내용
사진
사진 업로드
DSS Images Other Images
관련 글
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).
| New light on faint stars. I - The luminosity function in the solar neighbourhood
From photoelectric photometry of red dwarf stars identified in anobjective prism survey, a magnitude-limited complete sample has beendefined. Applying photometric parallaxes, calibrated for theKron-Cousins system by observations of trigonometric parallax stars,this sample is used to determine the space densities of stars withabsolute magnitudes between + 7 and + 12. The resultant luminosityfunction is consistent with the Luyten and Wielen functions for thesolar neighbourhood. An analysis of the stellar kinematics shows littlesignificant evidence of a substantial local population of low spacemotion M-dwarfs.
| Photometry of Southern Hemisphere red dwarf stars
Results are presented for a photometric investigation of aspectroscopically selected sample of red dwarf stars in the SouthernHemisphere. Absolute magnitudes and distances for the stars areestimated from broadband red colors. Three stars which may besubluminous are identified, as are several stars which may be within 25pc. The tangential velocity and velocity dispersion of the sample aresimilar to values found in other studies of nearby late-type stars.
| The space density and kinematics of dwarf M stars
The results of an objective-prism survey for dwarf stars, K7 and later,are presented. One hundred twenty-one red sensitive plates covering 1720sq. degrees of the southern sky were obtained with the Curtis Schmidttelescope at C.T.I.O. The resulting luminosity function rises from log N+ 10 = 7.9 at MV = 8 to about 8.7 at MV = 11 and12. About 75% of the dwarfs in this survey are identified with BPMstars, but inserting the proper motions given into the equations of themethod of mean absolute magnitudes yields values of MB aboutthree magnitudes brighter than the spectral types would indicate. Thatthe method of mean absolute magnitudes appears to be calibrated on starsof higher than average proper motion lends credence to the luminosityfunction result. A galactic mass density is found for the dwarfsconsidered.
|
새 글 등록
관련 링크
새 링크 등록
다음 그룹에 속해있음:
|
관측 및 측정 데이터
천체목록:
|
