Electronic Telegram No. 2170 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@cfa.harvard.edu; dwe_green@eps.harvard.edu URL http://www.cfa.harvard.edu/iau/cbat.html APPARENT NOVAE IN M81: M81N 2010-01a AND M81N 2010-01b K. Hornoch, Astronomical Institute, Ondrejov; J. Prieto, Carnegie Observatories; R. Khan and O. Pejcha, Department of Astronomy, Ohio State University; J. Gorosabel and M. Jelinek, Instituto de Astrofisica de Andalucia, Consejo Superior de Investigaciones Cientificas; and P. Kubanek, Image Processing Laboratory, Universidad de Valencia, report the discovery of another apparent nova in the galaxy M81 on CCD frames taken with RETROCAM on the 2.4-m Hiltner telescope at MDM observatory and with ALFOSC on the 2.6-m Nordic Optical Telescope at La Palma. The new object, designated M81N 2010-01b, was first marginally detected on two co-added 600-s Sloan r' CCD frames taken by Prieto and Khan with the 2.4-m Hiltner telescope on Jan. 14.394 and 14.407 UT. The third detection was made on a co-added 900-s narrow-band H-alpha CCD frame taken by Gorosabel, Jelinek, and Kubanek with the 2.6-m Nordic Optical Telescope during IAA time on Jan. 17.218. The apparent nova was definitely confirmed on co-added 600-s Sloan r' CCD frame taken by J. A. L. Aguerri (Instituto de Astrofisica de Canarias) and R. Sanchez-Janssen (European Southern Observatory) with the 2.6-m Nordic Optical Telescope (+ ALFOSC) on Jan. 21.292; and on a co-added 1200-s narrow-band H-alpha CCD frame taken by G. Jozsa and P. Serra (Netherlands Foundation Research in Astronomy) of the HALOGAS (Hydrogen Accretion in LOcal GAlaxieS) survey team, with the 2.5-m Isaac Newton Telescope (+ WFC) on Feb. 4.125. M81N 2010-01b is located at R.A. = 9h55m35s.16, Decl. = +69o03'30".4 (equinox 2000.0), which is 10".7 east and 24".7 south of the center of M81. Nothing is present at this position on numerous archive images from the 2.54-m Isaac Newton Telescope, the 4.2-m William Herschel Telescope, the 4-m Mayall telescope, and the 8.2-m Subaru telescope, down to limiting magnitudes as faint as Sloan r' = 23.0, R = 23.1, V = 23.4, and H-alpha = 21.3. Available Sloan r' and H-alpha magnitudes for nova M81N 2010-01b, as measured by Hornoch: Jan. 8.333, [22.2 (Prieto and Khan, 2.4-m Hiltner telescope + Sloan r' filter); 14.394, r' = 20.9: (Prieto and Khan); 14.407, r' = 20.7: (Prieto and Khan); 17.218, H-alpha = 18.8 +/- 0.3 (Gorosabel, Jelinek, and Kubanek, 2.6-m Nordic Optical Telescope); 21.292, r' = 21.5 +/- 0.3 (Aguerri and Sanchez-Janssen, 2.6-m Nordic Optical Telescope); 31.999, [21.7 (Kubanek, N. Morales, J. L. Ortiz, Gorosabel, and Jelinek, 1.23-m telescope at Calar Alto + R filter); Feb. 4.125, H-alpha = 20.5 +/- 0.3 (Jozsa and Serra, 2.5-m Isaac Newton Telescope). Hornoch et al. also report additional magnitudes for M81N 2010-01a (cf. CBET 2132), measured by Hornoch: Jan. 21.292, r' = 21.0 +/- 0.15 (Aguerri and Sanchez-Janssen, 2.6-m Nordic Optical Telescope); 28.961, R = 21.3 +/- 0.3 (Kubanek, Morales, Ortiz, Gorosabel, and Jelinek, 1.23-m telescope); 31.012, R = 21.3 +/- 0.3 (Kubanek, Morales, Ortiz, Gorosabel, and Jelinek); 31.999, R = 21.6 +/- 0.3 (Kubanek, Morales, Ortiz, Gorosabel, and Jelinek); Feb. 3.190, R = 21.7: (Kubanek, Morales, Ortiz, Gorosabel, and Jelinek); 4.125, H-alpha = 20.0 +/- 0.15 (Jozsa and Serra, 2.5-m Isaac Newton Telescope). NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2010 CBAT 2010 February 10 (CBET 2170) Daniel W. E. Green