Resolved Millimeter Emission from the HD 15115 Debris Disk

TL;DR

This study used 1.3 mm observations to resolve the debris disk around HD 15115, revealing a circumstellar belt and potential asymmetries that inform theories of dust distribution and disk dynamics.

Contribution

First resolved millimeter emission from HD 15115's debris disk, linking the dust belt to optical asymmetries and discussing possible mechanisms for observed features.

Findings

Disk extends to ~110 AU, matching the optical break.

Detected a tentative millimeter extension aligned with optical asymmetry.

Disfavoring interstellar gas interactions as sole cause of asymmetry.

Abstract

We have used the Submillimeter Array (SMA) to make 1.3 millimeter observations of the debris disk surrounding HD 15115, an F-type star with a putative membership in the beta Pictoris moving group. This nearly edge-on debris disk shows an extreme asymmetry in optical scattered light, with an extent almost two times larger to the west of the star than to the east (originally dubbed the "Blue Needle"). The SMA observations reveal resolved emission that we model as a circumstellar belt of thermal dust emission. This belt extends to a radius of ~110 AU, coincident with the break in the scattered light profile convincingly seen on the western side of the disk. This outer edge location is consistent with the presence of an underlying population of dust-producing planetesimals undergoing a collisional cascade, as hypothesized in "birth ring" theory. In addition, the millimeter emission shows a ~3 sigma feature aligned with the asymmetric western extension of the scattered light disk. If this millimeter extension is real, then mechanisms for asymmetry that affect only small grains, such as interactions with interstellar gas, are disfavored. This tentative feature might be explained by secular perturbations to grain orbits introduced by neutral gas drag, as previously invoked to explain asymmetric morphologies of other, similar debris disks.