Cbet: 20210626: COMET P/2021 A12 = P/2008 CL_94 (LEMMON)

C. A. Schambeau and Y. R. Fernandez, Florida Space Institute and Department of Physics, University of Central Florida; M. Micheli, NEO Coordination Centre, European Space Agency; A. McKay, Department of Physics, American University and Goddard Space Flight Center, NASA; M. S. P. Kelley, Department of Astronomy, University of Maryland; and I. Wong, Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, report their recovery of comet P/2008 CL_94 (cf. IAUC 9028) on CCD images taken on 2021 Jan. 9 and 15 with the Gemini Multi-Object Spectrograph (GMOS) on the 8.1-m Gemini North telescope at Mauna Kea. Their astrometry is provided below.

2021 UT R.A. (2000) Decl. Mag. Observer

Jan. 9.27046 5 55 31.08 +32 06 05.2 22.5 Schambeau

9.27435 5 55 30.97 +32 06 05.2 22.7 "

9.27823 5 55 30.84 +32 06 05.1 22.9 "

9.28212 5 55 30.72 +32 06 05.1 22.6 "

9.30214 5 55 30.07 +32 06 04.9 23.0 "

9.31537 5 55 29.65 +32 06 04.8 22.5 "

15.31673 5 52 30.39 +32 03 59.4 22.9 "

15.32831 5 52 30.05 +32 03 59.1 22.8 "

15.33217 5 52 29.94 +32 03 59.0 22.6 "

15.36181 5 52 29.08 +32 03 58.2 23.0 "

15.36567 5 52 28.96 +32 03 58.1 22.7 "

GMOS r' imaging from Jan. 9 shows a very-condensed object with size 0".82 (FWHM; compared to 0".79 for nearby stars) that is located within 1" of an ephemeris generated from all the existing (2008-2009) astrometry and 1'.7 from an ephemeris generated from the Minor Planet Center's Ephemeris Service. A slight extension of the comet in p.a. 260 degrees is consistent with the presence of a persistent large-grain dust tail based on a syndyne analysis. Photometry of this source yields an apparent magnitude r' = 22.70 +/- 0.04 and (assuming all the flux is from the nucleus) an effective nucleus radius estimate of 1.49 +/- 0.02 km using an assumed geometric albedo of 0.1. Additionally, they find that the claim by Wong et al. [2019, A.J. 157(6),

art. 225] of seeing a bare nucleus of this comet in 2017 Aug. was erroneous, in that they were observing the main-belt asteroid (270262) 2001 UY_137 and not P/2008 CL_94; new inspection of the imaging data from Wong et al. has confirmed that P/2008 CL_94 was not detected in the 2017 data to a limiting R-band magnitude of 23.5.

The residuals for the recovery observations are -92" in R.A. and -11" in Decl. from the prediction in NK 1837 and in the ICQ's 2020 and 2021 Comet Handbooks, with a corresponding correction of Delta(T) = +0.26 day. The following linked orbital elements by S. Nakano (CBAT) are from 74 observations spanning 2008-2021 (mean residual 0".4). The comet passed 0.66 AU from Jupiter in 1921 July, 0.91 AU from Jupiter on 1986 Oct. 11, and 3.78 AU from Saturn on 2007 Sept. 10 UT. Nakano was unable to find additional observations of this comet in archival data.

Epoch = 2006 July 4.0 TT

T = 2006 July 10.02644 TT Peri. = 82.73938

e = 0.1204454 Node = 33.54111 2000.0

q = 5.4382646 AU Incl. = 8.34188

a = 6.1829757 AU n = 0.06410734 P = 15.37 years

Epoch = 2021 Sept.23.0 TT

T = 2021 Sept.19.96368 TT Peri. = 80.40416

e = 0.1205187 Node = 33.31403 2000.0

q = 5.4209427 AU Incl. = 8.34613

a = 6.1637950 AU n = 0.06440681 P = 15.30 years

Epoch = 2037 Apr. 12.0 TT

T = 2037 Apr. 2.18534 TT Peri. = 84.06712

e = 0.1181556 Node = 33.13692 2000.0

q = 5.4381836 AU Incl. = 8.32544

a = 6.1668292 AU n = 0.06435928 P = 15.31 years

The following ephemeris by the undersigned from the above orbital elements uses photometric power-law parameters H = 10.0 and 2.5n = 7.5 for the magnitudes (from the 2008-2009 apparition, which were all post-perihelion observations).

Date TT R. A. (2000) Decl. Delta r Elong. Phase Mag. 2021 09 03 08 12.56 +27 21.9 6.133 5.421 41.6 7.1 19.4 2021 09 13 08 20.83 +27 06.0 6.022 5.421 49.4 8.1 19.4 2021 09 23 08 28.48 +26 52.0 5.896 5.421 57.3 9.0 19.4 2021 10 03 08 35.42 +26 40.6 5.759 5.421 65.5 9.7 19.3 2021 10 13 08 41.54 +26 32.6 5.612 5.421 73.9 10.2 19.3 2021 10 23 08 46.71 +26 28.7 5.459 5.422 82.6 10.5 19.2 2021 11 02 08 50.83 +26 29.3 5.303 5.422 91.6 10.5 19.1 2021 11 12 08 53.77 +26 35.0 5.147 5.423 100.9 10.3 19.1 2021 11 22 08 55.43 +26 45.9 4.997 5.423 110.5 9.8 19.0 2021 12 02 08 55.75 +27 01.8 4.857 5.424 120.5 9.0 18.9 2021 12 12 08 54.68 +27 22.1 4.731 5.425 130.7 7.9 18.9 2021 12 22 08 52.29 +27 45.6 4.625 5.426 141.1 6.5 18.8 2022 01 01 08 48.70 +28 10.8 4.542 5.427 151.6 4.9 18.8 2022 01 11 08 44.12 +28 35.7 4.487 5.429 161.6 3.3 18.8 2022 01 21 08 38.89 +28 58.1 4.461 5.430 169.1 2.0 18.8 2022 01 31 08 33.40 +29 16.3 4.466 5.432 167.4 2.3 18.8 2022 02 10 08 28.08 +29 28.9 4.502 5.433 158.8 3.8 18.8 2022 02 20 08 23.33 +29 35.1 4.567 5.435 148.6 5.4 18.8 2022 03 02 08 19.49 +29 34.7 4.657 5.437 138.3 7.0 18.9