From solarlike to mira stars: a unifying description of stellar pulsators in the presence of stochastic noise
Abstract
We discuss and characterize the power spectral density properties of a model aimed at describing pulsations in stars from the mainsequence to the asymptotic giant branch. We show that the predicted limit of the power spectral density for a pulsation mode in the presence of stochastic noise is always well approximated by a Lorentzian function. While in stars predominantly stochastically driven the width of the Lorentzian is defined by the mode lifetime, in stars where the driving is predominately coherent the width is defined by the amplitude of the stochastic perturbations. In stars where both drivings are comparable, the width is defined by both these parameters and is smaller than that expected from pure stochastic driving. We illustrate our model through numerical simulations and propose a welldefined classification of stars into predominantly stochastic (solarlike) and predominately coherent (classic) pulsators. We apply the model to the study of the Mira variable U Per, and the semiregular variable L2 Pup and, following our classification, conclude that they are both classical pulsators. Our model provides a natural explanation for the change in behaviour of the pulsation amplitudeperiod relation noted in several earlier works. Moreover, our study of L2 Pup enables us to test the scaling relation between the mode line width and effective temperature, confirming that an exponential scaling reproduces well the data all the way from the main sequence to the asymptotic giant branch, down to temperatures about 1000 K below what has been tested in previous studies.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 December 2020
 DOI:
 10.1093/mnras/staa2932
 arXiv:
 arXiv:2009.09873
 Bibcode:
 2020MNRAS.499.4687C
 Keywords:

 stars: evolution;
 stars: interiors;
 stars: oscillations;
 Astrophysics  Solar and Stellar Astrophysics;
 Astrophysics  Astrophysics of Galaxies
 EPrint:
 11 pages, 8 figures, accepted for publication in MNRAS