Садржај
Слике
Уплоадјуј своје слике
DSS Images Other Images
Везани чланци
Interstellar Medium Sculpting of the HD 32297 Debris Disk
We detect the HD 32297 debris disk in scattered light at 1.6 and 2.05?m. We use these new observations together with a previous scatteredlight image of the disk at 1.1 ?m to examine the structure andscattering efficiency of the disk as a function of wavelength. Inaddition to surface brightness asymmetries and a warped morphologybeyond ~1farcs5 for one lobe of the disk, we find that there exists anasymmetry in the spectral features of the grains between thenortheastern and southwestern lobes. The mostly neutral color of thedisk lobes implies roughly 1 ?m-sized grains are responsible for thescattering. We find that the asymmetries in color and morphology canplausibly be explained by HD 32297's motion into a dense interstellarmedium cloud at a relative velocity of 15 km s-1. Wemodel the interaction of dust grains with H I gas in the cloud. Weargue that supersonic ballistic drag can explain the morphology of thedebris disks of HD 32297, HD 15115, and HD 61005.
| 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).
| Occultations of stars by asteroids in 1995 and 1996
Predictions, based on a computerized comparison of asteroid ephemerideswith the catalog positions of 567,500 stars, are given for 155occultations of stars by asteroids in 1995 and 1996. On average, thepredictions are expected to be more accurate than in earlier searchesbecause of the use of more modern star catalogs. A number of veryfavorable occultations, visible in North America and elsewhere, arediscussed.
|
Додај нови чланак
Линкови у сродству са темом
Додај нови линк
Чланови следећих група \:
|
Посматрања и Астрометриски подаци
| Сазвежђа: | Кит |
| Ректацензија: | 02h25m53.75s |
| Deклинација: | -09°54'07.6" |
| Apparent магнитуда: | 8.238 |
| Даљина: | 117.509 parsecs |
| Proper motion RA: | -5.2 |
| Proper motion Dec: | -22.8 |
| B-T magnitude: | 8.885 |
| V-T magnitude: | 8.292 |
Каталог и designations:
|
