Electronic Telegram No. 5057 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 C/2021 G2 (ATLAS) Further to CBET 4988, the reports of cometary activity listed therein have been confirmed. C. Holt, University of Maryland, writes that 120-s CCD exposures taken on Sept. 29 using the Goodman spectrograph's blue camera on the 4.1-m SOAR telescope at Cerro Pachon in Chile (using AEON queued mode) in 1".5 seeing, and measured by M. Micheli, show a condensed coma of size 7".8, being slightly asymmetric toward p.a. about 315 degrees; the total magnitude was measured to be 19.2 using an aperture of size 5" in the g-band. The astrometry is tabulated below. 2021 UT R.A. (2000) Decl. Mag. Observer Sept.29.34173 7 36 09.26 -24 39 08.9 20.0 Holt 29.35168 7 36 09.41 -24 39 12.1 19.9 " 29.36177 7 36 09.59 -24 39 15.4 19.9 " 29.33671 7 36 09.17 -24 39 07.4 19.6 " 29.34671 7 36 09.34 -24 39 10.5 19.9 " 29.35675 7 36 09.51 -24 39 13.7 19.5 " These latest observations indicate a residual of +2" (mainly in R.A.) from the orbit on CBET 4988. The following updated orbital elements by S. Nakano (CBAT) are from 91 observations spanning 2020 Nov. 3-2021 Sept. 29 (mean residual 0".4). The corresponding original and future values of 1/a are -0.000004 and -0.000289 AU**-1, respectively (+/- 0.000018 AU**-1, mean error). Epoch = 2024 Sept. 7.0 TT T = 2024 Sept. 9.11893 TT Peri. = 343.27809 e = 1.0003984 Node = 221.09570 2000.0 q = 4.9820697 AU Incl. = 48.47344 The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 6.0 and 2.5n = 8 for the magnitudes, following the comments on CBET 4988. Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2021 09 23 07 34.25 -24 06.3 9.540 9.220 68.5 5.8 18.6 2021 10 03 07 37.14 -24 58.6 9.383 9.165 74.5 6.0 18.6 2021 10 13 07 39.39 -25 53.2 9.221 9.111 80.6 6.2 18.5 2021 10 23 07 40.92 -26 48.8 9.057 9.057 86.9 6.3 18.4 2021 11 02 07 41.69 -27 44.2 8.893 9.003 93.2 6.3 18.4 2021 11 12 07 41.66 -28 38.0 8.733 8.949 99.4 6.3 18.3 2021 11 22 07 40.80 -29 28.5 8.580 8.895 105.5 6.1 18.3 2021 12 02 07 39.15 -30 14.0 8.436 8.840 111.2 6.0 18.2 2021 12 12 07 36.76 -30 52.8 8.305 8.786 116.4 5.8 18.1 2021 12 22 07 33.74 -31 23.4 8.188 8.732 120.8 5.6 18.1 2022 01 01 07 30.24 -31 44.4 8.088 8.679 124.1 5.4 18.0 2022 01 11 07 26.45 -31 54.9 8.007 8.625 126.2 5.3 18.0 2022 01 21 07 22.59 -31 54.5 7.945 8.571 126.8 5.3 18.0 2022 01 31 07 18.90 -31 43.5 7.903 8.517 125.8 5.4 17.9 2022 02 10 07 15.59 -31 22.4 7.879 8.464 123.5 5.6 17.9 2022 02 20 07 12.86 -30 52.8 7.874 8.410 119.9 5.9 17.9 2022 03 02 07 10.86 -30 16.1 7.884 8.356 115.4 6.2 17.9 2022 03 12 07 09.71 -29 34.2 7.908 8.303 110.2 6.4 17.8 2022 03 22 07 09.48 -28 49.3 7.943 8.250 104.5 6.7 17.8 2022 04 01 07 10.16 -28 03.1 7.987 8.196 98.6 6.9 17.8 2022 04 11 07 11.78 -27 17.4 8.036 8.143 92.6 7.1 17.8 2022 04 21 07 14.26 -26 33.9 8.088 8.090 86.6 7.1 17.8 2022 05 01 07 17.57 -25 53.9 8.140 8.037 80.6 7.1 17.8 2022 05 11 07 21.63 -25 18.5 8.190 7.984 74.8 7.0 17.8 2022 05 21 07 26.35 -24 48.6 8.235 7.932 69.2 6.8 17.8 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2021 CBAT 2021 October 11 (CBET 5057) Daniel W. E. Green