[Iaude] CBET 4821: COMET P/2019 LD2

quai at eps.harvard.edu quai at eps.harvard.edu
Sun Aug 2 02:03:05 EDT 2020

                                                  Electronic Telegram No. 4821
Central Bureau for Astronomical Telegrams
Mailing address:  Hoffman Lab 209; Harvard University;
 20 Oxford St.; Cambridge, MA  02138; U.S.A.
e-mail:  cbatiau at eps.harvard.edu (alternate cbat at iau.org)
URL http://www.cbat.eps.harvard.edu/index.html
Prepared using the Tamkin Foundation Computer Network

     C. A. Schambeau, Y. R. Fernandez, R. Belton, AND M. Womack, Florida Space
Institute, University of Central Florida; M. Micheli, NEO Coordination
Centre, European Space Agency; L. Woodney, California State University at San
Bernardino; J. Steckloff, Planetary Science Institute and University of Texas
at Austin; G. Sarid, SETI Institute; and T. Kareta, W. Harris, and K. Volk,
Lunar and Planetary Laboratory, University of Arizona, report on pre-discovery
imaging of comet P/2019 LD2 (cf. CBET 4780) from Dark Energy Camera (DECam)
CCD exposures downloaded using the Canadian Astronomical Data Centre's Solar
System Object Image Search.  DECam g' imaging from 2018 Aug. 10 UT shows a
very condensed object with size 1".0 (FWHM; compared to 0".8 for nearby stars)
located within 0".1 of an ephemeris generated by the orbit in MPEC 2020-O07.
Photometry of this source yields apparent magnitude g' = 21.44 +/- 0.05 and
is consistent with Pan-STARRS1 reported photometry included in MPEC 2002-K134.
Based on this photometry, an ersatz estimate for the nucleus' radius is 5.1
+/- 0.1 km assuming a 5-percent geometric albedo, or 3.4 +/- 0.1 km assuming
an 11.2-percent albedo (the average red-Centaur albedo reported by Romanishin
and Tegler 2018, A.J. 156, 19).  However, this size is inconsistent with
earlier DECam imaging data from 2017 March 6 and May 15, where no source was
detected within 10" of the comet's expected ephemeris position (1-sigma
ephemeris uncertainty +/- 0".2) as generated by the orbit in MPEC 2020-O07.
Three-sigma upper-limit photometry on the March 6 r' and May 15 z' imaging
data indicate that the upper limits on the nucleus' radius are (respectively)
1.2 and 3.4 km assuming a 5-percent albedo, or 0.8 and 2.3 km assuming an
11.2-percent albedo.  This inconsistency may be the result of a compact coma
present at the time of the 2018 Aug. 10 g' imaging, thus confusing the
nucleus-size estimate and/or the comet having an elongated nucleus.
Continued observations are encouraged to better constrain the comet's nucleus
size, monitor for its long-term activity behaviors, and monitor for possible
outburst activity.

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

                         (C) Copyright 2020 CBAT
2020 August 2                    (CBET 4821)              Daniel W. E. Green

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