Collaborative Research: The Seismic Technique for Accurate White Dwarf Parameters

A detailed understanding of white dwarf stars is important for a range of astrophysical questions, from post-main sequence exoplanet habitability to Type Ia supernova cosmology. Successful inference in these areas is limited by our knowledge of white dwarf properties. White dwarf masses and effective temperatures are most commonly estimated with the so-called spectroscopic technique. However, there is significant evidence that these results suffer systematic errors from incomplete physics of the stellar atmosphere models, as well as from the methods used to fit the observed absorption line profiles. The study of the vibrational modes of pulsating white dwarfs provides a way to sensitively map their interior structures. A research collaboration between the City University of New York Queens College and Penn State Scranton will apply a new “seismic technique” to bring seismic and astrometric data together to provide accurate white dwarf masses and effective temperatures. Undergraduate students will contribute to various aspects of the proposed work as part of the AstroCom NYC program, which fosters the careers of students from disadvantaged backgrounds with research and career mentoring. Classroom labs will be published and incorporated into the curriculum of the astronomy stream of the Freshman Research Initiative (FRI) program at the University of Texas at Austin. FRI provides hands-on learning opportunities to first-year undergraduate students from underrepresented backgrounds who wish to pursue STEM careers. The need for independent methods to determine the global parameters of white dwarf stars motivates the development of a new “seismic technique” for characterizing pulsating white dwarfs. This technique combines precision measurements of white dwarf pulsation periods with Gaia parallaxes in a probability estimate of mass and effective temperature (Teff). The measured quantities of mean pulsation period spacing and absolute G-band magnitude each permit solutions that follow monotonic trends in the mass-Teff plane, but in opposing directions. Analyzed together, these values reveal a unique solution. Focusing on the interface between data and models, the seismic technique will achieve accurate measurements due to its relative simplicity compared to the line broadening physics of the common “spectroscopic technique.” Reliable uncertainties will be obtained by marginalizing over a range of potential white dwarf interior structures and interstellar extinction values. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.