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Evolutionary state of magnetic chemically peculiar stars
Context: .The photospheres of about 5-10% of the upper main sequencestars exhibit remarkable chemical anomalies. Many of these chemicallypeculiar (CP) stars have a global magnetic field, the origin of which isstill a matter of debate. Aims: .We present a comprehensivestatistical investigation of the evolution of magnetic CP stars, aimedat providing constraints to the theories that deal with the origin ofthe magnetic field in these stars. Methods: .We have collectedfrom the literature data for 150 magnetic CP stars with accurateHipparcos parallaxes. We have retrieved from the ESO archive 142 FORS1observations of circularly polarized spectra for 100 stars. From thesespectra we have measured the mean longitudinal magnetic field, anddiscovered 48 new magnetic CP stars (five of which belonging to the rareclass of rapidly oscillating Ap stars). We have determined effectivetemperature and luminosity, then mass and position in the H-R diagramfor a final sample of 194 magnetic CP stars. Results: .We foundthat magnetic stars with M > 3 ~M_ȯ are homogeneouslydistributed along the main sequence. Instead, there are statisticalindications that lower mass stars (especially those with M ≤2~M_ȯ) tend to concentrate in the centre of the main sequence band.We show that this inhomogeneous age distribution cannot be attributed tothe effects of random errors and small number statistics. Our datasuggest also that the surface magnetic flux of CP stars increases withstellar age and mass, and correlates with the rotation period. For starswith M > 3~M_ȯ, rotation periods decrease with age in a wayconsistent with the conservation of the angular momentum, while for lessmassive magnetic CP stars an angular momentum loss cannot be ruledout. Conclusions: .The mechanism that originates and sustains themagnetic field in the upper main sequence stars may be different in CPstars of different mass.
| Magnetic Field and Chemical Composition of the Peculiar Star HD 10221
We analyzed the chemical composition of the chemically peculiar (CP)star HD 0221=43 Cas using spectra taken with the NES spectrograph of the6-m telescope with a spectral resolution of 45 000. The Hβ lineprofile corresponds most closely to T eff = 11 900 K and log g = 3.9.The rotational velocity is v e sin i = 27 ± 2 km s-1, and themicroturbulence is ξ t = 1 km s-1. The results of our abundancedetermination by the method of synthetic spectra show that the star haschemical anomalies typical of SrCrEu stars, although its effectivemagnetic field is weak, B e < 100 G. For silicon, we obtained anabundance distribution in atmospheric depth with a sharp jump of 1.5 dexat an optical depth of log τ 5000 = -0.3 and with siliconconcentration in deep atmospheric layers. Similar distributions werefound in the atmospheres of cooler stars with strong and weak magneticfields. A comparison of the chemical peculiarities in HD 10221 withknown CP stars with magnetic fields of various strengths leads us toconclude that a low rotational velocity rather than amagnetic field isthe determining factor in the formation mechanism of chemical anomaliesin the atmospheres of CP stars.
