Electronic Telegram No. 5389 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 13P/OLBERS Hidetaka Sato (Bunkyo-ku, Tokyo, Japan) found that comet 13P had a strongly condensed coma 8" in diameter in CCD exposures taken on 2023 Oct. 14.76 UT with a 0.51-m f/6.8 astrograph at Siding Spring, NSW; the magnitude was 19.5 as measured within a circular aperture of radius 4".3. On 2023 Dec. 3.11, using a "Deep Sky Chile" 0.51-m f/6.8 astrograph at Rio Hurtado, Chile, Sato found a strongly condensed coma 25" in diameter with a faint tail 1'.8 long toward p.a. about 0 degrees; the magnitude was 16.6 as measured within a circular aperture of radius 13".0. Hirohisa Sato reports the following total CCD magnitudes from images of comet 13P taken by T. Ikemura at Shinshiro, Japan: 2024 Jan. 14.48 UT, 15.3 (strongly condensed coma about 0'.9 in diameter, with a tail about 1'.0 long toward p.a. about 67 degrees in twenty-five stacked 60-s exposures); Feb. 12.47, 12.8 (strongly condensed inner coma about 2'.2 in diameter and a faint outer coma about 9'.9 in diameter in twenty-seven stacked 60-s exposures); Mar. 2.49, 12.4 (strongly condensed inner coma about 2'.3 in diameter and a faint outer coma about 10'.1 in diameter, on twenty-seven images 60-s exposures). K. Yoshimoto, Kumage, Yamaguchi, Japan, found a coma of total mag 11.3 and coma diameter 4'.0 on images obtained on 2024 Mar. 10.47 UT with a 0.20-m f/8 Ritchey-Chretien reflector; he later found a 4'.5 coma of total mag 10.5 on CCD images obtained remotely on Apr. 2.14 UT with a 0.43-m f/6.8 reflector located at the Utah Desert Remote Observatory (near Beryl Junction, UT, USA). K. Kadota, Ageo, reports the following total CCD magnitudes made with a 0.25-m f/5 reflector: 2023 Oct. 18.71 UT, 18.8; Nov. 13.65, 17.9; Dec. 3.57, 17.2; 17.48, 16.6; 2024 Jan. 1.51, 15.5; 15.46, 15.2; 27.42, 14.5; Feb. 12.39, 13.1; 28.46, 12.3; Mar. 14.45, 11.6; 29.47, 10.9; Apr. 14.45, 10.3; 19.44, 9.9. Visual total-magnitude and coma-diameter estimates: Feb. 5.84 UT, 13.4, 0'.9 (W. Hasubick, Buchloe, Germany, 0.44-m reflector); 12.42, [13.0, -- (S. Yoshida, Ibaraki, Japan, 0.40-m reflector); Mar. 5.84, 10.9, 3'.5 (J. J. Gonzalez, Leon, Spain, 0.20-m reflector); Apr. 8.89, 9.5, 3' (Gonzales); 12.86, 9.2, 3' (Gonzalez, 20x80 binoculars). S. Nakano, Central Bureau, reports the following updated linked orbital elements for comet 13P from 1347 observations spanning 1887 Aug. 28-2024 Apr. 19 (mean residual 0".9), with non-gravitational parameters A1 = +0.37 +/- 0.02 and A2 = +0.0588 +/- 0.0000. His earlier linked orbit (cf. CBET 5289) yields residuals of -8" in R.A. and -22" in Decl. for 2024 April observations. The comet passed 0.081 AU from Mars on 1887 July 28 and 1.52 AU from Jupiter on 1889 Jan. 11 UT. This orbit gives residuals of about +/- 0.35 deg or less for the 1815 observations. Epoch = 1887 Oct. 16.0 TT T = 1887 Oct. 8.97362 TT Peri. = 65.35617 e = 0.9309709 Node = 86.05746 2000.0 q = 1.1990812 AU Incl. = 44.57066 a = 17.3706596 AU n = 0.01361381 P = 72.40 years Epoch = 1956 June 16.0 TT T = 1956 June 19.14172 TT Peri. = 64.64500 e = 0.9303298 Node = 86.10429 2000.0 q = 1.1784568 AU Incl. = 44.60961 a = 16.9147846 AU n = 0.01416786 P = 69.57 years Epoch = 2024 June 19.0 TT T = 2024 June 30.04867 TT Peri. = 64.41663 e = 0.9303079 Node = 85.84752 2000.0 q = 1.1754853 AU Incl. = 44.66576 a = 16.8668467 AU n = 0.01422831 P = 69.27 years Epoch = 2094 Mar. 24.0 TT T = 2094 Mar. 20.46759 TT Peri. = 64.49629 e = 0.9308261 Node = 85.65483 2000.0 q = 1.1832168 AU Incl. = 44.57697 a = 17.1049702 AU n = 0.01393223 P = 70.74 years The comet is at small elongations from the sun now for several months. It is running about a magnitude brighter in April than the ephemeris suggested on CBET 5289. NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2024 CBAT 2024 April 29 (CBET 5389) Daniel W. E. Green