Electronic Telegram No. 5156 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 P/2020 A4 (PANSTARRS-LEMMON) S. Deen (Simi Valley, CA, USA) has reported that, in the course of his searching for interesting unlinked observations in the Minor Planet Center's "isolated tracklet file" (ITF), and starting with a single night of astrometry from the Mt. Lemmon Survey on 2020 Feb. 3, he was able to find numerous publicly available CCD images of the same object taken around that time using the 1.2-m Schmidt telescope at Palomar in the course of the "Zwicky Transient Facility" (ZTF) survey, which he found to be slightly cometary in appearance. In the course of this work, Deen also was able to link another ITF single- night observation from 2020 Jan. 1 in images obtained with the Pan-STARRS1 1.8-m Ritchey-Chretien reflector at Haleakala, Hawaii. In addition to finding ZTF images on nine nights (2020 Jan. 1-Feb. 19), Deen was able to identify three observations obtained by O. Contigiani on 2021 Jan. 15.3 UT with the Very Large Telescope facility at Cerro Paranal, when the comet was at magnitude r = 25.0. The discovery observations from the publicly available ITF file are tabulated below. 2020 UT R.A. (2000) Decl. Mag. Observer Jan. 1.50484 8 00 48.67 +36 04 17.2 21.4 Pan-STARRS1 1.51700 8 00 48.02 +36 04 13.2 21.5 " 1.52915 8 00 47.36 +36 04 09.2 21.4 " 1.54130 8 00 46.67 +36 04 04.8 21.5 " Feb. 3.20896 7 32 06.94 +31 49 22.3 19.6 Mt. Lemmon 3.21368 7 32 06.74 +31 49 19.6 19.6 " 3.21840 7 32 06.57 +31 49 16.5 19.4 " 3.22313 7 32 06.40 +31 49 12.4 18.9 " After R. Weryk (Department of Physics and Astronomy, University of Western Ontario) was alerted to this object, he searched for additional Pan-STARRS images and was able to identify the presence of the comet on nine nights in 2019 (Oct. 14-Dec. 24; seven nights with Pan-STARRS1 and two nights with Pan-STARRS2) and on one additional night in 2020 (Mar. 24, at mag 22.1-23.2 in Pan-STARRS1 images). The Pan-STARRS astrometry indicate a peak magnitude around 21.1-21.5 during Dec. 2019 and early Jan. 2020 (mag 22.7 on 2019 Oct. 14). The 2020 Jan. 1 images show the object to be "soft" in appearance, but Weryk would not claim it definitely a comet based solely on them; four 45-s w-band stacked survey images show a condensed head of size 1".6 (full-width- at-half-maximum) in 1".3 seeing with no obvious tail. Deen provides the following descriptive information from the images that he identified. On 2020 Jan. 5.4 UT, fifty-five stacked 30-s exposures show a very condensed small coma (or tail) asymmetric toward p.a. about 230 deg, which was "slightly hazier" than background stars (size about 1".4, FWHM, in 1".0 seeing). On 2020 Jan. 14.2-14.3, there was a faint, moderately diffuse, small coma of size about 2" (FWHM) with no tail in 1" seeing. On 2020 Jan. 16.2, there was a faint, moderately condensed, small coma of size about 1".2 (FWHM) in 1" seeing, with no tail. On 2020 Jan. 19.3-19.4, there was a moderately condensed small coma of size about 1".5 (FWHM) in 1" seeing with no tail. On Jan. 23.26, there was a condensed coma of size about 1".5 (FWHM) with no tail in 1" seeing. On 2020 Jan. 25.2, the object appears asteroidal. On 2020 Jan. 27.2, there was a faint, slightly diffuse, small coma of size about 2" (FWHM) in 1" seeing. On Jan. 28.2, there was a faint, slightly diffuse small coma of size about 3" (FWHM) in 1" seeing. On 2020 Jan. 29.2- 29.3, there was a faint, slightly condensed, small coma of size about 2".5 (FWHM) in 1".5 seeing. On Jan. 30.3, there was a faint, moderately diffuse small coma of size about 3" (FWHM) in 1".5 seeing. On 2020 Jan. 31.17-31.30, there was a faint, diffuse, small coma of size about 3" (FWHM) in 2" seeing. On Feb. 1.2, there was a bright, almost-asteroidal head with nearly the same size as nearby stars (1" FWHM). On 2020 Feb. 2.2, the comet appeared bright (mag 19.5) with a very condensed coma of size about 1".5 (FWHM) in 1" seeing. On Feb. 3.2, there was a very condensed coma of size about 1".5 (FWHM) in 1" seeing. On 2020 Feb. 12.14-12.25, there was a slightly condensed coma of size about 3" (FWHM) in 1" seeing. On Feb. 13.19-13.28, there was a slightly diffuse coma of size about 3" (FWHM) in 0".9 seeing. On 2020 Feb. 14.20- 14.26, there was a condensed coma of size about 2".5 (FWHM) in 1" seeing. On Feb. 15.2, there was a moderately condensed coma of size about 2".5 (FWHM) in 1" seeing. On 2020 Feb. 16.19-16.26, there was a condensed coma of size about 2" (FWHM) in 1" seeing. On Feb. 17.23-17.27, there was a moderately condensed coma of size about 3" (FWHM) in 1".5 seeing. On 2020 Feb. 19.16, there was a diffuse coma of size about 4".4 (FWHM) in 1".5 seeing. On Feb. 20.23-20.31, the comet was faint and apparently asteroidal. On 2020 Feb. 21.17-21.28, there was a diffuse coma of size about 3" (FWHM) in 1" seeing. On Feb. 24.2, there was a condensed coma of size about 3" (FWHM) in 1".5 seeing. On Feb. 25.2, there was a slightly condensed coma of size about 3".5 (FWHM) in 1" seeing. On 2021 Jan. 15.3, there was a faint, extremely diffuse coma (tail?) of size about 6" (FWHM) in 0".9 seeing, apparently elongated toward p.a. about 270 degrees, The astrometry by Deen and Weryk appear on MPEC 2022-P91. The following elliptical orbital elements by S. Nakano (Central Bureau) are from 105 observations spanning 2019 Oct. 14-2021 Jan. 15 (mean residual 0".4), indicating that the comet passed 1.51 AU from Saturn on 1992 Jan. 7. Epoch = 1996 Apr. 27.0 TT T = 1996 May 16.57751 TT Peri. = 144.75169 e = 0.6540984 Node = 312.57530 2000.0 q = 2.8353162 AU Incl. = 24.99110 a = 8.1968875 AU n = 0.04199819 P = 23.47 years Epoch = 2019 Nov. 13.0 TT T = 2019 Nov. 22.74012 TT Peri. = 144.88717 e = 0.6536904 Node = 312.43021 2000.0 q = 2.8425261 AU Incl. = 24.98983 a = 8.2080492 AU n = 0.04191256 P = 23.52 years Epoch = 2043 May 31.0 TT T = 2043 May 28.93987 TT Peri. = 145.02806 e = 0.6535847 Node = 312.25714 2000.0 q = 2.8389127 AU Incl. = 25.01586 a = 8.1951137 AU n = 0.04201183 P = 23.46 years NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2022 CBAT 2022 August 8 (CBET 5156) Daniel W. E. Green