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Statistical Constraints for Astrometric Binaries with Nonlinear Motion
Useful constraints on the orbits and mass ratios of astrometric binariesin the Hipparcos catalog are derived from the measured proper motiondifferences of Hipparcos and Tycho-2 (Δμ), accelerations ofproper motions (μ˙), and second derivatives of proper motions(μ̈). It is shown how, in some cases, statistical bounds can beestimated for the masses of the secondary components. Two catalogs ofastrometric binaries are generated, one of binaries with significantproper motion differences and the other of binaries with significantaccelerations of their proper motions. Mathematical relations betweenthe astrometric observables Δμ, μ˙, and μ̈ andthe orbital elements are derived in the appendices. We find a remarkabledifference between the distribution of spectral types of stars withlarge accelerations but small proper motion differences and that ofstars with large proper motion differences but insignificantaccelerations. The spectral type distribution for the former sample ofbinaries is the same as the general distribution of all stars in theHipparcos catalog, whereas the latter sample is clearly dominated bysolar-type stars, with an obvious dearth of blue stars. We point outthat the latter set includes mostly binaries with long periods (longerthan about 6 yr).
| Re-processing the Hipparcos Transit Data and Intermediate Astrometric Data of spectroscopic binaries. I. Ba, CH and Tc-poor S stars
Only 235 entries were processed as astrometric binaries with orbits inthe Hipparcos and Tycho Catalogue (\cite{Hipparcos}). However, theIntermediate Astrometric Data (IAD) and Transit Data (TD) made availableby ESA make it possible to re-process the stars that turned out to bespectroscopic binaries after the completion of the Catalogue. This paperillustrates how TD and IAD may be used in conjunction with the orbitalparameters of spectroscopic binaries to derive astrometric parameters.The five astrometric and four orbital parameters (not already known fromthe spectroscopic orbit) are derived by minimizing an objective function(chi 2) with an algorithm of global optimization. This codehas been applied to 81 systems for which spectroscopic orbits becameavailable recently and that belong to various families ofchemically-peculiar red giants (namely, dwarf barium stars, strong andmild barium stars, CH stars, and Tc-poor S stars). Among these 81systems, 23 yield reliable astrometric orbits. These 23 systems make itpossible to evaluate on real data the so-called ``cosmic error''described by Wielen et al. (1997), namely the fact that an unrecognizedorbital motion introduces a systematic error on the proper motion.Comparison of the proper motion from the Hipparcos catalogue with thatre-derived in the present work indicates that the former are indeed faroff the present value for binaries with periods in the range 3 to ~ 8years. Hipparcos parallaxes of unrecognized spectroscopic binaries turnout to be reliable, except for systems with periods close to 1 year, asexpected. Finally, we show that, even when a complete orbital revolutionwas observed by Hipparcos, the inclination is unfortunately seldomprecise. Based on observations from the Hipparcos astrometric satelliteoperated by the European Space Agency (ESA 1997).
| New CORAVEL spectroscopic-binary orbits of giant barium stars. II
This paper complements the set of spectroscopic orbits for giant bariumstars given in \cite[Udry et al. (1998)]{udry98} and provides data for20 binaries (18 orbits + 2 minimum-period determinations). Based onobservations obtained at the Haute-Provence Observatory (France) and atthe European Southern Observatory (ESO, La Silla, Chile).
| A CORAVEL radial-velocity monitoring of giant BA and S stars: Spectroscopic orbits and intrinsic variations. I.
