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Radial velocities for the HIPPARCOS-Gaia Hundred-Thousand-Proper-Motion project
Context. The Hundred-Thousand-Proper-Motion (HTPM) project willdetermine the proper motions of ~113 500 stars using a ~23-yearbaseline. The proper motions will be based on space-based measurementsexclusively, with the Hipparcos data, with epoch 1991.25, as first epochand with the first intermediate-release Gaia astrometry, with epoch~2014.5, as second epoch. The expected HTPM proper-motion standarderrors are 30-190 μas yr-1, depending on stellarmagnitude. Aims: Depending on the astrometric characteristics ofan object, in particular its distance and velocity, its radial velocitycan have a significant impact on the determination of its proper motion.The impact of this perspective acceleration is largest for fast-moving,nearby stars. Our goal is to determine, for each star in the Hipparcoscatalogue, the radial-velocity standard error that is required toguarantee a negligible contribution of perspective acceleration to theHTPM proper-motion precision. Methods: We employ two evaluationcriteria, both based on Monte-Carlo simulations, with which we determinewhich stars need to be spectroscopically (re-)measured. Both criteriatake the Hipparcos measurement errors into account. The first criterion,the Gaussian criterion, is applicable to nearby stars. For distantstars, this criterion works but returns overly pessimistic results. Wetherefore use a second criterion, the robust criterion, which isequivalent to the Gaussian criterion for nearby stars but avoids biasesfor distant stars and/or objects without literature radial velocity. Therobust criterion is hence our prefered choice for all stars, regardlessof distance. Results: For each star in the Hipparcos catalogue,we determine the confidence level with which the available radialvelocity and its standard error, taken from the XHIP compilationcatalogue, are acceptable. We find that for 97 stars, the radialvelocities available in the literature are insufficiently precise for a68.27% confidence level. If requiring this level to be 95.45%, or even99.73%, the number of stars increases to 247 or 382, respectively. Wealso identify 109 stars for which radial velocities are currentlyunknown yet need to be acquired to meet the 68.27% confidence level. Forhigher confidence levels (95.45% or 99.73%), the number of such starsincreases to 1071 or 6180, respectively. Conclusions: To satisfythe radial-velocity requirements coming from our study will be adaunting task consuming a significant amount of spectroscopic telescopetime. The required radial-velocity measurement precisions vary fromsource to source. Typically, they are modest, below 25 kms-1, but they can be as stringent as 0.04 km s-1for individual objects like Barnard's star.Fortunately, the follow-up spectroscopy is not time-critical since theHTPM proper motions can be corrected a posteriori once (improved) radialvelocities become available.The results data file is only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/546/A61
| Bayesian inference of stellar parameters and interstellar extinction using parallaxes and multiband photometry
Astrometric surveys provide the opportunity to measure the absolutemagnitudes of large numbers of stars, but only if the individualline-of-sight extinctions are known. Unfortunately, extinction is highlydegenerate with stellar effective temperature when estimated frombroad-band optical/infrared photometry. To address this problem, Iintroduce a Bayesian method for estimating the intrinsic parameters of astar and its line-of-sight extinction. It uses both photometry andparallaxes in a self-consistent manner in order to provide anon-parametric posterior probability distribution over the parameters.The method makes explicit use of domain knowledge by employing theHertzsprung-Russell Diagram (HRD) to constrain solutions and to ensurethat they respect stellar physics. I first demonstrate this method byusing it to estimate effective temperature and extinction from BVJHKdata for a set of artificially reddened Hipparcos stars, for whichaccurate effective temperatures have been estimated from high-resolutionspectroscopy. Using just the four colours, we see the expected strongdegeneracy (positive correlation) between the temperature andextinction. Introducing the parallax, apparent magnitude and the HRDreduces this degeneracy and improves both the precision (reduces theerror bars) and the accuracy of the parameter estimates, the latter byabout 35 per cent. The resulting accuracy is about 200 K in temperatureand 0.2 mag in extinction. I then apply the method to estimate theseparameters and absolute magnitudes for some 47 000 F, G, K Hipparcosstars which have been cross-matched with Two-Micron All-Sky Survey(2MASS). The method can easily be extended to incorporate the estimationof other parameters, in particular metallicity and surface gravity,making it particularly suitable for the analysis of the 109stars from Gaia.
