The Interior Angular Momentum of Core Hydrogen Burning Stars from Gravity-mode Oscillations

Abstract

A major uncertainty in the theory of stellar evolution is the angular momentum distribution inside stars and its change during stellar life. We compose a sample of 67 stars in the core-hydrogen burning phase with a log g value from high-resolution spectroscopy, as well as an asteroseismic estimate of the near-core rotation rate derived from gravity-mode oscillations detected in space photometry. This assembly includes 8 B-type stars and 59 AF-type stars, covering a mass range from 1.4 to 5 M ⊙ , i.e., it concerns intermediate-mass stars born with a well-developed convective core. The sample covers projected surface rotation velocities v sin i ∈ [9, 242] km s −1 and core rotation rates up to 26µHz, which corresponds to 50% of the critical rotation frequency. We find deviations from rigid rotation to be moderate in the single stars of this sample. We place the near-core rotation rates in an evolutionary context and find that the core rotation must drop drastically before or during the short phase between the end of the core-hydrogen burning and the onset of core-helium burning. We compute the spin parameter, which is the ratio of twice the rotation rate to the mode frequency (also known as the inverse Rossby number), for 1682 gravity modes and find the majority (95%) to occur in the subinertial regime. The ten stars with Rossby modes have spin parameters between 14 and 30, while the gravito-inertial modes cover the range from 1 to 15.

A Model of Rotating Convection in Stellar and Planetary Interiors. I. Convective Penetration

“…They provide a means for transporting angular momentum and mixing chemical species in these regions (e.g., Pantillon et al 2007;Mathis et al 2008;Mathis 2009;Lee et al 2014). They are one of the mechanisms that may explain the strong extraction of angular momentum in the Sun (e.g., Talon & Charbonnel 2005), in subgiant and red giant stars (e.g., Fuller et al 2014;Belkacem et al 2015a,b;Pinçon et al 2017), and in intermediate-mass and massive stars (e.g., Rogers 2015) as revealed by the weak differential rotation observed thanks to helio-and asteroseismology (e.g., García et al 2007;Beck et al 2012;Mosser et al 2012;Deheuvels et al 2012;Kurtz et al 2014;Saio et al 2015;Murphy et al 2016;Aerts et al 2017;Gehan et al 2018). However, their amplitude and frequency spectrum strongly depend on the properties of the turbulent convective flows that excite them stochastically at the radiation/convection interface and in the bulk of convective regions (e.g., Schatzman 1993;Zahn et al 1997;Rogers et al 2006;Belkacem et al 2009b;Lecoanet & Quataert 2013;Rogers et al 2013;Alvan et al 2014).…”

Asteroseismic masses, ages, and core properties of γ Doradus stars using gravito-inertial dipole modes and spectroscopy

“…The spin parameter for the gravito-inertial modes and Rossby modes of the stars in our sample ranges from 1 to 30 (cf., Fig. 2 of Aerts et al 2017). Given this broad range, it is not obvious to resort to analytical approximations for λ l,m,s in the case of γ Dor stars.…”

Three-dimensional Simulations of Massive Stars. I. Wave Generation and Propagation

“…IGWs are candidates for being the cause of some of the observed properties of stars that are poorly explained by current stellar models, such as the internal rotation structure of stars (Beck et al 2012;Aerts et al 2017a), stellar cores counter-rotating to their envelopes (Triana et al 2015;Rogers 2015), or the enhanced mass loss needed to explain certain classes of core-collapse supernovae (Quataert & Shiode 2012). Photometric observations suggest the presence of convectively generated IGWs in, at least, some massive stars since the observed velocity spectrum at the surface compares well to that obtained using numerical simulations of IGWs (Aerts & Rogers 2015;Bowman et al 2019).…”