title: The transiting dust clumps in the evolved disc of the Sun-like UXor RZ Psc.
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.
authors.affiliation: Institute of Astronomy , University of Cambridge , Madingley Road, Cambridge CB3 0HA, UK.
authors.forename: Grant M
authors.identifier: 0000-0001-6831-7547
authors.initials: GM
authors.lastname: Kennedy
authors.affiliation: Leiden Observatory , Leiden University , PO Box 9513, 2300 RA Leiden, The Netherlands.
authors.forename: Matthew A
authors.initials: MA
authors.lastname: Kenworthy
authors.affiliation: Department of Physics , Lehigh University , 16 Memorial Drive East, Bethlehem, PA 18015, USA.
authors.forename: Joshua
authors.initials: J
authors.lastname: Pepper
authors.affiliation: Harvard-Smithsonian Center for Astrophysics, 60 Garden Street MS-78, Cambridge, MA 02138, USA; Department of Physics and Astronomy, Vanderbilt University, 6301 Stevenson Center, Nashville, TN 37235, USA.
authors.forename: Joseph E
authors.initials: JE
authors.lastname: Rodriguez
authors.affiliation: Las Cumbres Observatory Global Telescope Network , 6740 Cortona Drive, Suite 102, Santa Barbara, CA 93117, USA.
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Siverd
authors.affiliation: Department of Physics and Astronomy, Vanderbilt University, 6301 Stevenson Center, Nashville, TN 37235, USA; Department of Physics, Fisk University, 1000 17th Avenue North, Nashville, TN 37208, USA.
authors.forename: Keivan G
authors.initials: KG
authors.lastname: Stassun
authors.affiliation: Institute of Astronomy , University of Cambridge , Madingley Road, Cambridge CB3 0HA, UK.
authors.forename: Mark C
authors.initials: MC
authors.lastname: Wyatt
keywords: circumstellar matter; debris discs; protoplanetary discs; variable stars