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Optical Spectroscopy of Nova M31N 2007-07c

ATel #1152; A. Rau (California Institute of Technology), V. Burwitz
on 24 Jul 2007; 16:46 UT
Credential Certification: Arne Rau (arne@astro.caltech.edu)

Subjects: Optical, Nova

Referred to by ATel #: 1153, 1186

On 2007 July 21.46 UT a spectrum of the nova candidate M31N 2007-07c (see ATEL#1146, ATEL#1149) was obtained with Double-Beam Spectrograph on the Palomar Hale-5m telescope. The 400/6000 grism (3.5 angstrom FWHM) and 158/7500 grating (8.6 angstrom FWHM) were used with 1200s exposure, each.
The H-alpha line displays a P-Cygni profile. The measured expansion velocity is -1630+/-20 km/sec (blue shifted), based on measurements of the Ca H+K lines, the G Band, H-beta, Mg lines and the near-infrared Ca-triplet. Taking into account the average radial velocity of M31 of about -300 km/sec, the actual expansion velocity for the nova is estimated to be approximately 1330 km/sec.
Further CCD imaging at the 1.3m Ritchey Chretien f/7.5 telescope at Skinakas Observatory, Crete, Greece showed the nova at a brightness of R=16.4, 15.8, 16.0, 17.1 (photometric solution based on Massey M31 catalogue) on 2007 July 20.0078, 21.0425, 22.0720, 24.0462 UT. We also have obtained unfiltered CCD images obtained with the 0.35m f/2 reflector of the Observatorio Astronomico de La Sagra, Spain on 2007 07 19.094, 20.054, 21.091, 22.016, 22.966, 24.140 that give us R = 18.3, 16.2, 15.4, 15.5, 16.5, 16.8 (photometric solution based on USNO-B1.0 catalogue).
The photometric evolution shows that the nova reached its maximum brightness in R around 2007 July 21 at about the same time as the spectrum was taken.
Novae like this, brighter than 16 mag in R stand, out among the ~20 novae expected in the central area of M31.