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Statistical Constraints for Astrometric Binaries with Nonlinear Motion
Useful constraints on the orbits and mass ratios of astrometric binariesin the Hipparcos catalog are derived from the measured proper motiondifferences of Hipparcos and Tycho-2 (Δμ), accelerations ofproper motions (μ˙), and second derivatives of proper motions(μ̈). It is shown how, in some cases, statistical bounds can beestimated for the masses of the secondary components. Two catalogs ofastrometric binaries are generated, one of binaries with significantproper motion differences and the other of binaries with significantaccelerations of their proper motions. Mathematical relations betweenthe astrometric observables Δμ, μ˙, and μ̈ andthe orbital elements are derived in the appendices. We find a remarkabledifference between the distribution of spectral types of stars withlarge accelerations but small proper motion differences and that ofstars with large proper motion differences but insignificantaccelerations. The spectral type distribution for the former sample ofbinaries is the same as the general distribution of all stars in theHipparcos catalog, whereas the latter sample is clearly dominated bysolar-type stars, with an obvious dearth of blue stars. We point outthat the latter set includes mostly binaries with long periods (longerthan about 6 yr).
| Some Comments on the Magnetic Braking of CP Stars
The low rotation velocities of magnetic CP stars are discussed.Arguments against the involvement of the magnetic field in the loss ofangular momentum are given: (1) the fields are not strong enough inyoung stars in the stage of evolution prior to the main sequence; (2)there is no significant statistical correlation between the magneticfield strength and the rotation period of CP stars; (3) stars with shortperiods have the highest fields; (4) a substantial number of stars withvery low magnetic fields (B e P>25 days, which form 12% of the total,probably lie at the edge of the velocity distribution for low massstars. All of these properties conflict with the hypothesis of magneticbraking of CP stars.
| 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
| 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
| Are Stellar Rotational Axes Distributed Randomly?
Stellar line widths yield values of Vsini, but the equatorial rotationalvelocities, V, cannot be determined for individual stars withoutknowledge of their inclinations, i, relative to the lines of sight. Forlarge numbers of stars we usually assume random orientations ofrotational axes to derive mean values of V, but we wonder whether thatassumption is valid. Individual inclinations can be derived only inspecial cases, such as for eclipsing binaries where they are close to90° or for chromospherically active late-type dwarfs or spotted(e.g., Ap) stars where we have independent information about therotational periods. We consider recent data on 102 Ap stars for whichCatalano & Renson compiled rotational periods from the literatureand Abt & Morrell (primarily) obtained measures of Vsini. We findthat the rotational axes are oriented randomly within the measuringerrors. We searched for possible dependence of the inclinations onGalactic latitude or longitude, and found no dependence.
| Speckle Interferometry of New and Problem Hipparcos Binaries. II. Observations Obtained in 1998-1999 from McDonald Observatory
The Hipparcos satellite made measurements of over 9734 known doublestars, 3406 new double stars, and 11,687 unresolved but possible doublestars. The high angular resolution afforded by speckle interferometrymakes it an efficient means to confirm these systems from the ground,which were first discovered from space. Because of its coverage of adifferent region of angular separation-magnitude difference(ρ-Δm) space, speckle interferometry also holds promise toascertain the duplicity of the unresolved Hipparcos ``problem'' stars.Presented are observations of 116 new Hipparcos double stars and 469Hipparcos ``problem stars,'' as well as 238 measures of other doublestars and 246 other high-quality nondetections. Included in these areobservations of double stars listed in the Tycho-2 Catalogue andpossible grid stars for the Space Interferometry Mission.
| Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521
| 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
| Speckle Interferometry of New and Problem HIPPARCOS Binaries
The ESA Hipparcos satellite made measurements of over 12,000 doublestars and discovered 3406 new systems. In addition to these, 4706entries in the Hipparcos Catalogue correspond to double star solutionsthat did not provide the classical parameters of separation and positionangle (rho,theta) but were the so-called problem stars, flagged ``G,''``O,'' ``V,'' or ``X'' (field H59 of the main catalog). An additionalsubset of 6981 entries were treated as single objects but classified byHipparcos as ``suspected nonsingle'' (flag ``S'' in field H61), thusyielding a total of 11,687 ``problem stars.'' Of the many ground-basedtechniques for the study of double stars, probably the one with thegreatest potential for exploration of these new and problem Hipparcosbinaries is speckle interferometry. Results are presented from aninspection of 848 new and problem Hipparcos binaries, using botharchival and new speckle observations obtained with the USNO and CHARAspeckle cameras.
