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  • ASTRONOMY  (2)
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  • 1
    Publikationsdatum: 2019-07-13
    Beschreibung: At McDonald Observatory, we have undertaken a major program of observation of Comet P/Shoemaker-Levy 9 in order to charcterize the dynamics and physical make-up of the fragments prior to their disappearance in July 1994 when they collide with Jupiter. Obserations have included astrometry, photometry, and spectroscopy. Our astrometric observations have been important for deriving accurate orbits for the individual fragments. With the photometry, we have derived (B-V) and (V-R) colors for a number of fragemnts. We show that they are slightly redder than the Sun in (B-V) and similar to the Sun in (V-R); they may show differences in colors for the individual fragments. We detected no gas with our spectroscopic observations and have derived sensitive upper limits on the quantity of gas. Our observations are consistent with the parent being a comet, as classified, but cannot rule out certain types of asteroids as progenitors.
    Schlagwort(e): ASTRONOMY
    Materialart: Icarus (ISSN 0019-1035); 112; 2; p. 528-532
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Publikationsdatum: 2019-08-28
    Beschreibung: Time-series photometric observations of the binary star V471 Tauri were conducted using the Whole Earth Telescope observing network. The purpose was to determine the mechanism responsible for causing the 555 and 277 s periodic luminosity variations exhibited by the white dwarf in this binary. Previous observers have proposed that either g-mode pulsations or rotation of an accreting magnetic white dwarf could cause the variations, but were unable to decide which was the correct model. The present observations have answered this question. Learning the cause of the white dwarf variations has been possible because of the discovery of a periodic signal at 562 s in the Johnson U-band flux of the binary. By identifying this signal as reprocessed radiation and using its phase to infer the phase of the shorter wavelength radiation which produces it, made it possible to compare the phase of the 555 s U-band variations to the phase of the X-ray variations. It was found that U-band maximum coincides with X-ray minimum. From this result it was concluded that the magnetic rotator model accurately describes the variations observed, but that models involving g-mode pulsations do not.
    Schlagwort(e): ASTRONOMY
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 391; 2 Ju; 773-783
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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