelativistic Hartree-Fock (HFR) calculations leads to theoreticallifetime values for some 4f6p levels of this ion in close agreement withrecent time-resolved laser-induced fluorescence measurements. These newatomic data, the most accurate to date, have allowed the refinement ofthe stellar abundance determination of cerium in the chemically peculiarstar HD 192913, but have not altered in a drastic way the conclusionsderived in recent analyses regarding the overabundance of this element.
| Measurements of stellar magnetic fields using synthetic spectrum fitting
A sample of Ap and Bp stars have been investigated with respect to theirsurface magnetic field using synthetic spectrum fitting. The advantageof this technique is the simplicity in determining the surface fieldstrength and the possibility to apply it to objects whose spectrum doesnot display resolved Zeeman components. We show the usefulness of themethod by demonstrations on stellar spectra with resolved Zeemancomponents, where the results have been compared with values based onmeasurements of the Zeeman splitting for the magnetically sensitive FeIi lambda 6149 line. The objects HD 192678 andHD 165474 have been observed over their rotationalperiod to investigate magnetic field variations. The analysis is thenextended to objects where no resolved structure is observed. The rapidlyrotating stars HD 22316 and HD10783 are used as examples where this method is useful toachieve a value of the surface field. The relative intensification ofthe Fe Ii lambda lambda 6147, 6149 lines is investigated in an attemptto understand its relation to the surface magnetic field strength forthe stars HD 22316 and HD 10783. Based on observations obtained with theNordic Optical Telescope, operated on the island of La Palma jointly byDenmark, Finland, Iceland, Norway, and Sweden, in the SpanishObservatorio del Roque de los Muchachos of the Instituto de Astrofisicade Canarias.
| 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.
| Experimental and theoretical studies of DyIII: radiative lifetimes and oscillator strengths of astrophysical interest
The lifetimes of three short-lived levels belonging to the4f96p configuration and of two long-lived levels of the4f95d configuration of DyIII have been measured for the firsttime using time-resolved laser-induced fluorescence techniques. They arein good agreement with theoretical values calculated within theframework of a pseudo-relativistic configuration interactionapproximation. Using the experimental lifetimes and the theoreticalbranching fractions, a first set of transition probabilities ofastrophysical interest has been obtained for DyIII.
| Measurement of lifetimes by laser-induced fluorescence and determination of transition probabilities of astrophysical interest in Nd III
Selective lifetime measurements by time-resolved laser-inducedfluorescence spectroscopy for 5 levels belonging to the 4f35dconfiguration of doubly ionized neodymium provide a first and usefulexperimental test of the relativistic Hartree-Fock calculations in thision of astrophysical interest. As a consequence, the accuracy of thetransition probabilities deduced in the present work is well assessed.These new data are expected to help astrophysicists in the future torefine the analysis of the composition of chemically peculiar starswhich frequently show large overabundances of lanthanides when comparedto the solar system standards.
| New periodic variables from the Hipparcos epoch photometry
Two selection statistics are used to extract new candidate periodicvariables from the epoch photometry of the Hipparcos catalogue. Theprimary selection criterion is a signal-to-noise ratio. The dependenceof this statistic on the number of observations is calibrated usingabout 30000 randomly permuted Hipparcos data sets. A significance levelof 0.1 per cent is used to extract a first batch of candidate variables.The second criterion requires that the optimal frequency be unaffectedif the data are de-trended by low-order polynomials. We find 2675 newcandidate periodic variables, of which the majority (2082) are from theHipparcos`unsolved' variables. Potential problems with theinterpretation of the data (e.g. aliasing) are discussed.
| The influence of the magnetic field orientation on the angular momentum loss in the pre-main sequence phase: The case of very slowly rotating magnetic Ap stars
Landstreet & Mathys (\cite{lan00}) have discovered that almost allthe magnetic Ap stars having rotation periods longer than about onemonth have their magnetic and rotation axes fairly closely aligned, incontrast to the more common magnetic Ap stars of shorter period, inwhich the two axes are usually inclined to one another at a large angle.Furthermore, as shown earlier by Mathys et al. (\cite{mathys}) and byHubrig et al. (\cite{hnm00}), these most slowly rotating magnetic Apstars have also magnetic fields several times larger than are typicalfor shorter period magnetic Ap stars, and generally have masses below 3Msun. In this paper, we present calculations to show that theobserved axial alignment in the slowest rotators may have arisen duringthe pre-main sequence (PMS) phase, when stars of a few solar masses areobserved as Herbig Ae/Be stars. During the PMS phase, a star is expectedto exchange angular momentum with a disk and with a stellar wind. Asshown by Stȩpień (\cite{ste00}), a disk around a PMSmagnetic Ap star tends to lock the rotation rate at a few days, whilemass loss in the absence of a disk is able to slow the star to quitelong periods. We argue that is it plausible to assume that the fractionof the PMS phase during which a disk persists depends on the orientationof the field axis to the plane of the disk, and that disk dissipationmay have occurred more quickly in magnetic stars with aligned magneticand rotation axes than in stars in which the angle between these axes islarge. In this case, the magnetic Ap stars with aligned rotation andmagnetic axes, especially those with large fields, could lose much moreangular momentum than the stars of large obliquity. However, it is alsoshown that loss of nearly all the angular momentum is only possible forstars with masses below about 3 Msun (and with relativelylarge fields); for higher masses the available time is too short. Ourmodel thus provides a reasonable explanation for all of the principleobservational facts about the very slowly rotating magnetic Ap stars.
