Discovery of δ Scuti Pulsations in the Young Hybrid Debris Disk Star HD 156623

Abstract

The bRing robotic observatory network was built to search for circumplanetary material within the transiting Hill sphere of the exoplanet $\\beta$ Pic b across its bright host star $\\beta$ Pic. During the bRing survey of $\\beta$ Pic, it simultaneously monitored the brightnesses of thousands of bright stars in the southern sky ($V$ $\\simeq$ 4-8, $\\delta$ $\\lesssim$ -30$^{\\circ}$). In this work, we announce the discovery of $\\delta$ Scuti pulsations in the A-type star HD 156623 using bRing data. HD 156623 is notable as it is a well-studied young star with a dusty and gas-rich debris disk, previously detected using ALMA. We present the observational results on the pulsation periods and amplitudes for HD 156623, discuss its evolutionary status, and provide further constraints on its nature and age. We find strong evidence of frequency regularity and grouping. We do not find evidence of frequency, amplitude, or phase modulation for any of the frequencies over the course of the observations. We show that HD 156623 is consistent with other hot and high frequency pre-MS and early ZAMS $\\delta$ Scutis as predicted by theoretical models and corresponding evolutionary tracks, although we observe that HD 156623 lies hotter than the theoretical blue edge of the classical instability strip. This, coupled with our characterization and Sco-Cen membership analyses, suggest that the star is most likely an outlying ZAMS member of the $\\sim$16 Myr Upper Centaurus-Lupus subgroup of the Sco-Cen association.