A probabilistic method for detecting solar-like oscillations using meaningful prior information

Abstract

Context. Current and future space-based observatories such as the Transiting Exoplanet Survey Satellite (TESS) and PLATO are set to provide an enormous amount of new data on oscillating stars, and in particular stars that oscillate similar to the Sun. Solar-like oscillators constitute the majority of known oscillating stars and so automated analysis methods are becoming an ever increasing necessity to make as much use of these data as possible.Aims. Here we aim to construct an algorithm that can automatically determine if a given time series of photometric measurements shows evidence of solar-like oscillations. The algorithm is aimed at analyzing data from the TESS mission and the future PLATO mission, and in particular stars in the main-sequence and subgiant evolutionary stages. Methods. The algorithm first tests the range of observable frequencies in the power spectrum of a TESS light curve for an excess that is consistent with that expected from solar-like oscillations. In addition, the algorithm tests if a repeating pattern of oscillation frequencies is present in the time series, and whether it is consistent with the large separation seen in solar-like oscillators. Both methods use scaling relations and observations which were established and obtained during the CoRoT, Kepler, and K2 missions. Results. Using a set of test data consisting of visually confirmed solar-like oscillators and nonoscillators observed by TESS, we find that the proposed algorithm can attain a 94.7% true positive (TP) rate and a 8.2% false positive (FP) rate at peak accuracy. However, by applying stricter selection criteria, the FP rate can be reduced to ≈ 2%, while retaining an 80% TP rate.

Catalogue of solar-like oscillators observed by TESS in 120-s and 20-s cadence

“…Starting with a smaller set of targets that were identified as the most likely to oscillate above the 30-min FFI Nyquist frequency (Schofield et al 2019), we have identified 400 candidate solar-like oscillators by eye. These were used to optimise a detection algorithm presented in Nielsen et al (2022; henceforth referred to as N22). We then passed the remaining stars observed during the aforementioned sectors to this tuned pipeline.…”

FRA–A new fast, robust, and automated pipeline for the detection and measurement of solar‐like oscillations in time‐series photometry of red‐giant stars

“…The novelty of FRA lies in its ability to assess whether or not a given star exhibits oscillations. To that matter, FRA performs a totally blind search for $$$ {\nu}_{\mathrm{max}} $$$, independent from the $$$ \Delta \nu $$$ measurement and using a different approach than that used by Nielsen et al (2022). We describe in the following the different steps we implemented.…”

“…TESS completed its 2‐year, all‐sky nominal survey in July 2020 and is dramatically increasing the number of red giants with detected oscillations, which is expected to be on the order of $$$ 1{0}^5 $$$ (Campante et al 2016; Hon et al 2021; Hon et al 2022; Mackereth et al 2021; Silva Aguirre et al 2020; Stello et al 2022). TESS enables in particular the measurement of the two global asteroseismic properties $$$ {\nu}_{\mathrm{max}} $$$ and $$$ \Delta \nu $$$, for red giants (Hon et al 2021, 2022; Mackereth et al 2021; Stello et al 2022) as well as for main‐sequence (MS) and subgiant (SG) stars (Nielsen et al 2022). The frequency of maximum oscillation power $$$ {\nu}_{\mathrm{max}} $$$ is proportional to the surface gravity $$$ g $$$ and effective temperature $$$ {T}_{\mathrm{eff}} $$$ of the star such that (Brown et al 1991; Kjeldsen & Bedding 1995) $$$$ {\nu}_{\mathrm{max}}\propto \frac{g}{\sqrt{T_{\mathrm{eff}}}}.$$…”

“…On the other side, the method of Hon et al (2018) aims at mimicking a visual detection of oscillations by an expert eye and does not rely on statistical criteria. Nielsen et al (2022) developed a new method for evaluating the probability that stars observed by TESS exhibit solar‐like oscillations, based on the successive search for $$$ {\nu}_{\mathrm{max}} $$$ and $$$ \Delta \nu $$$, both required to be consistent with what is expected for a solar‐like oscillator. Their method targets the 2‐mins cadence TESS data, hence MS and SG stars.…”

Dealing with large gaps in asteroseismic time series

“…This is because the power spectrum is calculated with a step size that must sample the frequency resolution, and this is inversely proportional to the total duration of the time series (including the gap). Because solar-like oscillators have finite mode lifetimes, it has become tempting to close large gaps by shifting time stamps and we are aware of several cases in which this has been done, both in published works (e.g., Hekker et al 2010;Nielsen et al 2022) and in papers in preparation. The justification is that mode lifetimes are much shorter than the gap, so shifting segments should not have much effect on the power spectrum.…”