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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
Password Certification: Arne Rau (arne@astro.caltech.edu)

Subjects: Optical, Nova

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.


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