NASA’s TESS enables breakthrough study of perplexing stellar pulsations

Astronomers have detected elusive pulsation patterns in dozens of young, rapidly rotating stars thanks to data from NASA’s Transiting Exoplanet Survey Satellite (TESS). The discovery will revolutionize scientists’ ability to study details like the ages, sizes and compositions of these stars — all members of a class named for the prototype, the bright star Delta Scuti.

“Delta Scuti stars clearly pulsate in interesting ways, but the patterns of those pulsations have so far defied understanding,” said Tim Bedding, a professor of astronomy at the University of Sydney. “To use a musical analogy, many stars pulsate along simple chords, but Delta Scuti stars are complex, with notes that seem to be jumbled. TESS has shown us that’s not true for all of them.”

Geologists studying seismic waves from earthquakes figured out Earth’s internal structure from the way the reverberations changed speed and direction as they traveled through it. Astronomers apply the same principle to study the interiors of stars through their pulsations, a field called asteroseismology.

Sound waves travel through a star’s interior at speeds that change with depth, and they all combine into pulsation patterns at the star’s surface. Astronomers can detect these patterns as tiny fluctuations in brightness and use them to determine the star’s age, temperature, composition, internal structure and other properties.

To determine if order exists in Delta Scuti stars’ apparently chaotic pulsations, astronomers needed to observe a large set of stars multiple times with rapid sampling. TESS monitors large swaths of the sky for 27 days at a time, taking one full image every 30 minutes with each of its four cameras. This observing strategy allows TESS to track changes in stellar brightness caused by planets passing in front of their stars, which is its primary mission, but half-hour exposures are too long to catch the patterns of the more rapidly pulsating Delta Scuti stars. Those changes can happen in minutes.

But TESS also captures snapshots of a few thousand pre-selected stars — including some Delta Scuti stars — every two minutes. When Bedding and his colleagues began sorting through the measurements, they found a subset of Delta Scuti stars with regular pulsation patterns. Once they knew what to look for, they searched for other examples in data from Kepler, which used a similar observing strategy. They also conducted follow-up observations with ground-based telescopes, including one at the W.M. Keck Observatory in Hawaii and two in the global Las Cumbres Observatory network. In total, they identified a batch of 60 Delta Scuti stars with clear patterns.

“This really is a breakthrough. Now we have a regular series of pulsations for these stars that we can understand and compare with models,” said co-author Simon Murphy, a postdoctoral researcher at the University of Sydney. “It’s going to allow us to measure these stars using asteroseismology in a way that we’ve never been able to do. But it’s also shown us that this is just a stepping-stone in our understanding of Delta Scuti stars.”

Source: “NASA’s TESS enables breakthrough study of perplexing stellar pulsations” NASA, 13 May 2020. <https://www.nasa.gov/feature/goddard/2020/nasa-s-tess-enables-breakthrough-study-of-perplexing-stellar-pulsations>

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