DiRAC Fellow Keaton Bell is coordinating an international collaboration of asteroseismologists to study the brightness variations of pulsating white dwarf stars recorded by the Transiting Exoplanet Survey Satellite.
The Transiting Exoplanet Survey Satellite (TESS) is capable of much more than its name suggests. It orbits the Earth, recording the brightness of millions of stars in search of temporary dimming caused by exoplanets orbiting across the faces of their hosts, blocking small amounts of starlight from reaching us. While these data promise to reveal thousands of new planets, they are also a treasure trove for stellar astrophysics research. DIRAC Researcher and NSF Postdoctoral Fellow Keaton Bell coordinates an international subgroup of the TESS Asteroseismic Science Collaboration that is making the most of TESS observations of pulsating white dwarf stars. He led the first publication from the group, “TESS first look at evolved compact pulsators: asteroseismology of the pulsating helium-atmosphere white dwarf TIC 257459955,” which was recently published in Astronomy & Astrophysics.
White dwarf stars are the final remnant objects that 97% of all stars in our Galaxy (including the Sun) will become when they run out of fuel, and their properties betray details of the complicated late stages of stellar evolution. A million times denser than the Sun, white dwarf stars also provide remote cosmic laboratories for studying the physics of matter under extreme compression. Keaton utilizes a powerful method for sounding the interiors of these compact stars called asteroseismology, meaning seismology of the stars. Some white dwarf stars spontaneously vibrate with waves that pass through and are affected by their deep interiors. These stellar pulsations cause miniscule brightness variations that afford asterosesimologists the rare opportunity to probe below a star’s surface, similar to how waves from earthquakes can be used to map the interior of the Earth.
TESS’s month-long recording of white dwarf target TIC 257459955 allowed the team to accomplish some of the most precise measurements ever obtained of white dwarf pulsation frequencies. TIC 257459955 also turns out to exhibit one of the richest sets of pulsations observed from any white dwarf, providing great potential for constraining its properties. The paper includes two independent interpretations of these measurements led by stellar theorists from both the National University of La Plata in Argentina and Penn State Worthington Scranton. Collaborating through the working group, these teams came together for the first time to directly compare the results of their methods. They find close agreement that reinforces confidence in white dwarf asteroseismology, and the research collaboration is now proceeding to analyze dozens of additional pulsating white dwarf stars that TESS is observing.