Abstract

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 DoAr44 have been interpreted in terms of a central warp. We report new ALMA observations of DoAr44 in the continuum at 230 and 350GHz (at similar to 10au), 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 336GHz data. The scattered light image constrains the dips, which correspond to a misaligned inner disc with a relative inclination xi =21.4(-8.3)(+6.7) 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 xi similar to 30 deg to xi similar to 20 deg. The intensity dips probably correspond to temperature decrements, as their mm-spectral index, alpha(230GHz)(350GHz) similar to 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 eta=14.95deg and eta = 7.92deg. For a retrograde disc, such shifts are expected from a thermal lag and imply gas surface densities of Sigma(g) = 117 +/- 10 gcm(-2) and Sigma(g) = 48 +/- 10gcm(-2). A lopsided disc, with contrast ratio f(r) = 2.4 +/- 0.5, is also consistent with the large continuum crescent.