Electronic Telegram No. 2319 Central Bureau for Astronomical Telegrams INTERNATIONAL ASTRONOMICAL UNION CBAT Director: Daniel W. E. Green; Room 209; Dept. of Earth and Planetary Sciences; Harvard University; 20 Oxford St.; Cambridge, MA 02138; U.S.A. e-mail: cbat@iau.org; cbatiau@eps.harvard.edu URL http://www.cfa.harvard.edu/iau/cbat.html NOVA IN M31: M31N 2010-05a Kamil Hornoch, Astronomical Institute, Ondrejov; Rubab Khan, Jonathan Bird, and Ondrej Pejcha, Department of Astronomy, Ohio State University; Peter Garnavich, Colin Littlefield, and Nancy Paul, University of Notre Dame; and Samia Bouzid, Rutgers University, report low-resolution optical spectroscopy (range 450-670 nm, resolution R = 1600) and optical photometry of M31N 2010-05a (cf. CBET 2305). Spectra were obtained using the OSMOS spectrograph and the VPH grism on the 2.4-m Hiltner telescope at MDM Observatory. Magnitude measurements were obtained from co-added R-band images taken with the OSMOS spectrograph and imager on the 2.4-m Hiltner telescope, with the Vatt4k imager on the 1.83-m Vatican Advanced Technology Telescope, and with the 0.65-m telescope (+ G2CCD-3200) at Ondrejov. A spectrogram taken by Bird on June 5.47 UT (8.43 days after its first optical detection by Hornoch et al.) exhibits H-alpha, H-beta, and Fe II emission lines. The HWZI of H-alpha and H-beta is about 2000 km/s. They did not see any trace of an He II 468.6-nm line. This suggests that the object is an "Fe II"-class nova. The following additional R-band magnitudes were obtained for M31N 2010-05a: June 5.024, 17.2 +/- 0.1 (Hornoch and P. Hornochova, 0.65-m telescope); 5.468, 17.1 +/- 0.1 (Bird, 2.4-m telescope); 6.038, 17.2 +/- 0.1 (Hornoch and Hornochova); 6.473, 17.1 +/- 0.1 (Bird); 7.464, 17.2 +/- 0.1 (Bird); 8.044, 17.4 +/- 0.25 (Hornoch and Hornochova); 9.036, 17.35 +/- 0.1 (Hornoch); 9.459, 17.18 +/- 0.03 (Garnavich, Littlefield, Paul, and Bouzid, 1.83-m telescope). The 1.83-m telescope image also shows M31N 2010-03a (cf. CBETs 2192, 2212) at R = 20.1 +/- 0.2. The novae M31N 2010-02a (cf. CBETs 2190, 2192, 2212), 2010-03b (cf. CBET 2212), and 2010-04a (cf. CBET 2267) are not present on the same image down to R magnitudes 20.7, 20.6, and 20.5, respectively. Correcting their initial report on CBET 2305, Koichi Nishiyama and Fujio Kabashima note that M31N 2010-05a is located 95" west and 29" north of the center of M31 (not 9" north, as stated on CBET 2305). They add that the nova brightened to unfiltered mag 16.5 on June 4.779 UT (same instrumentation details as given on CBET 2305). NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2010 CBAT 2010 June 11 (CBET 2319) Daniel W. E. Green