Orbital elements, ephemeris and urgent request for further astrometry. ---------------------------------------------------------------------- On May 2, 1996, Brian Marsden (IAU Central Bureau for Astronomical Telegrams) published new elements and an improved ephemeris for Comet Hyakutake on IAU Circular 6391. They are reproduced below. Brian Marsden has also approached observers with an urgent request for follow-up positional measurements. On May 6, he writes: 'We have a problem concerning the observations HST hopes to secure of C/1996 B2 (Hyakutake) on June 1. The ephemeris on IAUC 6391 differs by then by more than 1 arcminute in each coordinate from its immediate predecessor. The reason for this is that we allowed for nongravitational forces. But if one does not allow for nongravitational forces, the observations from about April 17 onwards, and particularly the final observations (April 20, two different observatories), cannot be properly represented.' Please contact Brian Marsden (marsden@cfa0.harvard.edu) as soon as possible if you think that you will be able to perform such observations. Excerpt from IAUC 6391 (May 2, 1996): COMET C/1996 B2 (HYAKUTAKE) Improved orbital elements from MPC 27080 include consideration of nongravitational parameters A1 = +1.97 +/- 0.14, A2 = -0.22 +/- 0.12: Epoch = 1996 Apr. 27.0 TT T = 1996 May 1.3965 TT Peri. = 130.1996 e = 0.999635 Node = 188.0438 2000.0 q = 0.230103 AU Incl. = 124.9147 1996 TT R. A. (2000) Decl. Delta r Elong. Phase m1 May 2 2 25.85 +20 51.3 1.206 0.231 6.2 27.9 -0.5 3 2 24.27 +19 08.9 1.221 0.237 5.4 23.6 -0.3 4 2 23.06 +17 25.0 1.231 0.248 5.6 23.3 -0.1 5 2 22.24 +15 41.2 1.238 0.263 6.6 26.1 0.2 6 2 21.78 +13 58.7 1.242 0.281 8.0 30.1 0.5 7 2 21.66 +12 18.4 1.244 0.302 9.7 34.4 0.8 8 2 21.84 +10 40.6 1.243 0.324 11.5 38.4 1.1 9 2 22.27 + 9 05.2 1.241 0.348 13.3 41.9 1.4 10 2 22.92 + 7 32.2 1.238 0.372 15.1 45.0 1.7 11 2 23.77 + 6 01.3 1.234 0.397 16.9 47.6 1.9 12 2 24.79 + 4 32.5 1.230 0.422 18.6 49.8 2.2 13 2 25.97 + 3 05.3 1.224 0.447 20.3 51.8 2.4 14 2 27.28 + 1 39.7 1.219 0.473 22.0 53.4 2.7 15 2 28.71 + 0 15.4 1.213 0.498 23.7 54.8 2.9 16 2 30.25 - 1 07.9 1.207 0.523 25.4 55.9 3.1 17 2 31.90 - 2 30.1 1.201 0.548 27.0 56.9 3.3 18 2 33.65 - 3 51.6 1.195 0.573 28.6 57.7 3.5 19 2 35.49 - 5 12.5 1.188 0.598 30.2 58.3 3.6 20 2 37.42 - 6 32.8 1.182 0.623 31.8 58.9 3.8 21 2 39.43 - 7 52.7 1.176 0.647 33.3 59.3 4.0 22 2 41.52 - 9 12.3 1.170 0.671 34.9 59.6 4.1 23 2 43.69 -10 31.6 1.164 0.695 36.4 59.8 4.3 24 2 45.94 -11 50.8 1.159 0.719 37.9 60.0 4.4 25 2 48.27 -13 09.8 1.153 0.742 39.4 60.0 4.5 26 2 50.67 -14 28.7 1.148 0.766 40.9 60.0 4.6 27 2 53.15 -15 47.6 1.143 0.789 42.4 60.0 4.8 28 2 55.70 -17 06.5 1.139 0.812 43.8 59.9 4.9 29 2 58.33 -18 25.3 1.134 0.835 45.3 59.7 5.0 30 3 01.03 -19 44.2 1.130 0.857 46.7 59.5 5.1 31 3 03.82 -21 03.1 1.127 0.880 48.2 59.2 5.2 June 1 3 06.68 -22 22.0 1.123 0.902 49.6 58.9 5.3 (C) Copyright 1996 CBAT 1996 May 2 (6391) Brian G. Marsden