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Atmospheric Elemental Abundances for the Components of the Multiple System ADS 11061. 41 Draconis
We obtained speckle interferometric and spectroscopic observations ofthe system 41 Dra during its periastron passage in 2001. Thecomponents’ lines are resolved in the spectral interval 3700 9200Å. The observed wavelength dependence of the brightness differencebetween the components is used to estimate the B-V indices separatelyfor each of the components: B-V = 0.511 for component a and B-V = 0.502for component b. We derived improved effective temperatures of thecomponents from their B-V values and hydrogen-line profiles. Theobservations can be described with the parameters for the components Teff a = 6370 K, log g a = 4.05 and T eff b = 6410 K, log g b = 4.20. Theiron, carbon, nitrogen, and oxygen abundances in the atmospheres of thecomponents are log N(Fe)a = 7.55, log N(Fe)b = 7.60, log N(C)a = 8.52,log N(C)b = 8.58, log N(N)a = 8.05, log N(N)b = 7.99, log N(O)a = 8.73,log N(O)b = 8.76.
| HD 153720 - A SB2 system with twin metallic-line components
We report the results of abundance determinations for the components ofthe SB2 star HD 153720 from high resolution (R=60 000) echelle highsignal-to-noise spectra of the wavelength region 3595-10 260 Åtaken with the 2.7 m telescope of the McDonald Observatory We found thevalues of the atmospheric parameters of the primary to be effectivetemperature Teff = 7425 K and surface gravity log g,= 4.0cgs, and of the secondary to be Teff = 7125 K and log g,= 3.9cgs. The microturbulent velocity is vmicro= 2.7 kms-1 for both components, and the projected rotationalvelocity is v sin i ,= 15 km s-1 also for both components.The abundances of about 20 elements were determined with the method ofspectrum synthesis. The components of HD 153720 are metallic-linestars. Possible inconsistencies between old and new measurements ofradial velocities may be explained by the existence of third body inthis system. A review of recent high resolution spectral observations ofeight A4-F1 binaries shows that only one of these systems can beclassified as normal.Based on observations obtained at the 2.7-m telescope of the McDonaldObservatory.The data are only available in electronic form athttp://www.edpsciences.org
| Orbital solutions for SB2 systems with a HgMn component
From a new set of spectroscopic observations we determined orbitalparameters of six SB2 systems with one or both components being HgMnstars.We slightly refined the orbital periods for HD 32964,HD 173524, HD 174933 andHD 216494. Our results for HD 358are in agreement with the previous literature studies. RegardingHD 33647, our orbital period is shorter than previousdeterminations. HD 173524 is a triple system. Fromthe variations of the γ-velocity deduced from our and literaturedata, we refined the orbital period and we estimated the eccentricity ofthe third companion, for which we get e ≈ 0.13 and Porb =36 ± 3 years. HD 191110 and HD216494 seem to be the only synchronous SB2 within our sample.Following the hypothesis of rotational axes perpendicular to the orbitalplane, we estimated the angle of the orbital plane to the line of sight.We identified in our spectra the signature of the Hβ ofthe third component of HD 216494 and we highlight aslight variation of the γ-velocity due to the presence of thiscomponent.Based on observations collected at the Stellar Station ``M. G.Fracastoro'' of the Catania Astrophysical Observatory, Italy.Appendix A is only available in electronic form athttp://www.edpsciences.org
| HD 191110 a SB2 system with HgMn and Hg components. Orbital elements and abundance analysis
In this paper we present the first quantitative abundance analysis ofthe SB2 system with HgMn and Hg components HD 191110. Time-resolved(R=14 000) spectroscopic observations of this system have been obtainedduring September and October 2002 at the Catania AstrophysicalObservatory. Combining these observations with spectra (R = 50 000-110000) taken from the CFHT archive, we refined the orbital period of thissystem (P=9.34661 +/- 0.00002 d) and then we recalculated thefundamental parameters characterizing its orbit. From the fit of theHbeta profiles, obtained at different orbital phases, wedetermined the effective temperatures and surface gravities of eachcomponent and the light ratio: TeffA=11 000 K, loggA=3.60, TeffB= 10 700 K, loggB=3.90, LA/LB=1.20. Regarding thechemical composition, both components have solar abundances of sulfur,titanium and iron; magnesium and silicon are slightly underabundant;platinum and yttrium are overabundant. Manganese lines have beendetected only in the spectrum of the primary. As to rare-earths, twolines of NdIII have been identified in the secondary's spectrum. Otherlines we identified in our spectra belong to PII, CrII, NiII, SrII, ZrIIand AuII. We also discuss the isotopic structure of the HgII lambda3983.9 Å line.
