Contents
Images
Upload your image
DSS Images Other Images
Related articles
Elemental Abundance Studies of CP Stars. The Silicon Stars HD 87240 and HD 96729
We compared elemental abundances of field and open cluster Ap Si stars.In particular, an analysis of the Ap Si stars HD 87240 and HD 96729 ispresented using an ATLAS9 model atmosphere and observational materialtaken with a REOSC echelle spectrograph attached to the Jorge Sahade2.15 m telescope at CASLEO. These chemically peculiar (CP) stars belongto the southern hemisphere open clusters NGC 3114 and NGC 3532,respectively. For HD 87240 and HD 96729, C is mostly solar, Mg and S areslightly underabundant, Si and Ca are overabundant by factors between1--10. Heavier elements are all overabundant, TiCrFe by factors of 10, SrYZr by factors between 100--1000 and rare earths by factors of 1000 or more.
| Abundance Analysis of the Silicon Star HR 6958
The elemental composition of the chemically peculiar star HR6958 hasbeen studied with emphasis on doubly ionized rare earths. A visualregion spectrum taken with the ELODIE spectrograph at the Haute-ProvenceObservatory was analyzed. A total of 40 elements including Pr III , Nd III , Tb III , Dy III , Ho III , and Er III were identified andtheir abundances computed. He is deficient by over 1dex with respect tothe Sun; the light elements (C-Ca), except for Si, have solarabundances; the iron group elements (Sc-Fe) are overabundant by 1 dex to2dex, with Ti and Cr highly overabundant; and the lanthanide rare earthsare overabundant by 3dex to 4dex. This abundance pattern with Hedeficient, Si, Ti, Cr, Sr, and Pr overabundant indicates that HR6958 isa member of Si 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
| On the Periods of the Magnetic CP Stars
An HR diagram annotated to show several ranges of photometericallydetermined periods has been constructed for the magnetic CP stars whoseperiods have been determined by the author and his collaborators. Thedistribution of periods reflects both the initial conditions as well asthe subsequent stellar histories. Since the stellar magnetic field doesnot penetrate the convective core, eventually a shear zone near thecore-radiative envelope boundary may develop which produces turbulenceand modifies the field. Many, but not all, of the most rapidly rotatingmCP stars are close to the ZAMS and some of the least rapidly rotatingmCP stars are the furthest from the ZAMS.
| 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
| Elemental abundance study of the CP star HD 206653
An analysis of the abundances of the Silicon star HD 206653 is presentedusing an ATLAS9 model atmosphere and observational material taken with aREOSC echelle spectrograph attached to the Jorge Sahade 2.15 m telescopeat CASLEO. The light elements are solar or deficient except siliconwhich is overabundant by a factor of 5. The iron peak elements are alloverabundant by factors between 10 and 50. Sr and Y are around 1000times the solar values. Among the Rare Earths only Ce and Eu areidentified; both are overabundant by large factors.
| 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.
| Elemental abundance studies of CP stars. III. The magnetic CP stars alpha Scl and HD 170973
Fine analyses of the magnetic CP stars alpha Scl and HD 170973 arepresented using ATLAS9 model atmospheres which have same bulkmetallicity as the deduced abundances. The light elements are mostlysolar except for silicon, and all the heavier elements except nickel inHD 170973, which is solar, are greatly overabundant. The iron peakelements are typically 10 times overabundant, Sr is of order of 1000times solar, Y and Zr are of order of 100 times solar. The rare earthsare 1000 or more times overabundant.
| 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
| On the effective temperatures, surface gravities, and optical region fluxes of the CP stars
We determined effective temperatures and surface gravities for 17magnetic Chemically Peculiar (mCP) stars by comparing optical regionspectrophotometry and Hγ profiles with the predictions of ATLAS9model atmospheres. Although solar composition models can fit the energydistributions of the normal and many Mercury-Manganese stars, theycannot match the optical energy distributions of the mCP stars,especially the lambda 5200 broad, continuum regions. The role ofmetallicity and microturbulence to provide appropriate energydistributions which fit those observed for the mCP stars isinvestigated. Using metal-rich models with the opacity distributionfunctions for microturbulent velocities of 4 and 8 km s-1,their lambda 5200 broad, continuum features are often fit as part ofthis process. For some stars it is impossible to fit simultaneously boththis feature and the line blanketing in the Hγ region. Thissuggests that this continuum feature is produced by elements other thanthose which contribute most of the general line blanketing. A systematicdifference in the temperatures found by the photometric andspectrophotometric approaches is discovered for the hotter mCP stars. Aninvestigation of 10 Mercury-Manganese stars shows a similar effect. Thismay be due to the photospheric compositions becoming less solar withincreasing temperature.
