Asteroseismology revealing trapped modes in KIC 10553698A

TL;DR

This study uses Kepler data to identify and analyze trapped pulsation modes in the subdwarf-B star KIC 10553698A, revealing mode trapping and a binary companion through photometric and spectroscopic evidence.

Contribution

First detection of l=1 mode trapping in a subdwarf-B star, confirming theoretical predictions and providing detailed mode identification using Kepler data.

Findings

Identified 156 pulsation modes as l=1 or l=2 multiplets.

Detected mode trapping indicating stratified stellar envelope.

Confirmed binary companion with Doppler-beaming effect.

Abstract

The subdwarf-B pulsator, KIC 10553698A, is one of 16 such objects observed with one-minute sampling for most of the duration of the Kepler Mission. Like most of these stars, it displays a rich g-mode pulsation spectrum with several clear multiplets that maintain regular frequency splitting. We identify these pulsation modes as components of rotationally split multiplets in a star rotating with a period of about 41 d. From 162 clearly significant periodicities, we are able to identify 156 as likely components of l=1 or l=2 multiplets. For the first time we are able to detect l=1 modes that interpose in the asymptotic period sequences and that provide a clear indication of mode trapping in a stratified envelope, as predicted by theoretical models. A clear signal is also present in the Kepler photometry at 3.387 d. Spectroscopic observations reveal a radial-velocity amplitude of 64.8 km/s. We find that the radial-velocity variations and the photometric signal have phase and amplitude that are perfectly consistent with a Doppler-beaming effect and conclude that the unseen companion, KIC 10553698B, must be a white dwarf most likely with a mass close to 0.6 solar masses.