Additional optical photometry of the recurrent nova M31N 1990-10a during its 2016 eruption

ATel #9435; V. Goranskij (Sternberg Astronomical Institute, Moscow University), E. Barsukova (Special Astrophysical Observatory, Russia), M. Henze (CSIC-IEEC)
on 31 Aug 2016; 07:58 UT
Credential Certification: Martin Henze (henze@ice.cat)

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We report additional optical measurements of the declining light curve of the recurrent nova M31N 1990-10a (see ATels #9276,#9280,#9281,#9383,#9386). All data were obtained with the 50-cm Maksutov meniscus telescope of the Crimean Astronomical Station of the Moscow University. The telescope is equipped with an Apogee Alta U8300 CCD. We calibrated the photometry relative to the nearby Local Group Galaxies Survey (Massey et al. 2006) standard No.240784 with the following magnitudes: U=17.451±0.005; V=16.711±0.005; B=15.786±0.005; Rc=15.201±0.005; no Ic magnitude. The Ic observations were referenced to the star No.244750 having Ic=17.289±0.004.

Measuring the nova brightness, we found that in the first night, 29/30 July, its contribution was only 3.6% over the bulge background in the V band, and 4.5% in the Rc band. In the last night, 7/8 August, this contribution was 2.5% in the V and 1.1% in the Rc band. Therefore, the uncertainty of the measurements mainly depends on the heterogeneity of the background instead of the exposure time. There were many dark nebulosities around the nova having a weak contrast and we attempted to choose by eye those background regions with similar properties to the vicinity of the nova. We used several methods of background measurements and the given values are mean quadratic ones. Below we list the observed magnitudes and corresponding uncertainties for the respective dates and filters.

 
Date [UT 2016] | JD - 2400000 |  mag  | rms  | Filter | Total exp.(s.) 
   Jul 30.0065 |   57599.5073 | 18.19 | 0.08 | V      |   400 
   Jul 30.0165 |   57599.5173 | 17.66 | 0.15 | Rc     |   400 
   Jul 30.0245 |   57599.5253 | 18.39 | 0.04 | B      |   400 
   Jul 30.0327 |   57599.5335 | 18.61 | 0.09 | Ic     |   400 
   Jul 31.0174 |   57600.5181 | 18.26 | 0.28 | V      |   200 
   Jul 31.0214 |   57600.5222 | 18.64 | 0.07 | B      |   200 
   Jul 31.0242 |   57600.5251 | 17.59 | 0.08 | Rc     |   200 
   Jul 31.0270 |   57600.5279 | 18.59 | 0.11 | Ic     |   200 
   Jul 31.9945 |   57601.4955 | 18.36 | 0.12 | V      |  1200 
   Aug  1.0128 |   57601.5138 | 17.95 | 0.10 | Rc     |  1600 
   Aug  2.0171 |   57602.5181 | 18.75 | 0.07 | V      |  1600 
   Aug  2.0399 |   57602.5409 | 17.94 | 0.12 | Rc     |  2000 
   Aug  2.9832 |   57603.4843 | 18.80 | 0.15 | V      |  3000 
   Aug  3.0266 |   57603.5278 | 18.11 | 0.18 | Rc     |  3600 
   Aug  4.0228 |   57604.5240 | 18.76 | 0.15 | V      |  2800 
   Aug  5.0234 |   57605.5247 | 18.19 | 0.20 | Rc     |  1800 
   Aug  5.9922 |   57606.4936 | 19.13 | 0.15 | V      |  3000 
   Aug  6.0368 |   57606.5382 | 18.39 | 0.12 | Rc     |  3000 
   Aug  6.9756 |   57607.4770 | 19.55 | 0.14 | V      |  3600 
   Aug  7.0275 |   57607.5289 | 18.85 | 0.17 | Rc     |  3000 
   Aug  8.0141 |   57608.5156 | 18.76 | 0.20 | Rc     |   200 
   Aug  8.0155 |   57608.5170 | 19.31 | 0.26 | V      |  6000