Abstract
Context. Direct imaging of debris discs gives important information about their nature, their global morphology, and allows us to identify specific structures possibly in connection with the presence of gravitational perturbers. It is the most straightforward technique to observe planetary systems as a whole. Aims. We present the first resolved images of the debris disc around the young F-type star HD 160305, detected in scattered light using the VLT/SPHERE instrument in the near infrared. Methods. We used a post-processing method based on angular differential imaging and synthetic images of debris discs produced with a disc modelling code (GRaTer) to constrain the main characteristics of the disc around HD 160305. All of the point sources in the field of the IRDIS camera were analysed with an astrometric tool to determine whether they are bound objects or background stars. Results. We detect a very inclined (~82°) ring-like debris disc located at a stellocentric distance of about 86 au (deprojected width ~27 au). The disc displays a brightness asymmetry between the two sides of the major axis, as can be expected from scattering properties of dust grains. We derive an anisotropic scattering factor g > 0.5. A second right-left asymmetry is also observed with respect to the minor axis. We measure a surface brightness ratio of 0.73 ± 0.18 between the bright and the faint sides. Because of the low signal-to-noise ratio (S/N) of the images we cannot easily discriminate between several possible explanations for this left-right asymmetry, such as perturbations by an unseen planet, the aftermath of the breakup of a massive planetesimal, or the pericenter glow effect due to an eccentric ring. Two epochs of observations allow us to reject the companionship hypothesis for the 15 point sources present in the field.
Highlights
IntroductionIn the current model of planetary system formation, a circumstellar disc evolves from the protoplanetary disc phase (optically thick, dominated by gas; Williams & Cieza 2011) to the debris disc phase (optically thin, with low or no gas content; Hughes et al 2018)
In the current model of planetary system formation, a circumstellar disc evolves from the protoplanetary disc phase to the debris disc phase
With the advent of dedicated instruments for high-contrast imaging (first the Hubble Space Telescope, see e.g. Schneider et al 1999; Kalas et al 2007; Choquet et al 2016 and more recently the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE), Beuzit et al 2019 and the Gemini Planet Imager (GPI), Macintosh et al 2014), a variety of morphologies were discovered among debris discs
Summary
In the current model of planetary system formation, a circumstellar disc evolves from the protoplanetary disc phase (optically thick, dominated by gas; Williams & Cieza 2011) to the debris disc phase (optically thin, with low or no gas content; Hughes et al 2018) This inside-out process lasts typically a few million years during which the primordial gas dissipates, leaving only planets, if already formed, and planetesimal belts (Hernández et al 2007). For most imaged asymmetric discs, where no companion has been detected (yet), other explanations than the planet-sculpting scenario might be possible Such scenarios include the breakup of a massive planetesimal (Kral et al 2015), or the interaction between dust and gas due for example to the photoelectric instability of the dust (Lyra & Kuchner 2013; Richert et al 2018)
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