Asteroseismic fingerprints of stellar mergers

Abstract

Stellar mergers are important processes in stellar evolution, dynamics, and transient science. However, it is difficult to identify merger remnant stars because they cannot easily be distinguished from single stars based on their surface properties. We demonstrate that merger remnants can potentially be identified through asteroseismology of red giant stars using measurements of the gravity mode period spacing together with the asteroseismic mass. For mergers that occur after the formation of a degenerate core, remnant stars have over-massive envelopes relative to their cores, which is manifested asteroseismically by a g mode period spacing smaller than expected for the star’s mass. Remnants of mergers which occur when the primary is still on the main sequence or whose total mass is less than ≈2 M⊙ are much harder to distinguish from single stars. Using the red giant asteroseismic catalogs of Vrard et al. (2016) and Yu et al. (2018), we identify 24 promising candidates for merger remnant stars. In some cases, merger remnants could also be detectable using only their temperature, luminosity, and asteroseismic mass, a technique that could be applied to a larger population of red giants without a reliable period spacing measurement.

Discovery of post-mass-transfer helium-burning red giants using asteroseismology

“…Our discovery of the post-mass-transfer CHeB stars follows recent identifications of mergers on the RGB 64,65 and demonstrates asteroseismology as a new way to find interesting binary systems in the red giant population. Expanding the current sample to brighter stars from the K2 and TESS missions will enable spectroscopic or astrometric measurements to solve the binary orbits, allowing detailed characterisation of the systems and a better understanding of the mass transfer channel 19 .…”

TIC 308396022: δ Scuti–γ Doradus hybrid with large-amplitude radial fundamental mode and regular g-mode period spacing

“…The absence of a compatible model implies that the star has different core and envelope formation histories, perhaps due to mass transfer from the secondary star. Some recent research has shown that asteroseismology has the ability to detect stellar merger or mass transfer in red giants (Rui & Fuller 2021;Deheuvels et al 2021), and we suggest that TIC 308396022 might be a MS counterpart showing mass transfer by asteroseismology. We also note that Miszuda et al (2021) performed binary-evolution and pulsational modellings of KIC 10661783, an δ Sct-γ Dor hybrid in an eclipsing binary system, and showed that a mass transfer has a significant impact on the g-mode excitations.…”

Seismic signature of electron degeneracy in the core of red giants: Hints for mass transfer between close red-giant companions

“…The study ofRui & Fuller (2021) is completely independent of ours, and we had knowledge of this work upon submission of the present paper.A106, page 11 of 14A&A 659, A106 (2022) …”

“…Another possibility would be that these peculiar red giants result from the merger between a red giant and a lower-mass star. It has very recently been proposed by Rui & Fuller (2021) that stellar mergers of this type might be detectable using seismology. The underlying idea is similar to the one that we exposed in this study, that is, the accretion of a significant amount of mass in the envelope of a red giant star can produce an intermediatemass giant with a degenerate core, which cannot be achieved with single-star evolution 1 .…”