OGLE discovers a possible classical Nova in the Galactic Bulge: OGLE-2012-NOVA-01

ATel #4323; S. Kozlowski (Warsaw Observatory), R. Poleski (Warsaw Observatory), A. Udalski (Warsaw Observatory), M. K. Szymanski (Warsaw Observatory), M. Kubiak (Warsaw Observatory), I. Soszynski (Warsaw Observatory), G. Pietrzynski (Warsaw Observatory & Universidad de Concepcion, Chile), L. Wyrzykowski (Warsaw Observatory & IOA Cambridge), K. Ulaczyk (Warsaw Observatory), P. Pietrukowicz (Warsaw Observatory), J. Skowron (Warsaw Observatory & Ohio State)
on 21 Aug 2012; 14:12 UT
Distributed as an Instant Email Notice Novae
Credential Certification: Szymon Kozlowski (simkoz@astrouw.edu.pl)

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We report the discovery of a relatively bright (I=12.5 mag near the peak) possible classical nova (OGLE-2012-NOVA-01) in the database of new objects from the fourth phase of the OGLE survey (OGLE-IV). The nova does not have a detectable progenitor in the OGLE-IV I-band images before 2012 May 2, meaning it was fainter than I>20.2 mag. Its brightness rose fast after 2012 April 24 (no detection on the image) reaching I=14.96 mag on 2012 May 2 (HJD=2456049.75193) and peaking on 2012 May 5 (HJD=2456052.83501) with I=12.53 mag. We then observed a slow magnitude decline, reaching approximately I=17 mag as of today. Location of the nova is (RA, Dec) = (17:56:49.39, -27:13:28.2) J2000, 1 arcsec from a faint I=18.99 mag star, that securely is not the progenitor.

There exist three OGLE-IV V-band images from 2012 season for this field. Only the third one, taken on 2012 July 25 (HJD=2456133.654162), was recorded during the eruption but we find no detection of the nova at the level of V>21.2 mag. This corresponds to the color of (V-I)>~5.1 mag or the extinction corrected color of (V-I)>~1.6 mag (see below).

Both analysis of the CMD and magnitude histograms for this field showed no presence of the red clump giant stars. We are unable to determine the extinction for this field from the OGLE data alone, but it must be higher than A_I>2.6 mag (the nearest OGLE-III field with determined extinction; Nataf et al. 2012, arXiv:1208.1263).

Using the VVV extinction map (Gonzalez et al., 2011, A&A, 534, 3 and Gonzalez et al., 2012, A&A, 543, 13), we find extinctions in V- and I-band to be A_V=6.8 mag and A_I=3.3 mag assuming the standard interstellar extinction law with R_V=3.1. This amount of extinction shifts the red clump giant stars to V=~22.1 mag, i.e., below the OGLE-IV detection limit. The I-band extinction corrected near peak magnitude would be then I=9.2 mag, what corresponds approximately to the absolute magnitude of M_I=-5.3 mag assuming the nova exploding in the Galactic bulge (at 8 kpc).

OGLE main website: http://ogle.astrouw.edu.pl/

This website provides both the up-to-date photometry file and finding charts for the nova.