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An Atlas of K-Line Spectra for Cool Magnetic CP Stars: The Wing-Nib Anomaly (WNA)
We present a short atlas illustrating the unusual Ca II K-line profilesin upper main-sequence stars with anomalous abundances. Slopes of theprofiles for 10 cool, magnetic chemically peculiar (CP) stars changeabruptly at the very core, forming a deep ``nib.'' The nibs show thesame or nearly the same radial velocity as the other atomic lines. Thenear wings are generally more shallow than in normal stars. In threemagnetic CP stars, the K lines are too weak to show this shape, althoughthe nibs themselves are arguably present. The Ca II H lines also showdeep nibs, but the profiles are complicated by the nearby, strongHɛ absorption. The K-line structure is nearly unchanged withphase in β CrB and α Cir. Calculations, including NLTE, showthat other possibilities in addition to chemical stratification mayyield niblike cores.
| Stable magnetic fields in stellar interiors
We investigate the 50-year old hypothesis that the magnetic fields ofthe Ap stars are stable equilibria that have survived in these starssince their formation. With numerical simulations we find that stablemagnetic field configurations indeed appear to exist under theconditions in the radiative interior of a star. Confirming a hypothesisby Prendergast (1956, ApJ, 123, 498), the configurations have roughlyequal poloidal and toroidal field strengths. We find that tori of suchtwisted fields can form as remnants of the decay of an unstable randominitial field. In agreement with observations, the appearance at thesurface is an approximate dipole with smaller contributions from highermultipoles, and the surface field strength can increase with the age ofthe star. The results of this paper were summarised by Braithwaite &Spruit (2004, Nature, 431, 891).
| Spiral waves and the secondary star in the nova-like variable V3885 Sgr
We present seven nights' blue (4300-5000Å) spectroscopy of thenova-like variable star V3885 Sgr. The line spectrum shows a typicalcombination of broad absorption and emission in Hγ, Hβ andHeI, which is associated with the accretion disc. We also observeantiphased narrow emission, which we attribute to irradiation of thesecondary star. The HeIIλ4686 and NIII-CIII-CIV emission linesare devoid of structure and are most likely formed in an outflow. Wemeasure radial velocity shifts in the absorption and emission lines,from which we fit an orbital period of 4.97126 +/- 0.00036h. From thevelocity semi-amplitudes of the disc and companion star, we are able toconstrain the binary mass ratio to q > 0.7.The phase-folded spectra provide dense coverage of the entire orbitalcycle. Doppler tomograms of the hydrogen and HeI lines reveal spiralstructure in the accretion disc and the irradiated donor star. Webelieve that this is the first unambiguous detection of spiral waves ina nova-like variable.
| High time resolution spectroscopy and magnetic variability of the cool Ap star HD965*
We present the results of an investigation of the magnetic Ap star HD965with high spectral and time resolution. We determine precise radialvelocities using spectra obtained with the Ultraviolet-Visual EchelleSpectrograph (UVES) on the European Southern Observatory Very LargeTelescope. Special attention is given to spectral lines of rare-earthelements which in rapidly oscillating Ap (roAp) stars exhibit thestrongest radial velocity variations with pulsation period. Careful timeseries analysis did not detect any convincing evidence of pulsation inHD965 with an upper limit in amplitude of 15-20 m s-1. Allproperties of HD965 are similar to the majority of roAp stars. A likelyreason for the apparent lack of pulsation could be connected with thegeometrical structure of the magnetic field and the aspect of the starat the time of observation. Longitudinal magnetic field measurements forHD965 showed that our UVES spectral observations were carried out whenthe longitudinal field was near zero and therefore, according to theoblique rotator model, near a time when the star was viewed from themagnetic equator. For a dipole oscillation aligned with the magneticfield, as is typical of roAp stars, no variation can be detected at thisaspect. We may, therefore, expect to detect rapid oscillations in HD965in the future, when the star will present one of the magnetic poles.
| 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.
