DZ Chamaeleontis: a bona fide photoevaporating disc^⋆

¹ Departamento de Física Teórica, Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain
e-mail: hcanovas@sciops.esa.int
² European Space Astronomy Centre (ESA), Camino Bajo del Castillo s/n, 28692 Villanueva de la Cañada, Madrid, Spain
³ Dept. of Astrophysics, Centre for Astrobiology (CAB, CSIC-INTA), ESAC Campus, Camino Bajo del Castillo s/n, 28692 Villanueva de la Cañada, Madrid, Spain
⁴ Departamento de Física y Astronomía, Universidad de Valparaíso, Casillo 5030, Valparaíso, Chile
⁵ Facultad de Ingeniería y Ciencias, Universidad Diego Portales, Av. Ejercito 441, Santiago, Chile
⁶ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
⁷ Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
⁸ European Southern Observatory, 3107 Alonso de Cordova, Vitacura, 1058 Santiago, Chile
⁹ Instituto de Ciencia de Materiales de Madrid (ICMM-CSIC), 28049 Cantoblanco, Madrid, Spain
¹⁰ Departamento de Ciencias Fisicas, Facultad de Ciencias Exactas, Universidad Andres Bello Av. Fernandez Concha 700, Las Condes, Santiago, Chile
¹¹ Millennium Nucleus, Protoplanetary discs in ALMA Early Science, 1058 Santiago, Chile
¹² Millennium Nucleus for Planet Formation, Chile

Received: 25 July 2017
Accepted: 9 October 2017

Abstract

Context. DZ Cha is a weak-lined T Tauri star (WTTS) surrounded by a bright protoplanetary disc with evidence of inner disc clearing. Its narrow Hα 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 Hα line profile in nine epochs covering a time baseline of ~20 yr. The optical spectra are dominated by chromospheric emission lines, but they also show emission from the forbidden lines [SII] 4068 and [OI] 6300Å that indicate a disc outflow. The polarized images reveal a dust depleted cavity of ~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 (~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 (≲10⁵ yr) predicted by this theory. DZ Cha is therefore an ideal target to study the initial stages of photoevaporation.