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# ξ Cep (Kurhah)

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 The epoch of the constellations on the Farnese Atlas and their origin in Hipparchus's lost catalogueNot Available Analysis of the Dynamical Instability of Several Multiple Stars with Weak HierarchyThe dynamical stability of 16 multiple stars is analyzed using MonteCarlo simulations with allowance for the errors in the observationaldata. The analysis was carried out by varying the uncertainties in theinitial observational data. Six different stability criteria wereconsidered, and the dynamical evolution was studied using numericalsimulations. Eleven of the systems are probably stable, whereas fivesystems (HD 40887, HD 136176, HD 150680, HD 217675, and HD 222326) areprobably unstable (the probability that they are unstable is 0.94 ormore accordingt o the results of forward and backward simulations overintervals of 106 yr). The results of the simulations were mostconsistent with the criteria of Mardling-Aarseth (the correlationcoefficient between the probabilities of disruption inferred from thestability criterion and numerical integration was r = 0.998),Valtonen-Karttunen (r = 0.998), and Eggleton-Kiseleva (r = 0.997). Inabout 92 93% of all cases, these criteria yield results that areconsistent with the numerical simulations. These criteria also yieldhigh disruption probabilities for the unstable systems. Scenarios forthe formation of such systems are discussed: temporary capture of afield star by a close binary, perturbation of a stable multiple systemby a massive field object, and disruption of small stellar groups orclusters. The probabilities that these scenarios are realized areanalyzed. Analysis of the Dynamic Stability of Selected Multiple Stars with Weak HierarchyThe stability of multiple systems with known orbital elements and withsubsystems occupying adjacent hierarchy levels is analyzed using sixstability criteria and numerical simulations of their dynamicalevolution. All the stability criteria considered are in qualitativeagreement with the numerical computations. Of the 16 systems studied, 11are confirmed to be stable and five (HD 40887, HD 136176, HD 150680, HD217675, and HD 222326) may be unstable on time scales of 106 yr orless. The small dynamical ages of the unstable systems may indicate thatthey have captured components during encounters between close binariesand field or moving cluster stars. The instability could also resultfrom the perturbation of a stable system when it approaches a massiveobject (star, black hole, or molecular cloud). It is possible that someof the unstable systems are remnants of small clusters or stellargroups. Differential photometry of speckle-interferometric binary and multiple starsA method for differential photometry of speckle-interferometric binaryand multiple stars is presented. Both the accuracy and sources ofsystematic errors of the method are analysed. The photometric accuracyranges between 0.02 m and 0.20 m, depending on the atmospheric seeing,the brightness and the separation of the system components. A comparisonbetween our magnitude differences and those of other authors ispresented. Speckle Observations of Binary Stars with the WIYN Telescope. IV. Differential PhotometryFive hundred seventy-six magnitude difference measures are presented for260 binary stars. These measures are derived from CCD-based speckleobservations taken at the WIYN 3.5 m telescope at Kitt Peak NationalObservatory during the period 1997-2000. Separations of the systemsrange from over 1" down to near the diffraction limit of the telescope.A study of multiple measures of the same targets indicates that themeasures have a typical uncertainty of better than 0.13 mag per 2 minuteobservation, and that multiple observations can be averaged to arrive atsmaller uncertainties. Results presented here are also compared, insofaras it is possible, with measures in the Hipparcos Catalogue and toprevious studies using adaptive optics. No major systematic errors wereidentified.The WIYN Observatory is a joint facility of the University ofWisconsin-Madison, Indiana University, Yale University, and the NationalOptical Astronomy Observatory. Speckle interferometry of nearby multiple stars. II.This paper is a continuation of diffraction-limited speckleinterferometry of binary and multiple stars carried out at the 6-mtelescope of the Special Astrophysical Observatory in Zelenchuk. Theprogram has concentrated on nearby (π>10 mas) close binariesdiscovered or measured during the Hipparcos mission. Here, we present132 measurements of relative positions and magnitude differences for 99pairs and 8 measurements for 6 triple systems. 