| On the HIPPARCOS photometry of chemically peculiar B, A, and F stars
The Hipparcos photometry of the Chemically Peculiar main sequence B, A,and F stars is examined for variability. Some non-magnetic CP stars,Mercury-Manganese and metallic-line stars, which according to canonicalwisdom should not be variable, may be variable and are identified forfurther study. Some potentially important magnetic CP stars are noted.Tables 1, 2, and 3 are available only in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Effective temperatures of AP stars
A new method of determination of the effective temperatures of Ap starsis proposed. The method is based on the fact that the slopes of theenergy distribution in the Balmer continuum near the Balmer jump for``normal" main sequence stars and chemically peculiar stars with thesame Teff are identical. The effective temperaturecalibration is based on a sample of main sequence stars with well knowntemperatures (\cite[Sokolov 1995]{sokolov}). It is shown that theeffective temperatures of Ap stars are derived by this method in goodagreement with those derived by the infrared flux method and by themethod of \cite[Stepien & Dominiczak (1989)]{stepien}. On the otherhand, the comparison of obtained Teff with Teffderived from the color index (B2-G) of Geneva photometry shows a largescatter of the points, nevertheless there are no systematicaldifferences between two sets of the data.
| The observed periods of AP and BP stars
A catalogue of all the periods up to now proposed for the variations ofCP2, CP3, and CP4 stars is presented. The main identifiers (HD and HR),the proper name, the variable-star name, and the spectral type andpeculiarity are given for each star as far as the coordinates at 2000.0and the visual magnitude. The nature of the observed variations (light,spectrum, magnetic field, etc.) is presented in a codified way. Thecatalogue is arranged in three tables: the bulk of the data, i.e. thosereferring to CP2, CP3, and CP4 stars, are given in Table 1, while thedata concerning He-strong stars are given in Table 2 and those foreclipsing or ellipsoidal variables are collected in Table 3. Notes arealso provided at the end of each table, mainly about duplicities. Thecatalogue contains data on 364 CP stars and is updated to 1996, October31. This research has made use of the SIMBAD database, operated at CDS,Strasbourg, France.
| Towards a fundamental calibration of stellar parameters of A, F, G, K dwarfs and giants
I report on the implementation of the empirical surface brightnesstechnique using the near-infrared Johnson broadband { (V-K)} colour assuitable sampling observable aimed at providing accurate effectivetemperatures of 537 dwarfs and giants of A-F-G-K spectral-type selectedfor a flux calibration of the Infrared Space Observatory (ISO). Thesurface brightness-colour correlation is carefully calibrated using aset of high-precision angular diameters measured by moderninterferometry techniques. The stellar sizes predicted by thiscorrelation are then combined with the bolometric flux measurementsavailable for a subset of 327 ISO standard stars in order to determineone-dimensional { (T, V-K)} temperature scales of dwarfs and giants. Theresulting very tight relationships show an intrinsic scatter induced byobservational photometry and bolometric flux measurements well below thetarget accuracy of +/- 1 % required for temperature determinations ofthe ISO standards. Major improvements related to the actual directcalibration are the high-precision broadband { K} magnitudes obtainedfor this purpose and the use of Hipparcos parallaxes for dereddeningphotometric data. The temperature scale of F-G-K dwarfs shows thesmallest random errors closely consistent with those affecting theobservational photometry alone, indicating a negligible contributionfrom the component due to the bolometric flux measurements despite thewide range in metallicity for these stars. A more detailed analysisusing a subset of selected dwarfs with large metallicity gradientsstrongly supports the actual bolometric fluxes as being practicallyunaffected by the metallicity of field stars, in contrast with recentresults claiming somewhat significant effects. The temperature scale ofF-G-K giants is affected by random errors much larger than those ofdwarfs, indicating that most of the relevant component of the scattercomes from the bolometric flux measurements. Since the giants have smallmetallicities, only gravity effects become likely responsible for theincreased level of scatter. The empirical stellar temperatures withsmall model-dependent corrections are compared with the semiempiricaldata by the Infrared Flux Method (IRFM) using the large sample of 327comparison stars. One major achievement is that all empirical andsemiempirical temperature estimates of F-G-K giants and dwarfs are foundto be closely consistent between each other to within +/- 1 %. However,there is also evidence for somewhat significant differential effects.These include an average systematic shift of (2.33 +/- 0.13) % affectingthe A-type stars, the semiempirical estimates being too low by thisamount, and an additional component of scatter as significant as +/- 1 %affecting all the comparison stars. The systematic effect confirms theresults from other investigations and indicates that previousdiscrepancies in applying the IRFM to A-type stars are not yet removedby using new LTE line-blanketed model atmospheres along with the updatedabsolute flux calibration, whereas the additional random component isfound to disappear in a broadband version of the IRFM using an infraredreference flux derived from wide rather than narrow band photometricdata. Table 1 and 2 are only available in the electronic form of thispaper
| 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
| 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
| The Tokyo PMC catalog 90-93: Catalog of positions of 6649 stars observed in 1990 through 1993 with Tokyo photoelectric meridian circle
The sixth annual catalog of the Tokyo Photoelectric Meridian Circle(PMC) is presented for 6649 stars which were observed at least two timesin January 1990 through March 1993. The mean positions of the starsobserved are given in the catalog at the corresponding mean epochs ofobservations of individual stars. The coordinates of the catalog arebased on the FK5 system, and referred to the equinox and equator ofJ2000.0. The mean local deviations of the observed positions from theFK5 catalog positions are constructed for the basic FK5 stars to comparewith those of the Tokyo PMC Catalog 89 and preliminary Hipparcos resultsof H30.
| Evolutionary estimates for 10 magnetic AP stars calculated from their rigid rotator geometries.
