Electronic Telegram No. 2769 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 NEW SATELLITE OF (134340) PLUTO: S/2011 (134340) 1 M. R. Showalter, SETI Institute; and D. P. Hamilton, University of Maryland -- on behalf of a team that includes S. A. Stern (Southwest Research Institute), H. A. Weaver (Applied Physics Laboratory, Johns Hopkins University), and A. J. Steffl and L. A. Young (Southwest Research Institute)) -- report the discovery of a new satellite of Pluto. The object, provisionally designated S/2011 (134340) 1, was detected in five separate sets of images taken by the Hubble Space Telescope WFC3/UVIS: two sets on 2011 June 28.6 UT, two on July 3.4, and one on July 18.92. The body is visible in individual 8-minute exposures, and S/N > 5 when the five images of each set are co-added. On June 28, the satellite was 2".48 from the center of Pluto in p.a. 335 deg; on July 3, it was 2".01 from Pluto at p.a. 27 deg; on July 18, it was 2".035 from Pluto at p.a. 198.1 degrees. The satellite's magnitude is V = 26.1 +/- 0.3, making the object about 10 percent as bright as Pluto II (Nix). The diameter depends on the assumed geometric albedo: 14 km if p_v = 0.35, or 40 km if p_v = 0.04. The motion is consistent with a body traveling on a circular, equatorial orbit. The inferred mean motion is 11.2 +/- 0.1 degrees per day (P = 32.1 +/- 0.3 days), and the projected radial distance from Pluto is 59000 +/- 2000 km, placing the satellite between the orbits of Pluto II (Nix) and III (Hydra). Subsequent to the discovery of S/2011 (134340) 1 by Showalter et al., A. J. Steffl and S. A. Stern, Southwest Research Institute (SwRI); M. R. Showalter, SETI Institute; H. A. Weaver, Applied Physics Laboratory, Johns Hopkins University; D. P. Hamilton, University of Maryland; and L. A. Young, SwRI, report the probable detection of S/2011 (134340) 1 in archival Hubble Space Telescope ACS/HRC images taken on 2006 Feb. 15. The object has a S/N of 2.5-3.0 in each of four images and V = 26.0 +/- 0.3. It appears at a distance of 2".26 from Pluto at position angle 1.7 deg on 2006 Feb 15.63 UT and at 2".26 from Pluto in position angle 2.7 deg on 2006 Feb 15.69. Subsequent to the discovery of S/2011 (134340) 1 by Showalter et al. and its possible identification in the Hubble archival images taken on 2006 Feb. 15 by Steffl et al. (see above), H. A. Weaver, Applied Physics Laboratory, Johns Hopkins University; D. P. Hamilton, University of Maryland; M. R. Showalter, SETI Institute; and A. J. Steffl, S. A. Stern, and L. A. Young, Southwest Research Institute, report the probable detection of S/2011 (134340) 1 in archival Hubble Space Telescope WF3/UVIS images taken on 2010 June 25. The object has S/N approximately 3 in each of four 180-s images taken through the F350LP filter. From a two-image composite taken on June 25.3014 UT, the object has V = 25.71 +/- 0.3 and appears at a distance of 2".38 from Pluto at position angle 172.0 deg. From a two-image composite taken on June 25.3153, the object has V = 25.96 +/- 0.3 and appears at a distance of 2".32 from Pluto at position angle 172.2 deg. NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2011 CBAT 2011 July 20 (CBET 2769) Daniel W. E. Green