Discovery of a Slowly-Evolving and Faint Probable Nova in M31

ATel #7189; K. Hornoch (Astronomical Institute, Ondrejov, Czech Republic), M. Wolf, H. Kucakova, J. Vrastil (Astronomical Institute, Charles U., Prague, Czech Republic)
on 9 Mar 2015; 02:19 UT
Credential Certification: Allen W. Shafter (aws@nova.sdsu.edu)

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We report the discovery of rather faint, slowly-evolving probable nova in M31 on a co-added 720-s R-band CCD frame taken on 2015 Mar. 7.751 UT with the 0.65-m telescope at Ondrejov. The object is visible also on several prediscovery images, but is not present on many archival images taken with various telescopes during last several years.

The object designated PNV J00420640+4108211 is located at R.A. = 0h42m06s.40, Decl. = +41o08'21".1 (equinox 2000.0), which is 428.0" west and 467.4" south of the center of M31.

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

2014 Dec. 13.742 UT, [21.0; 2015 Jan. 13.697, [20.3; Feb. 2.818, [19.5; 5.722, 19.6 ± 0.4; 15.734, 19.7 ± 0.3; 19.733, 19.4 ± 0.3; 19.838, 19.6 ± 0.3; 20.733, 19.5 ± 0.3; 20.742, V = 19.7 ± 0.2; 20.751, I = 19.7 ± 0.4; 20.818, 19.2 ± 0.3; 21.732, 19.6 ± 0.25; 26.748, 19.4 ± 0.35; Mar. 5.819, 18.2 ± 0.25; 7.751, 18.9 ± 0.2; 7.805, 19.1 ± 0.25; 7.830, I = 18.7 ± 0.35; 8.751, 19.0 ± 0.15.

The closest known variable star (having amplitude of brightness changes 0.50 and 1.58 mag in R-band and I-band, respectively and with period of 130 days) located 1.59" to the north-east of the position of the probable nova and cataloged in the WeCAPP Survey (Fliri et al. 2006, A&A, 445, 23) is coincident with an object cataloged in Massey's catalog (Massey et al. 2006, AJ, 131, 2478) and designated J004206.53+410821.4. A careful comparison of a co-added 6480-s R-band CCD frame of the probable nova (constructed from 72 individual images taken with the 0.65-m telescope at Ondrejov during 5 nights and available through the link below) with Massey's V, R, and I-band images shows that the star J004206.53+410821.4 is not spatially coincident with the probable nova. Also, the closest object in Massey's catalog designated J004206.46+410820.7 (V = 22.40 ± 0.10, R = 22.11 ± 0.14) located nominally only 0.79" from the position of the probable nova is also not spatially coincident with the probable nova. Thus, there are no spatially coincident sources in Massey's images brighter than V ~ 22.5, R ~ 22.5, and I ~ 22 mag, respectively. The observed (R-I) ~ -0.3 and ~ 0.3 mag on Feb. 20. 8 and Mar. 7.8 UT, respectively would be atypical of a red LPV.

Based on the nonexistence of a known counterpart down to such faint magnitudes (i.e. amplitude of brightness changes of the object is at least 2.7, 4.3, and 3.3 mag in V, R, and I-band, respectively) and its color and overall brightness evolution, we conclude that PNV J00420640+4108211 is probably a slowly-evolving faint nova in M31, similar to a slowly-evolving Fe-II nova M31N 2010-10b (CBET #2487, ATel #3039). Nevertheless, spectroscopic classification is strongly encouraged to firmly establish the nature of the object.

Image of PNV J00420640+4108211