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SALT high-resolution optical spectroscopy of ASASSN-18pe

ATel #11878; E. Aydi, L. Chomiuk, J. Strader (MSU), D. A. H. Buckley (SAAO), A. Bahramian (Curtin), M. J. Darnley (LJMU), A. Kawash, (MSU) K. Stanek, C. Kochanek (OSU), B. Shappee (Hawaii), & J. L. Prieto (UDP/MAS)
on 21 Jul 2018; 16:12 UT
Credential Certification: Elias Aydi (eaydi@saao.ac.za)

Subjects: Optical, Cataclysmic Variable, Transient

We report on high-resolution optical spectroscopy of ASASSN-18pe which was reported as a possible cataclysmic variable on a slow rise to eruption by Strader et al. (2018, ATel #11867).

We obtained a 1200 s spectrum of this object under the SALT Large Science Program on transients on 2018 July 19.2 (HJD 2458319.2), using the High Resolution Spectrograph (HRS; Crause et al. 2014, Proc. SPIE, 91476) mounted on the Southern African Large Telescope (SALT). Observations were taken in the LR mode of HRS, covering a spectral range of 3800-8900 Å at a resolution of R = 14000. The data were reduced with the SALT HRS MIDAS pipeline (Kniazev et al. 2016, MNRAS 459, 3068).

The spectrum shows a very blue continuum with a strong He II emission at 4686#8491 characterised by a single emission peak, a FWHM ~ 180 ± 10 km/s, and a heliocentric corrected Vr ~ 115 ± 5 km/s. The other lines of the Pickering series at 4542Å and 5412Å are also present in emission showing a similar Vr but are much weaker. Halpha also shows an emission feature characterised by a FWHM ~ 150 ± 10 km/s and Vr ~ 95 ± 5 km/s. The flux ratio of (He II/Halpha) is around 2.3. Hbeta shows a weak emission feature superimposed on a relatively broad absorption feature (FWHM ~ 1300 ± 200 km/s). The emission feature might be associated with He II at 4859Å. Hgamma is also present in absorption. We also identify weak emission lines of He I at 6678Å and 7065Å with Vr ~ 115 km/s and H I at 8598Å, 8665Å, and 8750Å with Vr between 160 and 180 km/s. The EW of the Na I D interstellar absorption doublet is consistent with a relatively low extinction towards the source (Av ~ 0.2) in fair agreement with the Galactic Extinction maps. The unusually strong He II 4686 emission and the photometric behaviour reported in ATels #11867 and #11875 are worth further investigation.