Astrometric Orbits for Hipparcos Stochastic Binaries (original) (raw)
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Astrometric Orbits for Hipparcos Stochastic Binaries
2008
Taking advantage of an improved genetic optimization algorithm for fitting unconstrained Kepler orbits to the Hipparcos intermediate astrometric data, we obtain additional orbital solutions for 81 Hipparcos stars with previous stochastic (failed) solutions. The sample includes astrophysically interesting objects, including the old disk wide binary HIP 754, the nearby AGB star HIP 34922 (L2 Pup), and the nearby M2 dwarf HIP 5496 (GJ 54, at 8 pc from the Sun) which has a resolved M dwarf companion.
Unconstrained Astrometric Orbits for Hipparcos Stars with Stochastic Solutions
The Astrophysical Journal Supplement Series, 2006
A considerable number of astrometric binaries whose positions on the sky do not obey the standard model of mean position, parallax and linear proper motion, were observed by the Hipparcos satellite. Some of them remain non-discovered, and their observational data have not been properly processed with the more adequate astrometric model that includes nonlinear orbital motion. We develop an automated algorithm based on "genetic optimization", to solve the orbital fitting problem in the most difficult setup, when no prior information about the orbital elements is available (from, e.g., spectroscopic data or radial velocity monitoring). We also offer a technique to accurately compute the probability that an orbital fit is bogus, that is, that an orbital solution is obtained for a single star, and to estimate the probability distributions for the fitting orbital parameters. We test this method on Hipparcos stars with known orbital solutions in the catalog, and further apply it to 1561 stars with stochastic solutions, which may be unresolved binaries. At a confidence level of 99%, orbital fits are obtained for 65 stars, most of which have not been known as binary. It is found that reliable astrometric fits can be obtained even if the period is somewhat longer than the time span of the Hipparcos mission, i.e., if the orbit is not closed. A few of the new probable binaries with A-type primaries with periods 444-2015 d are chemically peculiar stars, including Ap and λ Boo type. The anomalous spectra of these stars are explained as admixture of the light from the unresolved, sufficiently bright and massive companions. We estimate the apparent orbits of four stars which have been identified as members of the ≈ 300 Myr-old UMa kinematic group. Another four new nearby binaries may include low-mass M-type or brow dwarf companions. Follow-up spectroscopic observations in conjunction with 101 +127 −56
Statistics of Hipparcos binaries: probing the 1-10 AU separation range
Astronomy and Astrophysics
The observation of double stars by Hipparcos is modelled in order to check the statistics of double-star solutions in the Hipparcos Catalogue and to set quantitative limits on binary distributions. A Galaxy model is combined with models of binary distributions and of the observation process to derive the expected numbers of the different kinds of binary solutions in the Catalogue (component, acceleration, orbital and stochastic solutions). The observed number of component (C) and acceleration (G) solutions among bright (V<~ 7-8) main-sequence stars are not consistent with a model having the same binary frequency and distributions as found by Duquennoy & Mayor (1991) for solar-type field stars. The number of companions per primary is estimated to 25+/- 5% for semi-major axes from 1 to 10 AU, and to 43+/- 20% for the range 10-100 AU. The fitted model predicts about three times as many orbital solutions as actually found in the catalogue, which suggests that many more orbits could b...
Spectroscopically and Spatially Resolving the Components of the Close Binary Stars, 2004
Among the 120 000 objects in the Hipparcos catalogue, 235 were fitted with an orbital model, i.e. with up to seven additional parameters with respect to the default single star model. In their quest for the orbital inclination, spectroscopists promptly realized how useful the Hipparcos data could be. Besides the original 235 systems, most Hipparcos entries with a spectroscopic orbit (extrasolar planet or stellar companion) have now been reprocessed. Not all these revised fits were fruitful. Some were even awful. We present a survey of all the areas where the Hipparcos observations have been fitted with an orbital model so far.
Re-processing the Hipparcos Transit Data and Intermediate Astrometric Data of spectroscopic binaries
Astronomy and Astrophysics Supplement Series, 2000
Only 235 entries were processed as astrometric binaries with orbits in the Hipparcos and Tycho Catalogue (ESA 1997). However, the Intermediate Astrometric Data (IAD) and Transit Data (TD) made available by ESA make it possible to re-process the stars that turned out to be spectroscopic binaries after the completion of the Catalogue. This paper illustrates how TD and IAD may be used in conjunction with the orbital parameters of spectroscopic binaries to derive astrometric parameters. The five astrometric and four orbital parameters (not already known from the spectroscopic orbit) are derived by minimizing an objective function (χ 2 ) with an algorithm of global optimization. This code has been applied to 81 systems for which spectroscopic orbits became available recently and that belong to various families of chemically-peculiar red giants (namely, dwarf barium stars, strong and mild barium stars, CH stars, and Tc-poor S stars). Among these 81 systems, 23 yield reliable astrometric orbits. These 23 systems make it possible to evaluate on real data the so-called 'cosmic error' described by , namely the fact that an unrecognized orbital motion introduces a systematic error on the proper motion. Comparison of the proper motion from the Hipparcos catalogue with that re-derived in the present work indicates that the former are indeed far off the present value for binaries with periods in the range 3 to ∼ 8 years. Hipparcos parallaxes of unrecognized spectroscopic binaries turn out to be reliable, except for systems with periods close to 1 year, as expected. Finally, we show that, even when a complete orbital revolution was observed by Hipparcos, the inclination is unfortunately seldom precise.
