[IAUC] CBET 3295: 20121112 : COMET 168P/HERGENROTHER
quai en eps.harvard.edu
quai en eps.harvard.edu
Dom Nov 11 20:32:59 ART 2012
Electronic Telegram No. 3295
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
CBAT Director: Daniel W. E. Green; Hoffman Lab 209; Harvard University;
20 Oxford St.; Cambridge, MA 02138; U.S.A.
e-mail: cbatiau en eps.harvard.edu (alternate cbat en iau.org)
URL http://www.cbat.eps.harvard.edu/index.html
Prepared using the Tamkin Foundation Computer Network
COMET 168P/HERGENROTHER
Giovanni Sostero, Nick Howes, Alison Trip, Peter Phelps, and Ernesto
Guido observed comet 168P remotely on Sept. 26.6, Oct. 3.6, and 9.6 UT with
the 2.0-m f/10 Ritchey-Chretien "Faulkes Telescope South" (+ Bessel R filter)
at Siding Spring. Inspection of the stacked CCD images obtained on Sept. 26.6
shows the comet with a sharp central condensation measuring nearly 3" across;
the total coma was traced to a diameter of about 1'.7 (total magnitude 10.2).
On Oct. 3.6, the central condensation was somehow less sharp but had grown to
size 8", while the total coma diameter was nearly 3' (total magnitude 9.4).
On Oct. 9.6, the central condensation was ill-defined, and the total coma
diameter was nearly 4'.5 (total magnitude 9.2). Their Af(rho) data (proxy of
the dust abundance within the coma; cf. IAUC 7342) supports the observed
evolution: Sept. 26.6, Af(rho) = 670 cm; Oct. 3.6, 1210 cm; Oct. 9.6, 850 cm
(measurement aperture radius of about 3000 km at the comet distance). This
indicates a two-fold increase of the Af(rho) activity within the central
condensation in a matter of a week (Sept. 26-Oct. 3), as well its subsequent
decreasing thereafter (Oct. 3-Oct. 9).
G. Sostero, N. Howes, and E. Guido add that thirteen stacked 30-s R-band
exposures, obtained remotely with the 2.0-m f/10 Ritchey-Chretien "Faulkes
Telescope North" at Haleakala on Oct. 26.4 UT under good seeing conditions,
shows the presence of a secondary fragment (designated fragment B) placed
about 2" in p.a. 188 deg with respect to the main central condensation of
comet 168P; the magnitude of this fragment was measured to be about 17, and
there is a diffuse coma nearly 2" in diameter. The stacked image is posted
at website URL http://tinyurl.com/cgr5pn9, and an animation of images has
been posted at http://bit.ly/S0Nt9J (where east is to the left, and north
is to the bottom). There was no evidence of this fragment in their
previous stacked images obtained with the "Faulkes Telescope South" on
Oct. 3.6, and with the "Faulkes Telescope North" on Oct. 22.4, to a
limiting magnitude of about 19.
Follow-up R-band observations by G. Sostero, K. Rochowicz, P. Phelps, N.
Howes, and E. Guido with the "Faulkes Telescope North" on Nov. 7.43 and 7.45
UT show that the fragment that they observed on Oct. 26.4 and Nov. 2.4 was
no longer visible (limiting magnitude about 20); however, they noticed
instead the possible presence of a second, extremely weak fragment, having
mag about 19.5, placed nearly 8".4 in p.a. 142 deg with respect to the main
central condensation of 168P. Stacked images obtained by the Maui Community
College at the "Faulkes Telescope North" on Nov. 3.3 are posted at website
URL http://tinyurl.com/cyulo7e).