54 entries in the paperare new Hipparcos binaries. New triple systems with late-type dwarfcomponents, discovered in the course of observations, are HIP 8533 andHIP 25354.Based on data collected at the Special Astrophysical Observatory,Russia.{Tables 1-3 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?/A+A/422/627 Spectroscopic binary orbits from photoelectric radial velocities. Paper 168: HR 8361Not Available Determining the Minimum Sum of the Component Masses for a Binary with a Known Parallax from Observations of a Short Arc of Its Apparent MotionAn inequality that allows the minimum sum of the component masses for abinary, M_0, to be determined was derived from simple geometricconsiderations. This quantity satisfies the observed orbital motionaccording to Newton's law with a known parallax. The M_0 value can becalculated if the apparent-motion parameters for the components,including the curvature of the observed short orbital arc, weredetermined from observations. We estimated M_0 for 14 Pulkovo programstars for which the apparent orbital arc covered with observations wasno less than 10 deg. We compare M_0 with the masses estimated from themass-luminosity relation. A significant mass excess was found for thestar ADS 10329. Improved Astrometry and Photometry for the Luyten Catalog. II. Faint Stars and the Revised CatalogWe complete construction of a catalog containing improved astrometry andnew optical/infrared photometry for the vast majority of NLTT starslying in the overlap of regions covered by POSS I and by the secondincremental Two Micron All Sky Survey (2MASS) release, approximately 44%of the sky. The epoch 2000 positions are typically accurate to 130 mas,the proper motions to 5.5 mas yr-1, and the V-J colors to0.25 mag. Relative proper motions of binary components are measured to 3mas yr-1. The false-identification rate is ~1% for11<~V<~18 and substantially less at brighter magnitudes. Theseimprovements permit the construction of a reduced proper-motion diagramthat, for the first time, allows one to classify NLTT stars intomain-sequence (MS) stars, subdwarfs (SDs), and white dwarfs (WDs). We inturn use this diagram to analyze the properties of both our catalog andthe NLTT catalog on which it is based. In sharp contrast to popularbelief, we find that NLTT incompleteness in the plane is almostcompletely concentrated in MS stars, and that SDs and WDs are detectedalmost uniformly over the sky δ>-33deg. Our catalogwill therefore provide a powerful tool to probe these populationsstatistically, as well as to reliably identify individual SDs and WDs. Catalogue of averaged stellar effective magnetic fields. I. Chemically peculiar A and B type starsThis 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 Speckle Observations of Composite Spectrum Stars with PISCO in 1993-1998We present speckle interferometry observations of 47 composite spectrumstars obtained between 1993 and 1998 at the Pic du Midi Observatory withthe PISCO speckle camera. 76% of over 150 independent 10 minutesequences of observations led to a companion detection. Binary componentangular separations ranged from 0.05" to 1.2". We also obtained a seriesof 23 measurements of an additional nine close binaries. PISCOobservations confirm, for the first time since their discovery, theduplicity of HD 29104 (L4), HD 83808 (WGT 1Aa), HD 183912 Aa' (BON Ap),and HD 156729 (HR 6436). Discovered as double by Hipparcos, theparticularly difficult to resolve HD 156729 was observed despite thelarge magnitude difference, Δm=4.2, between its two components.Based on observations made with the Télescope Bernard Lyot at Picdu Midi Observatory, France. Speckle Observations of Binary Stars with the WIYN Telescope. II. Relative Astrometry Measures during 1998-2000Five hundred twelve relative astrometry measures are presented for 253double stars, including 53 double stars discovered by Hipparcos. In 15cases, relative astrometry is reported for the first time for newlyconfirmed pairs. In addition, 20 high-quality nondetections ofcompanions are reported for stars suspected of being nonsingle byHipparcos. Observations were taken using a fast-readout CCD camerasystem at the WIYN 3.5 m telescope at Kitt Peak, Arizona. In comparingthese measures with ephemeris predictions for binary stars with verywell known orbits, we find that the measurement precision is better than3 mas in separation and 1° in position angle per individualobservation. Measurement precision and detection capabilities are fullydiscussed, and confirmed orbital motion is reported in four cases of theHipparcos double star discoveries. The WIYN Observatory is a jointfacility of the University of