Electronic Telegram No. 5402 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 L1 (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, though it was initially reported as apparently asteroidal. P. Veres, Minor Planet Center, noticed the object in the MPC's "isolated tracklet file" and notified Weryk about the object's Centaur-like orbit, causing Weryk to look closely at the images and find cometary activity. Eight stacked 45-s w-band survey images taken on the discovery night in 1".0-1".2 seeing (and tabulated below) show a condensed head of size 1".6 (full-width-at-half-maximum) and no tail. 2024 UT R.A. (2000) Decl. Mag. June 1.28090 15 51 20.89 +26 47 49.8 21.6 1.29328 15 51 20.08 +26 47 46.1 21.7 1.29458 15 51 20.02 +26 47 45.6 21.1 1.30566 15 51 19.30 +26 47 42.0 21.5 1.30696 15 51 19.22 +26 47 41.7 21.2 1.31806 15 51 18.51 +26 47 38.2 21.4 1.31936 15 51 18.44 +26 47 37.9 21.2 1.50051 15 51 06.88 +26 46 41.4 21.0 1.50116 15 51 06.82 +26 46 41.1 21.2 Four 45-s Pan-STARRS2 w-band survey images taken on May 6.4 UT in 1".5-1".7 seeing show a condensed head of size 2".2 (FWHM) and mag 20.4-21.1 and no obvious tail. Four 45-s Pan-STARRS2 w-band survey images taken on May 29.3 in 1".1 seeing show a condensed head of size 1".7 (FWHM) and mag 21.0-21.1 and no tail. Weryk adds that three 60-s gri-band follow-up images obtained on June 2.5 with the 3.6-m Canada-France-Hawaii Telescope on Mauna Kea by R. Wainscoat and Weryk (queue observer L. Wells; queue coordinator T. Burdullis) in 0".9 seeing show a very condensed head of size 1".3 and a broad tail 8" long spanning p.a. 50-140 degrees. Weryk subsequently identified pre-discovery observations of the comet obtained with the Pan-STARRS1 1.8-m Ritchey-Chretien reflector at Haleakala on May 1.4 (at mag 21.1), May 2.4 (mag 20.6-20.8), May 4.6 (mag 21.1), May 8.4 (mag 21.9), May 18.5 (mag 21.9), May 21.4 (mag 21.2), and May 31.5 (mag 19.7). Previously unconnected single-night observations of this comet that were made with the Mt. Lemmon Survey 1.5-m reflector from Apr. 30.4 (mag 20.4-21.7) and May 14.4 UT (mag 20.8-21.1) were found in the ITF. The available astrometry appears on MPEC 2024-L59. The following elliptical orbital elements by S. Nakano (Central Bureau) are from 54 observations spanning 2024 Apr. 30-2024 June 5 (mean residual 0".3). There are no close approaches to major planets. The formal error/uncertainty in the period is +/- 34.2 days. T = 2025 Apr. 23.27405 TT Peri. = 171.78284 e = 0.5302908 Node = 45.15753 2000.0 q = 5.3485541 AU Incl. = 99.15183 a = 11.3869484 AU n = 0.02565034 P = 38.4 years The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 10.5 and 2.5n = 8 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2024 05 10 16 15.22 +27 58.9 4.945 5.666 131.6 7.7 20.0 2024 05 20 16 04.52 +27 38.0 4.918 5.648 132.2 7.6 20.0 2024 05 30 15 53.76 +26 59.2 4.920 5.632 130.6 7.9 20.0 2024 06 09 15 43.41 +26 02.8 4.948 5.615 126.8 8.3 20.0 2024 06 19 15 33.91 +24 50.6 5.002 5.600 121.4 8.9 20.0 2024 06 29 15 25.56 +23 25.2 5.079 5.584 114.9 9.5 20.0 2024 07 09 15 18.58 +21 49.8 5.175 5.569 107.7 10.0 20.0 2024 07 19 15 13.06 +20 07.4 5.287 5.554 100.0 10.4 20.1 2024 07 29 15 09.02 +18 20.9 5.409 5.540 92.1 10.6 20.1 2024 08 08 15 06.38 +16 32.9 5.538 5.527 84.1 10.5 20.2 2024 08 18 15 05.07 +14 45.3 5.669 5.513 76.0 10.3 20.2 2024 08 28 15 04.93 +12 59.5 5.798 5.501 68.1 9.8 20.2 2024 09 07 15 05.86 +11 16.8 5.920 5.489 60.1 9.2 20.3 2024 09 17 15 07.70 +09 37.9 6.032 5.477 52.4 8.4 20.3 2024 09 27 15 10.33 +08 03.4 6.131 5.465 44.8 7.4 20.3 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2024 CBAT 2024 June 6 (CBET 5402) Daniel W. E. Green