| Proper-motion binaries in the Hipparcos catalogue. Comparison with radial velocity data
Context: .This paper is the last in a series devoted to the analysis ofthe binary content of the Hipparcos Catalogue. Aims: .Thecomparison of the proper motions constructed from positions spanning ashort (Hipparcos) or long time (Tycho-2) makes it possible to uncoverbinaries with periods of the order of or somewhat larger than the shorttime span (in this case, the 3 yr duration of the Hipparcos mission),since the unrecognised orbital motion will then add to the propermotion. Methods: .A list of candidate proper motion binaries isconstructed from a carefully designed χ2 test evaluatingthe statistical significance of the difference between the Tycho-2 andHipparcos proper motions for 103 134 stars in common between the twocatalogues (excluding components of visual systems). Since similar listsof proper-motion binaries have already been constructed, the presentpaper focuses on the evaluation of the detection efficiency ofproper-motion binaries, using different kinds of control data (mostlyradial velocities). The detection rate for entries from the NinthCatalogue of Spectroscopic Binary Orbits (S_B^9) is evaluated, as wellas for stars like barium stars, which are known to be all binaries, andfinally for spectroscopic binaries identified from radial velocity datain the Geneva-Copenhagen survey of F and G dwarfs in the solarneighbourhood. Results: .Proper motion binaries are efficientlydetected for systems with parallaxes in excess of ~20 mas, and periodsin the range 1000-30 000 d. The shortest periods in this range(1000-2000 d, i.e., once to twice the duration of the Hipparcos mission)may appear only as DMSA/G binaries (accelerated proper motion in theHipparcos Double and Multiple System Annex). Proper motion binariesdetected among S_B9 systems having periods shorter than about400 d hint at triple systems, the proper-motion binary involving acomponent with a longer orbital period. A list of 19 candidate triplesystems is provided. Binaries suspected of having low-mass(brown-dwarf-like) companions are listed as well. Among the 37 bariumstars with parallaxes larger than 5 mas, only 7 exhibit no evidence forduplicity whatsoever (be it spectroscopic or astrometric). Finally, thefraction of proper-motion binaries shows no significant variation amongthe various (regular) spectral classes, when due account is taken forthe detection biases.Full Table [see full textsee full text] is only available in electronicform at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/464/377
| 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).
| Improved Astrometry and Photometry for the Luyten Catalog. II. Faint Stars and the Revised Catalog
We 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.
| Calán-ESO Proper-Motion Catalog
The Calán-ESO Proper-Motion Catalog (CE Catalog) contains 542stars with proper motions >=0.2" yr-1, identified in 14ESO areas in the southern hemisphere. Proper motions were measured fromred IIIa-F plates taken 6-16 yr apart. Comparing the CE catalog with theLuyten and the Luyten half-second catalogs, we find that both sufferfrom incompleteness, which is particularly serious (<~40% complete)for mR>~13, where many of the astrophysically interestingobject can be found. Proper motions, coordinates, estimated magnitudes,and finding charts for all objects in the catalog are provided. Based onplates obtained with the Schmidt Camera operated by ESO at La Silla,Chile. Project 64.H-0318.
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| קבוצת-כוכבים: | נחש מים |
| התרוממות ימנית: | 10h57m23.42s |
| סירוב: | -33°29'05.0" |
| גודל גלוי: | 9.334 |
| תנועה נכונה: | 208.9 |
| תנועה נכונה: | -114.1 |
| B-T magnitude: | 10.466 |
| V-T magnitude: | 9.428 |
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