The interaction of Type Iax supernova ejecta with a helium companion star

Abstract

Type Iax supernovae (SNe Iax) are an important sub-luminous class of SNe Ia. However, their progenitors and explosion mechanism have not been understood yet. It has been suggested that SNe Iax may be produced from weak deflagration explosions of Chandrasekhar-mass white dwarfs (WDs) in binary systems with a helium (He) star donor. In such progenitor systems, the stripped He companion material caused by the ejecta-companion interaction is expected to present some He features in their late-time spectra. However, the detection of He lines in late-time spectra of SNe Iax has not yet been successful, which gives an upper limit on the amount of stripped He mass of 2 × 10 −3 − 0.1 M . In this work, we study the interaction between SN Iax ejecta and a He star companion by performing three-dimensional hydrodynamical simulations with a weak pure deflagration explosion model. We find that about 4 × 10 −3 M of He material can be stripped off from the companion star by SN explosion, which is very close to (or lower than) the observational upper-limit on the total stripped He mass in SNe Iax. We, therefore, conclude that non-detection of He lines in late-time spectra of SNe Iax could be reasonably explained if they are indeed resulted from weak pure deflagration explosions of Chandrasekhar-mass WDs in progenitor systems with a He star donor.

Still Brighter than Pre-Explosion, SN 2012Z Did Not Disappear: Comparing Hubble Space Telescope Observations a Decade Apart

“…We again see no evidence in any of our HST photometry for an excess due to this line for SN 2012Z. Foley et al (2013) suggest that SN Iax could arise from He star donor systems, so we consider emission from He I 5876Å as a possible source of the excess V-band flux that could arise if He was stripped off of the donor star (see Zeng et al 2020). We fit a blackbody with a single He emission line to our photometry.…”

“…In Figure 10, we compare our observations to the models from (Zeng et al 2020; radiative transfer to be presented in Zeng et al in prep.). The solid line shows the optical flux which is too faint to contribute to our observations significantly.…”

“…As SN 2011fe enters its nebular phase, it becomes bluer, while the SNe Iax remain red for several hundred days. The solid line shows the optical luminosity from the helium star companion from Zeng et al (2020). The optical luminosity is much too low to contribute our late-time observations.…”

Type Iax supernovae from deflagrations in Chandrasekhar mass white dwarfs

“…The single degenerate scenario suffers the problem of stripped hydrogen or helium from the companion star: It is expected that the explosion of the WD will remove material from its donor which should be seen in the late-time spectra (Pakmor et al 2008;Lundqvist et al 2013;Bauer et al 2019). Since SNe Iax are less energetic than normal SNe Ia, Liu et al (2013) and Zeng et al (2020) argue that the stripped hydrogen or helium might stay below the detection limit. Magee et al (2019) also look for helium features in SNe Iax and find that their NIR spectra are compatible with only very small amounts of helium and that it is easier to detect in fainter models.…”