A method to identify the companion stars of type Ia supernovae in young supernova remnants

Abstract

We propose a method to identify the companion stars of type Ia supernovae (SNe Ia) in young supernova remnants (SNRs) by recognizing distinct features of absorption lines due to Fe I appearing in the spectrum. If a sufficient amount of Fe I remains in the ejecta, Fe I atoms moving toward us absorb photons by transitions from the ground state to imprint broad absorption lines exclusively with the blue-shifted components in the spectrum of the companion star. To investigate the time evolution of column depth of Fe I in the ejecta, we have performed hydrodynamical calculations for SNRs expanding into the uniform ambient media, taking into account collisional ionizations, excitations, and photo-ionizations of heavy elements. As a result, it is found that the companion star in Tycho's SNR will exhibit observable features in absorption lines due to Fe I at $\lambda \lambda =371.9935$ nm and 385.9911 nm if a carbon deflagration SN model is taken. However, these features may disappear by taking another model that emits a few times more intense ionizing photons from the shocked outer layers. To further explore the ionization states in the freely expanding ejecta, we need a reliable model to describe the structure of the outer layers.

arXiv comment5 pages, 2 figures, accepted for the publication of The Astrophysical Journal

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• Subaru high-resolution spectroscopy of Star G in the Tycho supernova remnant
• Searching for a Companion Star of Tycho's Type Ia Supernova with Optical Spectroscopic Observations
• Search for surviving companions in type Ia supernova remnants
• Stellar Binary Companions to Supernova Progenitors
• Investigation of the Progenitors of the Type Ia Supernovae Associated With the LMC Supernova Remnants 0505-67.9 and 0509-68.7
• No Surviving SN Ia Companion In SNR 0509-67.5: Stellar Population Characterization and Comparison To Models