| 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
| Study of Two Double Line CP3 Binaries
We present a study of two double-lined spectroscopic binaries selectedto contain one or more chemically peculiar components of the HgMn (CP3)type. The intent is to examine specific effects expected from theradiative diffusion model that is currently the accepted explanation forthe observed surface chemical anomalies. In one such system (66 Eri; P ~5 d) the two component stars are almost identical in their physicalproperties, differing in mass by no more than 5%, and in temperature byno more than 200 K, and having indistinguishable rotation velocities. Inspite of such physical similarities, only one component exhibits theelevated abundances of such elements as mercury (Hg) and yttrium (Y)while the other component is devoid of such elements at our detectionthreshold. The radiative diffusion mechanism cannot give an accountingof such a difference between stars that have a common history offormation and virtually identical physical properties. Additionally, thecomponent that exhibits the anomalous chemical composition appears to bedevoid of the elements Mn and Pt, commonly found in the CP3 stars. Inthe other binary system (46 Dra; P ~ 10 d) the component stars differ inmass by 15% and differ by 600 K in surface temperature, but bothcomponents exhibit the chemical peculiarities characterizing the HgMn(CP3) type, although not in the same abundances. In and of itself, thatis not inconsistent with radiative diffusion as the driving mechanism.However, our observations reveal a different isotopic structure for theHg II (3984 A) line in the two components which is not readily accountedfor by the radiative diffusion model. Our conclusion based upon thesecases is that the radiative diffusion model cannot by itself account forthe observed anomalies, and that it must be called into question as theexplanation for the chemical and isotopic anomalies observed in the CP3stars.
| The WARPS Survey. VI. Galaxy Cluster and Source Identifications from Phase I
We present in catalog form the optical identifications for objects fromthe first phase of the Wide Angle ROSAT Pointed Survey (WARPS). WARPS isa serendipitous survey of relatively deep, pointed ROSAT observationsfor clusters of galaxies. The X-ray source detection algorithm used byWARPS is Voronoi Tessellation and Percolation (VTP), a technique whichis equally sensitive to point sources and extended sources of lowsurface brightness. WARPS-I is based on the central regions of 86 ROSATPSPC fields, covering an area of 16.2 square degrees. We describe herethe X-ray source screening and optical identification process forWARPS-I, which yielded 34 clusters at 0.06
| Rotational Velocities of B Stars
We measured the projected rotational velocities of 1092 northern B starslisted in the Bright Star Catalogue (BSC) and calibrated them againstthe 1975 Slettebak et al. system. We found that the published values ofB dwarfs in the BSC average 27% higher than those standards. Only 0.3%of the stars have rotational velocities in excess of two-thirds of thebreakup velocities, and the mean velocity is only 25% of breakup,implying that impending breakup is not a significant factor in reducingrotational velocities. For the B8-B9.5 III-V stars the bimodaldistribution in V can be explained by a set of slowly rotating Ap starsand a set of rapidly rotating normal stars. For the B0-B5 III-V starsthat include very few peculiar stars, the distributions in V are notbimodal. Are the low rotational velocities of B stars due to theoccurrence of frequent low-mass companions, planets, or disks? Therotational velocities of giants originating from late B dwarfs areconsistent with their conservation of angular momentum in shells.However, we are puzzled by why the giants that originate from the earlyB dwarfs, despite having 3 times greater radii, have nearly the samerotational velocities. We find that all B-type primaries in binarieswith periods less than 2.4 days have synchronized rotational and orbitalmotions; those with periods between 2.4 and 5.0 days are rotating withina factor 2 of synchronization or are ``nearly synchronized.'' Thecorresponding period ranges for A-type stars are 4.9 and 10.5 days, ortwice as large. We found that the rotational velocities of the primariesare synchronized earlier than their orbits are circularized. The maximumorbital period for circularized B binaries is 1.5 days and for Abinaries is 2.5 days. For stars of various ages from 107.5 to1010.2 yr the maximum circularized periods are a smoothexponential function of age.
| 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
| Vertical Chromium Distribution in the Atmosphere of a Chemically Peculiar Star. I. Diagnostics
On the basis of CCD spectrograms obtained with high resolution at theCoudé focus of the 2.6-m telescope of the Crimean AstrophysicalObservatory, Cr II lines lying in the wings of the H hydrogen line areinvestigated. Vertical chromium stratification in the atmospheres of twonormal and eight chemically peculiar stars is diagnosed using the methodof spectral synthesis. An increase in Cr abundance with depth is foundfor the cool Ap stars CrB, HR 7575, Equ, and 10 Aql. Some increase in Crabundance in the upper layers of the atmosphere is presumed for all Amstars and for both HgMn components of 46 Dra. The verticalchromium distribution in the atmospheres of the hot, spotted Ap stars 17Com and 2 CVn is evidently uniform.
