Electronic Telegram No. 5209 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/2023 B1 (PANSTARRS) R. Weryk, Department of Physics and Astronomy, University of Western Ontario, reports the discovery of another comet in images obtained with the Pan-STARRS2 1.8-m Ritchey-Chretien reflector at Haleakala (discovery observations tabulated below). Four 45-s w-band survey images taken on Jan. 21.5 UT show a very condensed head of size 2".4 (full-width-at-half- maximum) in 1".8 seeing with no obvious tail. Weryk adds that three 40-s gri-band follow-up observations obtained with R. Wainscoat's time on the 3.6-m Canada-France-Hawaii Telescope on Jan. 22.57 (queue observer H. Januszewski; queue coordinator T. Burdullis) show a very condensed coma of size 1".0 (FWHM) in 0".6 seeing with no tail. 2023 UT R.A. (2000) Decl. Mag. Jan. 21.47610 11 06 47.75 +23 15 44.2 17.7 21.48834 11 06 47.56 +23 15 47.2 17.7 21.50058 11 06 47.42 +23 15 49.5 17.7 21.51285 11 06 47.23 +23 15 52.5 17.7 Single-night apparently asteroidal observations made on Jan. 13.5 UT with a 0.5-m f/2 Schmidt reflector at Haleakala in the course of the "Asteroid Terrestrial-Impact Last Alert System" (ATLAS) search program were identified in the MPC's "isolated tracklet file" (mag 16.6-16.9). Following a request from the Central Bureau, A. Fitzsimmons (Queen's University, Belfast) writes that further inspection shows that the Jan. 13 observations do indeed appear stellar in 4".4 seeing, but that inspection of another ATLAS image taken on Jan. 22.5 shows a faint coma of size 6".1 in 4".2 seeing, while K. Smith has identified yet another ATLAS image of the comet from Jan. 25.5 that shows a faint, symmetric coma of diameter 18" in 4".1 seeing. Fitzsimmons suggests that this is consistent with a Centaur that has just undergone an outburst. After the object was posted to the Minor Planet Center's PCCP webpage, other CCD astrometrists have commented on the cometary appearance. Ten stacked 60-s exposures taken remotely by H. Sato (Bunkyo-ku, Tokyo, Japan) with a 0.51-m f/6.8 astrograph located at Rio Hurtado, Chile, on Jan. 22.36 UT show a strongly condensed round coma 14" in diameter and no tail; the magnitude was 16.5 as measured within a circular aperture of radius 7".2. Three separate stacks of ten 30-s exposures by L. Buzzi, Varese, Italy, on Jan. 23.1 with a 0.84-m f/3.5 reflector reveal a compact, round coma 15" wide with no tail and with magnitude 17.0. F. D. Romanov, Yuzhno-Morskoy, Nakhodka, Russia, writes that three stacked 180-s images taken remotelly with an iTelescope 0.61-m f/6.5 (+ Luminance filter) at the Sierra Remote Observatory at Auberry, CA, USA, on Jan. 24.6 show a diffuse coma 15" in diameter (mag near 17.6) without a tail. The astrometry on MPEC 2023-B118 also includes pre-discovery observations (mag 16.9) from Xingming Observatory in Nanshan on Jan. 19.9 UT that were reported after the object was posted to the PCCP webpage. The following preliminary elliptical orbital elements by S. Nakano (Central Bureau) are from 90 observations spanning Jan. 13-25 (mean residual 0".3); the size of the semi-major is still uncertain, but it appears that there has been no close approaches to major planets since at least 1930 (when it may have passed 1 AU from Jupiter). T = 2023 Aug. 13.27501 TT Peri. = 88.76925 e = 0.1282211 Node = 78.52255 2000.0 q = 6.1260774 AU Incl. = 14.58442 a = 7.0271001 AU n = 0.05291026 P = 18.63 years The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 7.0 and 2.5n = 8 for the magnitudes (which represent the last two weeks of observations but which must be considered in light of a likely outburst of unknown size). Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2022 12 07 11 05.15 +21 19.3 5.987 6.157 95.3 9.2 17.2 2022 12 17 11 07.45 +21 34.3 5.830 6.155 104.8 8.9 17.1 2022 12 27 11 08.68 +21 56.1 5.681 6.152 114.4 8.4 17.1 2023 01 06 11 08.80 +22 23.8 5.543 6.150 124.2 7.6 17.0 2023 01 16 11 07.80 +22 56.4 5.423 6.148 134.1 6.6 17.0 2023 01 26 11 05.73 +23 32.2 5.324 6.146 143.8 5.4 16.9 2023 02 05 11 02.72 +24 09.0 5.250 6.144 152.9 4.2 16.9 2023 02 15 10 58.96 +24 44.5 5.204 6.142 160.3 3.1 16.9 2023 02 25 10 54.70 +25 16.3 5.187 6.141 163.1 2.7 16.9 2023 03 07 10 50.25 +25 42.3 5.200 6.139 159.5 3.3 16.9 2023 03 17 10 45.93 +26 00.8 5.242 6.137 151.9 4.4 16.9 2023 03 27 10 42.05 +26 10.8 5.311 6.136 142.8 5.6 16.9 2023 04 06 10 38.86 +26 12.0 5.405 6.135 133.3 6.8 17.0 2023 04 16 10 36.56 +26 04.6 5.518 6.133 123.8 7.8 17.0 2023 04 26 10 35.27 +25 49.3 5.647 6.132 114.5 8.6 17.1 2023 05 06 10 35.06 +25 26.7 5.788 6.131 105.3 9.1 17.1 2023 05 16 10 35.91 +24 58.0 5.935 6.130 96.3 9.4 17.2 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2023 CBAT 2023 January 25 (CBET 5209) Daniel W. E. Green