This is NUTS!

The Ultraviolet (UV) transient sky is one of the next frontiers in time-domain astrophysics with several space mission concepts planned for the middle of the decade. UV wavelengths are typically associated with hot phenomena, but we are focused on their use in measuring shock breakout and shock cooling from core-collapse supernovae (CCSNe) at very early times. These extreme events correspond to the shock emerging from the surface of the progenitor. If properly sampled, the UV peaks can be used to constrain properties of the progenitor stars, including the energy per unit mass of the SN ejecta and the stellar radius. Our HST survey of GOODS-S (#16706) will will represent the deepest and fastest UV time-domain survey to date. The survey will reach a depth of >26 mag AB over 73 square arcmin with a cadence of 2 days over 6 epochs out to a redshift of 1.3. Coordinated observations with the deep, ground-based Subaru Hyper Supreme Cam (HSC) SN survey will allow us to pinpoint the time and location of SNe.

By measuring the time delay between any pair of gravitationally lensed images, we can constrain the expansion rate of the universe and test dark energy models. Variable quasars have been used in this way with great success, and it is now possible to extend this technique to gravitationally lensed supernovae (SNe). These targets are especially promising because their predictable light curves can deliver precise time delay measurements in a relatively short period. Active projects in this field include improving our ability to measure SN time delays, projecting future constraints obtainable from the Roman Space Telescope, and an HST ToO program to provide follow-up observations of any ground-based lensed SN discovery.

We are living in a golden age for time domain astronomy thanks to new all-sky unbiased surveys (e.g. ZTF, PSST, ASASSN, etc.) that have opened the door to the discovery of new and exotic astronomical transients. For example, tidal disruption events: the bright flares produced when an unfortunate star comes in too close to a supermassive black hole and gets subsequently torn apart. Or superluminous supernovae, rare explosions that can be up to 100 times brighter than “normal” supernovae. It’s been theorized that the most massive stars (those greater than 95 times the mass of the sun) will explode in a pair or pulsational-pair instability supernova (PPISN). This transient class remains mostly elusive, but some good candidate PPISNe have emerged from all-sky surveys. While other rare transients that we have been able to discover thanks to these surveys, we simply did not expect.

We are excited to be a party of successful Cycle 1 GO proposals for JWST (GO #1860 and 2666)! These programs will study dust in the supernova environment. A growing number of SN subclasses have recently begun to show evidence for mid-infrared emission in excess of the expected emission from standard radioactive component as the SN light-curve decays. The mid-IR excess is typically associated with dust, but the origin and heating mechanism of the dust remains relatively unconstrained. These observations will distinguish between newly formed ejecta dust and pre-existing dust in the circumstellar medium (CSM). Each result will have implications on our understanding of the late stages of pre-SN massive star evolution and the dust budget of the Universe.

The debate over the origin of stripped-envelope supernova explosions (i.e., SNe IIb, Ib, and Ic) continues to waver between single and binary stellar models. Binary star physics is important for our understanding of massive-star evolution and many areas of astrophysics, from galactic chemical evolution to gravitational wave detection, but the detailed physics (e.g., winds, mass exchange, rotation) remain unconstrained. Observationally, the field is past the point of considering individual, isolated systems. We are, for the first time, building a comprehensive, statistically complete sample of direct companion observations to measure the binary fraction, stellar type, and mass distribution. This exciting project is supported by HST GO 16165, 14075, 13648.

The origins, physical mechanisms, and diversity of supernovae (SNe) and other explosive transients remain shrouded in mystery. The high-cadence light curves of Kepler and TESS with unprecedented precision provides critical early time data, probing a window that is inaccessible to traditional ground-based SN surveys. With exquisite Kepler and TESS light curves in combination with ground-based follow-up, we will be able to (1) determine the types of companions to progenitors of SNe Ia using features in the early light curves; (2) explore the explosion physics of SNe using subtle features during their rise; (3) constrain the radius and properties of progenitor stars of core-collapse SNe using the signatures of shock break-out; and (4) constrain the light curves of exotic and rare events like superluminous SNe (SLSNe), tidal disruption events (TDEs), kilonovae (KNe), and fast transients.