Occultations by Uranian Rings
Abstract
Further analysis, by the undersigned, of the occultation of SAO 158687 on 1977 Mar. 10 yields the following radii for the rings, assumed to lie in Uranus' equatorial plane (cf. IAUC 3051, 3061): Ring Distance Ring Distance alpha 44 835 km delta 48 408 km beta 45 788 epsilon1 51 697 gamma 47 732 epsilon2 51 030 These results (uncertainty +/- 30 km) are very similar to those by Wasserman et al. (1977, Bull. Am. Astron. Soc. 9, 498). As the result of observations of another predicted occultation on 1977 Dec. 23 (IAUC 3108; Astron. J. 1977, 82, 849, 929, 1036), Millis and Wasserman (1978, Astron. J. to be published) confirm the existence of the gamma, delta and epsilon rings and possibly also of the alpha ring; these measurements, obtained at a wavelength of 0.88 um at Cabezon Observatory, Tenerife, were difficult to make in the dawn sky. E. Persson, Hale Observatories; P. Nicholson, K. Matthews, P. Goldreich and G. Neugebauer, California Institute of Technology, report that successful observations at a wavelength of 2.2 um were made with the 250-cm du Pont telescope at the Las Campanas Observatory on 1978 Apr. 10 of a third occultation by the Uranian rings (only the occultation by Uranus itself could be detected in the case of a fainter star on 1978 Apr. 4). All five 'original' rings were detected, and assuming the above values for the alpha, beta, gamma and delta rings the radii of further rings were determined as follows: Ring Distance Ring Distance kappa1 42 029 km kappa2 42 148 km iota1 42 394 iota2 42 304 theta1 42 660 theta2 42 696 eta1 47 290 eta2 47 289 epsilon1 50 848 epsilon2 51 402 As before (IAUC 3051, 3061), subscripts refer to the western and eastern edges of the rings, respectively. The kappa ring is uncertain. The iota1 and theta1 events are undoubtedly identical with the alpha3 and beta3 events previously described by Millis et al. (IAUC 3051). The eta events were also subsequently reported by L. Elliot (unpublished) in the case of the SAO 158687 occultation. The more recent results for epsilon suggest that this is indeed a complete ring but that its width is relatively substantial, its shape non-circular and its structure complex. The possible zeta ring of J. Churms (IAUC 3051) has not been confirmed, and there appear to be no confirmed rings of any consequence outside epsilon.
- Publication:
-
International Astronomical Union Circular
- Pub Date:
- May 1978
- Bibcode:
- 1978IAUC.3215....3T