| A catalog of stellar magnetic rotational phase curves
Magnetized stars usually exhibit periodic variations of the effective(longitudinal) magnetic field Be caused by their rotation. Wepresent a catalog of magnetic rotational phase curves, Be vs.the rotational phase φ, and tables of their parameters for 136stars on the main sequence and above it. Phase curves were obtained bythe least squares fitting of sine wave or double wave functions to theavailable Be measurements, which were compiled from theexisting literature. Most of the catalogued objects are chemicallypeculiar A and B type stars (127 stars). For some stars we also improvedor determined periods of their rotation. We discuss the distribution ofparameters describing magnetic rotational phase curves in our sample.All tables and Appendix A are only available in electronic form athttp://www.edpsciences.org
| Possible Variability of the Magnetic Field of T Tau
Using the Main Stellar Spectrograph of the 6-m Special AstrophysicalObservatory telescope equipped with a polametric analyzer, we measuredthe longitudinal magnetic field component B|| for the T Tauristars T Tau and AS 507 on January 16 and 18 and February 15, 2003. Forboth stars, we determined only the upper limits on B|| fromphotospheric lines: +15 +/- 30 G for T Tau and -70 +/- 90 G for AS 507.The magnetic field of AS 507 was not measured previously, whileB|| for T Tau is lower than its values that we obtained in1996 and 2002 (B|| = 150 +/- 50 G), suggesting that thelongitudinal magnetic field component in the photosphere of T Tau isvariable. We also measured the longitudinal magnetic field component forT Tau in the formation region of the He I 5876 A emission line. We foundB|| in this region to be equal to +650, +350, and +1100 G onJanuary 16, 18, and February 15, 2003, respectively. Our observations onJanuary 18 and February 15 correspond to virtually the same phase of thestar's rotation period, but the profiles of the He I 5876 A line differmarkedly on these two nights. Therefore, we believe that the threefolddifference between the B|| values on these nights does notresult from observational errors. We discuss the possible causes of theB|| variability in the photosphere and the magnetosphere of TTau.
| 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
| Measurement of the Longitudinal Magnetic-Field Component for FU Ori
The Main Stellar Spectrograph of the 6-m Special AstrophysicalObservatory telescope equipped with a polarimetric analyzer was used tomeasure the longitudinal magnetic-field component of FU Ori on January24, 2002. The following (3 sigma) upper limits were obtained for themagnetic field B||: B|| < 350-400 G in the formation region of Fe I,Ni I, and Ca I absorption lines (disk + wind), and B|| < 200 G in theformation region of the absorption component of the H_alpha line with aP Cyg profile. We conclude that the strength of a large-scale magneticfield capable of collimating the disk wind does not exceed 300 G. Forthe region where the emission component of the H_alpha line is formed,we found that B|| < 100 G. Such a low value may have been obtainedbecause the magnetic field lines in this region were almostperpendicular to the line of sight at the time of our observations.
| Possible detection of a magnetic field in T Tauri
Medium-resolution (R =~ 15 000) circular spectropolarimetry of T Tauriis presented. The star was observed twice: on November 11, 1996 andJanuary 22, 2002. Weak circular polarization was found in photosphericabsorption lines, indicating a mean surface longitudinal magnetic fieldB| of 160+/- 40 G and 140+/- 50 G at the epoch of the firstand second observations respectively. While these values are near thedetection limit of our apparatus, we belive that they are real. One canconclude from our data that B| of T Tau does notsignificantly exceed 200 G, which is much less than surface magneticfield strength of the star (>2.3 kG) found by Guenther et al.(\cite{Guenther99}) and Johns-Krull et al. (\cite{Johns00}). We discusspossible reasons for this difference.
| Investigation of Weakly Magnetic CP Stars. I
The magnetic fields of a sample of chemically peculiar stars, in whichthey had not been detected earlier, are reinvestigated on the basis ofour own measurements and literature data. Despite the considerablyhigher measurement accuracy, again no magnetic fields were detected inany of them. An upper limit on the field of HD 10221 of 40 G wasobtained. Despite the weakness of the fields, the parameterscharacterizing an anomaly in chemical composition correspond to thosefor strong fields. The same parameters in stars with strong fieldsgenerally correspond in value, although they are lower than expected inthe case of HD 47152.