I present estimates of the evolutionary states (effective temperatures,masses, radii, luminosities and ages) of 10 magnetic Ap stars, andsubsequent constraints on the evolution of magnetic fields in theseobjects. Using rotational axis inclinations (sin i) reported by Leroy etal. (1996A&A...311..513L), combined with apparent rotationalvelocities (vsin i) and rotational periods (P_rot_) obtained from avariety of sources, the radii of these stars have been calculatedassuming rigid rotation. From the positions of these objects in theradius-effective temperature (log(R/Rsun_)-log(T_eff_)) planeI obtain their evolutionary states using the model evolutionarycalculations by Schaller et al. (1992A&AS...96..269S). The stars inthis study span the entire width of the main sequence, showing notendancy to cluster near the ZAMS or the TAMS. In this respect theseresults are consistent with the conclusion of North(1993IAUCo.138..577N) (who reports that the Ap (CP2) stars appear to bedistributed uniformly along the width of the main sequence) andinconsistent with that of Hubrig & Mathys (1994AN....315..343H) (whosuggest that the magnetic Ap stars may be near the end of their mainsequence life). When the magnetic field strengths of these stars aregraphed versus the fraction of main sequence evolution completed, nocorrelation is evident. However, it is of interest to note that strongmagnetic fields do exist in Ap stars at all evolutionary states (fromthe ZAMS to the TAMS), and that more than 70% of the stars discussed inthis paper have polar magnetic field strengths between 3 and 6kG. Asimilar graph of the magnetic axis obliquity angle β of each starversus age shows that intermediate values of β exist for stars asold as 10^9^yr. This indicates that, if β does evolve towardasymptotic values as suggested by Mestel et al. (1981MNRAS.195..979M),the timescale for this evolution is quite long, at least for stars with~5kG surface magnetic fields and rotational periods near 10 days.
| The Pulkovo Spectrophotometric Catalog of Bright Stars in the Range from 320 TO 1080 NM
A spectrophotometric catalog is presented, combining results of numerousobservations made by Pulkovo astronomers at different observing sites.The catalog consists of three parts: the first contains the data for 602stars in the spectral range of 320--735 nm with a resolution of 5 nm,the second one contains 285 stars in the spectral range of 500--1080 nmwith a resolution of 10 nm and the third one contains 278 stars combinedfrom the preceding catalogs in the spectral range of 320--1080 nm with aresolution of 10 nm. The data are presented in absolute energy unitsW/m(2) m, with a step of 2.5 nm and with an accuracy not lower than1.5--2.0%.
| The Stellar Content of Star Stream I
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....111.1615E&db_key=AST
| Linear polarimetry of AP stars. VI. A modified dipolar model consistent with the observations.
While some Ap variables display a linear polarization variation verysimilar to that computed for a pure magnetic dipole, several Ap starsshow conspicuous peculiarities which must be interpreted in terms ofdepartures from the standard, oblique rotator model (we have shownpreviously that abundances anomalies are not sufficient to explain oddpolarization diagrams). We have designed an inversion method, based on aresidues minimization process, which allows us to build the map of themagnetic peculiarities at the surface of non-dipolar stars. As thelinear polarization is but weakly sensitive to the variations of thefield modulus, we interpret the polarization anomalies in terms ofinclination changes of the lines of force within their meridian plane.Keeping the magnetic equator as a plane of symmetry, we show that it issufficient to assume slightly expanded lines of force, over some partsof the magnetic equator, to explain most peculiar polarization curves(Figs. 2 to 7). Such regions, where the lines of force expand outwards,seem to occur preferentially in the vicinity of the rotation poles forthose stars having a β angle not far from 90deg. In the case ofβ CrB, which was studied previously in detail (Leroy, 1995), thisregion nearly coincides with the equatorial patch of enhanced fieldstrength, which must be postulated to explain the surface fieldmeasurements. The present study, which also provides unambiguousdeterminations of the i and β angles for 15 stars, marks theprovisional end of our investigation based on broadband linearpolarization measurements. We expect that similar measurements, having agood spectral resolution, will be available soon: they will yield moresevere observational constraints enabling a more detailed modeling work.However, we think that the series of articles which ends with thepresent paper has demonstrated the great value of linear polarizationdata and may have opened fruitful research tracks bearing on themagnetic structure of Ap stars.
| The Relation between Rotational Velocities and Spectral Peculiarities among A-Type Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJS...99..135A&db_key=AST
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| Linear polarimetry of AP stars. V. A general catalogue of measurements.