| 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.
| Multiperiodicities from the Hipparcos epoch photometry and possible pulsation in early A-type stars
A selection criterion based on the relative strength of the largestpeaks in the amplitude spectra, and an information criterion are used incombination to search for multiperiodicities in Hipparcos epochphotometry. The method is applied to all stars which have beenclassified as variable in the Hipparcos catalogue: periodic, unsolvedand microvariables. Results are assessed critically: although there aremany problems arising from aliasing, there are also a number ofinteresting frequency combinations which deserve further investigation.One such result is the possible occurrence of multiple periods of theorder of a day in a few early A-type stars. The Hipparcos catalogue alsocontains a number of these stars with single periodicities: such starswith no obvious variability classifications are listed, and informationabout their properties (e.g., radial velocity variations) discussed.These stars may constitute a new class of pulsators.
| Spectropolarimetric measurements of the mean longitudinal magnetic field of chemically peculiar stars. II. Phase relating the magnetic and luminosity variabilities
For a sample of chemically peculiar stars, we report time-resolvedmeasurements of the effective magnetic field which were obtained withthe spectropolarimetry operating at the Catania AstrophysicalObservatory. These observations are combined with data from theliterature for better pointing out that periodic magnetic variabilitywhich characterises this class of stars. Periods given in the literaturehave been checked and, if possible, re-determined, not only by means ofthe magnetic measurements but referring also to the Hipparcosphotometry. The variability of the effective magnetic field of thealready known magnetic star 25 Sex is pointed out for the first time. Asto the suspected magnetic chemically peculiar star EP UMa, ourmeasurements confirm that this is really a magnetic star and we indicatea possible variability period. The accuracy of the variability periodfor CS Vir and FF Vir is improved. The suggestion that light variabilityis due to the re-distribution of ultraviolet flux towards the visiblewavelengths in metal rich regions, which are not homogeneouslydistributed on the stellar surface, appears not always and straightlyvalid. Local line-blocking is certainly important in the case of CS Virand a direct influence of the magnetic field on the infrared photometricvariability cannot be ruled out for 25 Sex. Based on observationscollected at the Catania Astrophysical Observatory, Italy.
| Theoretical Oscillator Strengths inPr III and Application to Some CP Stars
A set of transition probabilities is obtained for the first time formany transitions of Pr III of astrophysical interest. A relativisticHartree-Fock method, combined with a least-squares fitting of theavailable experimental levels, including a large number of newlydetermined values, has been used for the calculations in whichconfiguration interaction and core-polarization effects have beenintroduced. The interest of the new data set is illustrated byconsidering the chemical composition of the chemically peculiar (CP)stars HD 101065 (Przybylski's star) and HD 141556 (χ Lupi).
| 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.
| Ab initio calculations of oscillator strengths and Landé factors for Nd Iii
Theoretical calculations of oscillator strengths and Landég-factors made with the Cowan code are presented for the rare-earth ionNd Iii. The emphasis is on transitions in the optical region of thespectrum. Comparisons of previous ab initio calculations of this typefor other lanthanides (e.g., La Ii, Ce Iii, and Lu Ii) with publishedexperimental and theoretical data suggest that the accuracy of thelog(gf) values for individual transitions should be about +/-0.15 dex inthe absence of significant core polarization effects; the g-factorsshould be good to better than 5%, except in a few cases where termmixing is important. Applications of the data are made in thecalculation of neodymium abundances in the atmospheres of the chemicallypeculiar stars HD 101065 (``Przybylski's star") andHD 122970.
| The 75th Name-List of Variable Stars
We present the next regular Name-List of variable stars containinginformation on 916 variable stars recently designated in the system ofthe General Catalogue of Variable 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.
| 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
| On the cobalt abundances of early-type stars
Photographic region high-dispersion high signal-to-noise spectra of Aand F main sequence band stars which exhibit modest rotation show Co Ilines. In the hottest of these stars, we also found weak Co II lineswhose abundances are consistent with those from Co I lines. As a classthe Am stars have cobalt abundances which are greater than solar whilethe normal stars have solar values.
| The electron-impact broadening effect in CP stars: the case of La II , La II i, EU II , and EU II i lines
The electron-impact widths and shifts for six Eu ii lines and widths forthree La ii , and six La ii i multiplets have been calculated by usingthe modified semiempirical method. Estimation for Stark widths of664.506 nm (Eu ii ) and 666.634 nm (Eu ii i) lines are given as well.The influence of the electron-impact mechanism on line shapes andequivalent widths in hot star atmospheres has been considered.
| 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
| 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.
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | ברבור |
| התרוממות ימנית: | 21h01m14.32s |
| סירוב: | +43°43'18.4" |
| גודל גלוי: | 7.69 |
| מרחק: | 296.736 פארסק |
| תנועה נכונה: | 7.2 |
| תנועה נכונה: | 0.9 |
| B-T magnitude: | 7.568 |
| V-T magnitude: | 7.68 |
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