Vertical structure of debris discs

Thébault, P.

doi:10.1051/0004-6361/200912396

Cited by 72 publications

(82 citation statements)

References 37 publications

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“…The opening angle for the outer belt is smaller (θ lim, outer ∼ 0.9 • ). The lower limit for the opening angle θ lim, inner is in good agreement with the work presented in Thébault (2009), who found a minimum "natural" observed aspect ratio of ∼2.3 • (defined as θ/2).…”

Section: The Optical Depth and Opening Anglesupporting

confidence: 91%

“…For a given disk model, the D code returns a threshold value θ lim , which is the smallest opening angle for which the debris disk is still in the optically thin regime. One should note that for small opening angles, θ is comparable to twice the aspect ratio of the disk 2H/r (same formalism as in Thébault 2009). For the best-fit "2B" model, we found a θ lim, inner of about 3.8 • for the innermost belt, a value consistent with the one found by Lisse et al (2008, 4 • ).…”

Section: The Optical Depth and Opening Anglementioning

confidence: 99%

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The twofold debris disk around HD 113766 A

Olofsson

Henning

Nielbock

et al. 2013

A&A

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Context. Warm debris disks are a sub-sample of the large population of debris disks, and display excess emission in the mid-infrared. Around solar-type stars, very few objects (∼2% of all debris disks) show emission features in mid-IR spectroscopic observations that are attributed to small, warm silicate dust grains. The origin of this warm dust could be explained either by a recent catastrophic collision between several bodies or by transport from an outer belt similar to the Kuiper belt in the solar system.Aims. We present and analyze new far-IR Herschel/PACS photometric observations, supplemented by new and archival ground-based data in the mid-IR (VLTI/MIDI and VLT/VISIR), for one of these rare systems: the 10-16 Myr old debris disk around HD 113766 A. We improve an existing model to account for these new observations. Methods. We implemented the contribution of an outer planetesimal belt in the D code, and successfully used it to model the spectral energy distribution (SED) as well as complementary observations, notably MIDI data. We better constrain the spatial distribution of the dust and its composition. Results. We underline the limitations of SED modeling and the need for spatially resolved observations. We improve existing models and increase our understanding of the disk around HD 113766 A. We find that the system is best described by an inner disk located within the first AU, well constrained by the MIDI data, and an outer disk located between 9-13 AU. In the inner dust belt, our previous finding of Fe-rich crystalline olivine grains still holds. We do not observe time variability of the emission features over at least an eight-year time span in an environment subjected to strong radiation pressure. Conclusions. The time stability of the emission features indicates that µm-sized dust grains are constantly replenished from the same reservoir, with a possible depletion of sub-µm-sized grains. We suggest that the emission features may arise from multi-composition aggregates. We discuss possible scenarios concerning the origin of the warm dust observed around HD 113766 A. The compactness of the innermost regions as probed by the MIDI visibilities and the dust composition suggest that we are witnessing the results of (at least) one collision between partially differentiated bodies, in an environment possibly rendered unstable by terrestrial planetary formation.

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Section: The Optical Depth and Opening Anglesupporting

confidence: 91%

Section: The Optical Depth and Opening Anglementioning

confidence: 99%

The twofold debris disk around HD 113766 A

Olofsson

Henning

Nielbock

et al. 2013

A&A

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“…At this stage, we generated a limited number of models with some assumptions about the remaining free parameters taken from the literature (Schneider et al 2005;Moerchen et al 2007;Debes et al 2009), namely g = 0 (isotropic scattering), r 0 = 70 AU, 80,85,88] • , and α in = [0, 2]. The vertical height H 0 is consistent with the natural thickening of debris disks defined by Thébault (2009), although chosen close to the lower boundary of the proposed range in that paper. Hence, in our case, the aspect ratio was assumed to be constant at H/r 0.029.…”

