A prescription for the asteroseismic surface correction

Abstract

In asteroseismology, the surface effect refers to a disparity between the observed and the modelled frequencies in stars with solar-like oscillations. It originates from improper modelling of the surface layers. Correcting the surface effect usually requires using functions with free parameters, which are conventionally fitted to the observed frequencies. On the basis that the correction should vary smoothly across the H–R diagram, we parameterize it as a simple function of surface gravity, effective temperature, and metallicity. We determine this function by fitting a wide range of stars. The absolute amount of the surface correction decreases with luminosity, but the ratio between it and νmax increases, suggesting the surface effect is more important for red giants than dwarfs. Applying the prescription can eliminate unrealistic surface correction, which improves parameter estimations with stellar modelling. Using two open clusters, we found a reduction of scatter in the model-derived ages for each star in the same cluster. As an important application, we provide a new revision for the Δν scaling relation that, for the first time, accounts for the surface correction. The values of the correction factor, fΔν, are up to 2% smaller than those determined without the surface effect considered, suggesting decreases of up to 4% in radii and up to 8% in masses when using the asteroseismic scaling relations. This revision brings the asteroseismic properties into an agreement with those determined from eclipsing binaries. The new correction factor and the stellar models with the corrected frequencies are available at https://www.github.com/parallelpro/surface.

Red Giant Rotational Inversion Kernels Need Nonlinear Surface Corrections

“…, and s = 0.002. Using a value of A ∼ 1 alters its pure p-modes by about 1 μHz at n max , which is roughly in the range of values that Li et al (2023) find to be needed for similar first-ascent red giants (see their Figure 3). This is also roughly the size of the correction needed to bring the radial and quadrupole modes of this model into agreement with their observed values.…”

“…While alternative, nonlinear, helioseismic inversion techniques exist (e.g., Marchenkov et al 2000), these so far have relied on specific features of analytic approximations to p-modes (Roxburgh & Vorontsov 1996), and are thus not yet suitable for use on mixed or g-modes. However, Li et al (2023) report that typical sizes of the asteroseismic surface effect, as calibrated on Kepler red giants, are indeed large enough to advance modes along avoided crossings. Therefore, as this fundamental assumption of linearity no longer applies, the results of OBR21 immediately imply that the surface term changes the shape of inversion kernels in red giants too.…”

“…Their pand g-mode frequencies have been calculated using the prescription of Ong & Basu (2020). For each of these models, we compute the core leakages that would result from assigning the eMOLA coefficients of Equation (6), as computed from the nominal mixed modes, to the modes and mixing fractions of the surface-corrected mixed modes, corrected according to the prescription of OBR21, and with coefficients for the pure p-modes of the two-term Ball & Gizon (2014) parameterization computed from the calibration of Li et al (2023). These are shown as a function of the relative g-mode density n n = D DP  max 2 1 , a proxy for evolution up the red-giant branch, in Figure 2.…”

Asteroseismology and Spectropolarimetry of the Exoplanet Host Star λ Serpentis

“…Using the oscillation frequencies listed in Table 1, the spectroscopic constraints on T eff and [M/H] from Brewer et al (2016), and the luminosity from Section 2.5, five teams attempted to infer the properties of λ Ser from asteroseismic modeling. A variety of stellar evolution codes and fitting methods were employed, including ASTEC/AMP (Christensen-Dalsgaard 2008; Metcalfe et al 2009), GARSTEC/ BASTA ( Weiss et al 2008;Aguirre Børsen-Koch et al 2022), MESA (Paxton et al 2015;Li et al 2023), and YREC (Demarque et al 2008). We found reasonable agreement between the results for the stellar radius and mass, with individual estimates ranging from R = 1.33 to 1.38 R e and M = 1.03 to 1.13 M e , but there was a significant spread in stellar age with inferences between 5.4 and 8.6 Gyr around a median value of 7.0 ± 0.8 Gyr.…”

Asteroseismic Modeling of 1153 Kepler Red Giant Branch Stars: Improved Stellar Parameters with Gravity-mode Period Spacings and Luminosity Constraints

“…The surface term is caused by incorrect modeling of the nearsurface layers in stellar code. Given that the properties' nearsurface layers largely correlate to global parameters, the surface term is expected to vary smoothly as a function of effective temperature, surface gravity, and metallicity (Trampedach et al 2017;Compton et al 2018;Jørgensen et al 2020;Ong et al 2021;Li et al 2023). The star sample in this work makes it possible to systematically study the surface term and its dependencies on surface features in a wide parameter range.…”