Optical spectra of Nova SMC 2016a at quiescence

ATel #12385; M. Orio (National Institute of Astrophysics Padova, Italy and University of Wisconsin at Madison), S. Ciroi (Padova University), E. Aydi (Michigan State University), D. Buckley (South African Astronomical Observatory)
on 14 Jan 2019; 17:01 UT
Credential Certification: Marina Orio (orio@astro.wisc.edu)

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Nova SMC 2016a (ATel#9621, #9622, #9628, #9631, #9635, #9684, #9688) was observed with the SALT telescope and the Robert Stobie spectrograph on 2018 December 10 (JD 2458463.31150463) for 1775 s, on 2018 December 11 (JD 2458464.30116898) for 1622 s, and on 2018 December 13 (JD 2458466.306875 ) for 1200 s. The observations covered the 4465-7520 Å spectral range. We measured a strong He II λ 4686 line red-shifted in all spectra by about 175 km/s, with an error that we estimate to be less than 30 km/s. The other measurable lines are H α, which appears to have a complex profile with at least three components with different red-shift exceeding 180 km/s, and strong, blue-shifted broad lines of nebular [O III] at 5007 Å and 4959 Å. The O [III] lines are associated with the ejecta, while the He II λ 4686 line is typical of accretion disks and is usually produced close to the central object. We suggest that the red-shift of the He II λ 4686 line is mainly due to the systemic velocity of a binary system that is an intrinsic member of the Small Magellanic Cloud, thus proving that, during outburst, the nova exceeded Eddington luminosity for 3 months or longer (see Aydi et al. 2018, MNRAS 474, 2679; Orio et al. 2018, ApJ, 862, 164). The spectrum bears a strong resemblance to that of the "neon nova" Sct 1991, observed on 1992-4-4 by Williams et al. 1994 (ApJS, 90, 297), but a coronal line of [Fe X] at 6375 Å still observed with low S/N in that nova at the given date, is not measurable in our spectra and was not detected even in outburst by Aydi et al. 2018.