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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).
| MSX, 2MASS, and the LARGE MAGELLANIC CLOUD: A Combined Near- and Mid-Infrared View
The Large Magellanic Cloud (LMC) has been observed by the MidcourseSpace Experiment (MSX) in the mid-infrared and the Two Micron All SkySurvey (2MASS) in the near-infrared. We have performed across-correlation of the 1806 MSX catalog sources and nearly 1.4 million2MASS cataloged point and extended sources and find 1664 matches. Usingthe available color information, we identify a number of stellarpopulations and nebulae, including main-sequence stars, giant stars, redsupergiants, carbon- and oxygen-rich asymptotic giant branch (AGB)stars, planetary nebulae, H II regions, and other dusty objects likelyassociated with early-type stars. A total of 731 of these sources haveno previous identification. We compile a listing of all objects, whichincludes photometry and astrometry. The 8.3 μm MSX sensitivity is thelimiting factor for object detection: only the brighter red objects,specifically the red supergiants, AGB stars, planetary nebulae, and H IIregions, are detected in the LMC. The remaining objects are likely inthe Galactic foreground. The spatial distribution of the infrared LMCsources may contribute to understanding stellar formation and evolutionand the overall galactic evolution. We demonstrate that a combined mid-and near-infrared photometric baseline provides a powerful means ofidentifying new objects in the LMC for future ground-based andspace-based follow-up observations.
| ROSAT X-ray sources in the field of the LMC. I. Total LMC gas from the background AGN spectral fits
We analyzed a sample of 26 background X-ray sources in a ~ 60 squaredegree field of the Large Magellanic Cloud observed with the ROSAT PSPC.The sample has been selected from previously classified and opticallyidentified X-ray sources. In addition, pointlike and spectrally hardsources with at least 100 to 200 observed counts have been used for theanalysis. We performed X-ray spectral fitting and derived total hydrogenabsorbing column densities due to LMC gas in the range(1020-2 1021) cm-2. We compared thesecolumns with the H I columns derived from a 21-cm Parkes survey of theLMC. For 7 optically identified sources we find, within theuncertainties derived from the X-ray spectral fit, agreement for bothcolumns. For a further 19 sources, we constrain the LMC columns from theX-ray spectral fit assuming that the power law photon index is that ofAGN type spectra. We derive for 20 sources gas columns which are withinthe uncertainties, in agreement with the H I columns. We derive for twobackground sources (RX J0536.9-6913 and RX J0547.0-7040) hydrogenabsorbing column densities due to LMC gas, which are in excess comparedto the H I columns. These sources - located in regions of large ( ~ 31021 cm-2) LMC H I column densities - could beseen through additional gas which may be warm and diffuse, cold ormolecular. For 10 sources we derive upper limits for the gas columnsadditional to H I and constrain the molecular mass fraction to<(30-140)%.
| ROSAT HRI catalogue of X-ray sources in the LMC region
All 543 pointed observations of the ROSAT High Resolution Imager (HRI)with exposure times higher than 50 s and performed between 1990 and 1998in a field of 10°\ x 10°\ covering the Large Magellanic Cloud(LMC) were analyzed. A catalogue was produced containing 397 X-raysources with their properties measured by the HRI. The list wascross-correlated with the ROSAT Position Sensitive Propotional Counter(PSPC) source catalogue presented by Haberl & Pietsch (1999) inorder to obtain the hardness ratios for the X-ray sources detected byboth instruments. 138 HRI sources are contained in the PSPC catalogue,259 sources are new detections. The spatial resolution of the HRI washigher than that of the PSPC and the source position could be determinedwith errors mostly smaller than 15'' which are dominated by systematicattitude errors. After cross-correlating the source catalogue with theSIMBAD data base and the TYCHO catalogue 94 HRI sources were identifiedwith known objects based on their positional coincidence and X-rayproperties. Whenever more accurate coordinates were given in cataloguesor literature for identified sources, the X-ray coordinates werecorrected and the systematic error of the X-ray position was reduced.For other sources observed simultaneously with an identified source thecoordinates were improved as well. In total the X-ray position of 254sources could be newly determined. The catalogue contains 39 foregroundstars, 24 supernova remnants (SNRs), five supersoft sources (SSSs), nineX-ray binaries (XBs), and nine AGN well known from literature. Anothereight sources were identified with known candidates for these sourceclasses. Additional 21 HRI sources are suggested in the present work ascandidates for SNR, X-ray binary in the LMC, or background AGN becauseof their extent, hardness ratios, X-ray to optical flux ratio, or fluxvariability. Table 4 is only and Tables 1--3 are also available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html
| A ROSAT PSPC catalogue of X-ray sources in the LMC region
We analyzed more than 200 ROSAT PSPC observations in a 10 by 10 degreefield centered on the Large Magellanic Cloud (LMC) and performed between1990 and 1994 to derive a catalogue of X-ray sources. The list contains758 sources with their X-ray properties. From cross-correlations of thePSPC catalogue with the SIMBAD data base and literature searches we givelikely identifications for 144 X-ray sources based on positionalcoincidence, but taking into account X-ray properties like hardnessratios and source extent. 46 known sources are associated with supernovaremnants (SNRs) and candidates in the LMC, most of them already detectedby previous X-ray missions. Including the new candidates from\cite[Haberl & Pietsch (1999)]{HP99} based on variability studies ofthe sources in our PSPC catalogue, the number of X-ray binaries in theLMC increased to 17 and that of the supersoft sources (SSSs) to 9. Theremaining ~ 50% of the identified sources comprise mainly foregroundstars (up to 57) and background extragalactic objects (up to 15). Theoften distinguished X-ray properties of the different source types wereused for a first classification of new, unknown X-ray sources. Eight newPSPC sources are classified as SNRs from their hardness ratios and onepromising new SNR candidate with extended X-ray emission is foundfurther north than all known SNRs. Three soft X-ray sources havehardness ratios compatible to those of the known SSSs. A selection onhardness ratios and X-ray to optical flux ratio further suggests 27foreground stars and 3 AGN.
| UBV photometry of galactic foreground and LMC member stars. I - Galactic foreground stars
UBV photometry of 955 galactic foreground stars in the direction to theLarge Magellanic Cloud is presented. The stars have been chosen fromforeground star catalogs and have been measured to complete a new database containing entries of more than 5000 stars in the direction of theLMC. First and second order extinction coefficients at La Silla/Chileare given, which differ from the standard values because of the 1991eruption of the volcano Mt. Pinatubo.
| Positional reference stars in the Magellanic Clouds
The equatorial coordinates are determined of 926 stars (mainly ofgalactic origin) in the direction of the Magellanic Clouds at the meanepoch T = 1978.4 with an overall accuracy characterized by the meanvalues of the O-C coordinates, Sa = 0.35 arcsec and Sd = 0.38 arcsec,calculated from the coordinates of the Perth reference stars. Thesevalues are larger than the accuracy expected for primary standard stars.They allow the new positions to be considered as those of reliablesecondary standard stars. The published positions correspond to anunquestionable improvement of the quality of the coordinates provided inthe current catalogs. This study represents an 'astrometric step' in thestarting of a 'Durchmusterung' of the Magellanic Clouds organized by deBoer (1988, 1989).
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