Further visual total-magnitude and coma-diameter estimates (cf. CBET
3257): Oct. 19.82 UT, 9.4, 5' (J. J. Gonzalez, Asturias, Spain, 25x100
binoculars); 20.81, 9.7, 2' (M. L. Paradowski, Dabrowa, Poland, 0.20-m
reflector); 23.69, 10.1, 2'.2 (Yoshimoto, 0.25-m reflector); Nov. 4.82, 10.3,
3'.5 (Gonzalez, 0.20-m reflector); Nov. 6.90, 10.3, 3'.5 (Gonzalez). Note
that comet 168P was expected to peak around total mag 15 in late September
and early October, based on its previous two apparitions (when H_10 = 15.5;
cf. ICQ 2012 Comet Handbook).
Carl W. Hergenrother, Lunar and Planetary Laboratory, University of
Arizona, reports that, prior to the detection of individual companions, a mass
of material was observed moving away from the near-nuclear region towards the
anti-solar direction. The feature was first detected on images taken with the
Faulkes 2.0-m reflector on Oct. 16.45 UT by the Norman Lockyer Observatory
when it was comparable in brightness to the nuclear condensation of the
primary. Additional observations of the feature were obtained on Oct. 19.86
(Gianluca Masi, Ceccano, Italy; 0.35-m Virtual Telescope), Oct. 20.25 and
21.35 (Hergenrother; Kuiper 1.5-m reflector), Oct. 22.44 (Sostero et al.,
Faulkes 2.0-m reflector; see above), and Oct. 22.90 and 23.80 (Masi).
Position angles of the feature for a subset of dates are: Oct. 16.45, 142
deg; Oct. 20.25, 140 deg; Oct. 21.35, 141 deg; Oct. 22.44, 139 deg. These
position angles are larger than the anti-solar vector by 14-19 deg. The
Faulkes images from Oct. 26.42 no longer show the feature, although companion
C is located near its expected location.
Hergenrother also reports four separate companions to 168P observed in
data taken between Oct. 26.42 and Nov. 8.29 UT. The data for all dates from
the Kitt Peak 2.1-m reflector were obtained by Yanga Fernandez and Emily
Kramer and made available by Beatrice E. A. Mueller. Data from the Faulkes
2.0-m reflector were obtained by Sostero et al. (see above) on Oct. 26, by
the Dollar Academy and Queen's College on Nov. 2, and by the Maui Community
College on Nov. 3 as part of Faulkes Telescope Education project.
Date UT P.A. Sep. Comp. Telescope/
2012 (deg) (") measurer
Oct. 26.42 191.1 2.1 B Faulkes/Hergenrother
Nov. 2.44 167.4 3.3 B Faulkes/Hergenrother
3.28 165.3 3.1 B Faulkes/Hergenrother
6.28 160.9 3.3 B Faulkes/Hergenrother
6.30 164.8 3.6 B Kitt Peak/Hergenrother
7.30 162.4 3.6 B Kitt Peak/Hergenrother
7.32 165.6 3.5 B Kitt Peak/Hergenrother
Oct. 26.42 139.8 3.8 C Faulkes/Hergenrother
Nov. 2.44 133.7 5.8 C Faulkes/Hergenrother
3.28 131.7 6.4 C Faulkes/Hergenrother
Nov. 2.44 159.3 5.2 E Kitt Peak/Hergenrother
3.28 151.0 5.0 E Kitt Peak/Hergenrother
7.31 159.1 6.0 E Kitt Peak/Hergenrother
8.27 164.0 5.7 E Kitt Peak/Hergenrother
8.29 165.3 5.7 E Kitt Peak/Hergenrother
Nov. 6.28 148.3 9.1 F Kitt Peak/Hergenrother
6.30 149.1 9.3 F Kitt Peak/Hergenrother
7.31 143.9 9.5 F Kitt Peak/Hergenrother
R. A. Stevenson, J. M. Bauer, J. R. Masiero, and A. K. Mainzer, Jet
Propulsion Laboratory, report CCD observations of comet 168P taken from the
Gemini-North telescope atop Mauna Kea, Hawaii, following the report by Sostero
et al. (see above) of the outburst and detection of a fragement on Oct. 26.4
UT. Fragment B was detected 2".4 from the primary nuclear condensation on
Oct. 28.4 at a position angle of 172.9 deg using 10-s exposures; the
brightness of the fragment is 29 percent of the brightest region, which is
presumed to be the location of the nucleus. Two additional fragments were
detected in 30-s (unstacked) exposures taken on Nov. 2.3: Fragment B was
detected 2".9 from the primary nuclear condensation at a position angle of
