Electronic Telegram No. 5753 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 NEW CATALINA COMET Gregory J. Leonard, Lunar and Planetary Laboratory, University of Arizona, reports his discovery of a comet on Catalina Sky Survey CCD images obtained on Sept. 14 with the 0.68-m Schmidt telescope, noting a moderate to strongly condensed coma 4" across, with surrounding diffuse coma 10" across and no apparent tail as seen in four 14-s co-added images. The discovery astrometry is tabulated below. 2026 UT R.A. (2000) Decl. Mag. Observer Sept.14.14599 15 54 33.29 +63 56 17.8 18.2 Leonard 14.14863 15 54 33.55 +63 56 07.4 18.0 " 14.15127 15 54 33.79 +63 55 57.3 17.9 " 14.15391 15 54 34.02 +63 55 46.6 17.9 " After the comet was posted to the Minor Planet Center's PCCP webpage, other observers have commented on the cometary appearance. S. Deen (Simi Valley, CA, USA) reports the following positions for this comet from archival ATLAS imaging with 0.5-m f/2 Schmidt reflectors -- those on Sept. 9 taken from Haleakala, Hawaii, in the course of the "Asteroid Terrestrial-Impact Last Alert System" (ATLAS) search program, and the rest from Mauna Loa, Hawaii. The comet was too faint in most of the imagery to discern any clear activity or lack thereof, but it appeared possibly vaguely extended on most dates. However, on Sept. 12, it appears quite clearly cometary, with a roughly 8" coma (full-width-at-half-maximum) that appears moderately condensed in roughly 5" seeing. Deen used Tycho Tracker and Aladin software to measure the astrometry; the photometry is likely too faint because it comes from ATLAS's forced photometry server, which assumes a point source. 2026 UT R.A. (2000) Decl. Mag. Sept. 1.27540 15 36 16.02 +73 44 43.6 19.6 1.27861 15 36 16.54 +73 44 36.0 20.1 1.29097 15 36 17.01 +73 44 11.4 19.9 4.24813 15 39 40.11 +72 00 51.4 19.1 4.25502 15 39 40.42 +72 00 33.3 19.3 4.26101 15 39 40.74 +72 00 20.7 19.6 4.27164 15 39 41.33 +71 59 54.2 19.5 4.27301 15 39 41.15 +71 59 55.1 19.6 4.27675 15 39 41.87 +71 59 43.2 19.1 4.28270 15 39 42.24 +71 59 30.4 19.4 4.29370 15 39 42.75 +71 59 04.2 19.1 9.25848 15 46 40.28 +68 28 32.1 19.5 9.26165 15 46 40.69 +68 28 21.0 19.5 9.26300 15 46 40.57 +68 28 17.8 9.26664 15 46 40.83 +68 28 07.1 9.26936 15 46 41.01 +68 27 59.2 9.27751 15 46 41.60 +68 27 36.5 9.28115 15 46 41.76 +68 27 24.0 9.28615 15 46 42.25 +68 27 09.9 19.3 12.22196 15 51 22.21 +65 53 05.8 18.6 12.22517 15 51 22.59 +65 52 53.1 18.6 12.23296 15 51 23.33 +65 52 27.5 18.5 12.24304 15 51 24.23 +65 51 52.1 18.6 13.22575 15 53 01.30 +64 53 57.8 18.5 13.22900 15 53 01.55 +64 53 46.0 18.5 13.23448 15 53 01.95 +64 53 25.3 18.9 Imaging by W. Hasubick (Buchloe, Germany) with a 0.44-m reflector on Sept. 14.81 UT shows a diffuse 66" coma of mag 17.9-18.5 and no tail. Fifty stacked 60-s CCD exposures obtained during Sept. 14.87-14.92 UT by E. Bryssinck (Kruibeke, Belgium) with a 0.4-m f/3.8 reflector shows a faint, condensed coma about 16" in diameter with a central condensation and a faint tail 22" long toward p.a. 63 degrees; the magnitude was 18.0 within a circular aperture radius of 5".0. Ninety stacked 30-s CCD exposures taken as above on Sept. 21.83-21.87 show a faint, condensed, circular coma about 71" in diameter with a central condensation and a faint tail 42" long in p.a. 70.9 degrees; the magnitude was 17.8 within a circular aperture radius of 5".0. Fourteen stacked 60-s CCD exposures taken remotely by H. Sato (Bunkyo-ku, Tokyo, Japan) on Sept. 15.3 UT with a 0.43-m f/6.8 astrograph located at the Utah Desert Remote Observatory (near Beryl Junction, UT, USA) show a strongly condensed coma 15" in