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M81N 2017-04c is probably a red variable

ATel #10348; S. C. Williams (Lancaster), M. Henze (CSIC-IEEC), H. Meusinger, B. Stecklum (TLS), K. Hornoch (Ondrejov), M. J. Darnley (LJMU), A. Kaur, D. H. Hartmann (Clemson), G. Sala, J. Jose, J. Figueira (UPC-IEEC), M. Hernanz (CSIC-IEEC), A. W. Shafter (SDSU)
on 4 May 2017; 14:16 UT
Credential Certification: Steven Williams (scw@astro.ljmu.ac.uk)

Subjects: Optical, Nova, Transient, Variables

Here we report additional photometry of the M81 nova candidate M81N 2017-04c (AT 2017dfw; ATel #10312, TNS) taken with the 2-m Liverpool Telescope (LT) and the 2-m Alfred-Jensch-Telescope of the Tautenburg observatory (TLS):

  
Date [UT]      | Mag   | Err  | Filter  | Telescope  
2017-04-24.906 | 20.09 | 0.08 | i'      | LT  
2017-04-24.911 | 21.44 | 0.13 | r'      | LT  
2017-04-24.918 | 20.94 | 0.26 | Hα      | LT  
2017-04-26.878 | 21.5  | 0.4  | R       | TLS  
The red colour of the transient implies it is not a nova eruption and our photometry is consistent with it being a red variable.

The LT (Steele et al. 2004) is a fully robotic 2-m telescope operated on the island of La Palma by Liverpool John Moores University in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias with financial support from the UK Science and Technology Facilities Council. Our observations use the IO:O optical CCD camera of the LT. The 2-m TLS of the Tautenburg observatory, Germany, was operated in Schmidt camera mode using a 2k x 2k CCD with a 0.7 x 0.7 deg field of view. The LT and TLS photometry is based on the SDSS DR7 photometry catalogue. The Hα magnitude is defined on the AB system where m = 0 for fλ = 2.53 × 10-9 erg/cm2/s/Å. Through a 90 Å wide filter, this corresponds to a zero point flux of ~2.3 × 10-7 erg/cm2/s.