Circumstellar material in the Vega inner system revealed by CHARA/FLUOR

Context. Only a handful of debris disks have been imaged up to now. Due to the need for high dynamic range and high angular resolution, very little is known about the inner planetary region, where small amounts of warm dust are expected to be found. Aims. We investigate the close neighbourhood of Vega with the help of infrared stellar interferometry and estimate the integrated K-band flux originating from the central 8 AU of the debris disk. Methods. We performed precise visibility measurements at both short (∼30 m) and long (∼150 m) baselines with the FLUOR beamcombiner installed at the CHARA Array (Mt Wilson, California) in order to separately resolve the emissions from the extended debris disk (short baselines) and from the stellar photosphere (long baselines). Results. After revising Vega’s K-band angular diameter (θUD = 3.202 ± 0.005 mas), we show that a significant deficit in squared visibility (∆V 2 = 1.88 ± 0.34%) is detected at short baselines with respect to the best-fit uniform disk stellar model. This deficit can be either attributed to the presence of a low-mass stellar companion around Vega, or as the signature of the thermal and scattered emissions from the debris disk. We show that the presence of a close companion is highly unlikely, as well as other possible perturbations (stellar morphology, calibration), and deduce that we have most probably detected the presence of dust in the close neighbourhood of Vega. The resulting flux ratio between the stellar photosphere and the debris disk amounts to 1.29 ± 0.19% within the FLUOR field-of-view (∼7.8 AU). Finally, we complement our K-band study with archival photometric and interferometric data in order to evaluate the main physical properties of the inner dust disk. The inferred properties suggest that the Vega system could be currently undergoing major dynamical perturbations.

[1]  Stephen T. Ridgway,et al.  FLUOR fibered beam combiner at the CHARA array , 2003, SPIE Astronomical Telescopes + Instrumentation.

[2]  D. Segransan,et al.  Data reduction methods for single-mode optical interferometry Application to the VLTI two-telescopes beam combiner VINCI , 2004 .

[3]  Lynne Hillenbrand,et al.  Adaptive Optics Observations of Vega: Eight Detected Sources and Upper Limits to Planetary‐Mass Companions , 2003 .

[4]  H. Walker,et al.  Models of the dust structures around Vega-excess stars , 2000 .

[5]  Pierre Kervella,et al.  VLTI near-IR interferometric observations of Vega-like stars: Radius and age of a PsA, b Leo, b Pic, e Eri and t Cet , 2004 .

[6]  J. Weingartner,et al.  Dust Grain-Size Distributions and Extinction in the Milky Way, Large Magellanic Cloud, and Small Magellanic Cloud , 2001 .

[7]  M. Hanner.  A comparison of the dust properties in recent periodic comets , 1984 .

[8]  J. Weingartner,et al.  Dust Grain Size Distributions and Extinction in the Milky Way, LMC, and SMC , 2000, astro-ph/0008146.

[9]  Ralph C. Bohlin,et al.  Hubble Space Telescope Absolute Spectrophotometry of Vega from the Far-Ultraviolet to the Infrared , 2004 .

[10]  Hugo Fechtig,et al.  Collisional balance of the meteoritic complex , 1985 .

[11]  Deep Keck Adaptive Optics Searches for Extrasolar Planets in the Dust of Eridani and Vega , 2003, astro-ph/0303282.

[12]  G. Perrin,et al.  A catalogue of calibrator stars for long baseline stellar interferometry , 2002 .

[13]  F. J. Low,et al.  DISCOVERY OF A SHELL AROUND ALPHA-LYRAE , 1984 .

[14]  F. Thevenin,et al.  The diameters of $\alpha$ Centauri A and B - A comparison of the asteroseismic and VINCI/VLTI views , 2003 .

[16]  James A. Benson,et al.  Resolving the effects of rotation in early type stars , 2004, SPIE Astronomical Telescopes + Instrumentation.

[17]  M. Perryman.  Extra-solar planets , 2000, astro-ph/0005602.

[18]  G. Rieke,et al.  Absolute calibration of photometry at 1 through 5 microns , 1985 .

[19]  A. Merand,et al.  A catalog of bright calibrator stars for 200-m baseline near-infrared stellar interferometry , 2005 .

[20]  G. Rieke,et al.  An absolute photometric system at 10 and 20 microns , 1985 .

[21]  M. J. Selby,et al.  Narrow-band 1-to 5-μm photometry of A-type stars , 1986 .

[22]  Ages of A-Type Vega-like Stars from uvbyβ Photometry , 2000, astro-ph/0010102.

[23]  Olivier Guyon.  Wide field interferometric imaging with single-mode fibers , 2002 .

