MOST detects SPBe pulsations in HD 127756 & HD 217543: Asteroseismic rotation rates independent of vsini

TL;DR

This study uses MOST satellite data to detect SPBe pulsations in HD 127756 and HD 217543, revealing rotation rates independent of vsini and showing they are near critical rotation speeds.

Contribution

The paper presents the first detection of SPBe pulsations in these stars and derives their rotation rates independently of vsini using asteroseismic analysis.

Findings

Detected multiple pulsation frequencies consistent with nonradial g-modes.

Derived rotation rates close to critical velocity for both stars.

Pulsations are caused by opacity-driven modes near the iron bump.

Abstract

The MOST (Microvariability and Oscillations of Stars) satellite has discovered SPBe (Slowly Pulsating Be) oscillations in the stars HD 127756 (B1/B2 Vne) and HD 217543 (B3 Vpe). For HD 127756, 30 significant frequencies are identified from 31 days of nearly continuous photometry; for HD 217543, up to 40 significant frequencies from 26 days of data. In both cases, the oscillations fall into three distinct frequency ranges, consistent with models of the stars. The variations are caused by nonradial g-modes (and possibly r-modes) distorted by rapid rotation and excited by the opacity mechanism near the iron opacity bump. A comparison of pulsation models and observed frequency groups yields a rotation frequency for each star, independently of vsini. The rotation rates of these stars, as well as those of the SPBe stars previously discovered by MOST, HD 163868 and $\beta$ CMi, are all close to their critical values.