Spectral signatures of H-rich material stripped from a non-degenerate companion by a Type Ia supernova

Abstract

The single-degenerate scenario for Type Ia supernovae should yield metal-rich ejecta that enclose some stripped material from the non-degenerate H-rich companion star. We present a large grid of non-local thermodynamic equilibrium steady-state radiative transfer calculations for such hybrid ejecta and provide analytical fits for the Hα luminosity and equivalent width. Our set of models covers a range of masses for 56Ni and the ejecta, for the stripped material (Mst), and post-explosion epochs from 100 to 300 d. The brightness contrast between stripped material and metal-rich ejecta challenges the detection of H I and He I lines prior to ~100 d. Intrinsic and extrinsic optical depth effects also influence the radiation emanating from the stripped material. This inner denser region is marginally thick in the continuum and optically thick in all Balmer lines. The overlying metal-rich ejecta blanket the inner regions, completely below about 5000 Å, and more sparsely at longer wavelengths. As a consequence, Hβ should not be observed for all values of Mst up to at least 300 days, while Hα should be observed after ~100 d for all Mst ≥ 0.01 M⊙. Observational non-detections capable of limiting the Hα equivalent width to <1 Å set a formal upper limit of Mst < 0.001M⊙. This contrasts with the case of circumstellar-material (CSM) interaction, not subject to external blanketing, which should produce Hα and Hβ lines with a strength dependent primarily on CSM density. We confirm previous analyses that suggest low values of order 0.001 M⊙ for Mst to explain the observations of the two Type Ia supernovae with nebular-phase Hα detection, in conflict with the much greater stripped mass predicted by hydrodynamical simulations for the single-degenerate scenario. A more likely solution is the double-degenerate scenario, together with CSM interaction, or enclosed material from a tertiary star in a triple system or from a giant planet.

Nebular Hα emission in Type Ia supernova 2016jae

“…Using the relation introduced by Tucker et al (2020), which is based on the models of Botyánszki et al (2018), we can derive a mass of the hydrogen stripped material (M st ) of 0.002 M from the two nebular spectra of SN 2016jae. Similarly, following Dessart et al (2020) and considering the estimated 56 Ni mass for SN 2016jae in Section 3.1 (0.15 M 13 ), we obtain a comparable value for M st of 0.003 M . This estimated M st , is similar to that found for SNe 2018cqj and 2018fhw, and as already notice by Dessart et al (2020), it is much lower than expected (>0.1 M ) for standard models of SD scenarios for SNe Ia (see, e.g., Marietta et al 2000;Liu et al 2012;Botyánszki et al 2018).…”

“…Similarly, following Dessart et al (2020) and considering the estimated 56 Ni mass for SN 2016jae in Section 3.1 (0.15 M 13 ), we obtain a comparable value for M st of 0.003 M . This estimated M st , is similar to that found for SNe 2018cqj and 2018fhw, and as already notice by Dessart et al (2020), it is much lower than expected (>0.1 M ) for standard models of SD scenarios for SNe Ia (see, e.g., Marietta et al 2000;Liu et al 2012;Botyánszki et al 2018). We attempted to understand the evolution with time of the Hα luminosity considering the measurements for the three SNe with hydrogen detected.…”

“…It is expected that the stripped material has expansion velocities ≤ 1000 km s −1 (see, e.g., Mattila et al 2005;Liu et al 2012) that is consistent with the estimated velocity from the Hα line in SN 2016jae. In the recent simulations, Dessart et al (2020) found that the hydrogen stripped from a non-degenerate companion star can remain undetected at epochs <50d, begin to emerge at 100d and well visible between 150d and 200d (at this time the metal-rich ejecta become increasingly more transparent and faint). This is fully consistent with our observations of SN 2016jae.…”

The Whisper of a Whimper of a Bang: 2400 Days of the Type Ia SN 2011fe Reveals the Decay of $^{55}$Fe

“…Interactions between the donor star and the impacting ejecta are expected to produce several observational signatures (e.g., Wheeler et al 1975) including irregularities in the rising light curve (Kasen 2010), supersoft Xray emission during accretion onto the WD (e.g., Langer et al 2000;Schwarz et al 2011), and radio and/or Xray emission produced by the high-velocity ejecta interacting with nearby circumstellar material (CSM). Additionally, the high-velocity ejecta will deposit energy into the companion star (Marietta et al 2000;Pan et al 2012a;Boehner et al 2017) increasing its luminosity for several thousand years after explosion (e.g., Pan et al 2012b;Shappee et al 2013a) and stripping/ablating 0.1 − 0.5 M of material from the star (Mattila et al 2005;Botyánszki et al 2018;Dessart et al 2020).…”

Helium stars exploding in circumstellar material and the origin of Type Ibn supernovae

“…7). This result is reminiscent of the differential optical depth effects affecting Hβ (which overlaps with the Fe ii line forest) and Hα (which sits in an opacity hole) in models of SNe Ia that contain in their innermost ejecta layers stripped material from a companion (Dessart et al 2020a).…”