Electronic Telegram No. 2781 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 C/2010 X1 (ELENIN) M. Drahus, University of California at Los Angeles; Bin Yang, University of Hawaii; and J. Hoge, Joint Astronomy Centre, report the detection of HCN in comet C/2010 X1 on July 30 when at heliocentric distance r = 1.07 AU. Observations between July 30.153 and 30.249 UT at the James Clerk Maxwell Telescope show the J = 4-3 line with area about 0.1 K km/s in antenna temperature scale. Assuming an isotropic production of gas at velocity 0.5 km/s and a Boltzmann distribution of energy levels at 50 K, the derived HCN production rate is 1.5 x 10**25 molecules/s, comparable to the mean level measured in comet 103P/Hartley at the same heliocentric distance in late 2010 (Drahus et al. 2011, Ap.J. 734, L4). NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2011 CBAT 2011 August 7 (CBET 2781) Daniel W. E. Green