| The calcium isotopic anomaly in magnetic CP stars
Chemically peculiar stars in the magnetic sequence can show the sameisotopic anomaly in calcium previously discovered for mercury-manganesestars in the non-magnetic sequence. In extreme cases, the dominantisotope is the exotic 48Ca. Measurements of Ca II linesarising from 3d-4p transitions reveal the anomaly by showing shifts upto 0.2 Å for the extreme cases - too large to be measurementerrors. We report measurements of miscellaneous objects, including twometal-poor stars, two apparently normal F-stars, an Am-star, and theN-star U Ant. Demonstrable anomalies are apparent only for the Ap stars.The largest shifts are found in rapidly oscillating Ap stars and in oneweakly magnetic Ap star, HD 133792. We note the possible relevance ofthese shifts for the GAIA mission.Based on observations obtained at the European Southern Observatory, LaSilla and Paranal, Chile (ESO programme Nos. 65.L-0316, 68.D-0254 and266.D-5655).
| Chemical composition of the magnetic B star HR 5049
A spectrum synthesis analysis for photospheric lines in the magnetic Bstar HR 5049 is presented, based on a high quality spectrogram obtainedwith the EMMI spectrograph attached to the NTT at ESO. It is found thatlight elements such as He, C and O are under-abundant. One of the mostnotable features is the deficiency of He by more than -2.0 dex. Co andCl are over-abundant by +3.5 dex and +1.9 dex, respectively. Other ironpeak elements are over-abundant ranging from +0.47 dex (Ti II) to +1.94dex (Cr I). For rare earth elements, the lines of once-ionized speciesare generally weak, while the third spectra (especially those of Pr andNd) are very prominent. Although rare earth elements show significantover-abundances ranging from +3.0 dex to as large as +4.0 dex, Ba hasthe solar abundance. The Nd-Pr abundance difference, which shows anapparent decreasing trend with increasing effective temperature among CPstars, is found to be unusually small in HR 5049.Based on observations collected at the La Silla Observatory, ESO (Chile)with the New Technology Telescope (NTT).The full Table 2 is 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/420/673
| 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
| Structure of the magnetic field in the Ap star HD 187474
We reconstruct the complex magnetic field in the Ap star HD 187474within the frame of the point field source model, where virtual magneticcharges are distributed in the stellar body. The best-fit modeldescribes sufficiently well the observed nonsinusoidal variability ofthe mean magnetic field modulus and the sinusoidal behaviour of the meanlongitudinal magnetic field with the phase of stellar rotation. The bestfit provides discrepancy on the level of chi 2=6.10 for allthe analyzed data. We show that in HD 187474 the magnetic dipole isdisplaced from centre of the star by 0.055 Rstar . The dipolehas a size ~ 0.035 Rstar . The angle between the stellarrotational axis and the magnetic dipole is beta =37degr .
| On the behavior of the Cii 4267.261, 6578.052 and 6582.882 Å lines in chemically peculiar and standard stars
With the aim of investigating the possible particular behavior of carbonin a sample of chemically peculiar stars of the main sequence withoutturning to modeling, we performed spectroscopic observations of threeimportant and usually prominent single ionized carbon lines: 4267.261,6578.052 and 6582.882 Å. In addition, we observed a large numberof standard stars in order to define a kind of normality strip, usefulfor comparing the observed trend for the peculiar stars. We paidparticular attention to the problem of the determination of fundamentalatmospheric parameters, especially for the chemically peculiar stars forwhich the abundance anomalies change the flux distribution in such a waythat the classical photometric methods to infer effective temperaturesand gravities parameter cannot be applied. Regarding CP stars, we founda normal carbon abundance in Hg-Mn, Si (with some exceptions) and Hestrong stars. He weak stars are normal too, but with a large spread outof the data around the mean value. A more complicated behavior has beennoted in the group of SrCrEu stars: four out of seven show a strongoverabundance, being the others normal.
| 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.
| Surface abundance distribution models of Si, Cr, Mn, Fe, Pr and Nd for the slowly rotating Ap star HD 187474
The very slowly rotating magnetic Ap star HD 187474 has strong and quitevariable spectral lines of several elements. An axisymmetric low-ordermultipole magnetic model has been obtained for this star by Landstreet& Mathys (2000). HD 187474 is one of the few very slowly rotatingmagnetic Ap stars that is suitable for abundance distribution modelling;because of the unusually large angle between the field and rotationaxes, the line of sight goes well into both magnetic hemispheres. Wehave used CASPEC and CES spectra with good phase coverage together withthe programme ZEEMAN to search for simple three-ring abundancedistributions of Si, Cr, Mn, Fe, Pr and Nd, symmetric about the assumedmagnetic field distribution axis, that match observed line profiles as afunction of rotational phase. Reasonably satisfactory fits to theobservations are found for all of these elements. In all cases,three-ring models work as well as more finely gridded models. Thededuced abundances are somewhat overabundant and somewhat non-uniformfor Fe; for the other elements quite large overabundances (up to 5 dexfor Nd) are found, with substantially higher (but somewhat unequal)abundances around the two magnetic poles compared to the magneticequator. All the elements studied are overabundant everywhere (exceptperhaps Si around the magnetic equator). This star poses a realchallenge to theories of chemical peculiarity. Based on observationscollected at the European Southern Observatory, La Silla, Chile.
