GTC OSIRIS z-band imaging of Y dwarfs

TL;DR

This study provides z-band imaging of Y dwarfs to analyze their spectral energy distribution, revealing high dispersion in optical-to-infrared colours possibly due to atmospheric cloud and composition variations.

Contribution

First z-band imaging of Y dwarfs with GTC, offering new insights into their optical properties and spectral energy distribution.

Findings

Detected five of seven Y dwarfs in z-band

Found high dispersion in z-J and z-H colours among Y0 dwarfs

Suggested atmospheric cloud and composition effects influence colour dispersion

Abstract

The aim of the project is to contribute to the characterisation of the spectral energy distribution of the coolest brown dwarfs discovered to date, the Y dwarfs. We obtained z-band far-red imaging for six Y dwarfs and a T9+Y0 binary with the OSIRIS (Optical System for Imaging and low Resolution Integrated Spectroscopy) instrument on the 10.4-m Gran Telescopio de Canarias (GTC). We detect five of the seven known Y dwarfs in the $z$-band, infer their optical-to-infrared colours, and measure their proper motions. We find a higher dispersion in the z-J and z-H colours of Y0 dwarfs than in T dwarfs. This dispersion is found to be correlated with H-w2. The high dispersion in the optical-to-infrared colours of Y dwarfs and the possible turn-over towards bluer colours may be a consequence of the presence of sulfide clouds with different thicknesses, the depletion of alcalines, and/or gravity effects.