An improved asteroseismic age of the rapid rotator Altair from TESS data

Abstract

Understanding the effects of rotation in stellar evolution is key to modelling early-type stars, half of which have equatorial velocities over 100 km/s. The nearby star Altair is an example of such fast-rotating stars, and furthermore, it has the privilege of being modelled by a detailed 2D concordance model that reproduces most of its observables. The aim of this paper is to include new asteroseismic frequencies to improve our knowledge of Altair, especially its age. We processed images of Altair obtained during July 2022 by the Transiting Exoplanet Survey Satellite using the halo photometry technique to obtain its light curve over this observation period. By analysing the light curve, we derived a set of 22 new frequencies in the oscillation spectrum of Altair and confirmed 12 previously known frequencies. Compared with model predictions, we could associate ten frequencies with ten axisymmetric modes. This identification is based on the modelled visibility of the modes. Moreover, nine of the modelled frequencies can be adjusted to simultaneously match their corresponding observed frequencies, once the core hydrogen mass fraction of the concordance model is set to $X_ core /X_ ini with ini =0.739$. Using the combined results of a 1D model computing the pre-main sequence and a 2D time-dependent model computing the main sequence, we find that this core hydrogen abundance sets the age of Altair to 88pm 10 Myrs, which is slightly younger than previous estimates.