| Sixth Catalogue of Fundamental Stars (FK6). Part III. Additional fundamental stars with direct solutions
The FK6 is a suitable combination of the results of the HIPPARCOSastrometry satellite with ground-based data, measured over a longinterval of time and summarized mainly in the FK5. Part III of the FK6(abbreviated FK6(III)) contains additional fundamental stars with directsolutions. Such direct solutions are appropriate for single stars or forobjects which can be treated like single stars. Part III of the FK6contains in total 3272 stars. Their ground-based data stem from thebright extension of the FK5 (735 stars), from the catalogue of remainingSup stars (RSup, 732 stars), and from the faint extension of the FK5(1805 stars). From the 3272 stars in Part III, we have selected 1928objects as "astrometrically excellent stars", since their instantaneousproper motions and their mean (time-averaged) ones do not differsignificantly. Hence most of the astrometrically excellent stars arewell-behaving "single-star candidates" with good astrometric data. Thesestars are most suited for high-precision astrometry. On the other hand,354 of the stars in Part III are Δμ binaries in the sense ofWielen et al. (1999). Many of them are newly discovered probablebinaries with no other hitherto known indication of binarity. The FK6gives, besides the classical "single-star mode" solutions (SI mode),other solutions which take into account the fact that hidden astrometricbinaries among "apparently single-stars" introduce sizable "cosmicerrors" into the quasi-instantaneously measured HIPPARCOS proper motionsand positions. The FK6 gives, in addition to the SI mode, the "long-termprediction (LTP) mode" and the "short-term prediction (STP) mode". TheseLTP and STP modes are on average the most precise solutions forapparently single stars, depending on the epoch difference with respectto the HIPPARCOS epoch of about 1991. The typical mean error of anFK6(III) proper motion in the single-star mode is 0.59 mas/year. This isa factor of 1.34 better than the typical HIPPARCOS errors for thesestars of 0.79 mas/year. In the long-term prediction mode, in whichcosmic errors are taken into account, the FK6(III) proper motions have atypical mean error of 0.93 mas/year, which is by a factor of about 2better than the corresponding error for the HIPPARCOS values of 1.83mas/year (cosmic errors included).
| 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.
| Loss of angular momentum of magnetic Ap stars in the pre-main sequence phase
A model for rotation evolution of an intermediate mass star with theprimordial magnetic field in the pre-main sequence (PMS) phase wasdeveloped. It takes into account the accretion of matter along themagnetic field lines, the stellar field-disk interaction and amagnetized wind. Variations of stellar moment of inertia were includedbased on evolutionary models of PMS evolution of such stars. Stellarmass and magnetic moment were assumed constant during the PMS evolution.Values of the parameters describing the strength of the magnetic field,accretion rate and mass loss rate were taken from observations. Inaddition, the life time of the disk was varied. An equation describingthe evolution of the rotation rate of a magnetic PMS star was derivedand solved for different stellar masses. The results indicate that theinteraction of the stellar ymagnetic field with circumstellarenvironment wipes out quickly a memory of the initial rotation period.The ZAMS period depends solely on the details of this interaction.Accretion spins up a star early in its PMS life and if the diskdisappears right after that the star may keep its faster rotation untilZAMS and appear there as a Be star. A wide variety of parametersdescribing the evolution of stellar AM results in typical ZAMS rotationperiods of magnetic stars several times longer than of normal stars.This agrees well with the observations. Under special circumstances astar can reach an exceptionally long rotation period of several years(up to 100 years). This requires a long PMS life time, an existence of adisk for only a part of the PMS phase and the wind in the strongmagnetic field existing for the rest of the PMS life. The observationsconfirm indeed that extremely slowly rotating Ap stars are lower massstars with strong magnetic fields.
| Do the physical properties of Ap binaries depend on their orbital elements?
