GAPS IN THE HD 169142 PROTOPLANETARY DISK REVEALED BY POLARIMETRIC IMAGING: SIGNS OF ONGOING PLANET FORMATION?

We present H-band VLT/NACO polarized light images of the Herbig Ae/Be star HD169142 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 sub-structures 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 - 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 / 120-250 AU separately with power-laws r^{-2.6} / r^{-3.9} provides a better fit hinting towards 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 HD169142 is an interesting system for future planet formation or disk evolution studies.

[1]  Sebastian Wolf,et al.  On the Observability of Giant Protoplanets in Circumstellar Disks , 2004, astro-ph/0410064.

[2]  David Mouillet,et al.  NAOS, the first AO system of the VLT: on-sky performance , 2003, SPIE Astronomical Telescopes + Instrumentation.

[3]  M. Barlow,et al.  Optical, infrared and millimetre-wave properties of Vega-like systems - II. Radiative transfer modelling , 1996 .

[4]  Richard P. Nelson,et al.  Tidally Induced Gap Formation in Protostellar Disks: Gap Clearing and Suppression of Protoplanetary Growth , 1999 .

[5]  C. Packham,et al.  HIGH-RESOLUTION MID-INFRARED IMAGING OF THE CIRCUMSTELLAR DISKS OF HERBIG Ae/Be STARS , 2011 .

[6]  S. Wolf,et al.  Signatures of planets in protoplanetary and debris disks , 2007 .

[7]  G. Sandell,et al.  A SUBMILLIMETER MAPPING SURVEY OF HERBIG AeBe STARS , 2010, 1011.3747.

[8]  D. Lin,et al.  On the tidal interaction between protoplanets and the protoplanetary disk. III. Orbital migration of protoplanets , 1986 .

[9]  Near‐infrared imaging polarimetry of dusty young stars , 2005, astro-ph/0511793.

[10]  Fortunat Joos,et al.  Limb polarization of Uranus and Neptune - I. Imaging polarimetry and comparison with analytic models , 2006 .

[11]  C. A. Grady,et al.  SPIRAL ARMS IN THE ASYMMETRICALLY ILLUMINATED DISK OF MWC 758 AND CONSTRAINTS ON GIANT PLANETS , 2012, 1212.1466.

[12]  Olivier Guyon,et al.  POLARIMETRIC IMAGING OF LARGE CAVITY STRUCTURES IN THE PRE-TRANSITIONAL PROTOPLANETARY DISK AROUND PDS 70: OBSERVATIONS OF THE DISK , 2012, 1208.2075.

[13]  E. Kokubo,et al.  DIRECT IMAGING OF FINE STRUCTURES IN GIANT PLANET-FORMING REGIONS OF THE PROTOPLANETARY DISK AROUND AB AURIGAE , 2011, 1102.4408.

[14]  R. P. Nelson,et al.  Dynamical modeling of large scale asymmetries in the beta Pictoris dust disk , 2001 .

[15]  O. Guyon,et al.  THE MISSING CAVITIES IN THE SEEDS POLARIZED SCATTERED LIGHT IMAGES OF TRANSITIONAL PROTOPLANETARY DISKS: A GENERIC DISK MODEL , 2012, 1203.1612.

[16]  J. D. Monnier,et al.  The Inner Regions of Protoplanetary Disks , 2010, 1006.3485.

[17]  Granada,et al.  The circumstellar disc around the Herbig AeBe star HD169142 , 2005, astro-ph/0511261.

[18]  Astrophysics,et al.  Resolving the inner regions of the HD 97048 circumstellar disk with VLT/NACO polarimetric differential imaging , 2011, 1112.1953.

[19]  Andreas Quirrenbach,et al.  The Disk and Environment of a Young Vega Analog: HD 169142 , 2007 .

[20]  Timothy D. Brandt,et al.  High-Resolution Near-Infrared Polarimetry of a Circumstellar Disk around UX Tau A , 2012, 1206.1215.

[21]  D. Wilner,et al.  A Keplerian Disk around the Herbig Ae Star HD 169142 , 2005, astro-ph/0512478.

[22]  H. Kataza,et al.  MID-INFRARED IMAGING OF THE TRANSITIONAL DISK OF HD 169142: MEASURING THE SIZE OF THE GAP , 2012, 1204.5364.

[23]  R. Lenzen,et al.  The instrumental polarization of the Nasmyth focus polarimetric differential imager NAOS/CONICA (NACO) at the VLT - Implications for time-resolved polarimetric measurements of Sgr A* , 2010, 1010.4708.

[24]  J. Kuhn,et al.  Imaging Polarimetric Observations of a New Circumstellar Disk System , 2001, astro-ph/0105239.

[25]  Michael C. Liu,et al.  Substructure in the Circumstellar Disk Around the Young Star AU Microscopii , 2004, Science.

[26]  J. M. Alacid,et al.  Gas in the protoplanetary disc of HD 169142: Herschel's view , 2010, 1005.3828.

[27]  M. Min,et al.  A 10 μm spectroscopic survey of Herbig Ae star disks: Grain growth and crystallization , 2005, astro-ph/0503507.

[28]  Wm. A. Wheaton,et al.  2MASS All Sky Catalog of point sources. , 2003 .

[29]  Hannah Jang-Condell,et al.  GAPS IN PROTOPLANETARY DISKS AS SIGNATURES OF PLANETS. I. METHODOLOGY AND VALIDATION , 2012, 1202.3465.

[30]  C. A. Grady,et al.  DISCOVERY OF SMALL-SCALE SPIRAL STRUCTURES IN THE DISK OF SAO 206462 (HD 135344B): IMPLICATIONS FOR THE PHYSICAL STATE OF THE DISK FROM SPIRAL DENSITY WAVE THEORY , 2012, 1202.6139.

[31]  M. E. van den Ancker,et al.  ISO spectroscopy of circumstellar dust in 14 Herbig Ae/Be systems: Towards an understanding of dust processing , 2001 .

[33]  Anne-Marie Lagrange,et al.  NAOS-CONICA first on sky results in a variety of observing modes , 2003, SPIE Astronomical Telescopes + Instrumentation.

[34]  J. Wisniewski,et al.  SUBARU IMAGING OF ASYMMETRIC FEATURES IN A TRANSITIONAL DISK IN UPPER SCORPIUS , 2012, 1211.3284.

[35]  Glenn Schneider,et al.  THE CASE OF AB AURIGAE’S DISK IN POLARIZED LIGHT: IS THERE TRULY A GAP? , 2009, 0911.1130.

[36]  Heidelberg,et al.  VERY LARGE TELESCOPE/NACO POLARIMETRIC DIFFERENTIAL IMAGING OF HD100546—DISK STRUCTURE AND DUST GRAIN PROPERTIES BETWEEN 10 AND 140 AU , 2011, 1106.1101.

[37]  D. Wilner,et al.  Gas and dust mass in the disc around the Herbig Ae star HD 169142 , 2008 .

[38]  H. Shibai,et al.  Subaru Near-Infrared Imaging of Herbig Ae Stars* , 2010 .

[39]  W. Corradi,et al.  Stellar parameters and evidence of circumstellar activity for a sample of Herbig Ae/Be stars , 2006 .

[40]  S. Wolf,et al.  Tracing large-scale structures in circumstellar disks with ALMA , 2012, 1212.1793.

[41]  H. Djie,et al.  Modeling of PMS Ae/Fe stars using UV spectra , 2006 .