Reggae: A Parametric Tuner for PBJam, and a Visualization Tool for Red Giant Oscillation Spectra

Abstract

The upcoming second release of PBJam -- a software instrument for fitting normal modes ("peakbagging") -- supplements the simple power-spectrum model used in the first version to additionally constrain other features. Dipole ($\ell = 1$) modes, which had been excluded in the initial version of the tool, are now specifically included. The primary samples of the PLATO mission consist mainly of main-sequence and subgiant stars, so PBjam implements a single parameterisation of dipole mixed-mode frequencies that reduces to pure p-modes in the former, and is suitable for use with the latter, outside the red-giant"asymptotic"regime. In keeping with the overall philosophy of PBjam's design, PBjam 2 will specify prior distributions on these parameters empirically, through predetermined values found for existing samples of solar-like oscillators. While the red-giant asymptotic regime has been extensively characterised observationally, the nonasymptotic construction for subgiants here has not, requiring us to construct this prior sample ourselves. To assist in this task, we built a tool -- Reggae -- to manually fine-tune and fit the dipole-mode model, and check the quality of both our initial guesses and fitted solutions. We have found it very helpful both for these tuning and visualisation tasks, and also as a didactic aid to understanding the dipole mixed-mode parameters. Moreover, no other tools currently exist for performing these tasks in the nonasymptotic parameterisation considered here. As such, we release Reggae publicly in advance of this update to PBjam, as we believe the community will benefit from access to such a visualisation tool. This will also assist future users of PBjam in devising ad-hoc prior constraints on the mixed-mode parameters, should they wish to perform mode identification for anomalous stars.