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ASASSN-14du: optical spectroscopy indicates z=0

ATel #6311; S. Schulze (PUC, MAS), D. Malesani (DARK/NBI), J. P. U. Fynbo (DARK/NBI), B. Milvang-Jensen (DARK/NBI), D. Xu (DARK/NBI), Z. Cano (Univ. Iceland), P. Jakobsson (Univ. Iceland), Y. Martinez-Osorio (Uppsala University)
on 15 Jul 2014; 13:50 UT
Credential Certification: Daniele Malesani (malesani@dark-cosmology.dk)

Subjects: Optical, Request for Observations, Cataclysmic Variable, Nova, Star, Transient, Variables

Referred to by ATel #: 6313

We observed ASASSN-14du (Holoien et al., ATel #6308) with the 2.54-m Nordic Optical Telescope (NOT) equipped with ALFOSC on 2014 July 14. We obtained a single 30-s exposure in the SDSS r band starting at 20:59:54 UT. The source detected by Holoien et al. (ATel #6308) is clearly detected. We measure r(AB) = 16.76 +- 0.04 mag (calibrated against several SDSS stars).

We also obtained an optical low-resolution spectrum, starting at 21:24:45 UT. We used grism #4 covering the wavelength range from 3750 to 9000 AA, though wavelengths above 7000 AA are affected by fringing. The observation consisted of two individual spectra with a total exposure time of 2x800 s. The flux calibrated spectrum shows a blue continuum which can be fit with a power-law F_nu propto nu^0.7 in the range 4000-7000 AA. We identify several broad Balmer absorption lines at z = 0, starting from Hbeta and up to H9, where our spectrum is cut, as well as He I 4471. No Halpha is present. The FWHM of Hbeta and Hgamma is around 3200 km/s. No emission features are visible in our spectrum.

Our data indicate a transient in the Galaxy, or in its immediate proximity, and can exclude a super-luminous SN. We encourage further observations to monitor the evolution of this source.