An analysis of spectroscopic, seismological, astrometric, and photometric masses of pulsating white dwarf stars

Abstract

Context. A central challenge in the field of stellar astrophysics lies in accurately determining the mass of stars, particularly when dealing with isolated ones. However, for pulsating white dwarf stars, the task becomes more tractable due to the availability of multiple approaches such as spectroscopy, asteroseismology, astrometry, and photometry, each providing valuable insights into the mass properties of white dwarf stars. Aims. Numerous asteroseismological studies of white dwarfs have been published, focusing on determining stellar mass using pulsational spectra and comparing it with spectroscopic mass, which uses surface temperature and gravity. The objective of this work is to compare these mass values in detail and, in turn, to compare them with the mass values derived using astrometric parallaxes or distances and photometry data from Gaia, employing astrometric and photometric methods. Methods. Our analysis involves a selection of pulsating white dwarfs with different surface chemical abundances that define the main classes of variable white dwarfs. We calculated their spectroscopic masses, compiled seismological masses, and determined astrometric masses. We also derived photometric masses, when possible. Subsequently, we compared all the sets of stellar masses obtained through these different methods. To ensure consistency and robustness in our comparisons, we used identical white dwarf models and evolutionary tracks across all four methods. Results. The analysis suggests a general consensus among the four methods regarding the masses of pulsating white dwarfs with hydrogen-rich atmospheres, known as DAV or ZZ Ceti stars, especially for objects with masses below approximately 0.75 M⊙, although notable disparities emerge for certain massive stars. For pulsating white dwarf stars with helium-rich atmospheres, called DBV or V777 Her stars, we find that astrometric masses generally exceed seismological, spectroscopic, and photometric masses. Finally, while there is agreement among the sets of stellar masses for pulsating white dwarfs with carbon-, oxygen-, and helium-rich atmospheres (designated as GW Vir stars), outliers exist, where mass determinations by various methods show significant discrepancies. Conclusions. Although a general agreement exists among different methodologies for estimating the mass of pulsating white dwarfs, significant discrepancies are prevalent in many instances. This shows the need to redo the determination of spectroscopic parameters and the parallax and/or improve asteroseismological models for many stars.