Electronic Telegram No. 5401 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/2024 FG_9 (NANSHAN-HAHN) An apparently asteroidal object that was discovered independently at several different observatories was curiously assigned the minor-planet designation 2024 FG_9 by the Minor Planet Center to a single-night set of Mt. Lemmon Survey discovery observations from Mar. 21. The comet had been discovered and followed on two nights at the Mt. Nanshan station of the Xinjiang Astronomical Observatory (details provided by Xing Gao, who participated in the observing and measurements, writing that Xi Liao first noted this object) in the course of the Xingming Sky Survey on images taken on Mar. 8 and 9 UT with a 1.0-m f/2.2 reflector. But the Xingming and Mt. Lemmon observations were not linked as a single object until an independent asteroidal discovery was made by Robson Henrique dos Santos Hahn (Moeckmuehl, Germany) on images obtained remotely on Apr. 10 and 12 with his 0.36-m f/2 Celestron 14 (+ Hyperstar) reflector located near Valdin, Ourenses, Spain. Hahn reported the object as potentially interesting, and it was placed at that time on the MPC's NEOCP webpage. The discovery observations are tabulated below. The Mt. Lemmon observations and Hahn's observationos first appeared on MPS 2157401 (dated 2024 Apr. 18) together with many observations obtained with the Pan-STARRS1 and Pan-STARRS2 1.8-m reflectors at Haleakala on seven nights from 2023 Nov. 4 (mag 22.2-23.3) to 2024 Mar. 6 (mag 20.2-20.5); only the Pan-STARRS2 astrometry from 2023 Nov. 18 (mag 21.8-21.9) had been reported to the MPC in real time (the rest reported as pre-discovery observations after the posting on the NEOCP). The Mar. 8 Xingming observations first appeared on MPS 2166265 (dated 2024 May 1), but curiously without the Mar. 9 observations (which remained unpublished until now, despite each set being reported the day that they made and under the same preliminary designation; i.e., the Xingming observers recognized in real time that the same object had been observed on Mar. 8 and 9). An orbit only for 2024 FG_9 was first published on Apr. 14 on MPEC 2024-G199 in a "Daily Orbit Update". 2024 UT R.A. (2000) Decl. Mag. Observer Mar. 8.57951 4 09 23.58 +20 14 55.6 19.7 Xingming 8.59395 4 09 25.41 +20 15 00.3 20.2 " 8.60840 4 09 27.23 +20 15 04.2 19.9 " 9.59481 4 11 31.49 +20 19 51.3 20.0 " 9.60617 4 11 32.86 +20 19 54.9 20.1 " 9.61710 4 11 34.30 +20 19 58.5 20.1 " 21.12415 4 37 17.98 +21 12 05.4 19.5 Mt. Lemmon Survey 21.12836 4 37 18.52 +21 12 06.9 19.5 " 21.13257 4 37 19.13 +21 12 07.3 19.8 " 21.13681 4 37 19.65 +21 12 08.5 " 21.14447 4 37 20.78 +21 12 09.9 20.1 " 21.15845 4 37 22.79 +21 12 13.6 19.4 " 21.16966 4 37 24.32 +21 12 16.4 19.7 " Apr. 10.86547 5 30 02.06 +22 13 12.5 18.7 Hahn 10.88035 5 30 04.36 +22 13 13.2 18.1 " 10.89527 5 30 06.86 +22 13 14.1 18.7 " 11.86239 5 32 44.60 +22 14 38.5 19.0 " 11.87700 5 32 47.05 +22 14 39.6 19.0 " 11.89163 5 32 49.41 +22 14 40.8 18.3 " Pre-discovery observations were later reported by S. Deen (Simi Valley, CA, USA), who found cometary activity in 2024 FG_9. An image obtained with the 4-m reflector (+ DECam) at the Cerro Tololo Interamerican Observatory (as part of the DECam Legacy Survey) on 2018 May 16.97 UT shows the comet as a diffuse object of size 1".8 (full-width-at-half-maximum) and magnitude z = 20.4 in 1".0 seeing, with a 3" tail toward p.a. 125 degrees. Deen also found five images of the comet obtained with the 1.2-m Schmidt telescope at Palomar taken on four nights in 2018 (Mar. 29, magnitude g = 20.8; Apr. 8, r = 20.0; Apr. 11, r = 20.2; and Apr. 15, r = 20.5), with all of the "Zwicky Transient Facility" survey images showing a "clearly hazy" and extended appearance. Deen also observed this comet on 2024 Apr. 17.0 with a 0.43-m telescope located at Rio Hurtado, Chile, when the object appeared diffuse with a size of about 3" (FWHM) in 1".5 seeing, with a possible tail 4" long toward p.a. 90 degrees. A. Hale, Cloudcroft, NM, USA, reports that 300-s exposures taken on 2024 Apr. 28.2 UT with a Las Cumbres Observatory 