On the Prospects for Detection and Identification of Low-Frequency Oscillation Modes in Rotating B Type Stars

TL;DR

This paper investigates how rotation influences the observability of high-order g- and mixed r/g-modes in rotating B-type stars, highlighting the impact on detection methods in light and radial velocity measurements.

Contribution

It introduces a nonadiabatic formalism based on the traditional approximation to analyze mode visibility in rotating stars, providing new insights into mode detection prospects.

Findings

Rotation reduces g-mode visibility in light variation.

Rotation enhances detection of modes in radial velocity.

Mixed modes are more detectable at high rotation speeds.

Abstract

We study how rotation affects observable amplitudes of high-order g- and mixed r/g-modes and examine prospects for their detection and identification. Our formalism, which is described in some detail, relies on a nonadiabatic generalization of the traditional approximation. Numerical results are presented for a number of unstable modes in a model of SPB star, at rotation rates up to 250 km/s. It is shown that rotation has a large effect on mode visibility in light and in mean radial velocity variations. In most cases, fast rotation impairs mode detectability of g-modes in light variation, as Townsend (2003b) has already noted, but it helps detection in radial velocity variation. The mixed modes, which exist only at sufficiently fast rotation, are also more easily seen in radial velocity. The amplitude ratios and phase differences are strongly dependent on the aspect, the rotational velocity and on the mode. The latter dependence is essential for mode identification.