Meteor Outburst of Gamma Ursae Minorids
P. Jenniskens, SETI Institute; and Esko Lyytinen, Helsinki, Finland, report that six Finnish observers using wide-angle video cameras (limiting magnitude +1) observed a possible outburst of gamma Ursae Minorids, a newly discovered stream (cf. CBET 1938) that until now was only known from radar observations (limiting magnitude +8) of much weaker meteors. On the night of 2010 Jan. 20/21 (solar long. = 300.7 deg), Ilkka Yrjola (Kuusankoski, Finland), Pekka Kokko (Ylikiiminki), Mika Jaervinen (Joutsa), Ari Jokinen (Jarvenpaa), Timo Kantola (Piksamaki), and Jarmo Moilanen (Vaala) detected meteors radiating from a radiant at R.A. = 228.0 deg, Decl. = +66.4 deg (10 meteors in total: 4, 1, 1, 1, 3, and 2 meteors per site, respectively). One three-station meteor on Jan. 20d17h17m55s had a radiant at R.A. = 230.2, Decl. = +67.1 and speed V_g = 29.6 km/s, corresponding to the following osculating orbital elements: a = 2.84 AU, q = 0.955 AU, e = 0.664, Peri. = 202.3 deg, Node = 300.404 deg, and i = 48.5 deg (equinox 2000.0). Within the error, this radiant is identical to that of the recently discovered (CBET 1938) gamma Ursae Minorids shower (IAU Meteor Shower No. 404), which peaks at solar long. = 299.0 deg and is active for 11 days. On the day of the video observation, the annual shower would have radiated from R.A. = 232.5 deg, Decl. = +66.2 deg, with V_g = 31.8 km/s, in good agreement with the radiant of what appears to be a meteor outburst. The observed 2010 meteors are relatively bright (+0.55 mean magnitude), which implies that the shower had a low magnitude-distribution index of chi = 1.65 ± 0.35.
This suggests that the shower had an outburst of relatively bright meteors. The shower was still weakly active on the night of Jan. 21/22, when Yrjola and Jaervinen captured a two-station meteor radiating from R.A. = 229.8 deg, Decl. = +66.4 deg, V_g = 29.6 km/s (solar long. = 301.612 deg). NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars.