The Period and the Cause of Variability of the Magnetic Ap Star V473 Tauri
The ground based UBV observations and Hipparcos Hp magnitudes of thiswell known magnetic variable are analyzed. The period of the star'slight variation is improved. The improved value, accounting for theavailable photometric data from the 1963--1964 Lowell observations ofRakosch to the 1990--1993 Hp magnitudes, is equal to1.4068541±0.0000029 d. The effective temperature and bolometriccorrection are then derived from the de-reddened B-V color index and thestar is plotted in the theoretical H--R diagram using the luminosityobtained from the Hipparcos parallax. Finally, the cause of variabilityof V473 Tau is discussed in terms of two propositions: (1) the obliquerotator model, and (2) pulsation in a high radial-order g-mode. Hitherto unpublished UBV photometry of V473 Tau is presented in theAppendix.
|
Evolutionary state of magnetic chemically peculiar stars
Context: .The photospheres of about 5-10% of the upper main sequencestars exhibit remarkable chemical anomalies. Many of these chemicallypeculiar (CP) stars have a global magnetic field, the origin of which isstill a matter of debate. Aims: .We present a comprehensivestatistical investigation of the evolution of magnetic CP stars, aimedat providing constraints to the theories that deal with the origin ofthe magnetic field in these stars. Methods: .We have collectedfrom the literature data for 150 magnetic CP stars with accurateHipparcos parallaxes. We have retrieved from the ESO archive 142 FORS1observations of circularly polarized spectra for 100 stars. From thesespectra we have measured the mean longitudinal magnetic field, anddiscovered 48 new magnetic CP stars (five of which belonging to the rareclass of rapidly oscillating Ap stars). We have determined effectivetemperature and luminosity, then mass and position in the H-R diagramfor a final sample of 194 magnetic CP stars. Results: .We foundthat magnetic stars with M > 3 ~M_ȯ are homogeneouslydistributed along the main sequence. Instead, there are statisticalindications that lower mass stars (especially those with M ≤2~M_ȯ) tend to concentrate in the centre of the main sequence band.We show that this inhomogeneous age distribution cannot be attributed tothe effects of random errors and small number statistics. Our datasuggest also that the surface magnetic flux of CP stars increases withstellar age and mass, and correlates with the rotation period. For starswith M > 3~M_ȯ, rotation periods decrease with age in a wayconsistent with the conservation of the angular momentum, while for lessmassive magnetic CP stars an angular momentum loss cannot be ruledout. Conclusions: .The mechanism that originates and sustains themagnetic field in the upper main sequence stars may be different in CPstars of different mass.
|
Catalogue of 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
|
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
|
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.
|
A new list of effective temperatures of chemically peculiar stars. II.
Not Available
|
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.
|
Radii and space orientation of the rotational axes of AP stars
The inclination of the rotation axis to the line of sight (i) has beendetermined for a carefully selected sample of Ap stars with reliablevalues of periods of rotation, and values of the stellar radius (R)times sin i have been compared with values of normal main-sequencestars. The findings that none of the obtained R x sin i values aresignificantly larger than the upper limit for the radius of a mainsequence stars and that the mean radius of Ap stars is close to thenormal main sequence value suggest that most Ap stars are main-sequenceobjects. The observed i distribution implies that the distribution ofthe rotational axes of Ap stars in space is random.
|
On the Effective Temperatures of Chemically Peculiar Stars
Not Available
|
Statistical Investigation of Chemically Peculiar Stars - Part One - the Stars with Known Periods
Not Available
|
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.
|
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.
|
IAU Archives of Unpublished Observations of Variable Stars
Not Available
|
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.
|
List of 333 variable, microvariable or suspected variable stars detected in the Geneva photometry
A list is presented of 333 stars, excluded from the GCVS and itssupplements, whose probability of variability ranges from high tocertain. The standard deviations observed in the V magnitude togetherwith the known spectral types, however, only allow speculation as to thetype of variable in question pending supplementary observations whichreveal the individual characteristics of these stars.
|
Is There a Magnetic Field - Period Relation for the Hotter Ap Stars?
Not Available
|
Catalogue of photometric data related to surface magnetic fields for B-type stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1980A&AS...41..111C&db_key=AST
|
On the intrinsic rotation of magnetic variables
It is observed that the rotational velocities of most Ap stars aredependent on their masses. Deviations from this general rule may beexplained in terms of multiplicity which affects the derived colors andradii. Spectroscopic binaries are found to have lower rotationalvelocities than the corresponding single Ap stars. The slope of therelationship between intrinsic rotational velocity and color indexappears to be the same for both single stars and binaries. Only in thecase of spectroscopic binaries is there a zero point shift. Associatedperiods of 4.23 and 2.675 days for HD 140728 and 140160, respectively,are suggested. The 34 kG star, HD 215441, is possibly a spectroscopicbinary seen pole-on.
|
Lichtelektrische Beobachtungen von 14 Ap-Sterne.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1978A&AS...31...83R&db_key=AST
|
Line identification list for the Ap star HD 215038.
Abstract image available at:http://adsabs.harvard.edu/abs/1977PASP...89..770R
|
A photoelectric parameter of the peculiarity of the AP stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1976A&AS...26...49H&db_key=AST
|
Photometry of peculiar A stars.
Not Available
|
The radii of the Ap stars.
Abstract image available at:http://adsabs.harvard.edu/abs/1974A&A....34..153S
|
UBV photometry of four magnetic stars
Abstract image available at:http://adsabs.harvard.edu/abs/1974AJ.....79..124W
|
Photoelectric observations of magnetic stars. V. HD 140728, HD 215038, and HD 215441.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1973AJ.....78..734B&db_key=AST
|
On the light variation of peculiar A-type stars.
Abstract image available at:http://adsabs.harvard.edu/abs/1973A&A....26..385K
|
INHABITED SKY
