ABSTRACT

Supernovae (SNe), or stellar explosions, are important astronomical events for many reasons: they produce and distribute heavy atomic elements into the galaxy, and they can be used as indicators of distances to far-away galaxies, which is vital for studying cosmology. One of the major unsolved problems in supernova science is the nature of the progenitor of the explosion. A research group at Michigan State University (MSU) will attempt to better understand SNe by investigating the circumstellar medium (CSM) around supernovae. The CSM records the history of mass-loss in the millennia prior to explosion, and therefore is a key to determining SN progenitors. The investigators will focus on detecting atomic line emission at ultraviolet (UV) wavelengths associated with the interaction shock from SN ejecta impacting a CSM shell. They will use UV image archival databases and interpret derived fluxes in the context of published shell-interaction models. As part of the project, the researchers will work with the Charles Drew Science Scholars program at MSU and the National Astronomy Consortium to involve undergraduate students from diverse backgrounds in summer and academic year research in supernova science.

For Type Ia SNe, the CSM can reveal the identity of the mass-donor companion, which reveals the physics of both the binary interaction and supernova explosion. The single-degenerate (main sequence/red giant companion) and double-degenerate (white dwarf companion) channels are two dominant progenitor hypotheses. In recent years, SNe Ia have been discovered with detached shells of CSM that the ejecta impact months or years after explosion (i.e., delayed interaction). The origin of this material is unknown, but there are two likely possibilities which can distinguish between progenitor channels. In the single-degenerate channel, a SN may be preceded by multiple nova eruptions, which can form sub-solar-mass shells?while in the double-degenerate channel, a common envelope is expelled before the SN, forming a few-solar-mass shell. The investigators will search for more examples of delayed-interaction SNe Ia and use an appropriate theoretical framework to determine the range of properties of detached CSM shells. They will interpret derived fluxes in the context of published shell-interaction models, and will calculate the UV and optical emission line signals from the models to produce a grid of light curves whose luminosity and duration depend on the CSM mass, radius, extent, and geometry. By comparing these simulated light curves to data, they will calculate the probability of SNe Ia hosting CSM shells across a range of CSM properties. This will provide the most stringent constraints on the presence and properties of CSM shells around SNe Ia to date, and provide a rigorous test of the hypothesis that SNe Ia can occur while the ejected common envelope is still in the system.

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