Gaps in the HD 169142 protoplanetary disk revealed by polarimetric imaging: Signs of ongoing planet formation?

Abstract

We present H-band Very Large Telescope/NACO polarized light images of the Herbig Ae/Be star HD 169142 probing its protoplanetary disk as close as 0.″1 to the star. Our images trace the face-on disk out to 1.″7 (250 AU) and reveal distinct substructures for the first time: (1) the inner disk (≲20 AU) appears to be depleted in scattering dust grains; (2) an unresolved disk rim is imaged at 25 AU; (3) an annular gap extends from 40 to 70 AU; (4) local brightness asymmetries are found on opposite sides of the annular gap. We discuss different explanations for the observed morphology among which ongoing planet formation is a tempting, but yet to be proven, one. Outside of 85 AU the surface brightness drops off roughly r -3.3, but describing the disk regions between 85-120 AU and 120-250 AU separately with power laws r -2.6 and r -3.9 provides a better fit hinting toward another discontinuity in the disk surface. The flux ratio between the disk-integrated polarized light and the central star is 4.1 × 10 -3. Finally, combining our results with those from the literature, 40% of the scattered light in the H band appears to be polarized. Our results emphasize that HD 169142 is an interesting system for future planet formation or disk evolution studies. © 2013 The American Astronomical Society. All rights reserved.