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Asiago spectroscopic classification of ASASSN-17fd and PS17ckw

ATel #10306; L. Tomasella, S. Benetti, E. Cappellaro, A. Pastorello, P. Ochner, M. Turatto (INAF-OAPd), G. Terreran (INAF-OAPd, QUB, Univ. di Padova)
on 22 Apr 2017; 08:41 UT
Distributed as an Instant Email Notice Supernovae
Credential Certification: Stefano Benetti (stefano.benetti@oapd.inaf.it)

Subjects: Optical, Supernovae

The Asiago Transient Classification Program (Tomasella et al. 2014, AN, 335, 841) reports the spectroscopic classification of ASASSN-17fd in Ark481 (AT 2017dfb), discovered during the ongoing All Sky Automated Survey for SuperNovae (ASAS-SN), cf. Atel #10300, and PS17ckw in SDSS J164539.02+013713.1 (AT 2017dgd), discovered by Pan-STARRS1 survey.

The observations were performed with the Asiago 1.82 m Copernico Telescope equipped with AFOSC (range 340-820 nm; resolution 1.4 nm).

Survey Name   | IAI Name      | Discovery date (UT) | Discovery mag | Observation (UT)    |  Type  | z        | Notes| 
ASASSN-17fd   | SN 2017dfb    |2017-04-19.51        |      16.5     |2017-04-22.02        |  SN Ia | 0.025955 | (1)  | 
PS17ckw       | SN 2017dgd    |2017-04-19.52        |      17.76    |2017-04-22.05        |  SN IIb| 0.022    | (2)  | 

(1) The spectrum is consistent with that of a Type Ia SN 1991T-like events before maximum light, at a redshift 0.0259, as deduced from the position of Halpha emission from the host galaxy (which is in agreement with the redshift of the host galaxy, Ark481 provided by Falco et al. 1999, PASP 111, 438), and in agreement with Cannizzaro et al. 2017 (Atel #10298). The strong Na I doublet absorption at the host galaxy redshift (we measured an EW ~ 2.15 A, which corresponds to a reddening of E(B-V)~0.3 when applying the Turatto et al. 2003 relation, published in ESO ASTROPHYSICS SYMPOSIA "From Twilight to Highlight: The Physics of Supernovae"), suggests large line-of-sight dust absorption.

(2) The red continuum and spectral features are best fitted by the type IIb supernovae before maximum. The spectrum is dominated by deep H-alpha and He-I 587.6 nm absorptions.

Classification were done with GELATO (Harutyunyan et al. 2008, A&A, 488, 383) and SNID (Blondin and Tonry 2007, ApJ, 666, 1024). The Asiago classification spectra are posted at the website http://sngroup.oapd.inaf.it.