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Testing the companion hypothesis for the origin of the X-ray emission from intermediate-mass main-sequence stars
Context: .The X-ray emission from B-type main-sequence stars is alongstanding mystery in stellar coronal research. Since there is notheory at hand that explains intrinsic X-ray emission fromintermediate-mass main-sequence stars, the observations have often beeninterpreted in terms of (unknown) late-type magnetically activecompanion stars. Aims: .Resolving the hypothesized companionsrequires high spatial resolution observations in the infrared and inX-rays. We use Chandra imaging observations to spatially resolve asample of main-sequence B-type stars with recently discovered companionsat arcsecond separation. Methods: .Our strategy is to search forX-ray emission at the position of both the B-type primary and the faintcompanion. Results: .We find that all spatially resolvedcompanions are X-ray emitters, but seven out of eleven intermediate-massstars are also X-ray sources. If this emission is interpreted in termsof additional sub-arcsecond or spectroscopic companions, this implies ahigh multiplicity of B-type stars. Firm results on B star multiplicitypending, the alternative, that B stars produce intrinsic X-rays, cannotbe discarded. An appropriate scenario would be a magnetically confinedwind, as suggested for the X-ray emission of the magnetic Ap star IQAur. However, the only Ap star in the Chandra sample is not detected inX-rays, and therefore does not support this picture.
| Evolution of interacting binaries with a B type primary at birth
We revisited the analytical expression for the mass ratio distributionfor non-evolved binaries with a B type primary. Selection effectsgoverning the observations were taken into account in order to comparetheory with observations. Theory was optimized so as to fit best withthe observed q-distribution of SB1s and SB2s. The accuracy of thistheoretical mass ratio distribution function is severely hindered by theuncertainties on the observations. We present a library of evolutionarycomputations for binaries with a B type primary at birth. Some liberalcomputations including loss of mass and angular momentum during binaryevolution are added to an extensive grid of conservative calculations.Our computations are compared statistically to the observeddistributions of orbital periods and mass ratios of Algols. ConservativeRoche Lobe Over Flow (RLOF) reproduces the observed distribution oforbital periods but fails to explain the observed mass ratios in therange q in [0.4-1]. In order to obtain a better fit the binaries have tolose a significant amount of matter, without losing much angularmomentum.
| Observed Orbital Eccentricities
For 391 spectroscopic and visual binaries with known orbital elementsand having B0-F0 IV or V primaries, we collected the derivedeccentricities. As has been found by others, those binaries with periodsof a few days have been circularized. However, those with periods up toabout 1000 or more days show reduced eccentricities that asymptoticallyapproach a mean value of 0.5 for the longest periods. For those binarieswith periods greater than 1000 days their distribution of eccentricitiesis flat from 0 to nearly 1, indicating that in the formation of binariesthere is no preferential eccentricity. The binaries with intermediateperiods (10-100 days) lack highly eccentric orbits.
| Tidal Effects in Binaries of Various Periods
We found in the published literature the rotational velocities for 162B0-B9.5, 152 A0-A5, and 86 A6-F0 stars, all of luminosity classes V orIV, that are in spectroscopic or visual binaries with known orbitalelements. The data show that stars in binaries with periods of less thanabout 4 days have synchronized rotational and orbital motions. Stars inbinaries with periods of more than about 500 days have the samerotational velocities as single stars. However, the primaries inbinaries with periods of between 4 and 500 days have substantiallysmaller rotational velocities than single stars, implying that they havelost one-third to two-thirds of their angular momentum, presumablybecause of tidal interactions. The angular momentum losses increase withdecreasing binary separations or periods and increase with increasingage or decreasing mass.
