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Abstract: Helium core white dwarfs WDs with mass M <~ 0.20 Msun undergo several Gyrsof stable hydrogen burning as they evolve. We show that in a certain range ofWD and hydrogen envelope masses, these WDs may exhibit g-mode pulsationssimilar to their passively cooling, more massive carbon-oxygen corecounterparts, the ZZ Cetis. Our models with stably burning hydrogen envelopeson helium cores yield g-mode periods and period spacings longer than thecanonical ZZ Cetis by nearly a factor of 2. We show that core composition andstructure can be probed using seismology since the g-mode eigenfunctionspredominantly reside in the helium core. Though we have not carried out a fullynonadiabatic stability analysis, the scaling of the thermal time in theconvective zone with surface gravity highlights several low-mass helium WDsthat should be observed in search of pulsations: NLTT 11748, SDSS J0822+2753,and the companion to PSR J1012+5307. Seismological studies of these He core WDsmay prove especially fruitful, as their luminosity is related via stablehydrogen burning to the hydrogen envelope mass, which eliminates one modelparameter.



Autor: Justin D. R. Steinfadt, Lars Bildsten, Phil Arras

Fuente: https://arxiv.org/



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