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STScI's 2019 Spring Symposium

T. Temim (ttemim[at]stsci.edu) co-chair, and the SOC

This past April, 140 astronomers from over a dozen countries attended the Spring Symposium at STScI entitled The Deaths and Afterlives of Stars. Stellar deaths involve violent and often rapid expulsions of matter and energy, a process that itself represents an initial condition for many astrophysical topics. The rich diversity of stellar outcomes, their connections to progenitor properties, and the influence of these afterlife processes on shaping galaxies remain among the most exciting fields of astrophysics today, and have been further sparked by the discovery of new classes of transients and the first detections of gravitational waves.

The program consisted of 19 invited and 33 contributed talks, as well as 65 electronic posters that were displayed during the coffee breaks. The SOC successfully assembled a speaker list with balanced gender and career stage representation. Roughly half of the invited speakers and ~37% of the total number of speakers were women. We also had excellent international representation, with half of the speakers coming from institutions outside of the United States.

The wide range of topics covered at this year's Spring Symposium brought together leading experts on the late evolution, death, and aftermath of both low- and high-mass stars. The first day was kicked off by review talks summarizing the current theoretical understanding of which stars undergo explosions. The afternoon session featured talks on the physical effects that control stellar death, such as rotation, metallicity, and binarity.

The second day of the Symposium focused on the various processes through which stars end their lives, from stellar mass loss of low‐ to intermediate-mass stars to extreme supernovae and black hole progenitors detected through gravitational waves. We heard about fascinating observations of UV resonance line echoes from a shell around a hydrogen-poor superluminous supernova. As different parts of the ejected shell light up at different times due to differing path lengths, the shell's physical properties can be derived and compared to theoretical models. In this case, the characteristics are consistent with a shell ejection caused by pulsational pair-instability and point to an astonishingly massive progenitor star of about 115 M.

The symposium concluded with a session on the aftermath of stellar death, covering topics such as compact object mergers, origin of the chemical elements, dust, planetary nebulae, supernova remnants, and Galactic winds. One of the highlights was a perplexing result about the progenitor of the Cas A supernova remnant, which resulted from a stripped-envelope supernova. Based on the properties of the Gaia-identified cluster from which Cas A's progenitor likely originated, the progenitor could not have been massive enough to blow away its envelope in a wind. Since deep searches have not yet detected a companion star, the remaining explanation for envelope stripping is a very compact companion, making Cas A a possible future source of gravitational waves.

On the last day there were several talks discussing detections of gravitational wave counterparts (i.e., kilonovae). This science segued into a trailing two-day STScI Workshop on Enabling Multi-Messenger Astrophysics (EMMA).  On the first day of the workshop (and one day after the Symposium) one of the most unique compact object mergers was detected with LIGO: a black hole–neutron star merger. This exciting event gave the attendees a chance to execute everything they were learning in real time.

We have many people to thank for the success of the 2019 Spring Symposium, including the invaluable administrative support from Martha Devaud and Sherita Hannah, co-chair Martha Boyer, Jason Kalirai, who served as chair before moving to APL, and the other members of the SOC (Ori Fox, Andrew Fruchter, Suvi Gezari, Tuomas Kangas, Daniel Kasen, Emily Levesque, Armin Rest, and Beth Sargent).

View the 2019 Spring Symposium agenda and webcast.