GG Carinae: Discovery of orbital phase dependent 1.583-day periodicities in the B[e] supergiant binary

TL;DR

This paper reports the discovery of a 1.583-day orbital phase-dependent periodicity in the B[e] supergiant binary GG Carinae, linked to tidal oscillations of the primary star, alongside known orbital variations.

Contribution

It identifies a previously neglected short-period oscillation in GG Carinae and links it to tidal excitation of stellar oscillation modes, providing new insights into binary interactions.

Findings

Discovered a 1.583-day periodicity in photometry and emission lines.

The short-period amplitude varies with orbital phase, peaking at periastron.

The period matches the expected l=2 f-mode of the primary star.

Abstract

GG Carinae is a binary whose primary component is a B[e] supergiant. Using photometric data from TESS, ASAS, OMC, and ASAS-SN, and spectroscopic data from the Global Jet Watch to study visible He\,I, Fe\,II and Si\,II emission lines, we investigate the short-period variations which are exhibited in GG Car. We find a hitherto neglected periodicity of $1.583156\pm0.0002$\,days that is present in both its photometry and the radial velocities of its emission lines, alongside variability at the well-established $\sim$31-day orbital period. We find that the amplitudes of the shorter-period variations in both photometry and some of the emission lines are modulated by the orbital phase of the binary, such that the short-period variations have largest amplitudes when the binary is at periastron. There are no significant changes in the phases of the short-period variations over the orbital period. We investigate potential causes of the 1.583-day variability, and find that the observed period agrees well with the expected period of the $l=2$ f-mode of the primary given its mass and radius. We propose that the primary is periodically pulled out of hydrostatic equilibrium by the quadrupolar tidal forces when the components are near periastron in the binary's eccentric orbit ($e=0.5$) and the primary almost fills its Roche lobe. This causes an oscillation at the $l=2$ f-mode frequency which is damped as the distance between the components increases.