Pulsational instability of pre-main-sequence models from accreting protostars II. Modelling echelle diagrams of $\delta$ Scuti stars without rotational splitting

TL;DR

This study improves asteroseismic modelling of pre-main-sequence delta Scuti stars by incorporating early accretion physics, leading to more accurate stellar parameters and better methods for analyzing pulsation spectra.

Contribution

It introduces an extensive grid of pre-main-sequence models with accretion physics and develops a simple algorithm for extracting echelle diagrams from observed pulsation frequencies.

Findings

Model grids with proper physics reduce systematic errors.

Application to HD 139614 yields different stellar parameters than previous studies.

Strong evidence favors a 6-day accretion model over a 10-day model.

Abstract

The physics of early stellar evolution (e.g. accretion processes) is often not properly included in the calculations of pre-main-sequence models, leading to insufficient model grids and hence systematic errors in the results. We aim to investigate current and improved approaches for the asteroseismic modelling of pre-main-sequence delta Scuti stars. We calculated an extensive grid of pre-main-sequence models including the early accretion phase and used the resulting equilibrium models as input to calculate theoretical frequency spectra. These spectra were used to investigate different approaches in modelling echelle diagrams to find the most reliable methods. By applying Petersen diagrams, we present a simple algorithm to extract echelle diagrams from observed pulsation frequencies. We show that model grids with insufficient input physics and imperfect modelling approaches lead to underestimated uncertainties and systematic errors in the extracted stellar parameters. Our re-discussion of HD 139614 leads to different stellar parameters than the ones derived by Murphy et al. (2021). We performed a model comparison between this previous investigation and our results by applying the Akaike and Bayesian information criteria. While the results with regard to our 10-d model are inconclusive, they show (very) strong evidence of a 6-d model with fixed accretion parameters (leading to almost identical stellar parameters to those of the 10-d model) to be preferred over the model applied by Murphy et al. (2021). In general, our modelling approach can provide narrow constraints on the stellar parameters (\Delta R ~ 0.05 R_\odot, \Delta log g <~ 0.01, and \Delta M_\star ~ 0.1 M_\odot). The extensively tested modelling approaches and automatic extraction of echelle diagrams should allow us to study many more pre-main-sequence delta Scuti stars in the future and lead to reliable stellar parameters.