Electronic Telegram No. 5003 Central Bureau for Astronomical Telegrams Mailing address: Hoffman Lab 209; Harvard University; 20 Oxford St.; Cambridge, MA 02138; U.S.A. e-mail: cbatiau@eps.harvard.edu (alternate cbat@iau.org) URL http://www.cbat.eps.harvard.edu/index.html Prepared using the Tamkin Foundation Computer Network COMET C/2021 N3 (PANSTARRS) Y. Ramanjooloo, Institute for Astronomy, University of Hawaii, reports the discovery of another comet in four 45-s w-band images obtained on July 13 with the Pan-STARRS1 1.8-m Ritchey-Chretien reflector at Haleakala (discovery observations tabulated below, along with numerous pre-discovery observations going back an additional month that were identified by R. Weryk (Physics and Astronomy Department, University of Western Ontario). Ramanjooloo notes a diffuse coma of diameter 2".5 in 1".0 seeing in the stacked images taken on July 13; there may have been a broad, very-low- surface-brightness tail towards p.a. 200 degrees. 2021 UT R.A. (2000) Decl. Mag. June 13.57173 21 55 51.78 -26 10 36.5 20.7 13.58228 21 55 51.74 -26 10 36.2 20.1 13.59285 21 55 51.71 -26 10 35.9 20.2 13.60344 21 55 51.68 -26 10 35.7 20.4 20.56904 21 55 20.79 -26 08 00.3 20.0 20.57637 21 55 20.75 -26 08 00.3 20.3 20.58373 21 55 20.69 -26 08 00.1 20.3 20.59106 21 55 20.63 -26 08 00.1 20.1 July 6.46331 21 52 13.97 -26 06 12.4 20.1 6.47456 21 52 13.78 -26 06 12.5 20.0 6.48583 21 52 13.57 -26 06 12.6 19.8 6.50229 21 52 13.30 -26 06 12.6 20.2 13.51529 21 50 04.24 -26 06 16.4 20.5 13.52573 21 50 04.00 -26 06 16.4 20.6 13.53617 21 50 03.81 -26 06 16.3 20.8 13.54660 21 50 03.58 -26 06 16.4 20.7 Weryk notes that four 45-s w-band survey images from June 13 taken in 1".1 seeing show a condensed coma of size about 1".9 (full-width-at-half-maximum) with no obvious tail; four 45-s w-band survey images from June 20 taken in 1".2 seeing show the same appearance, while four 45-s w-band survey images from July 6 taken in 1".5 seeing show a condensed 2".3 (FWHM) coma, again with no obvious tail. Weryk and R. Wainscoat obtained three 60-s gri-band follow-up images in 1".0 seeing with the 3.6-m Canada-France-Hawaii Telescope at Mauna Kea (queue observer C. Crowder; queue coordinator T. Burdullis) on July 14.54 UT that show a broad tail > 10" long spanning p.a. 200-240 degrees with a very condensed coma of size 2".0. Weryk adds that four stacked follow-up 45-s w-band Pan-STARRS1 images taken on July 17.52-17.55 show a condensed coma of size 2".35 (FWHM) in 1".6 seeing with a very faint, broad tail 15" long in p.a. 200-240 degrees. After the comet was posted on the Minor Planet Center's PCCP webpage, other CCD astrometrists have also commented on the cometary appearance. E. Guido, Castellammare di Stabia, Italy, writes that sixteen stacked 180-s unfiltered exposures taken remotely by a large group of observers on July 14.3 UT with a "Telescope Live" 0.61-m f/6.5 astrograph located at El Sauce, Chile, show a compact coma about 9" in diameter with mag 19.4-19.6. Twelve stacked 60-s exposures taken remotely on July 21.8 by H. Sato (Tokyo, Japan) using a 0.51-m f/6.8 astrograph at Siding Spring, NSW, Australia, show a strongly condensed coma 9" in diameter with no tail; the magnitude was 19.3 as measured within a circular aperture of radius 6".6. Additional astrometry appears on MPEC 2021-O39. The following preliminary orbital elements by S. Nakano (CBAT) are from 31 observations spanning 2021 June 13-July 21 (mean residual 0".2) and suggest an orbital period around 1600 yr. T = 2020 Aug. 19.94340 TT Peri. = 304.82322 e = 0.9577844 Node = 337.47847 2000.0 q = 5.7159531 AU Incl. = 26.76886 The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 9.5 and 2.5n = 8 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2021 07 05 21 52.62 -26 06.2 5.324 6.136 139.9 6.1 19.4 2021 07 15 21 49.56 -26 06.3 5.265 6.162 149.4 4.8 19.4 2021 07 25 21 45.74 -26 05.8 5.231 6.188 158.6 3.4 19.4 2021 08 04 21 41.40 -26 03.3 5.224 6.215 166.3 2.2 19.4 2021 08 14 21 36.82 -25 57.7 5.246 6.242 168.5 1.9 19.5 2021 08 24 21 32.29 -25 47.9 5.297 6.270 162.7 2.7 19.5 2021 09 03 21 28.11 -25 33.3 5.377 6.298 153.9 4.0 19.5 2021 09 13 21 24.55 -25 13.8 5.483 6.327 144.3 5.3 19.6 2021 09 23 21 21.80 -24 49.3 5.613 6.357 134.5 6.5 19.7 2021 10 03 21 20.02 -24 20.3 5.764 6.387 124.7 7.4 19.7 2021 10 13 21 19.28 -23 47.2 5.932 6.418 115.0 8.1 19.8 2021 10 23 21 19.60 -23 10.4 6.112 6.449 105.5 8.5 19.9 2021 11 02 21 20.96 -22 30.4 6.300 6.481 96.1 8.8 20.0 2021 11 12 21 23.30 -21 47.7 6.492 6.514 86.9 8.7 20.1 2021 11 22 21 26.53 -21 02.5 6.684 6.546 77.8 8.5 20.2 2021 12 02 21 30.55 -20 15.3 6.871 6.580 68.9 8.0 20.2 2021 12 12 21 35.26 -19 26.1 7.050 6.614 60.0 7.4 20.3 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2021 CBAT 2021 July 22 (CBET 5003) Daniel W. E. Green