THE ASTRONOMER Electronic Circular No 402 1990 April 15 14.45UT Microlink:MAG60138 JANET:GUYH at UK.AC.SUSSEX.CLUSTER Ed:Guy M Hurst, 16,Westminster Close, Kempshott Rise, Basingstoke, Hants, RG22 4PP, England. Telephone: (0256)471074 Int:+44256471074 Telex: 94082518 Answerback: TAGUY ------------------------------------------------------------------ COMET AUSTIN (1989c1) M. Fulle, Osservatorio Astronomico, Trieste; and L. Pansecchi, Osservatorio di San Vittore, Bologna, write: "Around the date of the earth crossing through the plane of the comet orbit (June 6.8 UT), geometrical circumstances will be favorable for the so-called 'neck-line structure' to appear in the dust tail of comet Austin. Such a structure should appear as a strong dust streamer within the main tail, having a short, thin, sunward spike lying inside the comet orbit with respect to the sun. Similar structures were already detected in comet Bennett 1970 II (Pansecchi et al. 1987, A.Ap. 176, 358) and P/Halley 1986 III (Cremonese and Fulle 1989, Icarus 80, 267). Following are listed the date; the latitude of the earth on the plane of the comet orbit; the predicted position angles of the 'neck line' and of the sunward spike; the synchrone ejection time for the streamer, measured in days before perihelion; and the sky-projected length of the sunward spike, which is directly proportional to the dust ejection velocity from the inner coma and is computed for a velocity of 10 m/s and given both in units of 10E6 km and arcmin: June 2.0 UT, -12.9 deg, 327 deg, 146 deg, 12 days, 0.14, 11'; June 5.0, -4.3 deg, 332 deg, 152 deg, 12 days, 0.14, 10'; June 6.0, -1.8 deg, 333 deg, 153 deg, 11 days, 0.15, 9'; June 7.0, +0.5 deg, 335 deg, 155 deg, 11 days, 0.15, 9'; June 8.0, +2.7 deg, 336 deg, 156 deg, 11 days, 0.15, 9'; June 9.0, +4.6 deg, 338 deg, 158 deg, 11 days, 0.15, 9'; June 12.0, +9.0 deg, 342 deg, 163 deg, 11 days, 0.16, 8'; June 17.0, +14.3 deg, 347 deg, 169 deg, 10 days, 0.16, 7'; June 22.0, +17.9 deg, 352 deg, 173 deg, 10 days, 0.17, 6'; June 27.0, +20.2 deg, 355 deg, 177 deg, 9 days, 0.18, 5'. The orbital elements on IAUC 4972 were used for these calculation. Deep red or infrared photographs (calibrated if possible) would be useful for analyzing the dust in the comet, though the moon will be a problem during the best geometrical times." IAUC 4991 Recent estimates: 1990 Apr 10.79UT, m1=4.8 (H.Mikuz, Yugoslavia, 15x80B) 1990 Apr 11.82UT, m1=5.6 (J.Jahn, W.Germany, 0.20-m refl) 1990 Apr 13.81UT, m1=4.0 (R.Stuart, Rhayader, 20x60B) AAVSO MEETING BRUSSELS 1990 JULY 24-28 Readers are reminded of this event which covers "International Cooperation and Coordination in Variable Star Research". Further details regarding booking arrangements can be obtained by e-mailing Storm Dunlop: MAFD5 @ UK.AC.SUSSEX.CLUSTER Guy M Hurst