| 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
| Atmospheric chemical composition of the "twin" components of equal mass in the CP SB2 system 66 Eri
We determine the atmospheric chemical composition of the components ofthe CP SB2 system 66 Eri with approximately equal masses (M_A / M_B =0.97) by using two CCD echelle spectra of the star. These spectra havebeen taken with the 1-m telescope at Special Astrophysical Observatorywith a spectral resolution of 36 000 and a signal-to-noise ratio no lessthan 100 in the wavelength range 4385-6695 A. The model-atmosphereparameters for the components are estimated by analyzing all availablephotometric and spectrophotometric data and the equivalent widths ofiron lines. For components A and B, we have obtained Teff_A =11 100 K, Teff_B = 10 900 K, lg(g_A) = 4.25, lg(g_B)= 4.25,Vturb_A = 0.9 km/s, Vturb_B = 0.7 km/s, and vsin(i_{A,B}) = 17 km/s. The derived projected rotational velocities ofthe components, together with the HIPPARCOS parallax and photometricobservations, show that their rotation may be synchronized with theorbital period. The star exhibits a considerable infrared excess atwavelengths longer than 25 micrometers. The synthetic-spectrum andmodel-atmosphere methods are used to determine the atmosphericabundances of 26 chemical elements in component B and 15 chemicalelements in component A. The components differ markedly in chemicalcomposition. The peculiar component B exhibits no chemical anomaliesthat are typical of the Hg-Mn group, such as an underabundance of He andAl and an enhancement of P and Ga, but shows large heavy-elementoverabundances reaching 4-5 dex. The atmosphere of component A alsoexhibits moderate overabundances of Mn and Ba, but no lines of otherheavy elements have been found in its spectrum. However, an estimate ofthe upper limit on their abundances does no rule out small heavy-elementoverabundances in the atmosphere of component A either. 66 Eri is thefirst and the only close SB2 system with CP non-Hg-Mn components studiedto date.
| Mercury Elemental and Isotopic Abundances in Mercury-Manganese Stars
Hg II abundances have been determined for 42 mercury-manganese (HgMn)stars by fitting synthetic spectra to observed spectra of the 3984Å Hg II line. Twenty of the stars had lines sharp enough to allowtheir Hg isotopic abundance mixes to be estimated. The Hg abundance isreported for more HgMn stars here than in any other single work. Nocorrelation was found between Hg II abundance and T_eff or the meancentral wavelength of HgMn lambda3984 stars. The mean central wavelengthof lambda3984 , an indicator of the Hg isotopic mix, is looselycorrelated with T_eff: stars with primarily heavy Hg isotopes tend to becooler, although one star, 46 Aql, has almost pure ^204Hg and T_eff inabout the middle of the temperature range for HgMn stars. We find thatthere is no evidence that any of the HgMn stars have ^196Hg or ^198Hg.For the very sharp-lined stars, the ^204Hg abundance decreases withincreasing T_eff. No correlation is seen between the mean centralwavelength and the surface gravity. No correlation was found between theprojected rotational velocity and the Hg II abundance or the centralwavelength of lambda3984, although this result may be biased by theselection of stars with low reported vsini. Hg I lambda4358 was measuredat high spectral resolution for seven HgMn stars. The isotopic shiftsare too small, and the hyperfine components are too weak to allowunambiguous isotopic abundance ratios to be found. Hg I abundancescorrelate fairly well with Hg II abundances. Some of the Hg isotopicmixtures are difficult to explain using only diffusion. HR 7245 hasapproximately equal abundances of ^199Hg, ^200Hg, ^202Hg, and ^204Hg butvery little ^201Hg, and 11 Per has Hg that is mostly ^199Hg and ^204Hg.Calculations show that hyperfine splitting of ^201Hg changes theradiative forces it feels compared with other isotopes, which may alterdiffusion of that isotope enough to explain its absence in HR 7245, butwe have found no possible explanation for the Hg isotopic mix found in11 Per. These are the first very high resolution measurements of Hg IIlambda3984 for HR 7245 and 11 Per. Although diffusion may be acting inHgMn stars, either there are one or more other mechanisms acting to helpproduce the overabundances and isotopic mixtures seen or ourunderstanding of diffusion is lacking on some important point.
