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NASA's exoplanet-hunting TESS space telescope moonlights in studying stars

NASA's TESS mission was designed to identify exoplanets, but that's no reason not to use its data to better understand stars as well.
NASA's TESS mission was designed to identify exoplanets, but that's no reason not to use its data to better understand stars as well.
(Image: © MIT)

In order to study planets, you have to look at stars, so you may as well analyze what you see.

Astrophysicists are doing just that with the data gathered by NASA's Transiting Exoplanet Survey Satellite (TESS). That spacecraft has spent a year and a half staring at bright, nearby stars, looking for the blips in brightness that can reveal alien worlds. But these dips can also represent different types of stellar hiccups, which means that TESS data is also a treasure trove for scientists studying how stars work.

"Really, TESS has been secretly all along a stellar activity and stellar variability mission," James Davenport, an astronomer at the University of Washington, said last month during the 235th meeting of the American Astronomical Society, held in Honolulu.

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TESS data takes the form of light curves, lines that each track the brightness of a star over time. An extremely quiet star with no transiting planets would look like a more-or-less flat line — the more active the star or the more transiting planets that periodically block its light, the more jagged the light curve.

"There's so many cool, wiggly things here," Davenport said of a collection of light curves from the first year of TESS observations.

Some of those cool, wiggly things are individual stars. A host of stellar features can cause light curves to act up. Flares are unpredictable bursts that cause spikes in a star's light curve. Stars rotate, so when a dark sunspot develops, it drifts across the face of the star as seen by TESS, causing the light curve to periodically dip. That rhythm lets scientists calculate how quickly the star is spinning, and perhaps its age.

Other light curves represent pairs of stars that twirl around each other. If that dance happens at a convenient angle compared to TESS's orientation, making it an eclipsing binary, the spacecraft can measure the difference in total light as it sees first two stars, then one, then both again.

That said, these dances look inconveniently similar to the TESS mission's other type of target, exoplanets. "There are so many eclipsing binaries, and I know this is particularly the bane of the other half of the TESS mission," Davenport said. "These things tend to show up as looking like really big planets, but they're amazing."

For both rotating stars and eclipsing binaries, TESS's surveying work could help scientists find a whole lot more of these types of stellar spectacles. But astrophysicists turning to TESS data are limited by the same mission constraint that lets the spacecraft study so many different stars: Every four weeks or so, the spacecraft pivots, studying a new stretch of the sky.

Such a pattern means that TESS can't really identify something like our sun, which takes 25 days to rotate, as an object of astrophysical interest. The slow-paced objects it can study are those conveniently located where TESS's imagery bands overlap, at the poles. Here, the spacecraft can study stars for months on end, potentially illuminating even more languid stars.

"I think TESS is arguably as impactful for stars as it is for exoplanets," Davenport said. "TESS is going to change what we know about nearby bright stars in our galaxy."

Email Meghan Bartels at mbartels@space.com or follow her @meghanbartels. Follow us on Twitter @Spacedotcom and on Facebook.

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  • rod
    Admin said:
    In order to study planets, you have to look at stars, so you may as well analyze what you see.

    NASA's exoplanet-hunting TESS space telescope moonlights in studying stars : Read more

    "Other light curves represent pairs of stars that twirl around each other. If that dance happens at a convenient angle compared to TESS's orientation, making it an eclipsing binary, the spacecraft can measure the difference in total light as it sees first two stars, then one, then both again. That said, these dances look inconveniently similar to the TESS mission's other type of target, exoplanets. "There are so many eclipsing binaries, and I know this is particularly the bane of the other half of the TESS mission," Davenport said. "These things tend to show up as looking like really big planets, but they're amazing."

    The study of binary star systems is very important in astronomy. Binary stars like Sirius A and B that are visual binaries, gravity and elliptical orbits and masses can be measured and checked with high accuracy, same for well documented eclipsing binary star systems. This is not the chief mission of TESS which is focused on exoplanets but I think it is good to find and document various binary star systems that TESS sees so others can follow up.
    Reply
  • rod
    Another note. The report says "Astrophysicists are doing just that with the data gathered by NASA's Transiting Exoplanet Survey Satellite (TESS). That spacecraft has spent a year and a half staring at bright, nearby stars, looking for the blips in brightness that can reveal alien worlds. But these dips can also represent different types of stellar hiccups, which means that TESS data is also a treasure trove for scientists studying how stars work."

    Bright, nearby stars are very interesting that are confirmed with exoplanets now. This site, The Extrasolar Planets Encyclopaedia, shows a total of 4173 exoplanets confirmed as of 03-Feb-20. I did a MS SQL query for bright stars with apparent magnitudes +1.15 to +6.0. 155 exoplanets reported for duty and many are quite large. The average mass is nearly 12.8 Jupiters. The eccentricities are large too, ranging 0 to 0.76, distances 10 to 959 light-years from Earth. I am looking forward to more reports on exoplanets from TESS.
    Reply
  • N2Space
    You might want to mention that TESS has also discovered/observed objects in our own solar system that occasionally occlude another star.
    Reply