The dust of RZ Psc (W. J. de Wit et al.)

Vol. 553
In section 1. Letters

Active asteroid belt causes the UXOR phenomenon in RZ Piscium

RZ Psc is a solar-type K0IV star well known for its variability, which is similar to the so-called UXOR variability seen in pre-main sequence stars and is attributed to the occultation by optically thick dust in stars with circumstellar disks. However, with an inferred age of 30 Ma, RZ Psc is relatively old compared to the usual UXOR-variable stars. de Wit et al. use infrared data (from WISE, IRAS, AKARI, and 2MASS) and visible photometric observation from the past 40 years to understand what this object is made of. The spectral energy distribution has a very significant excess that corresponds to a well-defined blackbody temperature of 500K. The photometric data show a 12.4-year period and very pronounced minima at random times. The authors interpret these as evidence for an optically thick dust ring around 0.7 AU and a substellar ("planet") companion at an orbital distance of 5.3 AU that apparently perturbs/wraps this ring and causes it to partially occult the star. The authors propose that the sharp photometric minima might be caused by the collision of planetesimals; which would produce an estimated 1e20 g of dust (equivalent to a full 20 km radius object reduced to dust). While these results have to be put to the test (observationally and theoretically), they show that RZ Psc is indeed an intriguing object that could help us understand disk evolution and planet formation.