------------------------------------------------------------------- THE ASTRONOMER Electronic Circular No 1247 1997 Nov 1 09.00UT Ed:Guy M Hurst, 16,Westminster Close, Kempshott Rise, Basingstoke, Hants, RG22 4PP,England.Telephone/FAX(01256)471074Int:+441256471074 INTERNET: GUY@TAHQ.DEMON.CO.UK GMH at AST.STAR.RL.AC.UK WORLD WIDE WEB http://www.demon.co.uk/astronomer ------------------------------------------------------------------- SATELLITES OF URANUS B. J. Gladman, Canadian Institute for Theoretical Astrophysics; P. D. Nicholson and J. A. Burns, Cornell University; and J. J. Kavelaars, McMaster University, report the discovery of two probable distant satellites of Uranus on CCD frames obtained with the COSMIC camera on the Hale 5-m telescope at Palomar. The objects were detected by Gladman in early October on a set of twelve 360-s frames obtained on Sept. 6 and 7. The fainter object, S/1997 U 1, about 6' east of Uranus, was estimated at R = 21.9. The brighter object, S/1997 U 2, about 7' west-northwest of Uranus, was at R = 20.4--but with B about 22 is fainter than the limit of the 1948 McDonald 2.1-m survey (Kuiper 1961, Planets and Satellites, p. 587); Uranus has hitherto differed from the other giant planets in that it was not known to have any distant satellites. At the request of the Central Bureau, W. Offutt, Cloudcroft, NM, began observing S/1997 U2 on Oct. 9. Both satellites were reobserved with the 5-m reflector in late October, although bad seeing permitted detection of S/1997 U 1 on only one night, when it was found some 30" from the prediction by Nicholson on the basis of a circular uranicentric orbit. D. J. Tholen (assisted by C. Herrick and R. J. Whiteley) observed both satellites on Oct. 29 with the University of Hawaii's 2.2-m reflector. Selected observations follow (for S/1997 U 1 and S/1997 U 2, respectively). IAUC 6764 Orbital computations by B. G. Marsden and G. V. Williams, Harvard-Smithsonian Center for Astrophysics, suggest that the observations of S/1997 U 2 (cf. IAUC 6764) are incompatible with a heliocentric orbit and that the best-fitting uranicentric orbits are quite eccentric, with a retrograde solution being significantly preferable to a direct solution. The poorer distribution of observations of S/1997 U 1 renders this situation very much less conclusive. Absolute magnitudes are H about 9.0 and 7.5, for S/1997 U1 and S/1997 U2 respectively; for an albedo of 0.07, the radii of the objects would be about 40 and 80 km. IAUC 6765 Martin Mobberley