2018A&A...616A..88V

Context. A wide variety of ring-like dust structures have been detected in protoplanetary disks, but their origin and frequency are still unclear.
Aims. We aim to characterize the structure of an extended, multi-ringed disk discovered serendipitously in the Atacama Large Millimeter/submillimeter Array (ALMA) Lupus disk survey and put it in the context of the Lupus disk population.
Methods. ALMA observations in Band 6 at 234GHz and Band 7 at 328GHz at 0.3'' resolution toward the K6 star V1094 Sco in Lupus III are presented, and its disk structure analyzed. The spectral index α_mm is determined in the inner 150AU of the disk.
Results. The ALMA continuum data show a very extended disk with two gap-ring pairs. The gaps are located at 100AU and 170AU, the bright rings at 130AU and 220AU. Continuum emission is detected out to a 300AU distance, similar to IM Lup but a factor of five larger than typically found for Lupus disks at this sensitivity and resolution. The bright central region of the disk (within 35AU) is possibly optically thick at 1mm wavelengths, and has a brightness temperature of only 13K. The spectral index increases between the inner disk and the first ring at the location of the first gap.
Conclusions. Due to the low temperature of the disk midplane, snow lines can be excluded as the drivers behind the ring and gap formation in this disk. Disks the size of V1094 Sco are rare, and only 2.1±1.5% of disks in Lupus show continuum emission beyond 200AU. Possible connections between the large primordial disk population, transition disks, and exoplanets are discussed.