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Candidate M31N 2010-08a is not a nova

ATEL # 2841; E. Barsukova, A. Valeev, O. Sholukhova, S. Fabrika (Special Astrophysical Observatory), W. Pietsch (MPE, Germany), K. Hornoch (Astronomical Institute, Ondrejov, Czech Republic)
on 12 Sep 2010; 18:08 UT
Password Certification: Barsukova E.A. (bars@sao.ru)

Subjects: Optical, Nova, Variables, Stars

Possible nova in M31 galaxy M31N 2010-08a was discovered by R. Ferrando on Aug. 8.16 UT (mag about 18.5) from five 120-s unfiltered CCD frames (limiting mag 20.0) taken with a 0.40-m f/10 Ritchey-Chretien reflector (CBET 2412). Koichi Nishiyama (Kurume, Japan) and Fujio Kabashima (Miyaki, Japan) note that a star of red mag 18.8 in the USNO-B1.0 catalogue is located at R.A. = 00 43 28.269, Decl. = +41 41 25.26, J2000.0 (CBET 2425). This object is visible at this location on an image from 2009 Aug. 26.13, that was posted by R. Ferrando (CBET 2412). Also, Kamil Hornoch, Astronomical Institute, Ondrejov, reports a finding this object on archival images taken by J. Gallagher and P. Garnavich using the 0.91-m telescope at Kitt Peak (CBET 2425). Taking into account its presence on images from different years and its R-I = 1.85 mag, K. Hornoch has suggested that the object is not a nova, but very likely a red long-period variable star.

We obtained a spectrum of M31N 2010-08a on Sept. 7.348 UT with the Russian 6-m telescope (BTA) equipped with the SCORPIO spectral camera. The spectral range is 400-780 nm, the spectral resolution is 1.3 nm. Really, this candidate is not a nova. It has no emission lines but it has a typical spectrum of the supergiant of M5-M7 type. There are absorption bands of TiO and VO. According to the photometry it has the change of brightness in R-band about 1.4 mag. Rational nature of this flared up star may be established after additional investigations of its progenitor and its future behavior. This may be an oxygen-type Mira star if it will show periodic changes of brightness with an amplitude more than 2.5 mag in V-band and emission Balmer lines in its maximum light. As now we may attribute this object to LB-type according to GCVS variability types - slow irregular variables of late spectral types.

Spectrum of M31N 2010-08a


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