Abstract
Context. Debris disks are the natural by-products of the planet formation process. Scattered or polarized light observations are mostly sensitive to small dust grains that are released from the grinding down of bigger planetesimals. Aims. High angular resolution observations at optical wavelengths can provide key constraints on the radial and azimuthal distribution of the small dust grains. These constraints can help us better understand where most of the dust grains are released upon collisions. Methods. We present SPHERE/ZIMPOL observations of the debris disk around HR 4796 A, and we modeled the radial profiles along several azimuthal angles of the disk with a code that accounts for the effect of stellar radiation pressure. This enabled us to derive an appropriate description for the radial and azimuthal distribution of the small dust grains. Results. Even though we only modeled the radial profiles along, or close to, the semi-major axis of the disk, our best-fit model is not only in good agreement with our observations but also with previously published datasets (from near-infrared to sub-mm wavelengths). We find that the reference radius is located at 76.4 ± 0.4 au, and the disk has an eccentricity of 0.076−0.010+0.016 with the pericenter located on the front side of the disk (north of the star). We find that small dust grains must be preferentially released near the pericenter to explain the observed brightness asymmetry. Conclusions. Even though parent bodies spend more time near the apocenter, the brightness asymmetry implies that collisions happen more frequently near the pericenter of the disk. Our model can successfully reproduce the shape of the outer edge of the disk without requiring an outer planet shaping the debris disk. With a simple treatment for the effect of the radiation pressure, we conclude that the parent planetesimals are located in a narrow ring of about 3.6 au in width.
Highlights
Debris disks are the leftovers of stellar, and planetary, formation processes
We present SPHERE/ZIMPOL observations of the debris disk around HR 4796 A, and we modeled the radial profiles along several azimuthal angles of the disk with a code that accounts for the effect of stellar radiation pressure
We find that on the front the reference radius is side of the disk
Summary
Debris disks are the leftovers of stellar, and planetary, formation processes. As the primordial gas-rich, massive circumstellarThe reduced image is available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc. u-strasbg.fr/viz-bin/cat/J/A+A/630/A142Based on observations made with ESO Telescopes at the Paranal Observatory under program ID 097.C-0523, 082.C-0218, and 089.C0207.disk evolves, the small dust grains grow and form planetesimals, which may become the building blocks of future planets. With a half-life time of a few million years (Hernández et al 2007), this primordial disk rapidly transitions toward its debris disk phase, losing the vast majority of its gaseous content In this debris disk phase, the planetesimals leftover from the planet formation process collisionally erode to produce the small dust grains that are observed. Olofsson et al (2016) and Milli et al (2017) studied the scattering phase function over a wide range of scattering angles for HD 61005 and HR 4796 A, respectively, using the SPHERE instrument Such studies help better constrain the nature of the small dust grains in young debris disks. Thanks to the exquisite spatial resolution provided by this new generation of instruments, we are able to perform in-depth studies of young and bright debris disks, trying to constrain the collisional activity responsible for the production of small dust grains
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