Herschel imaging of 61 Vir: implications for the prevalence of debris in low-mass planetary systems

Abstract

This paper describes Herschel observations of the nearby (8.5pc) G5V\nmulti-exoplanet host star 61 Vir at 70-500micron carried out by the DEBRIS\nsurvey. These reveal emission that is extended out to >15arcsec with a\nmorphology that can be fitted by a nearly edge-on (77deg inclination) radially\nbroad (from 30AU to >100AU) debris disk of fractional luminosity 2.7x10^-5,\nwith two unrelated sources nearby that are more prominent at longer\nwavelengths. Chance alignment with a background object seen at 1.4GHz provides\npotential for confusion, but the star's 1.4"/yr proper motion allows Spitzer\n70micron images to confirm that what we are interpreting as disk emission\nreally is circumstellar. Although the exact shape of the disk's inner edge is\nnot well constrained, the region inside 30AU must be significantly depleted in\nplanetesimals. This is readily explained if there are additional planets in the\n0.5-30AU region, but is also consistent with collisional erosion. We also find\ntentative evidence that the presence of detectable debris around nearby stars\ncorrelates with the presence of the lowest mass planets that are detectable in\ncurrent radial velocity surveys. Out of an unbiased sample of the nearest 60 G\nstars, 11 are known to have planets, of which 6 (including 61 Vir) have planets\nthat are all less massive than Saturn, and 4 of these have evidence for debris.\nThe debris toward one of these planet-hosts (HD20794) is reported here for the\nfirst time. This fraction (4/6) is higher than that expected for nearby field\nstars (15%), and implies that systems that form low-mass planets are also able\nto retain bright debris disks. We suggest that this correlation could arise\nbecause such planetary systems are dynamically stable and include regions that\nare populated with planetesimals in the formation process where the\nplanetesimals can remain unperturbed over Gyr timescales.\n