M31N 2005-09c: a fast Fe II nova in the disk of M 31

¹ University of Crete, Department of Physics, PO Box 2208, 71003 Heraklion, Greece e-mail: dh@physics.uoc.gr
² IESL, Foundation for Research and Technology, 71110 Heraklion, Greece
³ Max-Planck-Institut für extraterrestrische Physik, 85741 Garching, Germany

Received: 27 June 2006
Accepted: 5 January 2007

Abstract

Context.Classical novae are quite frequent in M 31. However, very few spectra of M 31 novae have been studied to date, especially during the early decline phase.

Aims.Our aim is to study the photometric and spectral evolution of a M 31 nova event close to outburst.

Methods.Here, we present photometric and spectroscopic observations of M31N 2005-09c, a classical nova in the disk of M 31, using the 1.3 m telescope of the Skinakas Observatory in Crete (Greece), starting on the 28th September, i.e. about 5 days after outburst, and ending on the 5th October 2005, i.e. about 12 days after outburst. We also have supplementary photometric observations from the La Sagra Observatory in Northern Andalucía, Spain, on September 29 and 30, October 3, 6 and 9 and November 1, 2005. The wavelength range covered by the spectra is from 3565 Å to 8365 Å. The spectra are of high S/N allowing the study of the evolution of the equivalent widths of the Balmer lines, as well as the identification of non-Balmer lines.

Results.The nova displays a typical early decline spectrum that is characterized by many weak multiplet emissions. It is classified as a P_fe nova. From the nova light curve, we have also derived its speed class, days. As the nova evolved the Balmer lines became stronger and narrower. The early decline of the expansion velocity of the nova follows a power law in time with an exponent of -0.2.