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Asiago spectroscopic classification of AT 2016cxa and SN 2016cxb

ATel #9182; L. Tomasella, A. Pastorello, S. Benetti, E. Cappellaro, N. Elias-Rosa, P. Ochner, L. Tartaglia, G. Terreran, M. Turatto, S. Yang, (INAF OAPd); S. Ascenzi (INAF OAR, Uni. Roma, Tor Vergata)
on 23 Jun 2016; 09:08 UT
Distributed as an Instant Email Notice Supernovae
Credential Certification: Enrico Cappellaro (enrico.cappellaro@oapd.inaf.it)

Subjects: Optical, Supernovae

The Asiago Transient Classification Program (Tomasella et al. 2014, AN, 335, 841) reports the spectroscopic observations of AT 2016cxa and SN 2016cxb (discovered by Pan-STARRS1, aka PS16cvb and PS16cvc, respectively), obtained with the Asiago 1.82 m Copernico Telescope (+AFOSC; range 340-820 nm; resolution 1.4 nm).

Name                  | Discovery UT      | Obs. Date UT    | z        |   Type    | Phase                 |Notes  
AT 2016cxa            |  20160619.60      | 20160623.01     | 0        |   CV      | —                     | (1)   
SN 2016cxb            |  20160619.51      | 20160623.07     | 0.029    |   Ia      | a few days before max | (2)   

1) The spectrum shows a blue continuum with narrow Halpha, Hbeta and Hgamma in emission at the rest wavelength. The object is therefore not a supernova but most likely a cataclismic variable (CV). The Balmer decrement from the emission components, with the presence of a fairly strong Halpha and higher members of the series showing progressively stronger absorptions, confirms the classification as a dwarf nova. Also the He I emission at 587.6 nm is clearly visible.

2) A good match is obtained with the Type Ia SN 1998bu (Hernandez et al. 2000, MNRAS, 319, 223), a few days before maximum light. From the position of the minimum of the Si II 635nm feature, we infer an expansion velocity of 11100 km/s for the ejected material.

Classification was performed using 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.