SIMBAD references

Greg Bock, Windaroo, Queensland, Australia, reports the discovery of an apparent supernova (red mag 18.1) by Stuart Parker (Oxford, Canterbury, New Zealand) on a 30-s unfiltered CCD image taken on July 17.54 UT with a 28-cm Celestron C11 reflector (+ ST10 camera). The new object is located at R.A. = 0:56:38.88, Decl = -9:54:09.1 (equinox 2000.0; reference stars from USNO-B and UCAC3 catalogues; measured by Bock), which is 50" west and 48" north of the nucleus of the galaxy NGC 309. Nothing is visible at this position on Digitized Sky Survey red and infrared images (limiting mag > 19). The variable was designated PSN J00563888-0954091 when it was posted at the Central Bureau's TOCP webpage and is here designated SN 2012dt based on the spectroscopic confirmation reported below. Additional magnitudes for 2012dt: June 30, [18.5 (Parker); July 18.768, 18.3 (J. Brimacombe, Cairns, Australia, 41-cm RCOS telescope + infrared filter; bandpass > 700 nm); July 19.096, 18.4 (F. Luppi and L. Buzzi, Varese, Italy, 0.38-m f/6.8 reflector; position end figures 38s.85, 09".7; reference stars from CMC-14 catalogue; image posted at website URL http://www.astrogeo.va.it/pub/TOCP/PSN_N309.jpg); 20.425, 18.0 (Brimacombe; luminance filter inferred; position end figures 38s.85, 09".3; image posted at URL http://www.flickr.com/photos/43846774@N02/7613256578/). Brimacombe's July 18 image is posted at URL http://www.flickr.com/photos/43846774@N02/7600273288/. The type-IIb supernova 2008cx also appeared in NGC 309 (cf. CBET 1399).