Садржај
Слике
Уплоадјуј своје слике
DSS Images Other Images
Везани чланци
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.
| Evolution of magnetic fields in stars across the upper main sequence: I. Catalogue of magnetic field measurements with FORS 1 at the VLT
To properly understand the physics of Ap and Bp stars it is particularlyimportant to identify the origin of their magnetic fields. For that, anaccurate knowledge of the evolutionary state of stars that have ameasured magnetic field is an important diagnostic. Previous resultsbased on a small and possibly biased sample suggest that thedistribution of magnetic stars with mass below 3 M_ȯ in the H-Rdiagram differs from that of normal stars in the same mass range (Hubriget al. 2000). In contrast, higher mass magnetic Bp stars may well occupythe whole main-sequence width (Hubrig, Schöller & North 2005b).In order to rediscuss the evolutionary state of upper main sequencemagnetic stars, we define a larger and bias-free sample of Ap and Bpstars with accurate Hipparcos parallaxes and reliably determinedlongitudinal magnetic fields. We used FORS 1 at the VLT in itsspectropolarimetric mode to measure the magnetic field in chemicallypeculiar stars where it was unknown or poorly known as yet. In thisfirst paper we present our results of the mean longitudinal magneticfield measurements in 136 stars. Our sample consists of 105 Ap and Bpstars, two PGa stars, 17 HgMn stars, three normal stars, and nine SPBstars. A magnetic field was for the first time detected in 57 Ap and Bpstars, in four HgMn stars, one PGa star, one normal B-type star and fourSPB stars.
| The diagnosis of the mean quadratic magnetic field of Ap stars
Aims.We assess the validity of the method of determination of the meanquadratic field modulus and we explore its limits. Methods.Weanalyse high spectral resolution, high signal-to-noise spectra of a fewAp stars, and of a superficially normal main-sequence A star, recordedover a broad wavelength range with EMMI at the NTT.Results.Weintroduce a revised form of the regression equation describing thedependence of the second-order moment of the line profiles about theircentre, in natural light, on various parameters of the correspondingtransitions. We show that interpretation of the observed dependencesallows one to determine the mean quadratic magnetic field modulus of thestudied stars, and their v sin i. We explain why the contributions tothe quadratic field of the mean square magnetic field modulus and of themean square longitudinal field cannot in general be disentangled. Forthose stars of the sample that have resolved magnetically split lines,we show that the derived values of the quadratic field are mostlyconsistent with the values of the mean longitudinal magnetic field andof the mean magnetic field modulus at the observed phase. However thereare some hints that they may occasionally slightly underestimate theactual field. This suggests that the method is unlikely to yieldspurious field detections. In addition, we illustrate the importance forthis type of analyses of using, as far as possible, samples of lines ofa single ion, and to specify in the presentation of the results whichion was used.Conclusions.The results presented in this paper lendstrong support to the validity of the quadratic field diagnostic methodto obtain a realistic quantitative characterisation of the magneticfields Ap and related stars.
| 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.
| 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).
| 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
| Radial velocities and axial rotation for a sample of chemically peculiar stars.
As part of a systematic project we have determined radial velocities andprojected rotational velocities for a sample of 186 chemically peculiarstars which have been observed by the Hipparcos' satellite. The purposeis to provide necessary data to study the space velocities of peculiarstars.
| 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.
| The Cape rapidly oscillating AP star survey - III. Null results of searches for high-overtone pulsation.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1994MNRAS.271..129M&db_key=AST
| AP stars with resolved magnetically split lines
New high-resolution spectroscopic observations of Ap stars with resolvedmagnetically split spectral lines are presented. Six new such stars havebeen discovered: HD 2453, HD 9996, HD 18078, HD 50169, HD 137949, and HD192678. This raises the total number of known Ap stars with resolvedmagnetically split lines to 21. The spectral line profiles observed intwo more stars, HD 111133 and HD 147010, are strongly affected by themagnetic field, but they are not fully resolved, due to nonnegligiblerotational Doppler effect. Observations of fairly sharp-lined Ap starswhose lines are unresolved are also presented. The relative differencebetween the equivalent widths of the Fe II lines 6147.7 A and 6149.2 Ais shown to increase with the mean magnetic field modulus. The existenceof a simple, unambiguous correlation between the mean magnetic fieldmodulus and the index Z of Geneva photometry, which had previously beenadvocated, is not confirmed. At most, stars with large negative valuesof Z may be more prone to have strong magnetic fields, but the evidencefor this is not statistically strong.
| The third spectrum of praseodymium in magnetic AP stars
The identification of Pr III lines in the red spectrum of magnetic Apstars, whose great strength contrasts with the weakness of the secondspectrum of Pr in upper main-sequence, chemically peculiar stars, ispresently reported. This identification is judged to be a critical steptoward a knowledge of the abundance systematics of the lanthanides inchemically peculiar stars, as well as toward characterization of thechemical fractionation processes which they undergo.
| AP stars with resolved Zeeman split lines
High-resolution, high SNR observations of a sample of sharp-lined Astars and of Ap stars showing resolved Zeeman split lines are presented.The Fe II lines 6147.7 A and 6149.2 A unexpectedly appear to beasymmetric in all stars where they are resolved. The blue component ofthe 6149.2 line, which is a Zeeman doublet, is deeper and narrower thanits red component. For line 6147.7, whose Zeeman pattern does not differmuch from a quadruplet, the red components are deeper than the blueones. It is shown that a partial Paschen-Back effect can account forthese properties. The potential implications of this finding for studiesof magnetic Ap stars are discussed.
| The magnetic field of the AM star Omicron Pegasi
Evidence is presented that the hot Am star Omicron Peg (= HD 214994) hasa magnetic field of the order of 2 kG, with a complex structure. Twoindependent approaches support this conclusion. The first one is ananalysis by the Stenflo-Lindegren (1977) technique of the widths of astatistical sample of lines. The other relies on a line-intensityanomaly that is found in magnetic stars. The implications of thisprobable detection of a field in a member of a class of stars that werenot previously known as magnetic is discussed.
| 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.
| 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.
| Variable and Potential Variable Stars in the Bright Star Catalogue
Not Available
| Radial velocities of southern OB stars and supergiants
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1969MNRAS.143....1B&db_key=AST
| Catalogue et bibliographie des étoiles A à spectre particulier - Deuxième supplément
Not Available
| Catalogue et bibliographie des étoiles A à spectre particulier Premier supplément
Not Available
| Southern Peculiar A Stars
Not Available
| Catalogue et bibliographie des étoiles A à spectre particulier
Not Available
|
Додај нови чланак
Линкови у сродству са темом
Додај нови линк
Чланови следећих група \:
|
Посматрања и Астрометриски подаци
| Сазвежђа: | Шестар |
| Ректацензија: | 15h09m25.50s |
| Deклинација: | -63°38'34.0" |
| Apparent магнитуда: | 6.28 |
| Даљина: | 170.358 parsecs |
| Proper motion RA: | -9.6 |
| Proper motion Dec: | -20.2 |
| B-T magnitude: | 6.317 |
| V-T magnitude: | 6.254 |
Каталог и designations:
|
INHABITED SKY
