Researchers from the Yunnan Observatories of the Chinese Academy of Sciences (CAS) have conducted a detailed asteroseismic analysis on an extremely low-mass white dwarf (WD) that exhibits suspected pressure mode (p-mode) pulsations. They not only detect the abundance profiles inside the WD, but also provide theoretical support for the reality of the p-modes.
The study was published in The Astrophysical Journal.
Some WDs have been found to exhibit pulsations. One type of pulsation is the p-mode with high frequency, and the other is the gravity mode (g-mode) with low frequency.
The periods of p-mode pulsations are usually in the order of seconds or less on WDs, which makes it a challenge to detect these pulsations. However, for low-mass WDs, the periods of p-mode pulsations can be as long as 100 seconds and has an observable amplitude.
SDSS J111215.82+111745.0 is an extremely low-mass WD. Two shortperiod pulsations, 107.56 seconds and 134.275 seconds, were detected on this star. If the reality of these two suspected p-mode pulsations is confirmed, they would be the first p-mode pulsations observed on a WD.
In this study, the researchers tried to provide strong support for the confirmation of these suspected p-mode pulsations through modeling and analysis.
They made a detailed asteroseismic modeling for SDSS J111215.82+111745.0, in which the hydrogen abundance profile was taken as a variable. They took the whole set of seven pulsating periods (two p-modes and five g-modes) into account and fitted them with the models’ eigenfrequencies.
The two suspected p-modes were well represented in the best-fit model. They have found a model with p-mode pulsations consistent with the periods observed on SDSS J111215.82+111745.0, which provides theoretical support for the reality of the two p-mode pulsations.
Moreover, the main parameters, M = 0.1650 ± 0.0137 solar mass and Teff = 9750 ± 560 K, and the chemical profiles of this star were determined from the best-fit model.
The stellar parameters determined from their model were in good agreement with that derived from spectroscopy and with the results of other asteroseismic analysis.
Jie Su et al, Asteroseismology of the Pulsating Extremely Low-mass White Dwarf SDSS J111215.82 + 111745.0: A Model with p-mode Pulsations Consistent with the Observations, The Astrophysical Journal (2023). DOI: 10.3847/1538-4357/aca533
Chinese Academy of Sciences
Theoretical support for reality of pressure mode pulsations on a white dwarf (2023, February 24)