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On the early June outburst of 174P/Echeclus

ATel #3449; Institute of Space Sciences (CSIC-IEEC)
on 23 Jun 2011; 14:05 UT
Distributed as an Instant Email Notice Comets
Credential Certification: Josep M. Trigo-Rodriguez (trigo@ieec.uab.es)

Subjects: Optical, Comet

We report enhanced photometric activity of Centaur 174P/Echeclus during early June. The comet was followed in a continuous basis by our team from June 1st after reading an alert made by experienced astrophotographer Michael Jager (Austria) who reported on May 30 that this object was in +15 magnitude surrounded by a 1 arcmin coma. First images by our team members were taken by P. Montanes-Rodriguez (Instituto de Astrofisica de Canarias, IAC) on June 2.07 with the 0.82-m at f/11.3 IAC80 telescope. Three 300 seconds exposures taken in VRI Johnson-Bessell photometric bands reveal that the object was about two magnitudes brighter than expected, just in +17.38V, 16.93R and 16.38I magnitude in each band. The photometry was measured for a standardized aperture of 10 arcsec by D. A. Garcia-Hernandez (IAC) using the Image Reduction and Analysis Facility (IRAF) software distributed by the National Optical Astronomy Observatories. Standard Landolt stars were used to get photometric accuracy to hundredth of magnitude following a similar procedure as was previously reported in Trigo-Rodriguez et al. (2010, MNRAS 409, 1682-1690). We note from IAC80 observations that the comet was particularly bright in the I band where exhibited an irregular coma envelope with a large axis of about 40'' in the same direction than is perceptible a bright curved fan about 9" long in p.a. 300 deg. As the comet was located at a distance of 7.509 AU from Earth it suggests that the coma surrounding the nucleus was extended for about 13 milion kilometers, suggestive of a major outburst. Other small jet-like features surrounding the nucleus are close to the resolution limit of the images, but still perceptible. A few hours before, on June 1.94 a previous image taken by D. Rodriguez (MPC 458) shows the object in +16.94R magnitude. Additional observations taken during the following weeks by members of our team reveal the following magnitude estimates. J. Lacruz from MPC J87 on June 4.31: +19.09V, 18.13R, and 18.24I; J. Garcia-Rojas (IAC) using IAC80 telescope on June 19.07: +18.10V, 17.66R, and 16.72I; and J. Lacruz (MPC J87) on June 21.89: +18.1V, 17.9R, and 17.4I. We conclude that this object should have experienced an outburst during the last days of May, 2011, particularly if the coma behavior after the outburst is similar to the previously reported by P. Rousselot (2008, A&A 480, 543-550). Additional high-resolution imagery of the coma is required to study the fan evolution, and the location of the surface active regions.