quai at eps.harvard.edu quai at eps.harvard.edu
Wed Dec 13 00:39:29 EST 2023

                                                  Electronic Telegram No. 5324
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

     P. Jenniskens, SETI Institute and NASA Ames Research Center, reports that
a predicted earth encounter with 1974 ejecta from comet 46P (cf. Vaubaillon et
al. 2023, A.Ap, in press; website URL /https://arxiv.org/abs/2312.02636) was
detected as a new meteor shower in the southern hemisphere on 2023 Dec. 12.
Prior to this detection, comet 46P was not known as the parent body of a
meteor shower.  Vaubaillon et al. used several different dynamical models to
predict a radiant near the stars lambda^1 and lambda^2 Scl with coordinates in
the range R.A. = 7.3 to 9.2 deg, Decl. = -38.5 to -43.0 deg, and geocentric
velocity 9.8 to 10.3 km/s, with a time of maximum expected in the range Dec.
12d09h to Dec. 13d06h UTC, with most models in the range Dec. 12d09h.5 to
11h.6 UTC. The proposed name for the new shower was lambda-Sculptorids (with
code LSC).  Leading up to the predicted peak, CAMS Chile detected a meteor
from R.A. = 4.6 +/- 0.5 deg, Decl. = -36.4 +/- 0.9 deg, with geocentric
velocity 8.6 +/- 0.1 km/s at solar longitude 259.402 deg (equinox J2000.0);
corresponding orbital elements were a = 4.1 AU, q = 0.968 AU, e = 0.766, i =
7.6 deg, Peri. = 343.7 deg, and Node = 79.4 deg.
     The first indication of a meteor outburst was reported by H. Sugimoto
(cf. website URL https://www.iprmo.org/flash/gem-2023.html), who detected a
sharp increase in radio forward meteor reflections from 41 stations starting
at solar longitude 259.7 deg (Dec. 12d09h UTC).  Rates peaked at solar
longitude 259.9 deg (Dec. 12d13h UTC).  For an assumed meteor-magnitude
distribution index, the calculated equivalent peak visual zenith hourly rate
(ZHR) was given as 120 meteors/hr.  Subsequently, J. Scott (University of
Otago, New Zealand), from calculations by D. Vida (Global Meteor Network),
reported the detection of a cluster of 8 meteors from low-light video
triangulations with a radiant centered on R.A. = 7.9 +/- 1.1, Decl. = -38.8
+/- 0.3 deg and geocentric velocity 10.2 +/- 0.4 km/s (standard error given)
during the solar longitude interval 259.76-259.96 deg, centered on 259.86 +/-
0.02 deg (see map at website URL http://cams.seti.org/FDL/index-NZ.html for
the date 2023 Dec. 13).  Corresponding median orbital elements are a = 2.93
AU, q = 0.9846 +/- 0.0002 AU, e = 0.662 +/- 0.084, i = 9.6 +/- 0.9 deg, Peri.
= 0.1 +/- 1.4 deg, Node = 79.89 +/- 0.07 deg (standard deviations given here).
This confirms that the observed peak of radio forward reflections was due to
the meteors of comet 46P, but the actual peak ZHR for a visual observer was
likely lower.

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

                         (C) Copyright 2023 CBAT
2023 December 13                 (CBET 5324)              Daniel W. E. Green

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