Spatially resolved spectroscopy of the debris disk HD 32297

T Bhowmik,P Baudoz,A.-M Lagrange,R G Van Holstein,J Milli,C Perrot,A L Maire,A Boccaletti,J.-C Augereau,E Pantin,P Thébault,M Feldt,J Mazoyer,Q Kral,J Olofsson,T Henning,R Galicher

doi:10.1051/0004-6361/201936076

Abstract

Context. Spectro-photometry of debris disks in total intensity and polarimetry can provide new insight into the properties of the dust grains therein (size distribution and optical properties). Aims. We aim to constrain the morphology of the highly inclined debris disk HD 32297. We also intend to obtain spectroscopic and polarimetric measurements to retrieve information on the particle size distribution within the disk for certain grain compositions. Methods. We observed HD 32297 with SPHERE in Y, J, and H bands in total intensity and in J band in polarimetry. The observations are compared to synthetic models of debris disks and we developed methods to extract the photometry in total intensity overcoming the data-reduction artifacts, namely the self-subtraction. The spectro-photometric measurements averaged along the disk mid-plane are then compared to model spectra of various grain compositions. Results. These new images reveal the very inner part of the system as close as 0.15″. The disk image is mostly dominated by the forward scattering making one side (half-ellipse) of the disk more visible, but observations in total intensity are deep enough to also detect the back side for the very first time. The images as well as the surface brightness profiles of the disk rule out the presence of a gap as previously proposed. We do not detect any significant asymmetry between the northeast and southwest sides of the disk. The spectral reflectance features a “gray to blue” color which is interpreted as the presence of grains far below the blowout size. Conclusions. The presence of sub-micron grains in the disk is suspected to be the result of gas drag and/or “avalanche mechanisms”. The blue color of the disk could be further investigated with additional total intensity and polarimetric observations in K and H bands respectively to confirm the spectral slope and the fraction of polarization.

Highlights

Debris disks are a class of circumstellar disks in which the dust content is thought to be continuously replenished by collisions of planetesimals, usually distributed in a single belt or in multiple belts
The observations are compared to synthetic models of debris disks and we developed methods to extract the photometry in total intensity overcoming the data-reduction artifacts, namely the self-subtraction
In this paper we present new high-contrast imaging observations of HD 32297 with Spectro-Polarimetric High-contrast Exoplanet Research (SPHERE, Beuzit et al 2019) at VLT in Chile, in the NIR from Y to H band complemented with polarimetric observations in the J band

Summary

Introduction

Debris disks are a class of circumstellar disks in which the dust content is thought to be continuously replenished by collisions of planetesimals, usually distributed in a single belt or in multiple belts. Debris disks frequently show identifiable structures like blobs (AU Mic, Boccaletti et al 2018), warps (β Pic, Mouillet et al 1997), multiple belts (Bonnefoy et al 2017; Boccaletti et al 2019, HIP 67497 and NZ Lup), asymmetries (Mazoyer et al 2014, HD 15115), and other irregularities in the disk These structures might be sculpted by transient breakups of massive bodies (Jackson et al 2014; Kral et al 2015), stellar flybys (Lestrade et al 2011), stellar companions (Thébault 2012), or interactions with the inter-stellar medium

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