Abstract
Abstract An interesting opportunity offered by the detection of stellar oscillations is the possibility to infer the internal rotation rate of a star through the so-called rotational splittings. Such seismic measurements remained rather scarce for hot B subdwarf (sdB) stars until the advent of space observations with the Kepler spacecraft. Nowadays, however, a number of rotation measurements have become available, offering a glimpse on the global rotational properties of sdB stars. Here, we briefly discuss what asteroseismology starts to reveal on the rotation rate of these stars. We also make connections with the internal rotation of red-giant and white-dwarf stars. In particular, we show that the very slow rotation rates derived for single sdB stars, and their similarities with the dynamical properties of the cores of red-clump stars, strongly suggest that they evolved from red-giants rather than merger events.We also point out that no more angular momentum seems to be lost by stellar cores throughout the helium burning phase until the cooling white-dwarf stage, indicating that all the braking occurs before, most likely during red-giant branch evolution.
Highlights
Twenty years ago, was discovered the first pulsating hot B subdwarf star (Kilkenny et al 1997), oscillating rapidly in pressure (p-)modes
We show that the very slow rotation rates derived for single sdB stars, and their similarities with the dynamical properties of the cores of redclump stars, strongly suggest that they evolved from red-giants rather than merger events
The nonradial oscillations observed in pulsating hot B subdwarfs of either p- or g-type offer, among other opportunities, the possibility to explore the dynamical properties of these stars through the very distinct signature that rotation leaves on their pulsation spectrum
Summary
Twenty years ago, was discovered the first pulsating hot B subdwarf (sdB) star (Kilkenny et al 1997), oscillating rapidly in pressure (p-)modes. A few years later, the detection of slower (P ∼ 0.5 − 4 h) oscillations, involving this time gravity (g)modes, led to the identification of a second class of pulsators among hot B subdwarfs : the V1093 Her stars (Green et al 2003). The nonradial oscillations observed in pulsating hot B subdwarfs of either p- or g-type offer, among other opportunities, the possibility to explore the dynamical properties of these stars through the very distinct signature that rotation leaves on their pulsation spectrum Despite this well known potential, seismic measurements of rotation remained relatively rare for sdB stars until quite recently, with the advent of high precision photometric monitoring from space.
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