PLANETARY CONSTRUCTION ZONES IN OCCULTATION: DISCOVERY OF AN EXTRASOLAR RING SYSTEM TRANSITING A YOUNG SUN-LIKE STAR AND FUTURE PROSPECTS FOR DETECTING ECLIPSES BY CIRCUMSECONDARY AND CIRCUMPLANETARY DISKS

Abstract

<abridged> The large relative sizes of circumstellar and circumplanetary\ndisks imply that they might be seen in eclipse in stellar light curves. We\nestimate that a survey of ~10^4 young (~10 Myr old) post-accretion pre-MS stars\nmonitored for ~10 years should yield at least a few deep eclipses from\ncircumplanetary disks and disks surrounding low mass companion stars. We\npresent photometric and spectroscopic data for a pre-MS K5 star (1SWASP\nJ140747.93-394542.6), a newly discovered ~0.9 Msun member of the ~16 Myr-old\nUpper Cen-Lup subgroup of Sco-Cen at a kinematic distance of 128 pc. SuperWASP\nand ASAS light curves for this star show a remarkably long, deep, and complex\neclipse event centered on 29 April 2007. At least 5 multi-day dimming events of\n>0.5 mag are identified, with a >3.3 mag deep eclipse bracketed by two pairs of\n~1 mag eclipses symmetrically occurring +-12 days and +-26 days before and\nafter. Hence, significant dimming of the star was taking place on and off over\nat least a ~54 day period in 2007, and a strong >1 mag dimming event occurred\nover a ~12 day span. We place a firm lower limit on the period of 850 days\n(i.e. the orbital radius of the eclipser must be >1.7 AU and orbital velocity\nmust be <22 km/s). The shape of the light curve is similar to the lop-sided\neclipses of the Be star EE Cep. We suspect that this new star is being eclipsed\nby a low-mass object orbited by a dense inner disk, girded by at least 3 dusty\nrings of lower optical depth. Between these rings are at least two annuli of\nnear-zero optical depth (i.e. gaps), possibly cleared out by planets or moons,\ndepending on the nature of the secondary. For possible periods in the range\n2.33-200 yr, the estimated total ring mass is ~8-0.4 Mmoon (if the rings have\noptical opacity similar to Saturn's rings), and the edge of the outermost\ndetected ring has orbital radius ~0.4-0.09 AU.\n