New astrometry and photometry for the companion candidates of CT Cha

TL;DR

This paper reports new H-band observations of companion candidates around the T Tauri star CT Cha, confirming the companionship of CT Cha b and identifying another candidate as a likely background star, thereby refining the understanding of this system.

Contribution

First direct H-band imaging of CT Cha b and a second candidate, providing evidence for the physical association of CT Cha b and excluding the background nature of cc2.

Findings

CT Cha b is a bound companion with high confidence.

cc2 is likely a background star, not a companion.

Proper motion measurements support the companionship status of CT Cha b.

Abstract

In our ongoing search for close and faint companions around T Tauri stars in the Chamaeleon star-forming region, we recently (Schmidt et al 2008b) presented direct observations and integral field spectroscopy of a new common proper motion companion to the young T-Tauri star and Chamaeleon member CT Cha and discussed its properties in comparison to other young, low-mass objects and to synthetic model spectra from different origins. We now obtained for the first time direct H-Band observations of the companion CT Cha b and of another faint companion candidate (cc2) approximately 1.9 arcsec northeast of CT Cha using the Adaptive Optics (AO) instrument Naos-Conica (NACO) at the Very Large Telescope (VLT) of the European Southern Observatory (ESO) in February 2008. From these data we can now exclude by 4.4 & 4.8 sigma that CT Cha b is a non-moving background object and find cc2 to be most likely a background star of spectral type <= K4 with a proper motion of mu{alpha} cos{delta} = -8.5 +/- 5.7 mas/yr and mu{delta} = 12.0 +/- 5.6 mas/yr, not consistent with being a member of the Cha I star-forming region.