| Orbital elements and abundance analyses of the double-lined spectroscopic binary alpha Andromedae
We performed a spectroscopic study of the SB2 Mercury-Manganese staralpha And with Reticon and CCD spectra obtained at the Crimean and theDominion Astrophysical Observatories. Our measurements particularly ofthe secondary's radial velocities resulted in improved orbital elementswith a spectroscopic mass ratio m_B/m_A = 0.50 +/- 0.03 which is in goodagreement with the mass-luminosity solution for this system. Elementalabundance analyses using synthetic spectra show that the primary haselemental abundances somewhat similar to those of other HgMn stars whilethe cooler secondary probably is a metallic-line star. The possiblevariability of Hg II lambda 3984 is discussed.
| The nature of visual components in 82 multiple systems.
Not Available
| Chemical composition of the CP Hg-Mn components of approximately equal mass in the SB2 system 46 Draconis.
Not Available
| Elemental abundance analyses with DAO spectrograms - XVIII. The double-lined spectroscopic binary 46 Draconis
We present a study of the double-lined spectroscopic binary star 46Draconis (46 Dra). The variations of the gamma-velocity indicate thepresence of a third star which revolves around the mutual centre-of-massof the close binary system with a period of 33.6 yr. Perhaps this thirdstar is responsible for the observed X-ray radiation of 46 Dra. With atemperature difference of only 600 K, both components of the closebinary are mercury-manganese stars. This system demonstrates thechemical evolution of two apparently metal-rich objects with the sameinitial composition, but with slightly different masses and resultingeffective temperatures. Significant abundance differences are found forHe, Al, S, Sc, Mn, Sr, Ga, Xe and Pt. These provide tests for thetheories which purport to explain the anomalies.
| HgMn stars as apparent X-ray emitters
In the ROSAT all-sky survey 11 HgMn stars were detected as soft X-rayemitters. Prior to ROSAT, X-ray observations with the EinsteinObservatory had suggested that stars in the spectral range B5-A7 aredevoid of X-ray emission. Since there is no X-ray emitting mechanismavailable for these stars (also not for HgMn stars), the usual argumentin the case of an X-ray detected star of this spectral type is theexistence of an unseen low-mass companion which is responsible for theX-ray emission. The purpose of the present work is to use all availabledata for our sample of X-ray detected HgMn stars and conclude on thenature of possible companions.
| Abundance analysis of SB2 binary stars with HgMn primaries
We present a short review of the abundances in the atmospheres of SB2systems with Mercury-Manganese (HgMn) primaries. Up to now a carefulstudy has been made for both components of 8 out of 17 known SB2binaries with orbital periods shorter than 100 days and mass ratioranging from 1.08 to 2.2. For all eight systems we observe a lower Mnabundance in the secondary's atmospheres than in the primary's.Significant difference in the abundances is also found for some peculiarelements such as Ga, Xe, Pt. All secondary stars with effectivetemperatures less than 10 000 K show abundance characteristics typicalof the metallic-line stars.
| 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 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.
| A catalogue of [Fe/H] determinations: 1996 edition
A fifth Edition of the Catalogue of [Fe/H] determinations is presentedherewith. It contains 5946 determinations for 3247 stars, including 751stars in 84 associations, clusters or galaxies. The literature iscomplete up to December 1995. The 700 bibliographical referencescorrespond to [Fe/H] determinations obtained from high resolutionspectroscopic observations and detailed analyses, most of them carriedout with the help of model-atmospheres. The Catalogue is made up ofthree formatted files: File 1: field stars, File 2: stars in galacticassociations and clusters, and stars in SMC, LMC, M33, File 3: numberedlist of bibliographical references The three files are only available inelectronic form at the Centre de Donnees Stellaires in Strasbourg, viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5), or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Mesures de vitesses radiales. VIII. Accompagnement AU sol DU programme d'observation DU satellite HIPPARCOS
We publish 1879 radial velocities of stars distributed in 105 fields of4^{\circ} \times 4^{\circ}. We continue the PPO series \cite[(Fehrenbachet al. 1987;]{Feh87} \cite[Duflot et al. 1990, 1992 and 1995),]{Du90}using the Fehrenbach objective prism method. Table 1 only available inelectronic form at CDS via to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| MSC - a catalogue of physical multiple stars
The MSC catalogue contains data on 612 physical multiple stars ofmultiplicity 3 to 7 which are hierarchical with few exceptions. Orbitalperiods, angular separations and mass ratios are estimated for eachsub-system. Orbital elements are given when available. The catalogue canbe accessed through CDS (Strasbourg). Half of the systems are within 100pc from the Sun. The comparison of the periods of close and widesub-systems reveals that there is no preferred period ratio and allpossible combinations of periods are found. The distribution of thelogarithms of short periods is bimodal, probably due to observationalselection. In 82\% of triple stars the close sub-system is related tothe primary of a wide pair. However, the analysis of mass ratiodistribution gives some support to the idea that component masses areindependently selected from the Salpeter mass function. Orbits of wideand close sub-systems are not always coplanar, although thecorresponding orbital angular momentum vectors do show a weak tendencyof alignment. Some observational programs based on the MSC aresuggested. Tables 2 and 3 are only 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
| X-ray emission from Ap-Bp stars: a magnetically confined wind-shock model for IQ Aur.
