Electronic Telegram No. 4251 Central Bureau for Astronomical Telegrams Mailing address: 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 P/2015 PD_229 David A. Cameron, University of Rochester, reported astrometry on 2015 Aug. 14 to the Minor Planet Center of an apparent comet found on CCD images taken to search for trans-neptunian objects on 2015 Mar. 27 and 28 with the 4.0-m Blanco reflector (+ DECam + broad "VR"-band filter) at Cerro Tololo by E. E. Mamajek, F. Moolekamp, D. J. James, and himself; the object was apparently found by Cameron and described by him as a pointlike source (1".1 head) with a thin tail about 1".1 wide and approximately 12" long, trailing directly opposite the direction of motion of the comet. Their images have been posted at URL http://www.pas.rochester.edu/~emamajek/DECAM/COMET1/. After Cameron's report was received, a discovery report of an apparently asteroidal object observed on 2015 Aug. 15 with a 0.4-m f/2.4 reflector of the International Scientific Optical Network (ISON) at Siding Spring was received from L. Elenin; it received the minor-planet designation 2015 PD_229 when it was announced by the Minor Planet Center (cf. MPECs 2015-Q08, 2015-Q15) without linkage to the May comet. When the linkage was made and published on MPEC 2015-Q17, G. V. Williams wrote: "This object was reported as a comet (without any details on appearance) by the DECam team on Aug. 14. It was reported as a NEOCP candidate on Aug. 16 by the ISON-Siding Spring team. Details on the cometary appearance in May were submitted on Aug. 18, following prompting by [myself]. The linkage of the two sets of observations was made after the object was removed from the NEOCP and designated. None of the August reports have mentioned detecting cometary features, hence this announcement under a minor-planet designation. There is a roughly two- magnitude discrepancy in the absolute magnitudes determined from the May observations alone and from the August observations alone. Confirmation of any possible cometary activity is therefore very desireable." Even though no further cometary activity has been reported by observers elsewhere, the object was announced yesterday on MPEC 2016-C2 as a comet -- using the name "ISON-Cameron", which is under review by the IAU Working Group on Small Bodies Nomenclature (vs. the standard chronologically ordered "Cameron-ISON"). The discovery astrometry is tabulated below. 2015 UT R.A. (2000) Decl. Mag. Observer May 27.36183 22 42 27.81 - 8 47 57.6 22.3 Mamajek 27.38330 22 42 28.38 - 8 47 54.0 22.8 " 27.40479 22 42 28.93 - 8 47 50.4 22.6 " 27.42635 22 42 29.49 - 8 47 46.8 22.2 " 28.36108 22 42 54.13 - 8 45 12.3 22.1 " Aug. 15.71559 22 41 43.13 - 8 37 10.0 18.6 Elenin 15.72528 22 41 42.89 - 8 37 11.8 19.0 " 15.73484 22 41 42.63 - 8 37 12.7 19.2 " The available astrometry (spanning 2015 May 27-Dec. 9), the following elliptical orbital elements by G. V. Williams, and an ephemeris appear on MPEC 2016-C2. Epoch = 2015 Aug. 6.0 TT T = 2015 Aug. 14.52845 TT Peri. = 352.40460 e = 0.3267690 Node = 342.77290 2000.0 q = 4.8320382 AU Incl. = 2.02702 a = 7.1773857 AU n = 0.05125717 P = 19.229 years NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2016 CBAT 2016 February 2 (CBET 4251) Daniel W. E. Green