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We present  B   J  ,  R  59 F   and  I   N   photometry, and optical and near‐infrared spectroscopy, of a new ultracool white dwarf (UCWD) discovered in the SuperCOSMOS Sky Survey. The spectrum of SSS J1556−0806 shows strong flux suppression due to the presence of collisionally induced absorption by molecular hydrogen, a feature characteristic of the cool, high‐density environments found in the atmospheres of UCWDs. SSS J1556−0806 therefore joins a list of less than 10 UCWDs displaying extreme flux suppression. Synthetic model fitting suggests an effective temperature of &lt;3000 K, which if true would make this one of the coolest white dwarf currently known. We also exploit the similarity between the spectral energy distributions of SSS J1556−0806 and the well‐studied UCWD LHS 3250 to aid in the determination of the atmospheric parameters in a regime where models consistently fail to reproduce observations. SSS J1556−0806 is relatively bright ( R ∼ 17.8), making it particularly amenable to follow up observations to obtain trigonometric parallax and infrared photometry.

A new ultracool white dwarf discovered in the SuperCOSMOS Sky Survey