Abstract
RZ Psc is a young Sun-like star, long associated with the UXor class of variable stars, which is partially or wholly dimmed by dust clumps several times each year. The system has a bright and variable infrared excess, which has been interpreted as evidence that the dimming events are the passage of asteroidal fragments in front of the host star. Here, we present a decade of optical photometry of RZ Psc and take a critical look at the asteroid belt interpretation. We show that the distribution of light curve gradients is non-uniform for deep events, which we interpret as possible evidence for an asteroidal fragment-like clump structure. However, the clumps are very likely seen above a high optical depth midplane, so the disc’s bulk clumpiness is not revealed. While circumstantial evidence suggests an asteroid belt is more plausible than a gas-rich transition disc, the evolutionary status remains uncertain. We suggest that the rarity of Sun-like stars showing disc-related variability may arise because (i) any accretion streams are transparent and/or (ii) turbulence above the inner rim is normally shadowed by a flared outer disc.
Highlights
Discs of gas and dust surround essentially all young analogues of our Sun [1]
We found a weak periodic signal near 60–70 days, but neither of the methods described above show compelling evidence that the dimming events seen towards RZ Psc are periodic and not random
Using 10 years of WASP and KELT-North data, we investigated the periodicity of possible repeat events and the light curve gradients
Summary
Discs of gas and dust surround essentially all young analogues of our Sun [1]. The lifetime of the gas in these discs is very short compared with the stellar lifetime, and within a few million years has accreted onto the star, been lost to space in photoevaporative flows, and contributed to building planets. As argued by de Wit et al [40], a picture is emerging in which RZ Psc is surrounded by a massive young version of our own asteroid belt, in which planetesimals are continually being destroyed These collisions generate the large collective surface area of small dust that emits strongly in the mid-IR, and the system geometry means that this dust sometimes passes in front of the star. The only cyclical variation seen in light curves for RZ Psc is a 12.4 year variation with an amplitude of 0.5 mag, which is attributed to either a magnetic cycle or precession of an otherwise unseen outer disc owing to perturbations from an unseen companion [40]
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