Optical spectroscopy of the candidate nova M31N 2007-10b
ATel #1242; A. Rau (Caltech), V. Burwitz (MPE), S. B. Cenko (Caltech), A. Updike, D. Hartmann (Clemson), P. Milne, & G. Williams (Arizona)
on 16 Oct 2007; 22:17 UT
Credential Certification: Arne Rau (arne@astro.caltech.edu)
On 2007 October 16.29 UT a spectrum of the nova candidate M31N
2007-10b (ATel#1238, see also the CBAT M31 novae page) was obtained
with the Double-Beam Spectrograph on the Palomar 200-inch telescope.
The 400/6000 grism (3.5 angstrom FWHM) and 158/7500 grating (8.6
angstrom FWHM) were used with 1800s exposure, each.
The spectrum shows a blue continuum with strong hydrogen Balmer and He
(4685,5015,5876,6678,7065) emission lines. We further find indications
for weak NII emission at 5679 Angstrom, which suggests this nova to be
of the He/N class (Williams 1992, AJ, 104, 725). Note, that the
expansion velocity of 1450+/-100 km/sec (based on Halpha), is
atypically low for He/N novae.
Alternatively, the spectrum could be explained by a Galactic dwarf
nova in the foreground towards M31. However, the emission line
centroids are consistent with the average radial velocity of M31 of
about -300 km/sec, supporting the nova identification
Further CCD imaging at the robotic 60cm Livermore Optical Transient
Imaging System (Super-LOTIS, Steward Observatory, Kitt Peak) on 2007
Oct 14.259, 15.259, and 16.330 UT found the source at a brightness of
R=18.6, 19.3, and 19.6 (photometric solution based on Massey M31
catalogue). A comparison with the discovery magnitudes given in ATel
#1238 indicates a rapid decline, consistent with a He/N nova.
