Speaker
Description
Type Ia supernovae (SNe Ia) are thermonuclear explosions of white dwarfs in binary systems, and have been widely used for astronomical distance measurements for decades. Despite their long history of observation however, there are many unknowns about the physical parameters of the progenitor star and the explosion mechanism itself. One of these unknowns is the presence of so-called high-velocity features (HVFs).
High velocity (25-30000 km/s) features are absorption lines of Ca II, and sometimes Si II that can be seen in the early spectra of SNe Ia at velocities significantly higher than that of the photosphere. First discovered in 1999, they have since been proven to be ubiquitous in SNe Ia. However, their exact origin still remains unclear to this day. They appear to form in a higher velocity layer above the photosphere, and show varying strengths and velocity evolution from object to object.
We used 15 years of early-phase optical/near-infrared spectra obtained by the Hobby-Eberly Telescope (HET) of 57 supernovae to determine the velocity, strength and evolution of these features.
We confirm a connection between the light-curve width and the strength (and velocity) of the HVFs, with brighter SNe Ia showing stronger (and faster) high velocity lines. Through our investigation, we conclude that HVFs are most likely a consequence of the explosion mechanism itself, and their further study could help constrain the explosion mechanism.