With the aim of deriving the binary frequency among Ba and S stars, 56new spectroscopic orbits (46 and 10, respectively) have been derived forthese chemically-peculiar red giants monitored with the \coravel\spectrometers. These orbits are presented in this paper (38 orbits) andin a companion paper \cite[(Udry et al. 1998,]{Udry} Paper II; 18orbits). The results for 12 additional long-period binary stars (6 and6, respectively), for which only minimum periods (generally exceeding 10y) can be derived, are also presented here (10) and in Paper II (2). Theglobal analysis of this material, with a few supplementary orbits fromthe literature, is presented in \cite[Jorissen et al.(1998).]{Jorissen98} For the subsample of Mira S, SC and (Tc-poor) Cstars showing intrinsic radial-velocity variations due to atmosphericphenomena, orbital solutions (when available) have been retained if thevelocity and photometric periods are different (3 stars). However, it isemphasized that these orbit determinations are still tentative. Threestars have been found with radial-velocity variations synchronous withthe light variations. Pseudo-orbital solutions have been derived forthose stars. In the case of RZ Peg, a line-doubling phenomenon isobserved near maximum light, and probably reflects the shock wavepropagating through the photosphere. Based on observations obtained atthe Haute-Provence Observatory (France) and at the European SouthernObservatory (ESO, La Silla, Chile).
| Insights into the formation of barium and Tc-poor S stars from an extended sample of orbital elements
The set of orbital elements available for chemically-peculiar red giant(PRG) stars has been considerably enlarged thanks to a decade-longCORAVEL radial-velocity monitoring of about 70 barium stars and 50 Sstars. When account is made for the detection biases, the observedbinary frequency among strong barium stars, mild barium stars andTc-poor S stars (respectively 35/37, 34/40 and 24/28) is compatible withthe hypothesis that they are all members of binary systems. Thesimilarity between the orbital-period, eccentricity and mass-functiondistributions of Tc-poor S stars and barium stars confirms that Tc-poorS stars are the cooler analogs of barium stars. A comparative analysisof the orbital elements of the various families of PRG stars, and of asample of chemically-normal, binary giants in open clusters, revealsseveral interesting features. The eccentricity - period diagram of PRGstars clearly bears the signature of dissipative processes associatedwith mass transfer, since the maximum eccentricity observed at a givenorbital period is much smaller than in the comparison sample of normalgiants. be held The mass function distribution is compatible with theunseen companion being a white dwarf (WD). This lends support to thescenario of formation of the PRG star by accretion of heavy-element-richmatter transferred from the former asymptotic giant branch progenitor ofthe current WD. Assuming that the WD companion has a mass in the range0.60+/-0.04 Msb ȯ, the masses of mild and strong barium starsamount to 1.9+/-0.2 and 1.5+/-0.2 Msb ȯ, respectively. Mild bariumstars are not restricted to long-period systems, contrarily to what isexpected if the smaller accretion efficiency in wider systems were thedominant factor controlling the pollution level of the PRG star. Theseresults suggest that the difference between mild and strong barium starsis mainly one of galactic population rather than of orbital separation,in agreement with their respective kinematical properties. There areindications that metallicity may be the parameter blurring the period -Ba-anomaly correlation: at a given orbital period, increasing levels ofheavy-element overabundances are found in mild barium stars, strongbarium stars, and Pop.II CH stars, corresponding to a sequence ofincreasingly older, i.e., more metal-deficient, populations. PRG starsthus seem to be produced more efficiently in low-metallicitypopulations. Conversely, normal giants in barium-like binary systems mayexist in more metal-rich populations. HD 160538 (DR Dra) may be such anexample, and its very existence indicates at least that binarity is nota sufficient condition to produce a PRG star. This paper is dedicated tothe memory of Antoine Duquennoy, who contributed many among theobservations used in this study
| Barium stars, galactic populations and evolution.
In this paper HIPPARCOS astrometric and kinematical data together withradial velocities from other sources are used to calibrate bothluminosity and kinematics parameters of Ba stars and to classify them.We confirm the results of our previous paper (where we used data fromthe HIPPARCOS Input Catalogue), and show that Ba stars are aninhomogeneous group. Five distinct classes have been found i.e. somehalo stars and four groups belonging to disk population: roughlysuper-giants, two groups of giants (one on the giant branch, the otherat the clump location) and dwarfs, with a few subgiants mixed with them.The confirmed or suspected duplicity, the variability and the range ofknown orbital periods found in each group give coherent resultssupporting the scenario for Ba stars that are not too highly massivebinary stars in any evolutionary stages but that all were previouslyenriched with Ba from a more evolved companion. The presence in thesample of a certain number of ``false'' Ba stars is confirmed. Theestimates of age and mass are compatible with models for stars with astrong Ba anomaly. The mild Ba stars with an estimated mass higher than3Msun_ may be either stars Ba enriched by themselves or``true'' Ba stars, which imposes new constraints on models.
| Absolute magnitudes and kinematics of barium stars.