A systematic program of broadband linear polarimetry, bearing on 55 Apstars, has been developed during the 4 last years, at the Pic du MidiObservatory. While separate data have been already published, we presentin this paper a complete catalogue of our observational material,including more than 400 measurements. We complement these data withanother 100 measurements, obtained previously by other authors, so as toget a synthetic view of the phenomenon. Most of the observations havebeen dedicated to a small number (15) of stars, which show conspicuouschanges of the linear polarization, so that it is possible to knowaccurately the time variation of the Stokes parameters: we expect thatthese new data will really improve our knowledge of the magneticconfiguration, after a proper analysis which is currently beingdeveloped. For the other 40 stars, the polarization is either too small,or strongly contaminated by the interstellar polarization, so thatbroadband polarimetry is not very effective. Anyway, this firstsystematic investigation on the linear polarization of Ap stars will bea useful starting point for future measurements which should be madewith higher spectral resolution. Finally, our measurements have providednew determinations of the rotation period for several stars.
| A new list of effective temperatures of chemically peculiar stars. II.
Not Available
| Linear polarimetry of AP stars. II - New observations with a reappraisal of former ones
We have presented, in a previous paper, a canonical model which helpsone to understand the intrinsic linear polarization measured in thelight of magnetic Ap stars. This linear polarization, which provides atracer of the magnetic field component perpendicular to the line ofsight, can be observed in broad spectral regions, and it has beenactually observed in several stars. Such measurements can provide usefulinformation on the magnetism of Ap stars only when they sample correctlythe whole rotation period of the object under study. Up to now, thiscondition had been fulfilled only in the case of HD 65339; in othercases, a more limited amount of data was available. Adding our newobservations has enabled a first detailed analysis of HD 137909, HD 71866 and HD 115708; in particular, we can decide which of the angle i(between the line of sight and the rotation axis) and beta (between therotation axis and the magnetic axis) is larger. Altogether, this papercontains a general review on all existing measurements and acomprehensive investigation on the linear polarization of four Ap starsbased on previous observations and on our new measurements. Thecomparison of this observational material with the previouslyestablished model shows the capabilities and the limits of this methodof study of Ap stars.
| Fifth fundamental catalogue. Part 2: The FK5 extension - new fundamental stars
The mean positions and proper motions for 3117 new fundamental starsessentially in the magnitude range about 4.5 to 9.5 are given in thisFK5 extension. Mean apparent visual magnitude is 7.2 and is on average2.5 magnitudes fainter then the basic FK5 which has a mean magnitude of4.7. (The basic FK5 gives the mean positions and proper motions for theclassical 1535 fundamental stars). The following are discussed: theobservational material, reduction of observations, star selection, andthe system for the FK5 extension. An explanation and description of thecatalog are given. The catalog of 3117 fundamental stars for the equinoxand epoch J2000.0 and B1950.0 is presented. The parallaxes and radialvelocities for 22 extension stars with large forecasting effects aregiven. Catalogs used in the compilation of the FK5 fundamental catalogare listed.
| The correction in right ascension of 508 stars determinated with PMO photoelectric transit instrument.
Not Available
| Second supplement to the catalogue of observed periods of AP stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1991A&AS...87...59C&db_key=AST
| On the origin of the statistical correlation between rotation periods and apparent radii for CP 2 stars
Apparent rotational velocities and rotation periods for CP 2 stars areused to study the 'apparent' radius distribution of R sin i. It impliesa distribution for the radii of CP 2 stars which is almost normal fortheir temperatures when compared to main sequence stars. However, astatistical correlation exists between rotation period P and R sin i. Itis argued that, at least in the case of silicon stars, neitherconservation of angular momentum on the main sequence, nor bias in themeasured v sin i values are able to induce a correlation of the observedstrength. Thus, one has to postulate either additional rotationalbraking depending statistically on R, or a detection bias dependingstatistically on i. It is shown that the correlation might be explainedin both ways and the implications of each possibility are discussed.
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הכנס מאמר חדש
לינקים קשורים
הכנס לינק חדש
משמש של הקבוצה הבאה
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | אנדרומדה |
| התרוממות ימנית: | 00h50m18.30s |
| סירוב: | +45°00'08.0" |
| גודל גלוי: | 6.15 |
| מרחק: | 90.827 פארסק |
| תנועה נכונה: | 63 |
| תנועה נכונה: | 5 |
| B-T magnitude: | 6.172 |
| V-T magnitude: | 6.124 |
קטלוגים וכינוים:
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