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@eps.harvard.edu (alternate cbat@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