Asteroseismology of the pulsating extremely low-mass white dwarf SDSS J111215.82+111745.0: a model with $p$-mode pulsations consistent with the observations

TL;DR

This paper models the pulsations of the extremely low-mass white dwarf SDSS J111215.82+111745.0, providing evidence for $p$-mode pulsations and deriving stellar parameters consistent with observations.

Contribution

It presents the first asteroseismic model that includes $p$-mode pulsations for this white dwarf, aligning theoretical predictions with observed data.

Findings

Identification of $ ext{l}=1$ $g$-mode period spacing (~93.4 s)

Determination of stellar mass (~0.165 M_sun) and temperature (~9750 K)

Successful modeling of suspected $p$-modes consistent with observations

Abstract

SDSS J111215.82+111745.0 is the second pulsating extremely low-mass white dwarf discovered. Two short-period pulsations, 107.56 and 134.275 s, were detected on this star, which would be the first observed pressure mode ($p$-mode) pulsations observed on a white dwarf. While the two potential $p$-modes have yet to be confirmed, they make SDSS J111215.82+111745.0 an interesting object. In this work, we analyzed the whole set of seven periods observed on SDSS J111215.82+111745.0. We adopt three independent period-spacing tests to reveal a roughly 93.4 s mean period spacing of $\ell=1$ $g$-modes, which gives added credence to the $\ell=1$ identifications. Then we perform asteroseismic modeling for this star, in which the H chemical profile is taken as a variable. The stellar parameters $M=0.1650\pm0.0137$ $M_\odot$ and $T_\mathrm{eff}=9750\pm560$ K are determined from the best-fit model and the H/He chemical profiles are also defined. The two suspected $p$-modes are also well represented in the best-fit model, and both the stellar parameters and the pulsation frequencies are in good agreement with the values derived from spectroscopy.