First ESO Image of Comet 1996 J1 (Evans-Drinkwater)
20 May 1996
The active phase of Astronomy On-Line will start on October 1 and reach a climax on November 18 - 22, 1996. A new and unknown comet was discovered by Robert Evans on a photographic plate, obtained by M. J. Drinkwater on May 10, 1996, with the UK Schmidt telescope at Siding Spring Australia. More observations were made within the next days and the comet was soon given the designation 'Comet 1996 J1' (i.e. the first comet to be found in the period May 1 - 15, 1996). Following astronomical tradition, it was also named after the discoverers.
At the time of the discovery, the magnitude was estimated as about 16 (10,000 times fainter than what can be peceived with the unaided eye) and a first calculation of the orbit by Brian Marsden (IAU Minor Planet and Comet Bureau) indicates that the brightness will not change much during the coming months.
Soon after the announcement of the discovery (IAU Circular 6397; May 12), a CCD image of the new comet was obtained on May 13.15 UT with the MPI/ESO 2.2-metre telescope and the multi-mode EFOSC II instrument at La Silla. The exposure time was 5 min through a red (R) filtre.
Another series of images was obtained on May 14.1 UT. Two of these have been combined and are reproduced here as ESO Press Photo eso9626; it is available in two versions. The field of the B/W-frame measures 128 x 123 arcsec and that of the false-colour, 190 x 183 arcsec; 1 pixel = 0.336 arcsec. North is up and East is to the left.
At the time of the exposure, the comet was about 405 million km from the Earth and 492 million km from the Sun. The visible coma mostly consists of dust, emitted by the cometary nucleus, and it measures more than 2 arcminutes across (IAUC 6398; May 13).
A spectrum was obtained with the same telescope on May 14.15 UT. It shows weak lines of CN and C2, not unusual for a comet at the current heliocentric distance (IAUC 6400; May 17).
A new orbital computation by Brian Marsden (MPEC 1996-K02; May 17) now indicates that Comet Evans-Drinkwater will pass its perihelion on December 30, 1996, at a distance of 1.297 AU (194 million km) from the Sun. The orbit is near-parabolic. The comet will be observable during most of the current year, and best from the southern hemisphere.
Further information about IAU Circulars (IAUC) and Minor Planet Electronic Circulars (MPEC) may be obtained from the Headlines of the IAU Central Bureau for Telegrams.