Electronic Telegram No. 5018 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 252P/LINEAR The comet has been found to again be brighter than expected (similar to its previous return in 2016), and its position off somewhat from the prediction. M. Mattiazzo, Swan Hill, Victoria, Australia, writes that an image of comet 252P taken by R. Kaufman (Bright, Victoria, Australia) at Mattiazzo's suggestion on Aug. 8.39 UT shows the comet at V magnitude approximately 10.5. Mattiazzo obtained additional images of the comet using his Celestron 11 f/2.2 Rowe-Ackermann Schmidt Astrograph (+ Canon 6D camera), with his astrometry provided below (Gaia DR2 reference stars); he notes a coma diameter of 2'.8 and a total G magnitude of 11.1. 2021 UT R.A. (2000) Decl. Mag. Observer Aug. 9.37227 11 42 00.09 + 4 13 42.3 14.3 Mattiazzo 9.37626 11 42 00.75 + 4 13 40.5 12.4 " 9.37947 11 42 01.84 + 4 13 35.4 15.1 " 9.38306 11 42 02.95 + 4 13 33.4 14.9 " 9.38454 11 42 03.30 + 4 13 32.4 14.7 " 9.38734 11 42 04.27 + 4 13 27.8 12.1 " 9.38814 11 42 04.51 + 4 13 25.9 14.8 " 9.39053 11 42 04.48 + 4 13 23.1 11.1 " 15.37587 12 07 42.40 + 2 14 56.2 15.9 " 15.37791 12 07 42.91 + 2 14 54.9 16.2 " 15.37998 12 07 43.62 + 2 14 50.8 15.9 " 15.38413 12 07 44.55 + 2 14 48.2 15.4 " 15.38620 12 07 44.94 + 2 14 44.0 14.1 " 15.38744 12 07 45.41 + 2 14 42.8 16.3 " H. Sato, Tokyo, Japan (remotely observing at Siding Spring) provides his astrometry obtained with a 0.51-m f/6.8 astrograph as tabulated below; his CCD images show a strongly condensed coma 3'.6 in diameter, with the total magnitude measured to be 13.1 within a circular aperture of radius 109".5. 2021 UT R.A. (2000) Decl. Mag. Observer Aug. 10.35876 11 46 15.74 + 3 54 16.5 Sato 10.36146 11 46 16.42 + 3 54 13.5 " 10.36416 11 46 17.10 + 3 54 10.6 " 10.36685 11 46 17.79 + 3 54 06.9 13.1 " K. Kadota obtained the astrometry below using a 0.25-m f/5 reflector at Ageo, Japan; his CCD images taken in twilight at low altitude (about 10 degrees) show a weak central condensation in a faint coma of diameter 1'.5 of total magnitude 12.5 with no tail. 2021 UT R.A. (2000) Decl. Mag. Observer Aug. 10.44265 11 46 37.31 + 3 52 30.7 12.5 Kadota 10.44441 11 46 37.85 + 3 52 29.7 " Visual total-magnitude and coma-diameter estimates: Aug. 9.39 UT, 11.4, 2' (Mattiazzo, 0.2-m Newtonian reflector; altitude 17 degrees); 10.38, 11.6, 2'.3 (C. Wyatt, Walcha, NSW, Australia, 0.4-m Newtonian reflector; very diffuse, slight brightening toward the center; altitude 13.8 degrees); 10.91, 11.8, -- (J. G. de S. Aguiar, Campinas, Brazil, 0.27-m reflector). The residuals for the Aug. 9 observations above are -0.53 deg in R.A. and +0.11 deg in Decl. from the prediction in NK 3651 and the ICQ's 2021 Comet Handbook, with a corresponding correction of Delta(T) = +0.80 day. Three single-night observations on 2021 Jan. 13.2 UT reported from the Lowell Discovery Telescope and published by the Minor Planet Center are incorrectly attributed to comet 252P. The 2000 apparition can be no longer linked with the 