We reveal sufficient evidence that the physical characteristics of Apstars are related to binarity. The Ap star peculiarity [represented bythe Δ(V1-G) value and magnetic field strength] diminishes witheccentricity, and it may also increase with orbital period(Porb). This pattern, however, does not hold for largeorbital periods. A striking gap that occurs in the orbital perioddistribution of Ap binaries at 160-600d might well mark a discontinuityin the above-mentioned behaviour. There is also an interestingindication that the Ap star eccentricities are relatively lower thanthose of corresponding B9-A2 normal binaries for Porb>10d.All this gives serious support to the pioneering idea of Abt &Snowden concerning a possible interplay between the magnetism of Apstars and their binarity. Nevertheless, we argue instead in favour ofanother mechanism, namely that it is binarity that affects magnetism andnot the opposite, and suggest the presence of a newmagnetohydrodynamical mechanism induced by the stellar companion andstretching to surprisingly large Porb.
| Why are magnetic AP stars slowly rotating?
Observational data on rotation of Ap stars suggest that the bulk oftheir rotation rates orm a separate Maxwellian distribution with anaverage value 3-4 times lower than the normal star distribution. Noevidences for a significant angular momentum (AM) loss on the mainsequence (MS) have been found. It is thus concluded that Ap stars mustlose a large fraction of their initial angular momentum (AM) in thepre-MS phase of evolution, most probably as a result of the interactionof their primordial magnetic fields with accretion disks and stellarwinds. The observationally most acceptable values of accretion rate fromthe disk, 10^(-8) M_(Sun)/year, of mass loss rate via a magnetized wind,10^(-8) M_(Sun)/year, and of the surface magnetic field, 1 kG on theZAMS, result in the AM loss in full agreement with observations. Thereexists a separate group of extremely slowly rotating Ap stars, withperiods of the order of 10-100 years. They are too numerous to come fromthe distribution describing the bulk of Ap stars. It is conjectured thattheir extremely low rotation rates are the result of additional AM losson the MS.
| 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.
| Do SI stars undergo any rotational braking?
The old question of rotational braking of Ap Si stars is revisited onthe empirical side, taking advantage of the recent Hipparcos results.Field stars with various evolutionary states are considered, and it isshown that the loose correlation between their rotational period andtheir surface gravity is entirely compatible with conservation ofangular momentum. No evidence is found for any loss of angular momentumon the Main Sequence, which confirms earlier results based on lessreliable estimates of surface gravity. The importance of reliable,fundamental T_eff determinations of Bp and Ap stars is emphasized. Basedon data from the ESA Hipparcos satellite
| 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.
| The Lambda 6708 Feature in AP Stars
Not Available
| Abundance analysis of roAp stars. I. α Circini.
Based on high resolution, low noise spectroscopy in the spectral regionfrom 4200A to 6700A we derived T_eff_=7900+/-200K, logg=4.2+/-0.15,vsin(i)=12.5(-0.5,+1.5)km/s, and elemental abundances for the rapidlyoscillating (ro)Ap star αCir(HD128898, HR5463). We used thespectrum synthesis and the equivalent width technique and confirmed thepresence of a magnetic field in αCir. The underabundance of C, N,and O, and the overabundances of rare-earth and some other heavyelements are comparable to other cool Ap-stars. The most importantpeculiarity is that of Co, which is almost as overabundant as Cr, themost overabundant iron peak element in cool Ap-stars.
| Photometric Examination of CP2-Peculiarity for HD200405, HR44, HR7752 and HR9092
Not Available
| The Relation between Rotational Velocities and Spectral Peculiarities among A-Type Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJS...99..135A&db_key=AST
| Ca II H and K Filter Photometry on the UVBY System. II. The Catalog of Observations
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....109.2828T&db_key=AST
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
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Osservazione e dati astrometrici
| Costellazione: | Sagittario |
| Ascensione retta: | 19h51m50.60s |
| Declinazione: | -39°52'28.0" |
| Magnitudine apparente: | 5.33 |
| Distanza: | 103.95 parsec |
| Moto proprio RA: | 19.7 |
| Moto proprio Dec: | -13.2 |
| B-T magnitude: | 5.255 |
| V-T magnitude: | 5.31 |
Cataloghi e designazioni:
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INHABITED SKY