ASTRONOMY AND ASTROPHYSICS Visual binary orbits and masses post Hipparcos ⋆
2013
Abstract. The parallaxes from Hipparcos are an important ingredient to derive more accurate masses for known orbital binaries, but in order to exploit the parallaxes fully, the orbital elements have to be known to similar precision. The present work gives improved orbital elements for some 205 systems by combining the Hipparcos astrometry with existing ground-based observations. The new solutions avoid the linearity constraints and omissions in the Hipparcos Catalog by using the intermediate Transit Data which can be combined with ground-based observations in arbitarily complex orbital models. The new orbital elements and parallaxes give new mass-sum values together with realistic total error-estimates. To get individual masses at least for main-sequence systems, the mass-ratios have been generally estimated from theoretical isochrones and observed magnitudedifferences. For some 25 short-period systems, however, true astrometric mass-ratios have been determined through the observed ...
Binaries in the Hipparcos data: keep digging II. Modeling the IAD of known spectroscopic systems
We reprocess the Hipparcos Intermediate Astrometric Data of know spectroscopic binaries (retrived from the 9th catalogue of spectroscopic binary orbits, http://sb9.astro.ulb.ac.be) to see whether the orbital inclination, and thus the mass of the secondary, can be derived. Several statistical tests ) are used to ensure the reliability of the fit. About 70 systems (originally processed as single stars) out of 863 benefit from the orbital model.
Binaries in the Hipparcos data: Keep digging
Among the 120 000 objects in the Hipparcos catalogue, 235 were fitted with an orbital model, i.e. with up to seven additional parameters with respect to the default single star model. In their quest for the orbital inclination, spectroscopists promptly realized how useful the Hipparcos data could be. Besides the original 235 systems, most Hipparcos entries with a spectroscopic orbit (extrasolar planet or stellar companion) have now been re-processed. Not all these revised fits were fruitful. Some were even awful. We present a survey of all the areas where the Hipparcos observations have been fitted with an orbital model so far.
Double star data in the HIPPARCOS Catalogue
Astronomy & Astrophysics - ASTRON ASTROPHYS, 1997
The Hipparcos Catalogue contains astrometric results for 117955 catalogue entries, many of which are in reality double or multiple stars. For 17917 entries special solutions were made in order to cope with the various manifestations of multiplicity, and 6763 other entries were flagged as suspected binaries but solved as single stars. Details of the special solutions are contained in the Hipparcos Catalogue Double and Multiple Systems Annex, divided in five parts according to the type of solution: resolved systems (13211 entries with a total of 24588 components), astrometric binaries with curved proper motion (2622 entries) or orbital solutions (235 entries), `variability-induced movers' (288 entries) and `stochastic' solutions (1561 entries). Trigonometric parallaxes and the positions and proper motions in the extragalactic reference system ICRS are provided for all entries.
Visual binary orbits and masses post Hipparcos
Astronomy and Astrophysics, 1999
The parallaxes from Hipparcos are an important ingredient to derive more accurate masses for known orbital binaries, but in order to exploit the parallaxes fully, the orbital elements have to be known to similar precision. The present work gives improved orbital elements for some 205 systems by combining the Hipparcos astrometry with existing ground-based observations. The new solutions avoid the linearity constraints and omissions in the Hipparcos Catalog by using the intermediate Transit Data which can be combined with ground-based observations in arbitarily complex orbital models. The new orbital elements and parallaxes give new mass-sum values together with realistic total error-estimates. To get individual masses at least for main-sequence systems, the mass-ratios have been generally estimated from theoretical isochrones and observed magnitudedifferences. For some 25 short-period systems, however, true astrometric mass-ratios have been determined through the observed orbital curvature in the 3-year Hipparcos observation interval. The final result is an observed 'mass-luminosity relation' which falls close to theoretical expectation, but with 'outliers' due to undetected multiplicity or to composition-and age-effects in the nonuniform near-star sample.