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Further spectroscopy of the 2017 outburst of PT And

ATel #10692; S. C. Williams (Lancaster), M. J. Darnley (LJMU)
on 1 Sep 2017; 11:12 UT
Credential Certification: Steven Williams (scw@astro.ljmu.ac.uk)

Subjects: Optical, Cataclysmic Variable, Nova, Transient

We obtained our first spectrum of the 2017 outburst of PT And (AT 2017gay) on 2017 Aug 17.05 UT and reported the results in ATel #10647. Another spectrum, taken 2017 Aug 24.16 with the Nordic Optical Telescope was reported by ATel #10672. Here we report a further spectrum of the outburst taken 2017 Aug 30.19 UT with the SPRAT spectrograph (resolution R ~ 350; Piascik et al. 2014) on the Liverpool Telescope (LT; Steele et al. 2004).

This new LT spectrum taken Aug 30.19 shows Hβ absorption. There are no emission lines present in the spectrum. We use the acquisition images of the SPRAT spectrograph (which uses a longpass filter, blocking light shortward of 4000 Å) to estimate the light curve of PT And. The photometric data is calibrated against R-band standards from Massey et al. (2006). On 2017 Aug 17.05 UT we measure PT And to be at a magnitude of 16.1 +/- 0.1 and on 2017 Aug 30.19 UT we measure it at 17.6 +/- 0.1.

Given the fading of the transient by around 1.5 magnitudes, the spectrum rules out it being a nova, as one would expect strong Balmer emission lines in addition to emission lines from one or more of Fe II, N, He I and O I. PT And therefore must be a foreground Galactic dwarf nova and not a recurrent nova in M31.