| 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
| Kinematical Structure of the Local Interstellar Medium: The Galactic Anticenter Hemisphere
A survey of interstellar Na I D1 and D2 absorption features in thespectra of 104 early-type stars in the second and third Galacticquadrants reveals the large-scale kinematics of the interstellar gaswithin the Galactic anticenter hemisphere at distances from the Sunbetween ~70 and ~250 pc. Employing a technique that uses both the radialvelocities and column densities of the Na I absorptions produced by theintervening gas we have identified the velocity vectors and determinedthe spatial distribution of eight interstellar clouds in the volumeexplored. The average internal H I+H2 densities of the cloudsrange between 0.03 and 1.7 cm-3, and their masses between 80and 104 Msolar, although uncertainties in thesizes of the clouds, their possible extension beyond the regionexplored, and the presence of denser gas embedded in the larger cloudsimply that these will tend to be lower limits. We have clearlyidentified clumps of denser gas immersed in the low-density gas in oneof the clouds; these clumps show internal H I+H2 densities oforder 50 cm-3. Although we are not able to detect anyinterstellar Na I within 70 pc, the sizes of some of the clouds implythat their near edges are within that range of distances from the Sun.With respect to the local standard of rest the clouds move withvelocities between 19 and 54 km s-1. Their velocity vectorsdo not support the view of a local interstellar medium uniquelydominated by expansion from centers in the Scorpio-Centaurus OBassociation; our results suggest that this expansion is present in theGalactic center hemisphere but in the Galactic anticenter hemisphere isrestricted to the immediate neighborhood of the Sun.
| 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.
| 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.
| Statistics of spectroscopic sub-systems in visual multiple stars
A large sample of visual multiples of spectral types F5-M has beensurveyed for the presence of spectroscopic sub-systems. Some 4200 radialvelocities of 574 components were measured in 1994-2000 with thecorrelation radial velocity meter. A total of 46 new spectroscopicorbits were computed for this sample. Physical relations are establishedfor most of the visual systems and several optical components areidentified as well. The period distribution of sub-systems has a maximumat periods from 2 to 7 days, likely explained by a combination of tidaldissipation with triple-star dynamics. The fraction of spectroscopicsub-systems among the dwarf components of close visual binaries withknown orbits is similar to that of field dwarfs, from 11% to 18% percomponent. Sub-systems are more frequent among the components of widevisual binaries and among wide tertiary components to the known visualor spectroscopic binaries - 20% and 30%, respectively. In triple systemswith both outer (visual) and inner (spectroscopic) orbits known, we findan anti-correlation between the periods of inner sub-systems and theeccentricities of outer orbits which must be related to dynamicalstability constraints. Tables 1, 2, and 6 are only available inelectronic form at the 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/382/118
| Orbital Elements of SB2 System 66 Eri
On the base of 5 high resolution spectra and previously published datawe found a new set of orbital elements of this binary system. Allelements are in good agreement with previously published data.Additional observations of the star are necessary to confirm or rejectthe light variations of the system and to find the inclination of theorbit and the rotational periods of components.
| Search for low-mass PMS companions around X-ray selected late B stars
We have observed 49 X-ray-detected bright late B-type dwarfs to searchfor close low-mass pre-main sequence (PMS) companions using the EuropeanSouthern Observatory's ADONIS (Adaptive Optics Near Infrared System)instrument. We announce the discovery of 21 new companions in 9binaries, 5 triple, 4 quadruple system and 1 system consisting of fivestars. The detected new companions have K magnitudes between 6.5m and17.3m and angular separations ranging from 0.12 arcsec to 14.1 arcsec(18-2358 AU). Based on observations obtained at the European SouthernObservatory, La Silla, Chile (ESO programme No.~62.I-0477, and Swiss70~cm photometric telescope).
| 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
| Astrophysics in 1999
The year 1999 saw the arrival of a star with three planets, a universewith three parameters, and a solar corona that could be heated at leastthree ways. In addition, there were at least three papers on everyquestion that has ever been asked in astrophysics, from ``Will theUniverse expand forever?'' to ``Does mantle convection occur in one ortwo layers?'' The answers generally were, ``Yes,'' ``No,'' and ``None ofthe above,'' to each of the questions. The authors have done their bestto organize the richness around centers defined by objects, methods, andmadnesses.
| 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.
| The nature of visual components in 82 multiple systems.
