DZ Chamaeleontis: a bona fide photoevaporating disc

Canovas, H.;Montesinos, B.;Schreiber, M. R.;Cieza, L. A.;Eiroa, C.;Meeus, G.;de Boer, J.;Ménard, F.;Wahhaj, Z.;Riviere-Marichalar, P.;Olofsson, J.;Garufi, A.;Rebollido, I.;van Holstein, R. G.;Caceres, C.;Hardy, A.;Villaver, E. 2018. DZ Chamaeleontis: a bona fide photoevaporating disc. Astronomy and Astrophysics 610, DOI: 10.1051/0004-6361/201731640

DZ Cha is a weak-lined T Tauri star (WTTS) surrounded by a bright protoplanetary disc with evidence of inner disc clearing. Its narrow H alpha line and infrared spectral energy distribution suggest that DZ Cha may be a photoevaporating disc.

Aims. We aim to analyse the DZ Cha star + disc system to identify the mechanism driving the evolution of this object.

Methods. We have analysed three epochs of high resolution optical spectroscopy, photometry from the UV up to the sub-mm regime, infrared spectroscopy, and J-band imaging polarimetry observations of DZ Cha.

Results. Combining our analysis with previous studies we find no signatures of accretion in the H alpha line profile in nine epochs covering a time baseline of similar to 20 yr. The optical spectra are dominated by chromospheric emission lines, but they also show emission from the forbidden lines [SII] 4068 and [OI] 6300 angstrom that indicate a disc outflow. The polarized images reveal a dust depleted cavity of similar to 7 au in radius and two spiral-like features, and we derive a disc dust mass limit of M-dust < 3 M-Earth from the sub-mm photometry. No stellar (M-* > 80 M-Jup) companions are detected down to 0 ».07 (similar to 8 au, projected).

Conclusions. The negligible accretion rate, small cavity, and forbidden line emission strongly suggests that DZ Cha is currently at the initial stages of disc clearing by photoevaporation. At this point the inner disc has drained and the inner wall of the truncated outer disc is directly exposed to the stellar radiation. We argue that other mechanisms like planet formation or binarity cannot explain the observed properties of DZ Cha. The scarcity of objects like this one is in line with the dispersal timescale (less than or similar to 10(5) yr) predicted by this theory. DZ Cha is therefore an ideal target to study the initial stages of photoevaporation.

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