The Pre-main Sequence: Challenges and Prospects for Asteroseismology

Abstract

Stars do not simply pop up on the main sequence. Before the stars arrive on the zero-age main sequence, they form in the collapses of molecular clouds, gain matter through accretion processes, and compress their cores until hydrogen can burn in full equilibrium. Although this evolutionary phase lasts a relatively short time, it is the imprint of these important physical processes that is often ignored by simplified assumptions. While asteroseismology offers a great tool to investigate these physical processes, studying pre-MS oscillations in turn has the potential to further advance the field. Asteroseismology of pre-main sequence stars faces observational and theoretical challenges. The remnants of their birth environment which is often still surrounding the young stars causes variability that can interfere with the signal of pulsations. The lack of long time-base satellite observations in addition limits the applications of the method. Theoretical models of pre-main sequence stars include several assumptions and simplifications that influence the calculation of pulsation frequencies and excitation properties of pulsation modes. Keeping all this in mind, the prospects for pre-main sequence asteroseismology are manifold. An improved understanding of the structure of young stellar objects has the potential to answer some of the open questions of stellar evolution, including angular momentum transport and the formation of magnetic fields. While gyrochronology, for example, struggles to determine the ages of the youngest clusters, pulsations in pre-main sequence stars can function as an independent age indicator yielding higher precision for single stars. The increasing interest of stellar astrophysics in general to investigate the formation and early evolution of stars and planets illustrates the growing importance of pre-main sequence asteroseismology. In this work we discuss its potential for an advancement of our understanding of stellar structure and evolution.

Revisiting the δ Scuti star FG Virginis using Kepler K2 and TESS data

“…They have spectral types A through mid F, effective temperatures 6400-8600 K (Uytterhoeven et al, 2011), and masses 1.4-2.7 M ⊙ (Bowman and Kurtz, 2018). Most are in the main-sequence (core hydrogen burning) or slightly post-main-sequence (burning hydrogen in a shell just outside the hydrogen-exhausted core) evolutionary phases, but they have also been found in the pre-main-sequequence phase (see, e.g., Zwintz and Steindl 2022;Murphy et al, 2021). δ Scuti stars pulsate with frequencies 5-50 c/d (Balona et al, 2015) in one or more radial and non-radial low-order pressure (p) modes, low-order gravity (g) modes, and modes having a mixture of p-and g-type nodes.…”