Electronic Telegram No. 5405 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/2024 L2 (PANSTARRS) R. Weryk, Department of Physics and Astronomy, University of Western Ontario, reports the discovery of another comet in images obtained on June 13 with the Pan-STARRS1 1.8-m Ritchey-Chretien reflector at Haleakala (discovery observations tabulated below). Four 45-s stacked w-band survey images taken on June 13.5 UT in 1".2 seeing show the condensed head with size 2".0 (full- width-at-half-maximum) and no tail. Four 60-s stacked w-band follow-up images taken on June 14.5 in 1".7-1".9 seeing show a condensed head of size 2".4 (FWHM) and no tail. 2024 UT R.A. (2000) Decl. Mag. June 13.52926 20 29 17.40 -43 58 25.4 20.4 13.53705 20 29 17.02 -43 58 26.5 20.0 13.54481 20 29 16.65 -43 58 27.4 20.1 13.55256 20 29 16.26 -43 58 28.7 20.0 14.54728 20 28 28.09 -44 00 41.0 19.6 14.54811 20 28 28.06 -44 00 41.2 19.4 14.54892 20 28 28.02 -44 00 41.0 19.4 14.54974 20 28 27.98 -44 00 41.3 19.6 Weryk adds that he then found this comet in Pan-STARRS1 images from June 1.6 UT; four 45-s w-band survey images taken in 1".8-2".3 seeing show a condensed head of size 2".9 (FWHM) and magnitude 19.4-19.5, again with no tail. After the comet was posted on the Minor Planet Center's PCCP, T. Prystavski (Lviv, Ukraine) found that CCD exposures taken remotely with a 0.51-m f/4.4 reflector at Siding Spring, NSW, Australia, on June 18.8 show a very condensed coma about 9".9 in diameter (total mag 19.0) with a straight tail 0'.3 long in p.a. 98 degrees. The Minor Planet Center found three single-night observations from 2023 July 15 in its "isolated tracklet file", which were obtained using the 4-m reflector (+ DECam) at Cerro Tololo, as tabulated below. Following a request by the Central Bureau, S. Deen (Simi Valley, CA, USA) has examined the DECam images and finds the comet to be clearly cometary therein, with a tail about 20" long in p.a. 85 degrees. Deen adds that DECam images were also obtained of the area around the comet's predicted position in August 2023, but those data will not be publicly available until Aug. 2024. 2023 UT R.A. (2000) Decl. Mag. July 15.23005 21 57 41.03 -48 58 09.5 19.5 15.24530 21 57 40.26 -48 58 13.0 19.6 15.26052 21 57 39.48 -48 58 16.6 19.5 The available astrometry from June 2024 appears on MPEC 2024-M24. The following parabolic orbital elements by S. Nakano (Central Bureau) are from 20 observations spanning 2024 June 1-18 (mean residual 0".2). T = 2025 June 14.95019 TT Peri. = 345.72169 Node = 266.18737 2000.0 q = 8.3312117 AU Incl. = 139.57930 Nakano notes that the residuals for the 2023 July 15 observations with respect to the above parabolic elements are only +6" in R.A. and +16" in Decl. Nakano supplies the following linked orbital elements from 23 observations spanning 2023 July 15-2024 June 18 (mean residual 0".2), with corresponding "original" and "future" values of 1/a being -0.000076 and -0.000042 (+/- 0.000028) AU**-1, respectively. There are no close approaches to major planets. Epoch = 2025 June 14.0 TT T = 2025 June 17.44235 TT Peri. = 345.88681 e = 1.0043848 Node = 266.17945 2000.0 q = 8.3262340 AU Incl. = 139.58690 The following ephemeris by the undersigned from the linked orbital elements above uses photometric power-law parameters H = 7.0 and 2.5n = 8 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2024 05 10 20 49.76 -42 33.6 8.348 8.666 105.1 6.5 19.1 2024 05 20 20 45.36 -42 57.9 8.179 8.650 114.7 6.1 19.1 2024 05 30 20 39.71 -43 23.2 8.024 8.634 124.2 5.6 19.0 2024 06 09 20 32.81 -43 47.9 7.888 8.619 133.5 4.9 19.0 2024 06 19 20 24.75 -44 10.1 7.776 8.604 142.4 4.1 18.9 2024 06 29 20 15.72 -44 27.5 7.693 8.589 150.1 3.4 18.9 2024 07 09 20 05.96 -44 38.6 7.641 8.575 155.3 2.8 18.9 2024 07 19 19 55.82 -44 41.9 7.621 8.561 156.2 2.8 18.9 2024 07 29 19 45.68 -44 36.6 7.635 8.547 152.3 3.2 18.9 2024 08 08 19 35.90 -44 22.7 7.681 8.534 145.2 3.9 18.9 2024 08 18 19 26.83 -44 00.9 7.758 8.521 136.5 4.7 18.9 2024 08 28 19 18.76 -43 32.3 7.860 8.508 127.1 5.4 18.9 2024 09 07 19 11.87 -42 58.5 7.986 8.496 117.4 6.0 18.9 2024 09 17 19 06.26 -42 21.1 8.128 8.485 107.5 6.5 19.0 2024 09 27 19 01.97 -41 41.5 8.281 8.474 97.7 6.7 19.0 2024 10 07 18 58.95 -41 01.1 8.440 8.463 87.9 6.8 19.1 2024 10 17 18 57.13 -40 20.9 8.600 8.452 78.2 6.6 19.1 2024 10 27 18 56.40 -39 41.7 8.754 8.442 68.6 6.3 19.1 2024 11 06 18 56.62 -39 04.0 8.899 8.433 59.1 5.8 19.2 2024 11 16 18 57.67 -38 28.0 9.028 8.423 49.8 5.1 19.2 2024 11 26 18 59.40 -37 54.2 9.139 8.415 40.7 4.4 19.2 2025 02 14 19 21.28 -34 43.9 9.093 8.359 39.9 4.3 19.2 2025 02 24 19 23.07 -34 30.7 8.969 8.354 49.1 5.1 19.1 2025 03 06 19 24.23 -34 19.9 8.825 8.349 58.5 5.8 19.1 2025 03 16 19 24.63 -34 11.5 8.666 8.345 68.0 6.3 19.1 2025 03 26 19 24.18 -34 05.4 8.495 8.341 77.8 6.7 19.0 2025 04 05 19 22.76 -34 01.3 8.317 8.338 87.8 6.9 19.0 2025 04 15 19 20.30 -33 58.7 8.138 8.335 97.9 6.8 18.9 2025 04 25 19 16.73 -33 57.2 7.964 8.332 108.1 6.6 18.9 2025 05 05 19 12.02 -33 55.8 7.800 8.330 118.6 6.1 18.8 2025 05 15 19 06.22 -33 53.7 7.653 8.329 129.2 5.4 18.8 2025 05 25 18 59.39 -33 49.8 7.527 8.327 139.9 4.5 18.7 2025 06 04 18 51.68 -33 43.1 7.429 8.327 150.5 3.4 18.7 2025 06 14 18 43.32 -33 32.6 7.361 8.326 160.7 2.3 18.7 2025 06 24 18 34.57 -33 17.6 7.327 8.326 168.8 1.4 18.7 2025 07 04 18 25.73 -32 58.1 7.328 8.327 168.4 1.4 18.7 2025 07 14 18 17.13 -32 34.0 7.365 8.328 160.0 2.4 18.7 2025 07 24 18 09.04 -32 06.2 7.436 8.329 149.8 3.5 18.7 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2024 CBAT 2024 June 19 (CBET 5405) Daniel W. E. Green