V680 Mon -- a young mercury-manganese star in an eclipsing heartbeat system

Abstract

Chemically peculiar stars in eclipsing binary systems are rare objects that allow the derivation of fundamental stellar parameters and important information on evolutionary status and the origin of the observed chemical peculiarities. Here we present an investigation of the known eclipsing binary system BD+09 1467 = V680 Mon. Using spectra from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) and own observations, we identify the primary component of the system as a mercury-manganese (HgMn/CP3) star (spectral type kB9 hB8 HeB9 V HgMn). Furthermore, photometric time series data from the Transiting Exoplanet Survey Satellite (TESS) indicate that the system is a 'heartbeat star', a rare class of eccentric binary stars with short-period orbits that exhibit a characteristic signature near the time of periastron in their light curves due to the tidal distortion of the components. Using all available photometric observations, we present an updated ephemeris and binary system parameters as derived from a modelling of the system with the ELISa code, which indicate that the secondary star has an effective temperature of T e f f = 8300 +200 −200 (spectral type ∼A4). V680 Mon is only the fifth known eclipsing CP3 star, and the first one in a heartbeat binary. Furthermore, our results indicate that the star is located on the zero-age main sequence and a possible member of the open cluster NGC 2264. As such, it lends itself perfectly for detailed studies and may turn out to be a keystone in the understanding of the development of CP3 star peculiarities.

New eclipsing binaries with mercury-manganese stars

“…Two systems studied here, HD 36892 and 53004, exhibit heartbeat variations only recently discovered in HgMn binaries (Paunzen et al 2021a). The latter star is also the first example of an HgMn star with multi-periodic pulsations excited by tidal perturbations in an eccentric short period binary (e.g.…”

“…Torres et al 2010) and well-constrained ages (Tkachenko et al 2020). Despite an abundance of close spectroscopic binaries with HgMn components (Ryabchikova 1998;Catanzaro & Leto 2004), only four such objects, HD 10260, 34364, 267564, and TYC 455-791-1 (Kochukhov et al 2021;Paunzen et al 2021a, and references therein), were known in eclipsing systems. Eclipses in two more spectroscopic binaries with HgMn primaries, HD 72208 and HD 161701, suspected based on low-quality photometric measurements by the STEREO satellite (Wraight et al 2011), are yet to be confirmed by independent observations.…”

TESS survey of rotational and pulsational variability of mercury-manganese stars

“…Thompson et al 2012). Only one case of heartbeat variability in an HgMn star, corresponding to the eclipsing system V680 Mon, was previously known (Paunzen et al 2021a).…”

“…In other cases variability could not be unambiguously ascribed to spots (Hümmerich et al 2018) and interpretation in terms of g-mode pulsations was preferred (Alecian et al 2009). Recent studies identified another cause of variability of some HgMn stars -the ellipsoidal and heartbeat variation associated with the orbital motion in a close binary system (Kochukhov et al 2021;Paunzen et al 2021a). To summarise, variability of HgMn appears to be ubiquitous and diverse, emphasising the necessity of advancing from case studies of individual objects to statistical analyses of meaningful stellar samples.…”