| 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.
| 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
| Photometry from the HIPPARCOS Catalogue: Constant MCP Stars, Comparison and Check Stars
Photometry from the Hipparcos catalogue is used to verify the constancyof four magnetic CP stars, as well as the comparison and the check starsused for variability studies of normal and chemically peculiar B and Astars with the Four College Automated Photoelectric Telescope;variability in these stars can produce spurious results. A few of thecomparison stars are found to be variable and should be replaced forfuture differential photometric studies.
| 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.
| UVBY photometry of the magnetic chemically peculiar stars HD 37776, HR 2258, HR 6958, and 108 Aquarii
Differential Stromgren uvby photometric observations from the FourCollege Automated Photoelectric Telescope are presented for fourmagnetic chemically peculiar stars. Comparison with uvby photometry ofPedersen & Thomsen for HD 37776 yields an improved period of1.538675 days. New periods of 15.0305 days and 18.065 days are found forthe sharp-lined stars HR 2258 and HR 6958, respectively, rather than oneof their aliases. For HR 6958 each color shows a slightly different timeof maximum. Comparison of the four color photometry of 108 Aqr takenduring the fall of 1995 which well covers the period shows the presenceof a secondary minimum near primary maximum in u, v, and b. Comparisonwith published photometry indicates indicates that subtle changes in theshapes of the light curves have occurred suggesting that this star mightbe precessing. Tables 2-5 will be available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| 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.
| Spectropolarimetry of magnetic stars. V. The mean quadratic magnetic field.
Systematic determinations of the mean quadratic magnetic field of Apstars have been performed for the first time. The mean quadraticmagnetic field (or, in short, the quadratic field) is the square root ofthe sum of the mean square magnetic field modulus and of the mean squarelongitudinal magnetic field. The latter are averages over the visiblestellar disk of the square of, respectively, the modulus of the magneticfield and its component along the line of sight. These averages areweighted by the local emergent line intensities. The quadratic field isdiagnosed from the study of the magnetic broadening of the stellarspectral lines as observed in unpolarized light, through thecharacterization of the widths of the lines by the second-order momentsof their profiles (in the Stokes parameter I) about their centre. Thetheoretical basis of the interpretation of these moments in terms ofmagnetic field and the strategy followed in the analysis are presented.It is shown that this analysis yields, as a by-product, the projectedequatorial velocity v_e_sini of the studied stars. Observations of asample of 29 stars are analyzed. For 22 of them, meaningful values orupper limits of the quadratic field can be determined. The lower limitof detection of the quadratic fields, set by the spectral resolution ofthe observations, is of the order of 5 kG. The observed quadratic fieldsrange from this value up to 37 kG, in the star HD 137509. The magneticfield of this star is likely the second strongest known field in Apstars. Quadratic field values derived for stars where resolvedmagnetically split lines are observed in higher-dispersion spectra areconsistent with the values of the mean field modulus measured in thosestars from the line splitting. For the stars of the sample repeatedlyobserved through their rotation cycle, the variations of the quadraticfield are well represented by a cosine with the rotation frequency ofthe star, or by the superposition of such a cosine and of a cosine withtwice that frequency. However, it appears that it is essential to have alarge number of observations distributed sufficiently uniformly andsufficiently densely over the rotation phases to determine unambiguouslythe shape of the variations. The extrema of the quadratic field tend tooccur at phases close to those of the extrema of the longitudinal field,but in some stars, the two quantities definitely vary out of phase. Theratio between the maximum and the minimum of the quadratic field isalways smaller than 1.7.
| Spectropolarimetry of magnetic stars. IV. The crossover effect.