Section: Reliability Of the Spine Deviation From Midplanementioning

confidence: 99%

Morphology of the very inclined debris disk around HD 32297

Boccaletti

Augereau

Lagrange

et al. 2012

A&A

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Context. Direct imaging of circumstellar disks at high angular resolution is mandatory to provide morphological information that constrains their properties, in particular the spatial distribution of dust. For a long time, this challenging objective was, in most cases, only within the realm of space telescopes from the visible to the infrared. New techniques combining observing strategy and data processing now allow very high-contrast imaging with 8-m class ground-based telescopes (10 −4 to 10 −5 at ∼1 ) and complement space telescopes while improving angular resolution at near infrared wavelengths. Aims. We present the results of a program carried out at the VLT with NACO to image known debris disks with higher angular resolution in the near-infrared than ever before in order to study morphological properties and ultimately detect the signpost of planets. Methods. The observing method makes use of advanced techniques of adaptive optics, coronagraphy, and differential imaging, a combination designed to directly image exoplanets with the upcoming generation of "planet finders" such as GPI (Gemini Planet Imager) and SPHERE (Spectro-Polarimetric High contrast Exoplanet REsearch). Applied to extended objects such as circumstellar disks, the method is still successful but produces significant biases in terms of photometry and morphology. We developed a new model-matching procedure to correct for these biases and hence provide constraints on the morphology of debris disks. Results. From our program, we present new images of the disk around the star HD 32297 obtained in the H (1.6 μm) and Ks (2.2 μm) bands with an unprecedented angular resolution (∼65 mas). The images show an inclined thin disk detected at separations larger than 0.5−0.6 . The modeling stage confirms a very high inclination (i = 88 • ) and the presence of an inner cavity inside r 0 ≈ 110 AU. We also find that the spine (line of maximum intensity along the midplane) of the disk is curved, which we attribute to a large anisotropic scattering-factor (g ≈ 0.5, which is valid for an non-edge-on disk). Conclusions. Our modeling procedure is relevant to interpreting images of circumstellar disks observed with angular differential imaging. It allows us to both reduce the biases and estimate the disk parameters.

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“…Note, however, that Eq. (1) of TBO12 estimates the collision rate between similarly-sized bodies and that the typical impact velocities in debris discs are expected to be high enough for such collisions to lead to catastrophic fragmentation and thus produce a largest-remaining-fragment much smaller than the impactor (e.g., Thebault 2009) 5 so that one can assume that a given impactor loses its identitys after such an impact. Furthermore, for the smallest grains that dominate the system's brightness in scattered light, of sizes between the radiation pressure blow-out size s cut and a few s cut (Thebault & Augereau 2007), all produced collisional fragments will be smaller than s cut and thus very quickly removed from the system.…”

Section: Improvementsmentioning

confidence: 99%

Planet signatures in collisionally active debris discs: scattered light images

Thébault

Kral

Ertel

2012

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Context. Planet perturbations have been often invoked as a potential explanation for many spatial structures that have been imaged in debris discs. So far this issue has been mostly investigated with pure N-body numerical models, which neglect the crucial effect collisions within the disc can have on the disc's response to dynamical perturbations. Aims. We numerically investigate how the coupled effect of collisions and radiation pressure can affect the formation and survival of radial and azimutal structures in a disc perturbed by a planet. We consider two different set-ups: a planet embedded within an extended disc and a planet exterior to an inner debris ring. One important issue we want to address is under which conditions a planet's signature can be observable in a collisionally active disc. Methods. We use our DyCoSS code, which is designed to investigate the structure of perturbed debris discs at dynamical and collisional steady-state, and derive synthetic images of the system in scattered light. The planet's mass and orbit, as well as the disc's collisional activity (parameterized by its average vertical optical depth τ 0 ) are explored as free parameters. Results. We find that collisions always significantly damp planet-induced spatial structures. For the case of an embedded planet, the planet's signature, mostly a density gap around its radial position, should remain detectable in head-on images if M planet ≥ M Saturn . If the system is seen edge-on, however, inferring the presence of the planet is much more difficult, as only weak asymmetries remain in a collisionally active disc, although some planet-induced signatures might be observable under very favourable conditions. For the case of an inner ring and an external planet, planetary perturbations cannot prevent collision-produced small fragments from populating the regions beyond the ring. The radial luminosity profile exterior to the ring is in most cases close to the one it should have in the absence of the external planet. The most significant signature left by a Jovian planet on a circular orbit are precessing azimutal structures that can be used to indirectly infer its presence. For a planet on an eccentric orbit, we show that the ring becomes elliptic and that the well known pericentre glow effect is visible despite of collisions and radiation pressure, but that detecting such features in observed discs is not an unambiguous indicator of the presence of an outer planet.

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Vertical structure of debris discs

Cited by 72 publications

References 37 publications

The twofold debris disk around HD 113766 A

The twofold debris disk around HD 113766 A

Morphology of the very inclined debris disk around HD 32297

Planet signatures in collisionally active debris discs: scattered light images

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