Electronic Telegram No. 5344 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 B1 (LEMMON) An apparently asteroidal object discovered on Jan. 16 with the Mt. Lemmon Survey's 1.5-m reflector in Arizona has been found to show cometary appearance after posting on the Minor Planet Center's PCCP webpage. The discovery observations are tabulated below. 2024 UT R.A. (2000) Decl. Mag. Jan. 16.17491 3 54 33.40 -12 59 26.6 20.6 16.18055 3 54 33.09 -12 59 22.1 20.7 16.18618 3 54 32.89 -12 59 17.0 21.4 16.19182 3 54 32.57 -12 59 12.0 20.9 R. Weryk (Department of Physics and Astronomy, University of Western Ontario) writes that he found this object in pre-discovery exposures taken with both the Pan-STARRS1 and the Pan-STARRS2 1.8-m Ritchey-Chretien reflectors at Haleakala, spanning back to 2023 Oct. 13.6 UT, when Pan-STARRS1 images showed it at mag 22.5-22.8. Other Pan-STARRS1 images were found from 2023 Dec. 5.4 (mag 20.4-20.7), 9.4 (mag 21.1-22.0), and 15.4 (mag 20.2-20.8), as well as on 2024 Jan. 3.3 (mag 20.3-20.6). The four 45-s w-band survey images taken on Dec. 15.4 show seeing around 1".6 show a condensed, somewhat soft object of size around 2" (full-width-at-half-maximum) and no tail. Weryk also found images in Pan-STARRS2 exposures taken on 2023 Oct. 19.54-19.57 (mag 21.8-23), 2023 Oct. 23.6 (mag 22.4-23.7), 2023 Nov. 20.45-20.47 (mag 21.5-21.8), and 2023 Dec. 24.32-24.36 (mag 21.6-21.7). Twenty stacked 60-s CCD exposures taken remotely by H. Sato (Bunkyo-ku, Tokyo, Japan) with a "Deep Sky Chile" 0.51-m f/6.8 astrograph located at Rio Hurtado, Chile, on 2024 Jan. 31.05 UT show a strongly condensed coma 7" in diameter with no tail; the magnitude was 20.6 as measured within a circular aperture of radius 3".6. Two-hundred-forty 30-s CCD exposures taken by A. Aletti with a 0.36-m f/7.5 reflector at Varese, Italy, on 2024 Feb. 8.83-1.87 (and measured by Aletti and M. Auteri) show a slightly condensed coma 5" wide and of mag 20.5 that was extended toward the west. The astrometry appears on MPEC 2024-C86. The following nearly parabolic orbital elements by S. Nakano (Central Bureau) are from 53 observations spanning 2023 Oct. 13-2024 Feb. 2 (mean residual 0".4), with corresponding "original" and "future" values of 1/a being +0.000089 and -0.000463 (+/- 0.000019) AU**-1, respectively. These indicate that the comet will pass 2.65 AU from Jupiter on 2024 Mar. 20 UT. Epoch = 2024 Oct. 17.0 TT T = 2024 Oct. 7.71120 TT Peri. = 66.21223 e = 1.0007420 Node = 79.18809 2000.0 q = 1.6336364 AU Incl. = 70.90424 The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 13.0 and 2.5n = 8 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2024 01 11 03 58.71 -14 11.8 3.105 3.666 117.6 13.7 20.0 2024 01 21 03 51.18 -11 48.5 3.128 3.572 109.0 15.1 19.9 2024 01 31 03 45.77 -09 13.9 3.166 3.477 100.1 16.2 19.8 2024 02 10 03 42.56 -06 32.6 3.216 3.381 91.1 17.0 19.8 2024 02 20 03 41.50 -03 48.4 3.271 3.286 82.2 17.3 19.7 2024 03 01 03 42.44 -01 04.0 3.327 3.191 73.6 17.3 19.6 2024 03 11 03 45.24 +01 38.9 3.379 3.096 65.2 16.9 19.6 2024 03 21 03 49.72 +04 19.5 3.424 3.001 57.0 16.2 19.5 2024 03 31 03 55.72 +06 57.2 3.459 2.906 49.2 15.1 19.4 2024 09 07 09 25.72 +48 24.0 2.201 1.685 47.1 26.0 16.5 2024 09 17 10 19.10 +49 40.5 2.107 1.657 50.3 27.8 16.4 2024 09 27 11 17.06 +49 44.8 2.038 1.640 52.8 29.1 16.3 2024 10 07 12 15.70 +48 25.2 1.998 1.634 54.4 29.9 16.2 2024 10 17 13 10.72 +45 48.3 1.989 1.638 55.2 30.0 16.2 2024 10 27 13 59.44 +42 16.6 2.009 1.654 55.1 29.5 16.3 2024 11 06 14 41.18 +38 18.5 2.054 1.680 54.3 28.6 16.4 2024 11 16 15 16.53 +34 18.5 2.118 1.716 53.1 27.4 16.5 2024 11 26 15 46.55 +30 33.0 2.194 1.762 51.7 26.1 16.7 2024 12 06 16 12.25 +27 11.3 2.274 1.815 50.5 24.8 16.9 2024 12 16 16 34.44 +24 16.9 2.354 1.875 49.8 23.6 17.0 2024 12 26 16 53.72 +21 50.0 2.427 1.942 49.7 22.7 17.2 2025 01 05 17 10.52 +19 49.3 2.490 2.014 50.6 22.2 17.4 2025 01 15 17 25.08 +18 12.2 2.539 2.091 52.5 21.9 17.6 2025 01 25 17 37.56 +16 55.8 2.574 2.172 55.4 21.9 17.7 2025 02 04 17 48.01 +15 57.5 2.592 2.255 59.4 22.1 17.9 2025 02 14 17 56.39 +15 14.2 2.594 2.342 64.3 22.3 18.0 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2024 CBAT 2024 February 8 (CBET 5344) Daniel W. E. Green