Department of Physics and Astronomy
Stony Brook University
7:30 pm; via Zoom
Friday, September 03, 2021

Stellar Variability as viewed by TESS

Prof. Frederick Walter

We tend to think of stars as unvarying - the Sun is steady, and at night, though the stars twinkle, the sky changes little. Astronomers know that stars are not constant. The Sun's luminosity modulates by about 0.2% over the 11 year solar cycle. Betelgeuse, a red supergiant, faded by about a factor of 3 in early 2020, before recovering. Novae and supernovae explode, cataclysmic variables sputter chaotically, eclipsing stars occult each other, and starspots cross the surfaces of cool stars.

To this multi-act circus visible from the ground, we now add the discovery space afforded by the TESS satellite. TESS, the Transiting Exoplanet Survey Satellite, watches about 8% of the sky at any one time continuously for about 27 days. From above the atmosphere, there are no day/night cycles and no weather to interrupt observations, and no twinking except what the stars do on their own. The variability has given us fantastic new insights into the inner working of stars, and of their interactions with circumstellar matter. I shall focus on two types of stars:
- the T Tauri stars, which provide hints as to how stars and planets form and grow, and
- the magnetically active young suns, which give us clues to the most energetic magnetic flaring (and warnings about our Sun).

Prof. Walter, a resident of East Setauket, studies star birth, stellar weather, and star death using the Chandra and XMM-Newton X-ray observatories, the Hubble Space Telescope, TESS, and telescopes in Arizona, Hawaii and Chile. He has been a professor of Astronomy at Stony Brook since 1989.