Sebastian Marino

Warps have often been used to explain disc properties, but well-characterized examples are important due to their role in disc evolution. Scattered light images of discs with central gaps have revealed sharp warps, such that the outer rings are shadowed by tilted inner discs. The near-infrared intensity drops along the ring around T-Tauri star DoAr 44 have been interpreted in terms of a central warp. We report new ALMA observations of DoAr 44 in the continuum at 230 and 350 GHz (at ∼10 au), along with a new epoch of Spectro Polarimetric High-contrast Exoplanet REsearch (SPHERE)/Infrared Dual-band Imager and Spectrograph differential polarized imaging taken during excellent weather conditions. The ALMA observations resolve the ring and confirm the decrements proposed from deconvolution of coarse 336 GHz data. The scattered light image constrains the dips, which correspond to a misaligned inner disc with a relative inclination ξ = 21.4 $^{+6.7}_{-8.3}$ deg. The SPHERE intensity profile shows a morphological change compared to a previous epoch that may be interpreted as a variable orientation of the inner disc, from ξ ∼ 30 deg to ξ ∼ 20 deg. The intensity dips probably correspond to temperature decrements, as their mm-spectral index, $\alpha ^{230 \textrm {GHz}}_{350 \textrm {GHz}} \sim$ 2.0 ± 0.1, is indicative of optically thick emission. The azimuth of the two temperature decrements are leading clockwise relative to the infrared-dips, by η = 14.95 deg and η = 7.92 deg. For a retrograde disc, such shifts are expected from a thermal lag and imply gas surface densities of Σg = 117 ± 10 g cm−2 and Σg = 48 ± 10 g cm−2. A lopsided disc, with contrast ratio fr = 2.4 ± 0.5, is also consistent with the large continuum crescent.

$\kappa \,$ CrB is an ∼2.5 Gyr old K1 sub-giant star, with an eccentric exo-Jupiter at ∼2.8 au and a debris disc at tens of au. We present ALMA (Atacama Large Millimetre/submillimetre Array) Band 6 (1.3 mm) and Hubble Space Telescope scattered light (0.6$\, \mu$m) images, demonstrating $\kappa \,$CrB’s broad debris disc, covering an extent $50\!-\!180\,$au in the millimetre (peaking at 110 au), and $51\!-\!280\,$au in scattered light (peaking at 73 au). By modelling the millimetre emission, we estimate the dust mass as ${\sim }0.016\, {\rm M}_\oplus$, and constrain lower-limit planetesimal sizes as $D_{\rm {max}}{\gtrsim }1\,$km and the planetesimal belt mass as $M_{\rm {disc}}{\gtrsim }1\, {\rm M}_\oplus$. We constrain the properties of an outer body causing a linear trend in 17 yr of radial velocity data to have a semimajor axis 8–66 au and a mass $0.4\!-\!120\, M_{\rm {Jup}}$. There is a large inner cavity seen in the millimetre emission, which we show is consistent with carving by such an outer massive companion with a string of lower mass planets. Our scattered light modelling shows that the dust must have a high anisotropic scattering factor (g ∼ 0.8–0.9) but an inclination (i ∼ 30°–40°) that is inferred to be significantly lower than the i ∼ 61° millimetre inclination. The origin of such a discrepancy is unclear, but could be caused by a misalignment in the micrometre- and millimetre-sized dust. We place an upper limit on the CO gas mass of $M_{\rm {CO}}{\lt }(4.2\!-\!13) \times 10^{-7}\, {\rm M}_\oplus$, and show this to be consistent with levels expected from planetesimal collisions, or from CO-ice sublimation as $\kappa \,$CrB begins its giant branch ascent.