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Roche tomography of cataclysmic variables - IV. Star-spots and slingshot prominences on BV Cen
We present Roche tomograms of the G5-G8 IV/V secondary star in thelong-period cataclysmic variable BV Cen reconstructed from MagellanInamori Kyocera Echelle spectrograph echelle data taken on the MagellanClay 6.5-m telescope. The tomograms show the presence of a number oflarge, cool star-spots on BV Cen for the first time. In particular, wefind a large high-latitude spot which is deflected from the rotationalaxis in the same direction as seen on the K3-K5 IV/V secondary star inthe cataclysmic variable AE Aqr. BV Cen also shows a similar relativepaucity of spots at latitudes between 40° and 50° when comparedwith AE Aqr. Furthermore, we find evidence for an increased spotcoverage around longitudes facing the white dwarf which supports modelsinvoking star-spots at the L1 point to explain the low statesobserved in some cataclysmic variables. In total, we estimate that some25 per cent of the Northern hemisphere of BV Cen is spotted.We also find evidence for a faint, narrow, transient emission line withcharacteristics reminiscent of the peculiar low-velocity emissionfeatures observed in some outbursting dwarf novae. We interpret thisfeature as a slingshot prominence from the secondary star and derive amaximum source size of 75000 km and a minimum altitude of 160000 kmabove the orbital plane for the prominence.The entropy landscape technique was applied to determine the systemparameters of BV Cen. We find M1 = 1.18+/-0.280.16Msolar and M2 =1.05 +/-0.230.14Msolar and an orbitalinclination of i = 53° +/- 4° at an optimal systemic velocity ofγ = -22.3 km s-1. Finally, we also report on thepreviously unknown binarity of the G5IV star HD 220492.
| 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).
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Observation and Astrometry data
| Constellation: | Φοίνιξ |
| Right ascension: | 23h56m35.48s |
| Declination: | -50°18'13.5" |
| Apparent magnitude: | 9.31 |
| Proper motion RA: | -76.9 |
| Proper motion Dec: | -138.3 |
| B-T magnitude: | 10.321 |
| V-T magnitude: | 9.394 |
Catalogs and designations:
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