The absolute magnitude of barium stars has been obtained fromkinematical data using a new algorithm based on the maximum-likelihoodprinciple. The method allows to separate a sample into groupscharacterized by different mean absolute magnitudes, kinematics andz-scale heights. It also takes into account, simultaneously, thecensorship in the sample and the errors on the observables. The methodhas been applied to a sample of 318 barium stars. Four groups have beendetected. Three of them show a kinematical behaviour corresponding todisk population stars. The fourth group contains stars with halokinematics. The luminosities of the disk population groups spread alarge range. The intrinsically brightest one (M_v_=-1.5mag,σ_M_=0.5mag) seems to be an inhomogeneous group containing bariumbinaries as well as AGB single stars. The most numerous group (about 150stars) has a mean absolute magnitude corresponding to stars in the redgiant branch (M_v_=0.9mag, σ_M_=0.8mag). The third group containsbarium dwarfs, the obtained mean absolute magnitude is characteristic ofstars on the main sequence or on the subgiant branch (M_v_=3.3mag,σ_M_=0.5mag). The obtained mean luminosities as well as thekinematical results are compatible with an evolutionary link betweenbarium dwarfs and classical barium giants. The highly luminous group isnot linked with these last two groups. More high-resolutionspectroscopic data will be necessary in order to better discriminatebetween barium and non-barium stars.
| Taxonomy of barium stars
Spectral classification, barium intensity, radial velocity, luminosity,and kinematical properties are determined for 389 barium stars byanalyzing image-tube spectra and photometric observation data. Diskkinematics for the stars are based on whether they are Ba weak or Bastrong. Weak barium stars in general have smaller velocity dispersions,brighter apparent magnitude, and lower luminosity than strong bariumstars. These characteristics are confirmed by solving for meanspectroscopic distances, z-scale height distances, and reduced propermotions.
| Kinematic and spatial distributions of barium stars - Are the barium stars and AM stars related?
The possibility of an evolutionary link between Am stars and bariumstars is considered, and an examination of previous data suggests thatbarium star precursors are main-sequence stars of intermediate mass, aremost likely A and/or F dwarfs, and are intermediate-mass binaries withclose to intermediate orbital separations. The possible role of masstransfer in the later development of Am systems is explored. Masstransfer and loss from systems with a range of masses and orbitalseparations may explain such statistical peculiarities of barium starsas the large dispersion in absolute magnitude, the large range ofelemental abundances from star to star, and the small number of starswith large peculiar velocities.
| Objective-prism discoveries in the declination zone 0 deg to -20 deg
An inspection of 130 10-deg-prism plates taken for the University ofMichigan Southern Spectral Survey has yielded 154 new peculiar orotherwise interesting stars. The regions surveyed are mainly at fairlyhigh galactic latitudes; this fills a gap in previous work of this type.About three-quarters of the objects will eventually be reclassified byHouk in a systematic work on all of the Henry Draper Catalogue stars,but many of these are of sufficient interest to justify earlypublication.
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Datos observacionales y astrométricos
| Constelación: | Águila |
| Ascensión Recta: | 19h17m11.03s |
| Declinación: | +00°29'50.5" |
| Magnitud Aparente: | 7.639 |
| Distancia: | 296.736 parsecs |
| Movimiento Propio en Ascensión Recta: | -13.6 |
| Movimiento Propio en Declinación: | -23.2 |
| B-T magnitude: | 9.207 |
| V-T magnitude: | 7.769 |
Catálogos y designaciones:
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