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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).
| Photometric calibriation of the international Ultraviolet Explorer (IUE) for high resolution spectra
We present and discuss the high resolution absolute calibration for theSWP, LWP and LWR cameras on board IUE. The calibration was implementedin routine processing on 27 December, 1987 at VILSPA and on 30 August,1990 at GSFC. The calibration is applicable to high resolution spectraprocessed with the 'new' version of the IUE spectral image processingsoftware which was implemented in routine on 10 November, 1981 at GSFCand 11 March, 1982 at VILSPA. The high resolution calibration, for theway it is defined, is primarily determined by the efficiency of theshort or long wavelength spectrographs in the high resolution, relativeto the low resolution observing modes. This interpretation is consistentwith the high resolution calibration being the same for LWP and LWRspectra (which are obtained through the same spectrograph) and beingconstant with time. It is shown that the data extraction becomescritical for the higher orders of the IUE echelle spectrographs, causinghigh resolution calibration to depend on the data extraction algorithmused below about 1350 A in the SWP and below about 2350 A in the LWP andLWR cameras.
| Optical identifications of IRAS point sources - The Fornax, Hydra I and Coma clusters
Optical identifications are presented for 66 IRAS point sources in theregion of the Fornax cluster of galaxies, 106 IRAS point sources in theregion of the Hydra I cluster of galaxies (Abell 1060), and 59 IRASpoint sources in the region of the Coma cluster of galaxies (Abell1656). Eight other sources in Hydra I do not have optical counterpartsand are very probably due to IR cirrus. Twenty-three (35 percent) of theFornax sources are associated with stars and 43 (65 percent) withgalaxies; 48 (42 percent) of the Hydra I sources are associated withstars and 58 (51 percent) with galaxies; 18 (31 percent) of the Comasources are associated with stars and 41 (69 percent) with galaxies. Thestellar and infrared cirrus surface density is consistent with thegalactic latitude of each field.
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