2011-2021 observations. The following linked orbital elements by S. Nakano (CBAT) are from 1605 observations spanning 2011-2021 (mean residual 1".0), with non-gravitational parameters A_1 = +0.61 +/- 0.01 and A_2 = +0.0832 +/- 0.0007. The comet passed 0.0356 AU from the earth on 2016 Mar. 21.6 UT, and thus the distribution of 2016 residuals are not so good. Also, the comet will pass 0.050 AU from the earth on 2032 Mar. 18, and it will pass 0.76 and 0.11 AU from Jupiter on 2033 Dec. 22 and 2046 Aug. 3, respectively. Epoch = 2010 Nov. 20.0 TT T = 2010 Nov. 13.70410 TT Peri. = 343.30070 e = 0.6727413 Node = 190.99676 2000.0 q = 1.0000876 AU Incl. = 10.38978 a = 3.0559538 AU n = 0.18449470 P = 5.34 years Epoch = 2016 Apr. 2.0 TT T = 2016 Mar. 15.27115 TT Peri. = 343.31471 e = 0.6732872 Node = 190.95188 2000.0 q = 0.9960724 AU Incl. = 10.42315 a = 3.0487710 AU n = 0.18514708 P = 5.32 years Epoch = 2021 July 5.0 TT T = 2021 July 11.29784 TT Peri. = 343.30120 e = 0.6720229 Node = 190.94561 2000.0 q = 1.0005669 AU Incl. = 10.40964 a = 3.0507219 AU n = 0.18496951 P = 5.33 years Epoch = 2026 Nov. 16.0 TT T = 2026 Nov. 9.15627 TT Peri. = 343.36460 e = 0.6713325 Node = 190.90034 2000.0 q = 1.0036917 AU Incl. = 10.42033 a = 3.0538210 AU n = 0.18468801 P = 5.34 years Epoch = 2032 Mar. 29.0 TT T = 2032 Mar. 14.24339 TT Peri. = 343.45017 e = 0.6702015 Node = 190.84841 2000.0 q = 1.0074219 AU Incl. = 10.42626 a = 3.0546588 AU n = 0.18461204 P = 5.34 years The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 10.0 and 2.5n = 15 for the magnitudes, representing better the 2016 and 2021 "outbursts", although the comet seems to generally follow H = 14.5 and 2.5n = 15 outside of the 2016 and 2021 apparitions. The issues with non-gravitational forces and problems with linking the 2000 apparition is indicative of major non-uniform processes in this comet that will also make predictions of its brightness difficult. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2021 08 14 12 01.86 +02 42.2 1.705 1.105 38.3 34.6 11.8 2021 08 19 12 22.94 +01 03.4 1.726 1.135 39.0 34.1 12.0 2021 08 24 12 43.57 -00 34.0 1.753 1.168 39.6 33.5 12.2 2021 08 29 13 03.72 -02 09.0 1.785 1.204 40.1 32.7 12.5 2021 09 03 13 23.38 -03 40.4 1.822 1.241 40.4 31.8 12.7 2021 09 08 13 42.54 -05 07.6 1.864 1.280 40.6 30.8 13.0 2021 09 13 14 01.18 -06 29.9 1.910 1.320 40.6 29.8 13.2 2021 09 18 14 19.31 -07 46.9 1.959 1.362 40.5 28.6 13.5 2021 09 23 14 36.92 -08 58.2 2.013 1.404 40.2 27.5 13.7 2021 09 28 14 54.04 -10 03.7 2.069 1.447 39.7 26.2 14.0 2021 10 03 15 10.67 -11 03.4 2.128 1.491 39.1 25.0 14.2 2021 10 08 15 26.83 -11 57.3 2.190 1.535 38.2 23.8 14.5 2021 10 13 15 42.54 -12 45.4 2.253 1.580 37.3 22.5 14.7 2021 10 18 15 57.80 -13 27.9 2.318 1.624 36.2 21.2 15.0 2021 10 23 16 12.64 -14 05.0 2.384 1.669 34.9 20.0 15.2 2021 10 28 16 27.06 -14 36.9 2.451 1.714 33.6 18.7 15.5 2021 11 02 16 41.10 -15 03.8 2.519 1.758 32.1 17.4 15.7 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2021 CBAT 2021 August 15 (CBET 5018) Daniel W. E. Green