Not Available
| 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.
| Atmospheric abundances of CP SB2 star components of equal masses. II. 66 Eridani
We report the results of abundance determination for the components ofthe SB2 star 66 Eri (M(A)/M(B)=0.97) from high resolution CCD echellespectra with S/N > 100 taken with the 1-m telescope of SpecialAstrophysical Observatory (Zelenchuck, Russia). The atmosphericparameters of the components were determined using all availablephotometric, spectrophotometric and spectral data. The abundances of 27elements were found. The abundances of components are different. The Bcomponent, previously classified as an Hg-Mn star, does not showanomalies typical of this group such as deficit of He, Al and excess ofP, Ga but shows overabundances of heavy elements which amount up to 4-5dex. The A component also shows moderate Mn and Ba excess. Lines ofother heavy elements were not detected. Estimates of upper limits totheir abundances do not permit to exclude completely the presence offainter anomalies in the A component either.
| HgMn stars: new insights
Recent results obtained by various authors on the properties of HgMnstars are reviewed. Substantial progress has been achieved in the studyof abundances and isotopic anomalies. The results about the magneticfields and membership in multiple systems suggest further directions ofinvestigations to be followed in view of answering the question of thedevelopment of abundance peculiarities in HgMn stars.
| The ROSAT all-sky survey catalogue of optically bright main-sequence stars and subgiant stars
We present X-ray data for all main-sequence and subgiant stars ofspectral types A, F, G, and K and luminosity classes IV and V listed inthe Bright Star Catalogue that have been detected as X-ray sources inthe ROSAT all-sky survey; several stars without luminosity class arealso included. The catalogue contains 980 entries yielding an averagedetection rate of 32 percent. In addition to count rates, sourcedetection parameters, hardness ratios, and X-ray fluxes we also listX-ray luminosities derived from Hipparcos parallaxes. The catalogue isalso available in electronic form via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| 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
| An extensive Delta a-photometric survey of southern B and A type bright stars
Photoelectric photometry of 803 southern BS objects in the Deltaa-system as detection tool for magnetic chemically peculiar (=CP2) starshas been carried out and compared to published spectral types. Thestatistical yield of such objects detected by both techniques ispractically the same. We show that there are several factors whichcontaminate the search for these stars, but this contamination is onlyof the order of 10% in both techniques. We find a smooth transition fromnormal to peculiar stars. Our sample exhibits the largest fraction ofCP2 stars at their bluest colour interval, i.e. 10% of all stars in thecolour range -0.19 <= B-V < -0.10 or -0.10 <= b-y < -0.05.No peculiar stars based on the Delta a-criterion were found at bluercolours. Towards the red side the fraction of CP2 stars drops to about3% for positive values of B-V or b-y with red limits roughlycorresponding to normal stars of spectral type A5. The photometricbehaviour of other peculiar stars: Am, HgMn, delta Del, lambda Boo, Heabnormal stars, as well as Be/shell stars and supergiants shows someslight, but definite deviations from normal stars. Spectroscopic andvisual binaries are not distinguished from normal stars in their Delta abehaviour. The results of this work justify larger statistical work(e.g. in open clusters) employing more time-saving photometric methods(CCD). \newpage Based on observations obtained at the European SouthernObservatory, La Silla, Chile. This research has made use of the Simbaddatabase, operated at CDS, Strasbourg, France. Table 2 is only availablein electronic form via anonymous ftp 130.79.128.5 orhttp://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.
| 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
| 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
| A Catalogue of Correlations Between Eclipsing Binaries and Other Categories of Double Stars
Among the 9110 stars in The Bright Star Catalogue, there are 225eclipsing or ellipsoidal variables. A search has been made for these incatalogues of spectroscopic binaries, visual double or multiple stars,speckle interferometry, occulation binaries, and galatic clusters. Themajority of the photometric binaries are also members of groups ofhigher multiplicity. The variables are in systems ranging from one to 91stars, five on the average. 199 are either spectroscopic binaries (SB)or stars with variable radial velocity, with orbital periods known for160. Photometric periods are lacking for 48 while SB periods areavailable for 23 of these. Observers with photoelectric equipment areencouraged to plan observations to test if the SB periods are consistentwith photometric data. Observers are likewise encouraged to examinethose stars for which the photometric and SB periods appear to beinconsistent. Parallaxes are available for 86 of the stars, 41 of themindicating distances nearer than 50 parsecs.
| 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.
| Some remarks on the origin of the abundance anomalies in HgMn stars.
Not Available
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