| 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
| On the HIPPARCOS photometry of chemically peculiar B, A, and F stars
The Hipparcos photometry of the Chemically Peculiar main sequence B, A,and F stars is examined for variability. Some non-magnetic CP stars,Mercury-Manganese and metallic-line stars, which according to canonicalwisdom should not be variable, may be variable and are identified forfurther study. Some potentially important magnetic CP stars are noted.Tables 1, 2, and 3 are available only in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| The HR-diagram from HIPPARCOS data. Absolute magnitudes and kinematics of BP - AP stars
The HR-diagram of about 1000 Bp - Ap stars in the solar neighbourhoodhas been constructed using astrometric data from Hipparcos satellite aswell as photometric and radial velocity data. The LM method\cite{luri95,luri96} allows the use of proper motion and radial velocitydata in addition to the trigonometric parallaxes to obtain luminositycalibrations and improved distances estimates. Six types of Bp - Apstars have been examined: He-rich, He-weak, HgMn, Si, Si+ and SrCrEu.Most Bp - Ap stars lie on the main sequence occupying the whole width ofit (about 2 mag), just like normal stars in the same range of spectraltypes. Their kinematic behaviour is typical of thin disk stars youngerthan about 1 Gyr. A few stars found to be high above the galactic planeor to have a high velocity are briefly discussed. Based on data from theESA Hipparcos astrometry satellite and photometric data collected in theGeneva system at ESO, La Silla (Chile) and at Jungfraujoch andGornergrat Observatories (Switzerland). Tables 3 and 4 are onlyavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| The observed periods of AP and BP stars
A catalogue of all the periods up to now proposed for the variations ofCP2, CP3, and CP4 stars is presented. The main identifiers (HD and HR),the proper name, the variable-star name, and the spectral type andpeculiarity are given for each star as far as the coordinates at 2000.0and the visual magnitude. The nature of the observed variations (light,spectrum, magnetic field, etc.) is presented in a codified way. Thecatalogue is arranged in three tables: the bulk of the data, i.e. thosereferring to CP2, CP3, and CP4 stars, are given in Table 1, while thedata concerning He-strong stars are given in Table 2 and those foreclipsing or ellipsoidal variables are collected in Table 3. Notes arealso provided at the end of each table, mainly about duplicities. Thecatalogue contains data on 364 CP stars and is updated to 1996, October31. This research has made use of the SIMBAD database, operated at CDS,Strasbourg, France.
| 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.
| Radio continuum emission from stars: a catalogue update.
An updated version of my catalogue of radio stars is presented. Somestatistics and availability are discussed.
| Catalogue of CP stars with references to short time scale variability
A catalogue was compiled which contains all references in the literaturesince 1962 related to variations of CP stars on time scales shorter thanthe rotation period. The role of this catalogue lies in the unbiasedlisting of all available references, and not in a critical evaluation.
| A new list of effective temperatures of chemically peculiar stars. II.
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| The SVS Numbering Series Discontinued
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| 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.
| A search for the age-dependency of AP star parameters
Some observational data of the sample of the magnetic chemicallypeculiar stars (MCP stars) are investigated statistically. For the MCPstars of spectral types later than A2, both the frequency distributionand the (R) sin i-values suggest the existence of a linear relationbetween stellar diameter and rotation period. The MCP stars of spectraltypes earlier than B9 show an overpopulation of small (R) sin i whichmay indicate the existence of a second group with smaller radius in thissample. The equatorially symmetric rotator is used as the magneticmodel. With respect to its temporal behavior, the effective magneticfield is separated into dipolar and quadrupolar contribution. Both signsof the axisymmetric quadrupole moment appear with equal frequency. Thedipole moment which produces the amplitude of the Beff(t) curve formsfor longer periods two groups which are separated by a distinct gap.Both of the groups exhibit magnetic fields which are the stronger thegreater the stellar radius is, contrary to what is expected forfrozen-in fields. The dominance of magnetic curves without polarityreversal for longer-period stars is in accordance with predictions ofthe dynamo theory.
| The Magnetic Fields and another Parameters of the Chemically Peculiar Stars - Part One
Not Available
| On the Effective Temperatures of Chemically Peculiar Stars
Not Available
| Statistical Investigation of Chemically Peculiar Stars - Part Two - the Stars with the Dispersion of Continuum Spectrum at Lambda 5200A
Not Available
| Statistical Investigation of Chemically Peculiar Stars - Part One - the Stars with Known Periods
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| To the problem of the surface magnetic fields of the chemically peculiar stars.
