Asteroseismology of One of the Most Rapidly Rotating DBV Stars: EPIC 248705247

Abstract 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, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>env</mml:mi> </mml:mrow> </mml:msub> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>*</mml:mo> </mml:mrow> </mml:msub> <mml:mo stretchy="false">)</mml:mo> <mml:mo>=</mml:mo> <mml:mo>−</mml:mo> <mml:mn>2.01</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.01</mml:mn> </mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>He</mml:mi> </mml:mrow> </mml:msub> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>*</mml:mo> </mml:mrow> </mml:msub> <mml:mo stretchy="false">)</mml:mo> <mml:mspace width="0.25em"/> <mml:mo>=</mml:mo> <mml:mo>−</mml:mo> <mml:mn>4.90</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.05</mml:mn> </mml:math> . 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.