High-resolution spectroscopic observations of ASASSN-18fv

ATel #11468; L. Izzo (IAA-CSIC), P. Molaro, E. Mason (INAF-OATs), M. Della Valle (INAF-OAC), L. Vanzi (PUC-Chile), P. Bonifacio (GEPI-Obs. Paris), M. Hernanz (ICE-CSIC), Z. Cano, A. de Ugarte Postigo, C. Thoene (IAA-CSIC), G. Cescutti, P. Selvelli (INAF-OATs)
on 23 Mar 2018; 07:59 UT
Distributed as an Instant Email Notice Novae
Credential Certification: Luca Izzo (luca.izzo@gmail.com)

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We report spectroscopic observations of the bright transient ASAS-SN 18fv (ATel #11454, #11456, #11457, #11460) obtained on 2018 Mar 22 starting at UT 03:27 from Paranal and using the UVES spectrograph mounted on the VLT-UT2. The observations cover the spectral range between 3050 and 9500 Angstrom with a resolving power of ~65000. A preliminary analysis of the combined spectrum shows a bright continuum, resembling an A-type MS star peaking around 5300 Angstrom, characterised by the presence of hundreds of narrow absorption features and remarkable Balmer and Paschen jumps.  We note the presence of a Halpha P-Cygni profile with blue-shifted heliocentric velocity with a minimum at v $\sim$ -340 km/s, and a narrow emission line characterised by a measured FWZI = 670 km/s and FWHM = 325 km/s. The brightest non-Balmer emission line is the O I 7773 line. We also report the presence of several multiplets of Fe II, with a P-Cygni absorption centered at a heliocentric velocity of v $\sim$ -250 km/s. This velocity is also reported for the Na I doublet. The interstellar Na doublet show three resolved components at heliocentric velocities of -0.2, -3.1 and -13.2 km/s respectively. The lack of a strong blue continuum, that is however typical of classical nova outburst, and the low expansion velocities suggest a possible different nature for this object. The presence of many narrow absorptions also suggests a similarity with other peculiar explosions, like the luminous red variable V4332 Sgr (Martini et al. 1999), the possible luminous red novae V838 Mon and V1309 Sco (Tylenda et al. 2011, Mason et al. 2010) or the 'helium-flash' explosion observed in the Sakurai object (Duerbeck and Benetti 1996). Further spectroscopic observations are important to clarify the nature of this very interesting target.