diameter with no tail; the magnitude was 17.9 as measured within a circular aperture of radius 7".6. R. Weryk, Department of Physics and Astronomy, University of Western Ontario, reports that three stacked gri-band exposures taken in 1".1-1".2 seeing on Sept. 16.27 UT by R. Wainscoat and himself with the 3.6-m Canada- France-Hawaii Telescope at Mauna Kea (queue observer J. Nagasako; queue coordinator V. Khatu) show a very condensed head of size 1".5 (FWHM) and a 40" tail in p.a. 70 degrees. Thirty-six stacked 30-s CMOS exposures taken on Sept. 16.44-16.47 UT by K. Yoshimoto (Yamaguchi, Japan) with a 0.3-m f/4 reflector show a very diffuse coma 64" in diameter and no tail; the total magnitude was measured to be 15.7. Eighty-two stacked 30-s CMOS exposures taken on Sept. 20.45-20.48 show a very diffuse coma 2'.1 in diameter with a faint tail 1'.0 long in p.a. 75 deg; the total magnitude had brightened to 14.2 (APASS V-magnitude comparison stars). Fifty-eight stacked 30-s CMOS exposures taken (again, as above) during Sept. 22.44-22.48 show a very diffuse coma of size 1'.8 and a faint tail 1'.5 long in p.a. 78 deg; the total V-band magnitude was 13.8. M. Masek, Institute of Physics, Czech Academy of Sciences, reports on imaging of this comet obtained with the F/(Ph)otometric Robotic Atmospheric Monitor (FRAM) robotic observatory at the Cherenkov Telescope Array site on La Palma on Sept. 16.89 UT. He found a diffuse coma of diameter 3'.8 with central condensation and a total coma magnitude of 13.2 on fifty-eight stacked CCD images obtained with a 135-mm-f.l. f/2 telephoto lens (+ V filter). One-hundred-twenty stacked 120-s unfiltered CMOS images obtained remotely by A. Valvasori and F. Coccia on Sept. 17.8 UT with a 0.30-m f/4 reflector located at the ALMO Observatory in Padulle, Italy, show a 13".9 coma and no tail (mag 17.7). One-hundred-forty-five additional unfiltered 13-s exposures taken on Sept. 29.8 show a 20".2 coma and no tail; the magnitude was measured as 16.5-16.7. Eighty 12-s CCD exposures taken on Sept. 17.9 UT by P. Birtwhistle (Great Shefford, Berkshire, England) show a condensed coma of diameter 10" with a straight 32"-long tail in p.a. 72 degrees; the magnitude was G = 18.0 as measured within a circular aperture of radius 6".5. Twenty stacked 15-s CCD exposures taken on Sept. 23.4 UT by M. Yoshimi (Fukuchiyama, Japan) with a 0.25-m f/6.3 Schmidt-Cassegrain reflector show a condensed coma approximately 0'.3 in diameter and no tail; the total magnitude was measured to be 16.4 (V magnitudes from stars in the Tycho-2 catalogue). The available astrometry can be accessed via the MPC's PCCP webpage under the preliminary Catalina observatory designation C46K1R1; the MPC has inexplicably not yet issued an MPEC with a designation for this comet. The following two-body orbital elements by S. Nakano (Central Bureau) are from 644 observations spanning 2026 Sept. 1-30 (mean residual 0".5). The comet will pass 1.06 AU from Jupiter on 2028 Apr. 30 UT. T = 2026 Oct. 25.23227 TT Peri. = 205.52054 e = 0.8989535 Node = 179.22886 2000.0 q = 0.7895367 AU Incl. = 78.10275 a = 7.8136003 AU n = 0.04512605 P = 21.84 years The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 15.5 and 2.5n = 8 for the magnitudes. This object appears to be in outburst, and given its intrinsic faintness, it is difficult to assess what its brightness may be in the coming weeks and months. Photometric monitoring is highly encouraged. