TIC 5724661: A Long-Period Binary with a Pulsating sdB Star and δ Scuti Variable

Abstract

Using the novel TESS 20-sec cadence data, we have discovered an unusual combination of pulsating stars in what we infer to be a binary system. The primary is a standard δ Scuti star with pulsations over the range 32-41 d−1; this is in an inferred wide orbit with a hot subdwarf B (sdB) secondary, which itself has a large-amplitude p-mode pulsation at 524 d−1. We establish constraints on the period of the putative binary by using radial velocity measurements of the δ Scuti star and show that any sdB-mass companion star must have an orbital period greater than ∼35 d. Our identification of this sdB binary serves as an important addition to the relatively small amount of sdB binaries known to have a period longer than a few days. We show that such a binary can be formed through stable, nonconservative mass transfer, without undergoing a common envelope phase.