Not Available
| The rotation of AP stars
Photometric periods of silicon stars belonging to clusters andassociations as well as to the field are discussed in relation withtheories of magnetic braking taking place on the main sequence. It isshown that Si stars do not lose the bulk of their angular momentumduring their main-sequence lifetime, but must have lost it before. Anybraking mechanism which predicts an e-folding time of the order of, orshorter than, the star's lifetime seems ruled out. The theory of purelyhydromagnetic rotational braking is much too efficient to fit theobservations (unless under its earlier form proposed by Kulsrud, 1971),while the accretion theory does not fit them either, although it seemsmore realistic. Preinjection of cosmic rays by means of Ap stars appearsdoubtful.
| Evidence of decay of the magnetic fields of AP stars
Data obtained in the Geneva photometric system (Rufener, 1981) andappropriate calibrations of this system in terms of surface magneticfield and gravity are used to provide, on the basis of 708 field andcluster Ap stars, observational evidence that these stars undergo decayof their magnetic field on an evolutionary timescale. Justifications aregiven for the application of a photometric gravity calibration topeculiar stars. The dependence of the photometrically estimated surfacemagnetic field on gravity is found to differ markedly from availabletheoretical calculations. HgMn stars are found to show the same trend,strengthening the impression that they might be slightly magnetic.He-weak stars do not.
| Magnetic field structure in the Taurus dark cloud
Optical and infrared polarimetry of sources in the direction of theTaurus cloud are obtained in order to study the magnetic field in thiscloud and its possible role in the cloud's evolution. Most of the starsare background giant stars whose light shines through the cloud and ispolarized by the cloud material. The transverse component of themagnetic field, as delineated by the polarization vectors, is generallyperpendicular to the galactic plane, and the stratified structure of thecloud could be due to the effect of the magnetic field during the earlystages of collapse. Three of the 13 embedded stars are stronglypolarized with position angles nearly perpendicular to those of nearbyfield stars. The polarization of these stars is most likely intrinsic,and the direction of polarization indicates that the materialsurrounding these stars may be magnetic i.e., that the magnetic field isfrozen in this material.
| Catalog of observed periods for the AP stars
A preliminary catalog of the Ap stars, taken in the broad sense toinclude many Bp stars, is presented. The HD and HR numbers,variable-star names, spectral types, and proposed periods are listed;the nature of the periodic variability is indicated; and references tothe observations are provided. Companion stars, confirmed spectroscopicbinaries, and anomalies are mentioned in notes.
| Photometric properties of AP stars in the Geneva system
An examination of the properties in some photometric diagrams of morethan 600 Ap stars measured in the Geneva photometric system confirm thatthe Balmer discontinuity is smaller than for normal stars, along withthe link between a proposed peculiarity parameter and both rotationalvelocity and effective magnetic field. It is shown that the peculiarityparameter is sensitive to interstellar reddening, and it is foundthrough examination of the standard deviations for visual magnitudesthat cool CP 2 stars without Eu peculiarity have the greatestamplitudes. Rapid rotators have a mild peculiarity, while positivecorrelation exists for Si and SrCr stars.
| A search for stars with a strong magnetic field
The effective longitudinal magnetic field strength He on ninepeculiar stars with maximal values for their presumed surface field hasbeen measured on Zeeman spectrograms taken with the 6-m telescope. Fourof the stars do exhibit strong fields. The outstanding example is HD147010, whose peak value He = -4480 + or - 440 gauss placesit fifth among stars with the strongest fields known.
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Pozíciós és asztrometriai adatok
| Csillagkép: | Bika |
| Rektaszcenzió: | 04h49m16.00s |
| Deklináció: | +29°34'16.9" |
| Vizuális fényesség: | 7.26 |
| Távolság: | 163.399 parszek |
| RA sajátmozgás: | 7.2 |
| Dec sajátmozgás: | -30.2 |
| B-T magnitude: | 7.371 |
| V-T magnitude: | 7.27 |
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