The architecture of the LkCa 15 transitional disk revealed by high-contrast imaging^⋆

¹ Institute for Astronomy, ETH Zurich Wolfgang-Pauli-Strasse 27, 8093 Zurich, Switzerland
e-mail: thalmann@phys.ethz.ch
² Astronomical Institute “Anton Pannekoek”, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
³ Lunar and Planetary Laboratory, The University of Arizona, 1629 E. University Blvd., Tucson AZ 85721, USA
⁴ Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu HI 96822, USA
⁵ Astrophysics Research Center, Queen’s University Belfast, Belfast, UK
⁶ Eureka Scientific, 2452 Delmer, Suite 100, Oakland CA 96002, USA
⁷ Exoplanets and Stellar Astrophysics Laboratory, Code 667, Goddard Space Flight Center, Greenbelt MD 20771, USA
⁸ Goddard Center for Astrobiology, Goddard Space Flight Center, Greenbelt MD 20771, USA
⁹ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
¹⁰ Department of Physics & Astronomy, College of Charleston, 58 Coming Street, Charleston SC 29424, USA
¹¹ Astrophysics Department, Institute for Advanced Study, Princeton, USA
¹² Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
¹³ Department of Astronomy and Steward Observatory, 933 North Cherry Avenue, Rm. N204, Tucson AZ 85721-0065, USA
¹⁴ National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, 181-8588 Tokyo, Japan
¹⁵ Department of Astronomical Science, Graduate University for Advanced Studies (Sokendai), 181-8588 Tokyo, Japan

Received: 25 October 2013
Accepted: 5 February 2014

Abstract

We present four new epochs of K_s-band images of the young pre-transitional disk around LkCa 15 and perform extensive forward modeling to derive the physical parameters of the disk. We find indications of strongly anisotropic scattering (Henyey-Greenstein g = 0.67_-0.11^+0.18) and a significantly tapered gap edge (“round wall”) but see no evidence that the inner disk, whose existence is predicted by the spectral energy distribution, shadows the outer regions of the disk visible in our images. We marginally confirm the existence of an offset between the disk center and the star along the line of nodes; however, the magnitude of this offset (x = 27_-20⁺¹⁹ mas) is notably lower than that found in our earlier H-band images. Intriguingly, we also find an offset of y=69_-25⁺⁴⁹ mas perpendicular to the line of nodes at high significance. If confirmed by future observations, this would imply a highly elliptical – or otherwise asymmetric – disk gap with an effective eccentricity of e ≈ 0.3. Such asymmetry would most likely be the result of dynamical sculpting by one or more unseen planets in the system. Finally, we find that the bright arc of scattered light we see in direct imaging observations originates from the near side of the disk and appears brighter than the far side because of strong forward scattering.