162.5 deg, with a relative brightness of 27 percent with respect to the
nucleus-centered region. Fragment C was detected 6".2 from the nucleus-
centered region at a position angle of 132.1 deg with a brightness of 25
percent relative to the nucleus-centered region. Fragment D was detected
11".4 from the nuclear condensation at a position angle of 145.1 deg with a
relative brightness of 9 percent to the nucleus-centered region. All
fragments appear diffuse and without central condensations. Brightnesses
were measured using sky-subtracted aperture photometry; apertures were 1".022
in radius (with projected on-sky radii of 399 and 422 km for Oct. 28 and
Nov. 2, respectively). Fragment B is separating from the primary nuclear
condensation with a projected on-sky velocity of 0.6 +/- 0.1 m/s (1-sigma
uncertainty), measured using r-band (630 nm) data from the 8-m Gemini-North
telescope (Oct. 28.4 and Nov. 2.3) and J-band (1.25-micron) and H-band
(1.651-micron) images from the 3.5-m WIYN telescope (Oct. 29.2, 30.1, and
Nov. 1.1).
Z. Sekanina, Jet Propulsion Laboratory, reports that four of the five
companions apparently broke off from the primary nucleus A. Based on 9
offsets from Oct. 26-Nov. 7, companion B was found to have separated on Sept.
17.5 +/- 2.5 UT with a velocity of 0.18 +/- 0.05 m/s and was subjected to a
nongravitational deceleration of 15 +/- 3 units of 10^{-5} solar attraction.
Very similar solutions were obtained on the assumption that the separation of
B coincided with the onset of an outburst on Sept. 22. For companion C,
from four offsets between Oct. 26 and Nov. 3, Sekanina derived a separation
on Oct. 7.0 +/- 1.5 UT, with a velocity of 0.3 +/- 0.1 m/s, and a
deceleration of 53 +/- 12 units. Very similar solutions resulted assuming
that the separation of C coincided with the onset of another outburst, on
October 1. For companion D, the offset from Nov. 2 gave only very
approximate parameters, a separation around Sept. 28 (probably coinciding
with the same outburst as the separation of C) and a deceleration of 70
units. Companion E does not appear to have derived from A, but it may have
split off from B within days after B broke off from A. Companion F was found
to have separated from A on Sept. 24 (again at about the time of the outburst
of Sept. 22) and was subjected to a deceleration of about 40 units. As the
mass of material moved in the direction in which fragment C also appeared, and
fragment C split off around the time of the Oct. 1 outburst, the mass of
material was also a product of that same outburst. The apparent tendency of
some companions to grow elongated with time suggests that they already
represent clusters of subfragments subjected to a range of decelerations,
thus entering an advanced phase of disintegration. Because all the companions
appear to be short-lived (as also implied by their high decelerations), the
following ephemerides are terminated by the end of November. Predicted
separation distances from nucleus A and position angles at 0h ET: Nov. 9,
3".9, 163 deg (B); 8".4, 133 deg (C); 15".2, 144 deg (D); 6".1, 159 deg (E);
10".1, 147 deg (F); Nov. 19, 5".2, 160 deg (B); 12".0, 133 deg (C); 20".6,
144 deg (D); 8".0, 157 deg (E); 13".4, 146 deg (F); Nov. 29, 6".2, 161 deg
(B); 15".1, 135 deg (C); 25".0, 146 deg (D); 9".5, 158 deg (E); 16'.0, 148
deg (F).
NOTE: These 'Central Bureau Electronic Telegrams' are sometimes
superseded by text appearing later in the printed IAU Circulars.
(C) Copyright 2012 CBAT
2012 November 12 (CBET 3295) Daniel W. E. Green
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