MODELING the ASTEROSEISMIC SURFACE TERM ACROSS the HR DIAGRAM

Abstract

Asteroseismology is a powerful tool that can precisely characterize the mass, radius, and other properties of field stars. However, our inability to properly model the near-surface layers of stars creates a frequency-dependent frequency difference between the observed and the modeled frequencies, usually referred to as the "surface term." This surface term can add significant errors to the derived stellar properties unless removed properly. In this paper, we simulate surface terms across a significant portion of the HR diagram, exploring four different masses (M = 0.8, 1.0, 1.2, and 1.5 M⊙) at five metallicities ([Fe H] = 0.5, 0.0, -0.5, -1.0, and -1.5) from the main sequence to red giants for stars with Teff < 6500 K and explore how well the most common ways of fitting and removing the surface term actually perform. We find that the two-term model proposed by Ball and Gizon works much better than other models across a large portion of the HR diagram, including the red giants, leading us to recommend its use for future asteroseismic analyses.