This paper is devoted to the study of the crossover effect in magneticAp stars. It is shown that this effect can be measured by the secondorder moment about their centre of the profiles of spectral linesrecorded in the Stokes parameter V. The interpretation of thesemeasurements in terms of magnetic field is developed. It is shown thatone can derive from them a quantity called the mean asymmetry of thelongitudinal magnetic field, which is the first moment of the componentof the magnetic field along the line of sight, about the plane definedby the line of sight and the stellar rotation axis. The consistency ofthe determination of this quantity with that of the mean longitudinalmagnetic field from measurements of wavelength shifts of lines betweenright and left circular polarization is demonstrated. This technique ofanalysis is applied to observations of a sample of 29 stars, among which10 have a detectable crossover effect. For 8 of them, the availableobservational data allow the study of the variations of the asymmetry ofthe longitudinal field with rotation phase. In most cases, thisvariation is sinusoidal and essentially symmetric about 0, and it occursin quadrature with the variation of the mean longitudinal field. A morecomplex behaviour is definitely observed in HD 147010 and HD 175362,where the variation of the asymmetry of the longitudinal field is betterrepresented by the superposition of two sinusoids, one with the rotationfrequency of the star, and the other with twice that frequency.
| A new list of effective temperatures of chemically peculiar stars. II.
Not Available
| Spectropolarimetry of magnetic stars. III. Measurement uncertainties.
The estimation of the uncertainties affecting the determination ofvarious parameters characterizing spectral line profiles recorded inStokes I and V that are used in the diagnosis of stellar magnetic fieldsthrough the moment technique is described. Simple statisticalconsiderations are presented, to demonstrate that the errors areproperly assessed and to illustrate how their evaluation can beexploited to derive information about the physical properties of thestudied stars. It is shown that taking these uncertainties properly intoaccount allows one to achieve better determination of the meanlongitudinal magnetic field. Improved values of the latter are derivedfor observations already analysed in earlier work. The approach sketchedin this paper is intended as a basis for future studies of magneticfields of Ap stars.
| Spectrophotometry of Peculiar B-Stars and A-Stars - Part Nineteen - Variability of the Magnetic Cp-Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&AS..101..393A&db_key=AST
| The Gaii Lines in the Red Spectrum of Ap-Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&A...272..465L&db_key=AST
| A study of magnetic fields in AP SI and He weak stars
A survey of 44 Ap and Bp Si and He-weak stars for the presence ofdetectable longitudinal magnetic fields (Be) is reported. Fields havebeen detected in about half of the sample, with typical standard errorsin the range of 100-400 G. In 11 stars, fields have been detected forthe first time. For most of the stars with detected fields, thevariation of Be with rotational phase has been determined at leastapproximately. In a number of cases the phase relationship withphotometric or spectroscopic variations have also been established.Several of the newly detected fields are relatively large, with rmsvalues between 1 and 4 kG, and thus may be especially suitable fordetailed mapping and modelling. A particularly interesting result ofthese observations is the identification of at least four stars in whichextrema of the photometric or spectroscopic variations do not coincidewith the magnetic extrema, which implies that the distribution ofchemical elements over the stellar surface that leads to photometricvariations is definitely not symmetric about the magnetic axis of thestar.
| 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.
| Spectropolarimetry of magnetic stars. II - The mean longitudinal magnetic field
Longitudinal magnetic field measurements were carried out for a sampleof Ap stars based on CCD spectra recording simultaneously in bothcirculation polarizations using the Zeeman analyzer of the ESOCassegrain Echelle Spectrograph fed by the ESO 3.6-m telescope.Comparison with previous studies demonstrates the proper operation ofthe Zeeman analyzer. Most curves of the rotational variation of thelongitudinal field are closely sinuosidal, which confirms that theanharmonicities of curves that had been reported in the past were oftendue to problems with the measurements of the photographic plates, whichare avoided with the present low-noise CCD spectra.
| First supplement to the catalog of observed periods of AP stars
Supplementary data on the periods of Ap stars with references arepresented; 58 new stars are introduced for which periodic variabilityhas been discovered since 1983. For some of these stars periodicity wasknown before 1983 but they were not reported in the previous catalog.Recently attributed variable star names are also reported.
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
| Constellation: | Schlange |
| Right ascension: | 18h32m07.00s |
| Declination: | +03°39'35.0" |
| Apparent magnitude: | 6.43 |
| Distance: | 366.3 parsecs |
| Proper motion RA: | 7.9 |
| Proper motion Dec: | 4.5 |
| B-T magnitude: | 6.378 |
| V-T magnitude: | 6.403 |
Catalogs and designations:
|
INHABITED SKY
