Discovery of a Probable Nova in M31

ATel #7603; K. Hornoch (Astronomical Institute, Ondrejov, Czech Republic), H. Kucakova, K. Honkova and J. Vrastil (Astronomical Institute, Charles U., Prague, Czech Republic)
on 7 Jun 2015; 21:38 UT
Credential Certification: Martin Henze (martin.henze@sciops.esa.int)

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We report the discovery of rather faint, slowly rising probable nova in M31 on a co-added 1320-s R-band CCD frame taken on 2015 May 31.030 UT with the 0.65-m telescope at Ondrejov. The object is well visible also on a few pre-discovery images, but is not present on many archival images taken with various telescopes during last several years. Also, the object is not visible on R-band images of the Survey of Local Group Galaxies Currently Forming Stars: I. UBVRI Photometry of Stars in M31 and M33 by Massey et al. (2006, AJ, 131, 2478) down to R ~ 21.5 mag.

The object designated PNV J00423445+4116443 is located at R.A. = 0h42m34s.45, Decl. = +41o16'44".3 (equinox 2000.0), which is 111.3" west and 35.8" north of the center of M31 (see link to image taken on Jun. 3.047 UT below).

The following R-band magnitudes (unless otherwise noted) were obtained using the 0.65-m telescope at Ondrejov:

2015 Apr. 25.101 UT, [20.2; May 11.057, 18.8 ± 0.3; 12.072, 18.8 ± 0.3; 16.063, 19.2 ± 0.35; 31.030, 18.7 ± 0.25; Jun. 3.047, 18.3 ± 0.2; 5.007, 18.3 ± 0.2; 5.020, I = 17.7 ± 0.3; 6.024, 18.1 ± 0.15; 6.985, 18.2 ± 0.2.

A search for known variable sources close to the position of the PNV J00423445+4116443 did not reveal any known variable object located closer than 2.8" from the position of PNV J00423445+4116443. The closest known variable object is M31N 2008-03b discovered by K. Hornoch on 2008 Mar. 7.756 UT. A direct comparison of the best images available for M31N 2008-03b and PNV J00423445+4116443 shows that they are undoubtedly two distinct objects. The observed (R-I) ~ 0.6 mag is consistent with a nova around maximum brightness, but would be atypical for a red LPV. Nevertheless, spectroscopic classification is strongly encouraged to firmly establish the nature of the object.

Image of the PNV J00423445+4116443