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2026 07 19 18 30.31 +84 42.7 1.770 1.782 74.0 33.2 18.7 2026 07 24 17 41.83 +84 43.3 1.691 1.720 74.2 34.6 18.5 2026 07 29 16 56.79 +84 20.3 1.608 1.657 74.5 36.2 18.3 2026 08 03 16 21.25 +83 36.2 1.522 1.594 74.9 37.9 18.0 2026 08 08 15 56.63 +82 34.4 1.433 1.531 75.3 39.8 17.8 2026 08 13 15 41.50 +81 17.6 1.339 1.468 75.8 42.0 17.5 2026 08 18 15 33.69 +79 46.3 1.243 1.405 76.3 44.4 17.2 2026 08 23 15 31.26 +77 59.4 1.143 1.342 76.8 47.2 16.8 2026 08 28 15 32.75 +75 53.0 1.040 1.280 77.2 50.3 16.4 2026 09 02 15 37.05 +73 20.6 0.934 1.218 77.5 54.0 16.0 2026 09 07 15 43.37 +70 10.9 0.826 1.158 77.6 58.2 15.6 2026 09 12 15 51.03 +66 05.6 0.717 1.099 77.2 63.3 15.1 2026 09 17 15 59.41 +60 33.8 0.609 1.043 76.1 69.4 14.6 2026 09 18 16 01.12 +59 12.9 0.588 1.032 75.7 70.8 14.5 2026 09 19 16 02.83 +57 45.8 0.567 1.021 75.3 72.2 14.3 2026 09 20 16 04.53 +56 12.0 0.546 1.010 74.8 73.7 14.2 2026 09 21 16 06.22 +54 30.7 0.525 0.999 74.3 75.3 14.1 2026 09 22 16 07.89 +52 41.1 0.505 0.989 73.7 77.0 14.0 2026 09 23 16 09.53 +50 42.3 0.485 0.979 73.0 78.7 13.9 2026 09 24 16 11.15 +48 33.4 0.466 0.969 72.2 80.5 13.7 2026 09 25 16 12.74 +46 13.3 0.447 0.959 71.4 82.4 13.6 2026 09 26 16 14.29 +43 41.0 0.429 0.949 70.4 84.4 13.5 2026 09 27 16 15.79 +40 55.4 0.412 0.939 69.3 86.5 13.4 2026 09 28 16 17.25 +37 55.4 0.395 0.930 68.1 88.7 13.2 2026 09 29 16 18.65 +34 40.0 0.380 0.921 66.8 90.9 13.1 2026 09 30 16 19.99 +31 08.7 0.366 0.912 65.4 93.2 13.0 2026 10 01 16 21.26 +27 21.0 0.353 0.903 63.9 95.6 12.9 2026 10 02 16 22.46 +23 17.1 0.342 0.895 62.3 97.9 12.8 2026 10 03 16 23.59 +18 57.9 0.333 0.887 60.7 100.2 12.7 2026 10 04 16 24.63 +14 24.9 0.325 0.879 59.1 102.4 12.6 2026 10 05 16 25.59 +09 40.8 0.320 0.871 57.5 104.5 12.5 2026 10 06 16 26.46 +04 48.8 0.317 0.864 56.0 106.3 12.5 2026 10 07 16 27.22 -00 07.2 0.316 0.857 54.7 107.8 12.5 2026 10 08 16 27.89 -05 02.7 0.318 0.850 53.5 109.0 12.4 2026 10 09 16 28.45 -09 53.6 0.321 0.843 52.6 109.8 12.4 2026 10 10 16 28.89 -14 35.8 0.327 0.837 51.8 110.3 12.5 2026 10 11 16 29.22 -19 06.1 0.335 0.831 51.3 110.3 12.5 2026 10 12 16 29.43 -23 22.2 0.345 0.826 51.0 110.0 12.5 2026 10 13 16 29.51 -27 22.4 0.357 0.821 50.8 109.4 12.6 2026 10 14 16 29.47 -31 06.0 0.370 0.816 50.8 108.6 12.6 2026 10 15 16 29.29 -34 32.7 0.385 0.811 50.9 107.5 12.7 2026 10 16 16 28.98 -37 43.2 0.401 0.807 51.0 106.3 12.8 2026 10 17 16 28.53 -40 37.9 0.418 0.804 51.2 104.9 12.8 2026 10 18 16 27.94 -43 18.0 0.436 0.801 51.4 103.4 12.9 2026 10 19 16 27.22 -45 44.3 0.454 0.798 51.6 101.9 13.0 2026 10 20 16 26.35 -47 58.1 0.474 0.795 51.8 100.3 13.1 2026 10 21 16 25.35 -50 00.3 0.494 0.793 52.0 98.7 13.2 2026 10 22 16 24.21 -51 52.0 0.514 0.792 52.1 97.0 13.2 2026 10 23 16 22.94 -53 34.2 0.535 0.791 52.3 95.4 13.3 2026 10 24 16 21.54 -55 07.8 0.556 0.790 52.4 93.7 13.4 2026 10 25 16 20.01 -56 33.4 0.577 0.790 52.5 92.0 13.5 2026 10 26 16 18.36 -57 51.9 0.599 0.790 52.6 90.4 13.6 2026 10 27 16 16.59 -59 04.0 0.620 0.790 52.6 88.8 13.6 2026 11 01 16 06.28 -63 45.8 0.729 0.799 52.7 80.9 14.0 2026 11 06 15 54.23 -66 53.4 0.834 0.818 52.4 73.7 14.4 2026 11 11 15 41.46 -69 00.8 0.934 0.847 52.1 67.4 14.8 2026 11 16 15 28.77 -70 29.5 1.027 0.883 51.9 61.9 15.1 2026 11 21 15 16.61 -71 33.6 1.111 0.926 51.9 57.2 15.5 2026 11 26 15 05.09 -72 22.8 1.187 0.974 52.3 53.3 15.8 2026 12 01 14 54.06 -73 03.4 1.253 1.026 52.9 50.1 16.1 2026 12 06 14 43.14 -73 39.6 1.311 1.082 54.0 47.4 16.4 2026 12 11 14 31.80 -74 13.9 1.361 1.140 55.4 45.3 16.6 2026 12 16 14 19.41 -74 47.5 1.403 1.200 57.2 43.6 16.9 2026 12 21 14 05.32 -75 20.4 1.437 1.261 59.3 42.1 17.1 2026 12 26 13 48.84 -75 51.7 1.465 1.324 61.8 40.9 17.3 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2026 CBAT 2026 September 30 (CBET 5753) Daniel W. E. Green