Electronic Telegram No. 5363
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)
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Prepared using the Tamkin Foundation Computer Network


COMET C/2021 X2 (BOK)
     An apparently asteroidal object with a nearly parabolic orbit that was
discovered on CCD images obtained on 2021 Dec. 1 with the 2.25 "Bok" reflector
at Kitt Peak as part of the Catalina Sky Survey, and which was announced as
A/2021 X2 on MPEC 2021-X227, has been found to show cometary appearance
elsewhere in 2021 and 2022.

     2021 UT             R.A. (2000) Decl.       Mag.
     Dec.  1.37798    5 13 10.91   +55 56 12.7   21.6
           1.38287    5 13 09.79   +55 56 10.6   21.8
           1.38773    5 13 08.73   +55 56 08.8
           1.39260    5 13 07.60   +55 56 06.2   21.9

Thirty-second CCD images taken on 2021 Dec. 20.13-20.15 UT by R. A. Mastaler
(University of Arizona) with the Spacewatch/Steward Observatory Bok 2.3-m f/9
reflector (+ Tiffen/Wratten yellow filter; bandpass 515-950 nm) at Kitt Peak
in 0".8 seeing reveal a possible faint coma and no discernable tail; the
magnitude was given as 21.6-21.7.  M. Micheli reported that CCD images taken
on 2022 Feb. 5.2 with the 3.6-m Canada-France-Hawaii Telescope by K. J. Meech,
E. Bufanda, J. Kleyna, and J. V. Keane (measured by Micheli and Kleyna) show a
2" coma and a tail about 5" long at p.a. 50 degrees; the magnitude was
measured to be 21.4-21.7.
     Pre-discovery images of the comet as an apparently stellar object were
subsequently found in exposures obtained on 2021 Oct. 30.6 UT with the
Pan-STARRS1 1.8-m Ritchey-Chretien reflector at Haleakala (magnitude measured
as 22.4-23.3) and on 2021 Nov. 8.6 with the Pan-STARRS2 1.8-m Ritchey-Chretien
reflector at Haleakala (mag 22.5-23.1).  The available astrometry appears on
MPEC 2024-E8.
     The following orbital elements by S. Nakano (Central Bureau) are from 94
observations spanning 2021 Oct. 30-2022 Nov. 23 (mean residual 0".5), with
corresponding "original" and "future" values of 1/a (with respect to the
solar-system barycenter) being +0.000022 and -0.000252 (+/- 0.000004) AU**-1,
respectively.  The comet passed 2.57 AU from Jupiter on 2022 Oct. 28 UT.

                    Epoch = 2022 June 30.0 TT
     T = 2022 July  8.15660 TT        Peri. = 193.28399
     e = 1.0013243                    Node  = 228.79820 2000.0
     q = 2.9945481 AU                 Incl. = 137.14414

The comet is now too faint to be observed easily, at r = 6.2 AU, according
to photometric power-law parameters H = 14.0 and 2.5n = 8.


NOTE: These 'Central Bureau Electronic Telegrams' are sometimes
      superseded by text appearing later in the printed IAU Circulars.

                         (C) Copyright 2024 CBAT
2024 March 2                     (CBET 5363)              Daniel W. E. Green