Discovery of Five Probable Novae in M81

ATel #8180; K. Hornoch (Astronomical Institute, Ondrejov, Czech Republic), R. Errmann (ING, La Palma, Spain and Astrophysical Institute and University Observatory, Jena, Germany), P. Sowicka (ING, La Palma, Spain and Nicolaus Copernicus Astronomical Center, Warsaw, Poland), N. Humphries (ING, La Palma, Spain and University of Sheffield, UK), O. Vaduvescu (ING, La Palma, Spain)
on 17 Oct 2015; 17:08 UT
Credential Certification: Allen W. Shafter (ashafter@mail.sdsu.edu)

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We report the discovery of five probable novae in M81 on a co-added 2000-s narrow-band H-alpha CCD image taken with the 2.5-m Isaac Newton Telescope (INT) + WFC at La Palma under ~1.5" seeing on 2015 Oct. 14.198 UT. The new objects are well visible on the co-added image (see the finding charts linked below), but are not present on numerous narrow-band H-alpha archival images from the INT down to limiting magnitude as faint as H-alpha = 22.3. We obtained also Sloan r'-band images which helped us to classify the objects. Strong H-alpha emission together with relative faintness in the Sloan r'-band supports the classification of the objects as novae. Their currently observed relative low brightness and presence of excess H-alpha emission suggests that they were likely discovered well after their maximum light.

Designations, positions, and offsets of the new objects from the M81 center are summarized in the following table:

 
  TOCP designation    CBAT designation  R.A. (J2000)  Dec. (J2000)  Offset R.A.  Offset Dec. 
 
PNV J09554744+6907052  M81N 2015-10a?   09 55 47.44   +69 07 05.2     76.4" E     190.1" N 
PNV J09551983+6905566  M81N 2015-10b?   09 55 19.83   +69 05 56.6     71.5" W     121.5" N 
PNV J09551857+6904223  M81N 2015-10c?   09 55 18.57   +69 04 22.3     78.3" W      27.2" N 
PNV J09552053+6900438  M81N 2015-10d?   09 55 20.53   +69 00 43.8     67.8" W     191.3" S 
PNV J09543691+6908181  M81N 2015-10e?   09 54 36.91   +69 08 18.1    301.0" W     263.0" N 
 

The photometry obtained with the INT + WFC is summarized here:

 
 
                        2015 10 14.198     2015 10 14.197 
 
       Object             H-alpha mag       Sloan r' mag 
 
PNV J09554744+6907052     20.1 ± 0.1         22.2 ± 0.3 
PNV J09551983+6905566     21.2 ± 0.25          > 23.2 
PNV J09551857+6904223     19.5 ± 0.1         21.4 ± 0.2          
PNV J09552053+6900438     21.2 ± 0.25          > 23.1 
PNV J09543691+6908181     21.3 ± 0.25          > 23.5 
 

This work is based on observations made with the Isaac Newton Telescope operated on the island of La Palma by the ING in the Spanish Observatorio del Roque de los Muchachos.

Finding charts