Electronic Telegram No. 5061 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/2021 U2 = P/2007 R4 (GARRADD) Comet P/2007 R4 (cf. IAUC 8870) has been recovered independently on CCD images obtained by J. Drummond (Gisborne, New Zealand, 0.41-m f/4.5 Newtonian reflector) and by T. Prystavski (Ukraine; remotely using an iTelescope 0.51-m f/6.8 astrograph at Siding Spring, NSW, Australia). On Aug. 18, Drummond sent his astrometric observations from Aug. 15 of two objects that he noted were near the position of P/2007 R4; one of those two objects now has been confirmed as that of P/2007 R4, following the receipt of Prystavski's observations, along with with another night of observations on Sept. 5 by Drummond (which A. Gilmore had tentatively identified with P/2007 R4, pending additional subsequent observations). In the Sept. 5 images, Drummond noted that there might be a slight elongation on the northern side of the comet, but the elongation is inconclusive. Prystavski notes that four 120-s images obtained on Oct. 24.43 UT through a Luminance filter revealed a faint object with no clear coma and a possible tail 0'.3 long in p.a. 57 deg, while four 120-s images obtained on Oct. 26.42 revealed again a faint object with no clear coma evidence and a hint of tail (the comet appearly slightly elongated). F. D. Romanov, Yuzhno-Morskoy, Nakhodka, Russia, has only now (following the publication of MPEC 2021-U108) identified images of P/2007 R4 in 180-s CCD exposures that he had taken in August with an iTelescope 0.50-m f/6.8 reflector located at Siding Spring in attempts to recover this comet. The available astrometry is provided below. 2021 UT R.A. (2000) Decl. Mag. Observer Aug. 13.61410 22 04 27.66 -42 15 21.0 19.9 Romanov 13.61687 22 04 27.56 -42 15 23.4 20.5 " 15.61030 22 03 29.28 -42 38 56.6 20.2 Drummond 15.62982 22 03 28.69 -42 39 09.6 20.3 " 15.64825 22 03 28.01 -42 39 21.7 20.2 " Sept. 5.47134 21 52 38.6 -45 24 15 20.1 " 5.48342 21 52 38.2 -45 24 17 19.9 " 5.49470 21 52 37.9 -45 24 21 20.1 " Oct. 24.42847 22 07 01.96 -40 54 25.9 19.4 Prystavski 24.43008 22 07 02.02 -40 54 24.9 19.8 " 24.43331 22 07 02.22 -40 54 22.6 " 26.41608 22 09 15.29 -40 27 59.0 19.4 " 26.41944 22 09 15.49 -40 27 56.2 " The residuals of the recovery observations on 2021 Oct. 24 were +6'.0 in R.A. and +0'.3 in Decl. from the prediction in NK 1565 and in the ICQ's 2021 Comet Handbook, with a corresponding correction of Delta(T) = -0.20 day. The following linked orbital elements by S. Nakano (CBAT) are from 100 observations spanning 2007-2021 (mean residual 0".7). There are no close approaches to major planets. Epoch = 1993 Aug. 1.0 TT T = 1993 Aug. 2.05087 TT Peri. = 282.59426 e = 0.6718826 Node = 87.72841 2000.0 q = 1.9196791 AU Incl. = 20.17918 a = 5.8505863 AU n = 0.06964741 P = 14.15 years Epoch = 2007 Sept.17.0 TT T = 2007 Sept.27.28942 TT Peri. = 282.87315 e = 0.6714004 Node = 87.50152 2000.0 q = 1.9213819 AU Incl. = 20.22593 a = 5.8471824 AU n = 0.06970824 P = 14.14 years Epoch = 2021 Dec. 12.0 TT T = 2021 Dec. 8.50554 TT Peri. = 282.59428 e = 0.6699966 Node = 87.19262 2000.0 q = 1.9576142 AU Incl. = 20.20974 a = 5.9321040 AU n = 0.06821674 P = 14.45 years Epoch = 2036 May 27.0 TT T = 2036 May 9.41061 TT Peri. = 282.76417 e = 0.6696156 Node = 87.10691 2000.0 q = 1.9565545 AU Incl. = 20.22824 a = 5.9220541 AU n = 0.06839046 P = 14.41 years The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 15.5 and 2.5n = 10 for the magnitudes. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2021 09 23 21 48.69 -45 26.1 1.346 2.101 126.2 22.7 19.4 2021 10 03 21 50.81 -44 33.5 1.386 2.067 119.2 25.0 19.4 2021 10 13 21 56.49 -43 07.4 1.434 2.038 112.6 26.9 19.4 2021 10 23 22 05.50 -41 12.8 1.490 2.012 106.4 28.3 19.4 2021 11 02 22 17.34 -38 54.0 1.552 1.992 100.7 29.3 19.4 2021 11 12 22 31.48 -36 14.3 1.619 1.976 95.4 29.9 19.5 2021 11 22 22 47.38 -33 17.1 1.691 1.965 90.4 30.2 19.6 2021 12 02 23 04.55 -30 05.5 1.767 1.959 85.7 30.1 19.7 2021 12 12 23 22.64 -26 42.5 1.848 1.958 81.3 29.8 19.8 2021 12 22 23 41.35 -23 11.5 1.935 1.962 76.9 29.2 19.9 2022 01 01 00 00.46 -19 35.6 2.026 1.972 72.7 28.4 20.0 2022 01 11 00 19.84 -15 58.1 2.122 1.986 68.6 27.4 20.1 2022 01 21 00 39.38 -12 21.8 2.223 2.006 64.4 26.3 20.3 2022 01 31 00 59.02 -08 49.6 2.328 2.030 60.3 24.9 20.4 2022 02 10 01 18.74 -05 23.7 2.438 2.058 56.1 23.5 20.6 2022 02 20 01 38.50 -02 06.2 2.550 2.090 51.9 21.9 20.7 2022 03 02 01 58.28 +01 01.4 2.664 2.127 47.7 20.1 20.9 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2021 CBAT 2021 October 28 (CBET 5061) Daniel W. E. Green