Comet C/2018 O1 (Atlas)
Abstract
An apparently asteroidal object discovered on July 22 UT (discovery observations tabulated below) with a 0.5-m f/2 Schmidt reflector at Mauna Loa, Hawaii, in the course of the "Asteroid Terrestrial-impact Last Alert System" (ATLAS) search program has been found to show cometary appearance by CCD astrometrists elsewhere after it was posted on the Minor Planet Center's PCCP webpage. 2018 UT R.A. (2000) Decl. Nag, July 22.54515 20 58 02.04 +25 28 22.1 18.7 22.55244 20 57 57.72 +25 28 06.0 18.7 22.56451 20 57 50.53 +25 27 43.4 18.5 22.57295 20 57 45.46 +25 27 27.4 18.6 H. Sato, Tokyo, Japan, writes that twenty stacked 20-s exposures taken on July 23.4 UT with an iTelescope 0.43-m f/6.8 astrograph (located near Mayhill, NM, USA) shows a strongly condensed coma 10" in diameter and no obvious tail; the w-band magnitude was 18.8 as measured within a circular aperture of radius 7".6. L. Buzzi, Varese, Italy, finds a compact coma 10" in size that is softer and larger (by about 20 percent, full-width-at-half-maximum) than the images of nearby stars, and that the comet is possibly elongated toward the southwest, in images taken on July 24.0 with a 0.84-m f/3.5 reflector. P. Birtwhistle, Great Shefford, Berkshire, England, notes that his images taken on July 31.9 with a 0.40-m f/6 Schmidt-Cassegrain reflector show no tail, but FWHM measurements of the comet's image appear consistently 25-30 percent larger than those of nearby stars of similar magnitude in all three sets of exposures; Birtwhistle obtained additional astrometry on Aug. 9.94-9.97 that show a similar result. K. Sarneczky, Konkoly Observatory, reports that three stacked 20-s unfiltered images taken with the 0.60-m Schmidt telescope at Piszkesteto, Hungary, on Aug. 3.9 show a slightly diffuse, circular coma about 10" in diameter with no tail. H. Weiland writes that four stacked o-band images taken with the ATLAS discovery telescope on Aug. 6.4 (when the comet was accidentally re-discovered) show it to be larger than the stellar point-spread function but with no tail. R. Weryk also reports that images taken on Aug. 13.3 with the 1.8-m Pan-STARRS1 Ritchey-Chretien telescope at Haleakala show a FWHM of about 2" (measured perpendicular to its direction of motion), larger than the neighboring stars (which are 1".35 +/- 0".04 in the exposure with the best seeing); he adds that there is a tail at least 6" long towards the east.
- Publication:
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Central Bureau Electronic Telegrams
- Pub Date:
- August 2018
- Bibcode:
- 2018CBET.4543....1S