for NIR spectroscopic characterisation, we already obtained a spectrum of CFBDSIR1458, which we discuss in section 4.2.

[**Proper motion of CFBDSIR1458**]{}\
Since the $z'$ MegaCam image and the $J$ WIRCam image are co-aligned by the CFBDSIR pipeline the proper motion is easily measured from these 2 images. CFBDSIR1458 moves by +0.58 in RA and -0.95 in DEC between the July 15, 2004 date of the $z'$ image and April 1, 2007 date of the $J$ image. The centroiding and image alignment uncertainties are low, at 0.035, but the error budget has to include chromatic refraction and the uncertain parallactic motion. The estimated spectroscopic distance is $\sim$23pc, with a likely range of 15–30 pc (Table \[pm\]), which translates to a 0.04maximum error from the parallax. Due to the very steep spectral energy distribution in the $z'$ band, chromatic refraction here is of the order of the measurement error. We also measured the proper motion between the $J$-band WIRCam discovery image and the $J$ band NTT follow-up image, finding +0.32 in RA and -0.80 in DEC between April 1, 2007 and March 5, 2009. This second measurement has smaller centroiding and image-alignment uncertainties, 0.03, minimal chromatic refraction uncertainties since the two $J$-band 