[24]  M. Holman,et al.  Structure in the Dusty Debris around Vega , 2002 .

[25]  R. H. Brown,et al.  The Angular Diameters of 32 Stars , 1974 .

[26]  Patrick Morris,et al.  The mid-infrared spectrum of the zodiacal and exozodiacal light , 2003 .

[27]  J.-M. Mariotti,et al.  Deriving object visibilities from interferograms obtained with a fiber stellar interferometer , 1997 .

[28]  David Mozurkewich,et al.  Angular Diameters of Stars from the Mark III Optical Interferometer , 2003 .

[29]  Michael J. Barlow,et al.  Spectral irradiance calibration in the infrared. I - Ground-based and IRAS broadband calibrations , 1992 .

[30]  Olivier Absil,et al.  VLTI NIR-Interferometric Observations of Vega-Like Stars , 2003 .

[31]  H. Beust,et al.  Falling Evaporating Bodies as a Clue to Outline the Structure of the β Pictoris Young Planetary System , 2000 .

[32]  K. Nordsieck,et al.  The Size distribution of interstellar grains , 1977 .

[33]  L. Colangeli,et al.  Optical constants of cosmic carbon analogue grains — I. Simulation of clustering by a modified continuous distribution of ellipsoids , 1996 .

[34]  N. Ostroff,et al.  Millimeter-Wave Aperture Synthesis Imaging of Vega: Evidence for a Ring Arc at 95 AU , 2001, astro-ph/0109424.

[35]  F. Allard,et al.  The NextGen Model Atmosphere Grid for 3000 ≤ Teff ≤ 10,000 K , 1998, astro-ph/9807286.

[36]  Ari Laor,et al.  Spectroscopic constraints on the properties of dust in active galactic nuclei , 1993 .

[37]  Saul J. Adelman,et al.  VEGA : A RAPIDLY ROTATING POLE-ON STAR , 1994 .

[38]  F. Wildi,et al.  Adaptive Optics Nulling Interferometric Constraints on the Mid-Infrared Exozodiacal Dust Emission around Vega , 2004, astro-ph/0406587.

[39]  S. T. Ridgway,et al.  First Results from the CHARA Array. II. A Description of the Instrument , 2005 .

[40]  B. Zuckerman,et al.  Submillimetre images of dusty debris around nearby stars , 1998, Nature.

[41]  K. Tsiganis,et al.  Origin of the cataclysmic Late Heavy Bombardment period of the terrestrial planets , 2005, Nature.

[42]  E. L. Wright,et al.  The COBE Diffuse Infrared Background Experiment Search for the Cosmic Infrared Background. II. Model of the Interplanetary Dust Cloud , 1997, astro-ph/9806250.

[43]  Elizabeth A. Lada,et al.  On the Near-Infrared Size of Vega , 2001, astro-ph/0105561.

[44]  C. Dominik,et al.  Age Dependence of the Vega Phenomenon: Theory , 2003, astro-ph/0308364.

[45]  M. J. Selby,et al.  Absolute calibration of the infrared flux from Vega at 1.24, 2.20,3.76 and 4.6 μm by comparison with a standard furnace , 1983 .

[46]  D. Ciardi,et al.  Altair’s Oblateness and Rotation Velocity from Long-Baseline Interferometry , 2001 .

[47]  M. Bessell,et al.  JHKLM PHOTOMETRY: STANDARD SYSTEMS, PASSBANDS, AND INTRINSIC COLORS , 1988 .

[48]  S. T. Megeath,et al.  The Vega debris disk: A surprise from spitzer , 2005 .

[49]  Jean Kovalevsky,et al.  Astronomical Applications of Astrometry: The Hipparcos and Tycho Catalogues , 2008 .

[50]  G. Perrin.  The calibration of interferometric visibilities obtained with single-mode optical interferometers. Computation of error bars and correlations , 2003 .

[51]  H. Walker,et al.  Infrared mapping of the dust disc around Vega , 1998 .

[52]  R. Stencel,et al.  Infrared Space Observatory Photometric Search of Main-Sequence Stars for Vega-Type Systems , 1999 .

[53]  J. Hearnshaw.  The Measurement of Starlight: Two Centuries of Astronomical Photometry , 2005 .

[54]  M. C. Wyatt,et al.  RESONANT TRAPPING OF PLANETESIMALS BY PLANET MIGRATION: DEBRIS DISK CLUMPS AND VEGA'S SIMILARITY TO THE SOLAR SYSTEM , 2003 .

[55]  R. Laureijs,et al.  A 25 micron search for Vega-like disks around main-sequence stars with ISO , 2002 .