Electronic Telegram No. 5548 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/2007 SA_24 (LEMMON) On 2023 Oct. 10, David Rankin (Lunar and Planetary Laboratory, University of Arizona) reported his discovery of a comet with a condensed 6" coma on four 30-s and four 45-s CCD exposures taken with the Mt. Lemmon 1.5-m reflector. The discovery observations are tabulated below. He noted that the comet was still obviously active in Mt. Lemmon images taken on 2023 Dec. 16, with a coma and a wide tail toward p.a. about 270 degrees. 2023 UT R.A. (2000) Decl. Mag. Observer Oct. 10.37798 4 09 42.95 +21 22 34.7 20.2 Rankin 10.38314 4 09 42.88 +21 22 33.4 20.2 " 10.38832 4 09 42.77 +21 22 32.3 20.3 " 10.39348 4 09 42.71 +21 22 30.6 20.1 " 10.41060 4 09 42.44 +21 22 26.5 20.1 " 10.42375 4 09 42.22 +21 22 23.3 20.0 " 10.43702 4 09 42.00 +21 22 20.0 20.0 " The object was placed on the Minor Planet Center's PCCP webpage and was soon identified with an apparently asteroidal object discovered in 2007 with the same telescope (discovery observations tabulated below) and given the minor- planet designation 2007 SA_24 on MPS 326389 (dated 2010 May 16); the 2.7-year delay presumably had to do with the fact that the object was apparently discovered separately (and reported separately) as an apparently asteroidal object on six different nights (2007 Sept. 25-2008 Feb. 28) at three different observatories (including also Spacewatch on 2007 Oct. 19 and LINEAR on three nights) before the observations were linked together as a single object. 2007 UT R.A. (2000) Decl. Mag. Sept.25.27623 2 23 40.20 +24 44 56.5 20.6 25.28297 2 23 40.05 +24 44 54.4 20.1 25.28971 2 23 39.91 +24 44 53.2 21.2 25.29653 2 23 39.80 +24 44 51.4 20.7 The MPC apparently identified the 2023 comet with 2007 SA_24 in late 2023 and pulled it off of the PCCP webpage "with no further" word, according to Rankin. Apparently asteroidal observations of this object were obtained with the Pan-STARRS2 1.8-m Ritchey-Chretien reflector at Haleakala and reported as a new object twice, on two nights in 2022 (June 6.5 UT at mag 21.3-21.6, and June 27.5 at mag 20.8-21.1) and later identified as 2007 SA_24 in the MPC's "isolated tracklet file". Seven stacked 120-s CCD exposures taken remotely on 2023 Dec. 6.18 UT by H. Sato (Bunkyo-ku, Tokyo, Japan) with a 0.43-m f/6.8 astrograph located at the Utah Desert Remote Observatory (near Beryl Junction, UT, USA) showed a moderately condensed coma 7" in diameter with not tail; the magnitude was 19.2 as measured within a circular aperture of radius 3".7. The available astrometry appears on MPEC 2025-H103; unfortunately, P. Veres (MPC) neglected to assign the customary 2023 recovery designation. The following linked orbital elements by S. Nakano (Central Bureau) are from 99 observations spanning 2007 Sept. 25-2023 Dec. 21 (mean residual 0".4). The comet passed 0.91 AU from Jupiter in 1977 May. Epoch = 2007 Apr. 10.0 TT T = 2007 Mar. 30.34381 TT Peri. = 108.78028 e = 0.5688950 Node = 233.50350 2000.0 q = 2.6946916 AU Incl. = 17.11015 a = 6.2506625 AU n = 0.06306886 P = 15.63 years Epoch = 2022 Dec. 7.0 TT T = 2022 Dec. 5.44656 TT Peri. = 108.82178 e = 0.5697458 Node = 233.40474 2000.0 q = 2.7111175 AU Incl. = 17.10566 a = 6.3011999 AU n = 0.06231164 P = 15.82 years Epoch = 2038 Apr. 7.0 TT T = 2038 Apr. 15.88419 TT Peri. = 107.90976 e = 0.5681834 Node = 232.73330 2000.0 q = 2.6639226 AU Incl. = 17.08977 a = 6.1691067 AU n = 0.06432365 P = 15.32 years Epoch = 2053 Aug. 6.0 TT T = 2053 July 17.26480 TT Peri. = 107.68865 e = 0.5685369 Node = 232.57577 2000.0 q = 2.6614136 AU Incl. = 17.09838 a = 6.1683457 AU n = 0.06433555 P = 15.32 years The object is currently at mag 23 or fainter according to power-law parameters H = 12.5 and 2.5n = 8. NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2025 CBAT 2025 April 29 (CBET 5548) Daniel W. E. Green