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Photometric and Spectroscopic observations of M31N 2007-11d

ATel #1299; R. Quimby (Caltech), A. Shafter (SDSU), A. Rau, M. Kasliwal, E. Ofek, (Caltech), F. Yuan, C. Akerlof (University of Michigan), and J. C. Wheeler (University of Texas)
on 22 Nov 2007; 04:37 UT
Credential Certification: Robert Quimby (quimby@astro.as.utexas.edu)

Subjects: Optical, Nova, Transient

We report on the independent detection and follow-up of the bright optical transient M31N 2007-11d, which was first reported by S. Nakano et al. (IAUC 8898 ). The transient was detected in unfiltered ROTSE-IIIb images taken around Nov. 19.13 UT at about 15.3 mag. It brightened to 14.7 mag on Nov. 20.06.

We began photometric follow-up observations with the Palomar 60 inch telescope on Nov. 20.3886 and Nov. 21.0865 UT. Multiple images were obtained in the gri'z' bands yielding the following detections (calibrated against the SDSS):

JD-2400000.5     filter   Magnitude  
54424.3885637 g 15.24+-0.03
54425.0864711 g 15.40+-0.06
54424.3907901 r 15.13+-0.02
54425.0886947 r 15.20+-0.06
54424.3930187 i' 14.68+-0.04
54425.0909192 i' 15.05+-0.07
54424.3952417 z' 15.05+-0.05
54425.0961037 z' 14.97+-0.09
Thus the object has clearly faded in the g and i' bands.

No source was detected at this position in archival SDSS data to the following limits:

filter   uplim    abs. mag limit* 
g 21.82 -3.6
r 22.12 -3.0
i 21.53 -3.4
z 20.14 -4.7
(*) assuming D = 0.77 Mpc and corrected for Galactic extinction (E[B-V] =0.268; Schlegel et al. 1998).

A spectrum (420-900 nm) obtained ~4 days post discovery on Nov. 21.29 UT with the 9.2m Hobby-Eberly Telescope (+ Marcario Low-Resolution Spectrograph) by J. Caldwell and A. Westfall shows it likely to be a bright nova. The spectrum is characterized predominately by narrow Balmer and Fe II emission features with P Cygni profiles superimposed on a blue continuum. Overall, the spectrum is similar to both the FeII nova M31N 2007-11c around maximum (A. Rau in prep) and M31N 2007-07c 2.5 days after discovery (ATel #1153).