Wisconsin-Madison, Indiana University,Yale University, and the National Optical Astronomy Observatory. VV Cephei im Winter 2000/01.Not Available The long-period companions of multiple stars tend to have moderate eccentricitiesWe examined the statistics of an angle gamma between the radius vectorof a visual companion of a multiple star and the vector of its apparentrelative motion in the system. Its distribution f(gamma ) is related tothe orbital eccentricity distribution in the investigated sample. Wefound that for the wide physical subsystems of the 174 objects from theMultiple Star Catalogue f(gamma ) is bell-shaped. The Monte-Carlosimulations have shown that our f(gamma ) corresponds to the populationof the moderate-eccentricity orbits and is not compatible with thelinear distribution f(e)=2e which follows from stellar dynamics andseems to hold for wide binaries. This points to the absence of highlyelongated orbits among the outer subsystems of multiple stars. Theconstraint of dynamical stability of triple systems is not sufficient toexplain the rounded-off'' outer orbits; instead, we speculate that itcan result from the angular momentum exchange in multiple systems duringtheir early evolution. Dynamical Stability of Triple StarsThe dynamical stability of 38 observed hierarchical triple stars withknown orbital elements of the internal and external binary subsystemsand component masses is considered. Four different criteria of dynamicalstability are used. The observed stability parameters and their criticalvalues are calculated by taking into account errors in the orbitalelements and component masses. Most triple systems are stable. Accordingto some criteria, several triple stars (ADS440, xi Tau, lambda Tau,ADS3358, VV Ori, ADS10157, HZ Her, Gliese 795, ADS15971, and ADS16138)may be dynamically unstable. This result is probably associated withunreliability of the empirical stability criteria and/or with errors inthe observed quantities. Resolved double-lined spectroscopic binaries: A neglected source of hypothesis-free parallaxes and stellar massesDouble-lined spectroscopic binaries, once visually resolved (VB-SB2),provide hypothesis-free orbital parallaxes and masses of bothcomponents. Unlike eclipsing-spectroscopic binaries for which manyaccurate masses are already known (Andersen 1991; Andersen 1997), thenumber of VB-SB2 remains rather small. This paper presents 40 suchsystems for which published visual observations and radial velocitiesallow a simultaneous adjustment of both data sets. The precision of theindividual masses as well as the evolution of that precision withrespect to the published precision is investigated. Characterization of adaptive optics point spread function for anisoplanatic imaging. Application to stellar field deconvolutionThe point spread function (PSF) of an adaptive optics system evolves inthe Field Of View (FOV). This variation strongly limits the conventionaldeconvolution methods for the processing of wide FOV images. Atheoretical expression of this PSF variation is derived. This expressionis both validated on simulations and experimental data. It is thenapplied to the a posteriori processing of stellar fields. Using theavailable prior information about the object (point-like sources), thistechnique allows the restoration of the star parameters (positions andintensities) with a precision much better than the conventional methods,in a FOV much larger than the isoplanatic field. Evolution of the efficiency'' when different data sets are combined into a unified adjustmentUsing a sample of binaries which were observed visually (VB) as well asspectroscopically for both components (SB2), we show that the efficiencyalmost always increases when a combined VB-SB2 solution replaces onebased only on VB. A test of Hipparcos parallaxes on multiple stars.Not Available Using a CCD camera in Pulkovo programs of observations of binary and multiple stars and satellites of major planets with the 26-inch refractor.Not Available Diffraction-limited speckle masking interferometry of binary stars with the SAO 6-m telescope.Not Available The ROSAT all-sky survey catalogue of optically bright main-sequence stars and subgiant starsWe 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 starsThe 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 MSC - a catalogue of physical multiple starsThe 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 Spectral classifications in the near infrared of stars with composite spectra. II. Study of a sample of 180 starsA sample of 180 supposedly composite-spectrum stars has been studied onthe basis of spectra obtained in the near infrared (8370-8780 Angstroms)at a dispersion of 33 