No Stripped Companion Material in the Nebular Spectrum of the “Two-Component” Type Ia Supernova ASASSN-18bt. (arXiv:1811.09635v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Tucker_M/0/1/0/all/0/1">M. A. Tucker</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Shappee_B/0/1/0/all/0/1">B. J. Shappee</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Wisniewski_J/0/1/0/all/0/1">J. P. Wisniewski</a>

We analyze a KeckI/LRIS nebular spectrum taken 268 days after $B$-band
maximum of ASASSN-18bt (SN~2018oh), a Type Ia supernova (SN Ia) observed by
{it K2} at the time of explosion. ASASSN-18bt exhibited a two-component rise
to peak brightness, possibly the signature of an interaction between the SN
ejecta and a large ($gtrsim 20~R_odot$) nearby, non-degenerate companion. We
search for emission signatures of stripped material from a non-degenerate
companion in the nebular spectrum and find no evidence for any unbound
material. We place an upper limit of $< 0.006~M_odot$ on the amount of stripped/ablated H-rich material that could go undetected in our spectrum, effectively ruling out all hydrogen-rich donor stars. Additionally, we place a more tentative upper limit on HeI emission in the observed spectrum of $lesssim 0.02~M_odot$ which also rules out helium star companions. Our deep limits rule out a non-degenerate companion as the explanation for the early-time feature in ASASSN-18bt.

We analyze a KeckI/LRIS nebular spectrum taken 268 days after $B$-band
maximum of ASASSN-18bt (SN~2018oh), a Type Ia supernova (SN Ia) observed by
{it K2} at the time of explosion. ASASSN-18bt exhibited a two-component rise
to peak brightness, possibly the signature of an interaction between the SN
ejecta and a large ($gtrsim 20~R_odot$) nearby, non-degenerate companion. We
search for emission signatures of stripped material from a non-degenerate
companion in the nebular spectrum and find no evidence for any unbound
material. We place an upper limit of $< 0.006~M_odot$ on the amount of
stripped/ablated H-rich material that could go undetected in our spectrum,
effectively ruling out all hydrogen-rich donor stars. Additionally, we place a
more tentative upper limit on HeI emission in the observed spectrum of
$lesssim 0.02~M_odot$ which also rules out helium star companions. Our deep
limits rule out a non-degenerate companion as the explanation for the
early-time feature in ASASSN-18bt.

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