A hidden white dwarf found

Changes in the arrival time of pulsations (top) of the 342-s pulsation period in the stripped red giant BPM 36430, along with residuals after subtracting the best-fitting sinusoid from the data (bottom). The data reveal that this stripped red giant is being orbited by an unseen, cool, white dwarf that is at least 42% as massive as the Sun (credit Smith et al. 2022).

In September 2022, a manuscript led by undergraduate student at High Point University, Bryce Smith, and including members of the BUWD group has been published (Smith, Barlow, Rosenthal, Hermes & Schaffenroth 2022), which announces the discovery of an unseen, cool white dwarf using the stable pulsations of a stripped red giant star. This work implements the same timing method used to find the first exoplanets around a pulsar — looking for light-travel-time changes in an object with a steady pulsation period. The discovery was confirmed with spectroscopy showing the star really is wobbling from an unseen companion. The pulsation-timing changes were first discovered by a high-school student working with the BUWD group, Ben Rosenthal, who joined us as a RISE intern in July 2021; Ben is now an undergraduate at Yale University. The work has been accepted for publication in the Astrophysical Journal; a short thread on the discovery can be found here.

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