Anstroms/mm. The objective was to study the coolercomponents of the systems. Of our sample, 120 are true compositespectra, 35 are hot spectra of types B, F and 25 are Am stars. We find astrong concentration of the cooler components of the composite spectraaround G8III. In view of the difficulty of classifying compositespectra, because of the super position of an early type dwarf and a latetype giant or supergiant spectrum, we have made several tests to controlthe classification based upon the infrared region. Since all tests gavepositive results, we conclude that our classifications can be consideredas being both reliable and homogeneous. Table \ref{tab1} is alsoavailable electronically at the CDS via anonymous ftp 130.79.128.5 orhttp://cdsweb.u-strasbg.fr/Abstracts.html} Based upon observationscarried out at Observatoire de Haute-Provence (CNRS). On the nature of the AM phenomenon or on a stabilization and the tidal mixing in binaries. II. Metallicity and pseudo-synchronization.We reveal sufficient evidences that for Am binaries the metallicitymight depend on their orbital periods, P_orb_, rather than on vsini. Inparticular, δm_1_ index seems to decrease with increasing orbitalperiod up to at least P_orb_=~50d, probably even up to P_orb_=~200d.This gives further support to our "tidal mixing + stabilization"hypothesis formulated in Part I. Moreover, while the most metallic Amstars seem to have rather large periods the slowest rotators are foundto exhibit substantially shorter P_orb_. A questioning eye is thus caston the generally adopted view that Am peculiarity is caused by asuppressed rotationally induced mixing in slowly rotating single'stars. The observed anticorrelation between rotation and metallicity mayhave also other than the textbook' explanation, namely being the resultof the correlation between metallicity and orbital period, as themajority of Am binaries are possibly synchronized. We further argue thatthere is a tendency in Am binaries towards pseudo-synchronization up toP_orb_=~35d. This has, however, no serious impact on our conclusionsfrom Part I; on the contrary, they still hold even if this effect istaken into account. Twenty Years of Seeing DoubleNot Available VV Cephei : Alle 20 Jahre wieder : der "groesste aller Sterne" bedeckt seinen Begleiter.Not Available On the nature of the AM phenomenon or on a stabilization and the tidal mixing in binaries. I. Orbital periods and rotation.The paper casts a questioning eye on the unique role of the diffusiveparticle transport mechanism in explaining the Am phenomenon and arguesthat the so-called tidal effects might be of great importance incontrolling diffusion processes. A short period cutoff at =~1.2d as wellas a 180-800d gap were found in the orbital period distribution (OPD) ofAm binaries. The existence of the former can be ascribed to the state ofthe primaries with the almost-filled Roche lobes. The latter couldresult from the combined effects of the diffusion, tidal mixing andstabilization processes. Because the tidal mixing might surpassdiffusion in the binaries with the orbital periods P_orb_ less thanseveral hundred days and might thus sustain the He convection zone,which would otherwise disappear, no Am stars should lie below thisboundary. The fact that they are nevertheless seen there implies theexistence of some stabilization mechanism (as, e.g., that recentlyproposed by Tassoul & Tassoul 1992) for the binaries with orbitalperiods less than 180d. Further evidence is given to the fact that theOPD for the Am and the normal binaries with an A4-F1 primary arecomplementary to each other, from which it stems that Am stars are closeto the main sequence. There are, however, indications that they haveslightly larger radii (2.1-3 Rsun_) than expected for theirspectral type. The generally accepted rotational velocity cutoff at=~100km/s is shown to be of little value when applied on Am binaries ashere it is not a single quantity but, in fact, a function of P_orb_whose shape is strikingly similar to that of the curves of constantmetallicity as ascertained from observations. This also leads to thewell known overlap in rotational velocities of the normal and Am starsfor 402.5d.We have exploited this empirical cutoff function to calibrate thecorresponding turbulent diffusion coefficient associated with tidalmixing, having found out that the computed form of the lines of constantturbulence fits qualitatively the empirical shape of the curves ofconstant metallicity. As for larger orbital periods(20d55km/s found by Burkhart(1979) would then be nothing but a manifestation of insufficientlypopulated corresponding area of larger P_orb_.
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