Supernova 2016hnk
Theoretical astrophysicists have no shortage of ways they can blow up white dwarfs (WDs). One such model is the helium shell double detonation: a WD accretes helium from a companion, which then detonates on the stellar surface and leads to a second detonation of the entire star. The resulting SN can take a variety of forms and these simulations have predicted what the explosions spectroscopic and photometric evolution should be, if such an event is discovered. Below I summarize a recent paper on the discovery of SN 2016hnk, which is best modeled by a helium shell detonation scenario.
Figure 1
SN 2016hnk is a peculiar thermonuclear supernova that shows many observational similarities to both Type Ia SNe and Calcium-rich transients. It is intrinsically red in color, has a low luminosity relative to other SNe Ia and its spectra are dominated by high velocity Calcium lines that continue out to late-times.
Figure 2
Left, a 2D visualization of a helium shell double detonation model by Polin et al. 2019a. Here the first shell detonation happens on the WD edge and then triggers a second detonation of the star’s core. This model will pollute the SN ejecta with heavy elements that will suppress the radiation coming from “bluer” wavelengths.
Figure 3
SN 2016hnk is observationally distinct from typical WD explosions e.g., SNe Ia. Consequently, we model its light curve (right) with the helium shell detonation of a WD below the Chandrasekhar mass limit. The model shown in green is the result of a 0.85 Msun WD that detonates with 0.02 Msun of helium on its surface. This model is consistent with other wavelengths outside of i-band photometry shown in orange.
Figure 4
Remarkably, this helium shell model in green also reproduces the observed spectral evolution of SN 2016hnk at early (left) and late-times (shown in paper). SN 2016hnk is now the third observed helium shell detonation of a WD and future sky surveys will most likely find many more for us to study!