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We present a comprehensive analysis of oscillations of the helium-rich white dwarf DBV star EPIC 248705247 (SDSS J102106.69+082724.8). We extract the light curves from 79.7 days of K2 Campaign 14 data and identify 21 independent frequencies, including three complete and three incomplete dipole modes, with an average frequency splitting of 20.37 ± 0.40 μ Hz. Our analyses reveal a rotation period of EPIC 248705247 of approximately 6.82 ± 0.07 hr, making it one of the most rapidly rotating DBV stars currently known. We utilize the White Dwarf Evolution Code (WDEC) to compute models to look for the seismic best-fitted model, yielding the following stellar parameters: M / M ⊙ = 0.650 ± 0.003, T eff = 23,660 ± 68 K, log (M env / M *) = − 2.01 ± 0.01 and log (M He / M *) = − 4.90 ± 0.05 . We also explore the phenomenon of mode trapping, as well as the potential influence of a weak magnetic field. We find that this star is located near the red edge of the theoretical instability strip of DBVs. Hence, our asteroseismological analysis of EPIC 248705247 provides the properties and behaviors of a rapidly rotating DBV. [ABSTRACT FROM AUTHOR]

We present observations and analyses of eight white dwarf stars (WDs) that have accreted rocky material from their surrounding planetary systems. The spectra of these helium-atmosphere WDs contain detectable optical lines of all four major rock-forming elements (O, Mg, Si, and Fe). This work increases the sample of oxygen-bearing WDs with parent body composition analyses by roughly 33%. To first order, the parent bodies that have been accreted by the eight WDs are similar to those of chondritic meteorites in relative elemental abundances and oxidation states. Seventy-five percent of the WDs in this study have observed oxygen excesses implying volatiles in the parent bodies with abundances similar to those of chondritic meteorites. Three WDs have oxidation states that imply more reduced material than found in CI chondrites, indicating the possible detection of Mercury-like parent bodies, but are less constrained. These results contribute to the recurring conclusion that extrasolar rocky bodies closely resemble those in our solar system, and do not, as a whole, yield unusual or unique compositions. [ABSTRACT FROM AUTHOR]