A simple method to measure νmax for asteroseismology: application to 16 000 oscillating Kepler red giants

Abstract

ABSTRACT The importance of νmax (the frequency of maximum oscillation power) for asteroseismology has been demonstrated widely in the previous decade, especially for red giants. With the large amount of photometric data from CoRoT (Convection, Rotation, and planetary Transits), Kepler, and Transiting Exoplanet Survey Satellite, several automated algorithms to retrieve νmax values have been introduced. Most of these algorithms correct the granulation background in the power spectrum by fitting a model and subtracting it before measuring νmax. We have developed a method that does not require fitting to the granulation background. Instead, we simply divide the power spectrum by a function of the form $\rm \nu ^{-2}$, to remove the slope due to granulation background, and then smooth to measure νmax. This method is fast and simple and avoids degeneracies associated with fitting. The method is able to measure oscillations in 99.9 per cent of previously studied Kepler red giants, with a systematic offset of 1.5 per cent in νmax values that we are able to calibrate. On comparing the seismic radii from this work with Gaia, we see similar trends to those observed in previous studies. Additionally, our values of width of the power envelope can clearly identify the dipole mode suppressed stars as a distinct population, hence as a way to detect them. We also applied our method to stars with low νmax (0.19–18.35 µHz) and found that it works well to correctly identify the oscillations.