0.35-m f/3 Cassegrain reflector at Haleakala, HI, USA, show the comet to be marginally diffuse (but relatively condensed) when compared with stars of similar brightness; a coma size of 6" with no tail was given. Similar exposures obtained by Hale on Apr. 15 show no obvious cometary appearance. Additional images obtained by Hale on May 25.25 show a diffuse coma of size 24" with a prominent central condensation and no tail; the magnitude was given as 17.4-17.5, and Hale noted that the comet was then distinctly larger in size than during his previous observations. Fifteen stacked 30-s CCD exposures obtained remotely by H. Sato (Bunkyo-ku, Tokyo, Japan) with a 0.51-m f/6.8 astrograph located at Siding Spring, NSW, Australia, on 2024 May 13.4 show a strongly condensed coma 15" in diameter and a hint of tail eastward; the magnitude was 17.9 as measured within a circular aperture of radius 7".6. Sixteen stacked additional 30-s exposures taken by Sato on May 26.35-26.35 show a strongly condensed object with an outer coma 1'.2 in diameter and no tail; the magnitude was 14.9 as measured within a circular aperture of radius 37".8 (and Sato commented on the increase in size/brightness). One-hundred-forty-five 30-s CCD exposures taken by A. Aletti, F. Bellini, L. Buzzi, G. Galli, and M. Auteri with a 0.36-m f/8.4 reflector located at Hakos, Namibia, on 2024 May 21.74-21.77 in 3".6 seeing show a slightly condensed 7" coma. Additional astrometry appears on MPEC 2024-L4. The following orbital elements by S. Nakano (Central Bureau) are from 95 observations spanning 2018 Mar. 29-2024 May 26 (mean residual 0".5). The comet passed 0.20 AU from Jupiter on 2021 Apr. 30 and will again pass 0.20 AU from Jupiter on 2033 Apr. 16 UT. Nakano was unable to find earlier observations of this comet in astrometric archives. Epoch = 1999 Jan. 22.0 TT T = 1999 Jan. 4.81377 TT Peri. = 173.51077 e = 0.4084116 Node = 318.12254 2000.0 q = 2.0969019 AU Incl. = 10.34251 a = 3.5445283 AU n = 0.14769521 P = 6.67 years Epoch = 2005 Sept.27.0 TT T = 2005 Sept. 8.93263 TT Peri. = 173.71114 e = 0.4094045 Node = 318.05570 2000.0 q = 2.0912684 AU Incl. = 10.34940 a = 3.5409489 AU n = 0.14791921 P = 6.66 years Epoch = 2012 Mar. 14.0 TT T = 2012 Mar. 18.53711 TT Peri. = 184.30688 e = 0.4811829 Node = 311.51578 2000.0 q = 1.7129458 AU Incl. = 8.68876 a = 3.3016368 AU n = 0.16428962 P = 6.00 years Epoch = 2018 Mar. 23.0 TT T = 2018 Mar. 22.15412 TT Peri. = 184.47767 e = 0.4811437 Node = 311.45979 2000.0 q = 1.7134838 AU Incl. = 8.68671 a = 3.3024247 AU n = 0.16423083 P = 6.00 years Epoch = 2024 May 10.0 TT T = 2024 May 20.33931 TT Peri. = 245.90643 e = 0.5097333 Node = 253.04508 2000.0 q = 1.5963715 AU Incl. = 1.73108 a = 3.2561290 AU n = 0.16774581 P = 5.88 years Epoch = 2030 Apr. 9.0 TT T = 2030 Apr. 8.89452 TT Peri. = 246.16002 e = 0.5094058 Node = 252.89198 2000.0 q = 1.5980914 AU Incl. = 1.73047 a = 3.2574607 AU n = 0.16764295 P = 5.88 years Epoch = 2036 July 6.0 TT T = 2036 June 18.54697 TT Peri. = 351.94100 e = 0.4622931 Node = 148.08963 2000.0 q = 1.8177998 AU Incl. = 8.31473 a = 3.3806520 AU n = 0.15856356 P = 6.22 years The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 14.0 and 2.5n = 10 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2024 05 10 06 53.69 +21 39.5 1.990 1.600 53.0 30.3 17.5 2024 05 15 07 08.65 +21 16.3 2.014 1.597 51.6 29.8 17.6 2024 05 20 07 23.68 +20 47.8 2.039 1.596 50.4 29.2 17.6 2024 05 25 07 38.71 +20 14.1 2.064 1.597 49.1 28.7 17.6 2024 05 30 07 53.72 +19 35.3 2.090 1.599 47.9 28.1 17.6 2024 06 04 08 08.68 +18 51.5 2.118 1.603 46.7 27.4 17.7 2024 06 09 08 23.55 +18 03.0 2.146 1.608 45.6 26.8 17.7 2024 06 14 08 38.30 +17 10.0 2.175 1.614 44.4 26.1 17.8 2024 06 19 08 52.90 +16 12.9 2.205 1.622 43.3 25.4 17.8 2024 06 24 09 07.34 +15 12.1 2.236 1.631 42.1 24.7 17.9 2024 06 29 09 21.59 +14 07.9 2.268 1.642 41.0 23.9 17.9 2024 07 04 09 35.65 +13 00.7 2.302 1.654 39.8 23.2 18.0 2024 07 09 09 49.52 +11 50.9 2.336 1.667 38.6 22.4 18.1 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2024 CBAT 2024 June 1 (CBET 5401) Daniel W. E. Green