We present the results of a ROSAT-PSPC pointed observation on the hotA0p star IQ Aur (HD 34452). The X-ray luminosity obtained isL_X_=4.0x10^29^erg/s (logL_X_/L_Bol_=~-6.9) and the plasma temperatureis T_X_=0.29keV. Since A and B stars have no known magnetic activity,the only possibility is to invoke a wind origin for this emission. On IQAur, the expected mass loss rate driven by stellar radiation is small,around 10^-10^-10^-11^Msun_/yr withvinfinity_=800km/s, so that the kinetic energy flux of thewind is not much larger than the observed X-ray emission. This impliesthat the X-ray emission from IQ Aur must arise from a very efficientprocess. These constraints, together with the large observed magneticfield of IQ Aur, lead us to propose that the confinement of the wind bythe magnetic field leads to a collision from the wind components of thetwo hemispheres in the closed magnetosphere, leading to a strong shock.In this model the magnetic field confines the wind and also affects themass loss rate. We propose a self-consistent approach for the X-rayemission of IQ Aur, using radiatively driven wind models based on thestellar parameters of IQ Aur and including the effect of magneticconfinement of the wind. We also model the whole postshock region. Weshow that our shock model is able to satisfy the constraints on theobserved X-ray luminosity and temperature. The model also leads to theformation of a disk at the magnetic equator corotating up tor<~4R_*_. We show that ambipolar diffusion of hydrogen in the disk orcurrent sheet formation due to equipartition between the disk and themagnetic field might play a significant role in emptying themagnetosphere. We discuss the interplay between mass loss and particlediffusion. Our computations suggest that the onset of a wind on IQ Auris very recent, so that the abundance anomalies at the stellar surfacehave not yet been removed by the outflow, or that the wind exhibitstransient phases due to the mutual feedback between the wind andabundance anomalies. Finally, we point out that our wind-shock modelprovides a very convenient framework to explain the radio emission ofAp-Bp stars. It has been shown that the emission mechanism is opticallythick gyrosynchrotron, but instead of (or in addition to) the previouslyinvoked acceleration by magnetic reconnection in current sheets, wepropose that the electrons are accelerated by second-order Fermiacceleration mechanism ("stochastic" acceleration) often invoked for theacceleration of solar flare flare particles. We show that electronsaccelerated by the wind shock easily reach the required energies forradio emission in the GHz band throughout the magnetosphere. Given thesuccess of our model in explaining IQ Aur, we think that it has a fairlygeneral application to magnetic Ap-Bp stars. The wind-shock model alsoprovides a unified explanation for both the X-rays and the radioemission from these stars.
| The ROSAT all-sky survey catalogue of optically bright OB-type stars.
For the detailed statistical analysis of the X-ray emission of hot starswe selected all stars of spectral type O and B listed in the Yale BrightStar Catalogue and searched for them in the ROSAT All-Sky Survey. Inthis paper we describe the selection and preparation of the data andpresent a compilation of the derived X-ray data for a complete sample ofbright OB stars.
| Speckle observations of visual and spectroscopic binaries. VI.
Not Available
| Chemical Composition of Components A and B of the Hg-Mn Chemically-Peculiar Eclipsing SB2-Star AR-Aurigae
Not Available
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| Csillagkép: | Sárkány |
| Rektaszcenzió: | 18h42m37.90s |
| Deklináció: | +55°32'22.0" |
| Vizuális fényesség: | 5.04 |
| Távolság: | 111.607 parszek |
| RA sajátmozgás: | 0 |
| Dec sajátmozgás: | 0 |
| B-T magnitude: | 4.925 |
| V-T magnitude: | 5.013 |
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