We present the first mid-infrared spectra of two cool white dwarfs obtained with the Spitzer Space Telescope .
We also present 3.5 - 8 \mu m photometry for 19 cool white dwarfs with 5000 K \leq T _ { eff } \leq 9000 K. We perform a detailed model atmosphere analysis of these white dwarfs by fitting their UBVRIJHK and Spitzer photometry with state-of-the-art model atmospheres , and demonstrate that the optical and infrared spectral energy distributions of cool white dwarfs are well reproduced by our grid of models .
Our mid-infrared photometry and 7.5–14.5 \mu m spectrum of WD0018-267 are consistent with a T _ { eff } = 5720 K , pure hydrogen white dwarf model atmosphere .
On the other hand , LHS 1126 remains peculiar with significant mid-infrared flux deficits in all IRAC bands and a featureless spectrum in the 5.2–7.5 \mu m range .
Even though this deficit is attributed to collision induced absorption ( CIA ) due to molecular hydrogen , the shape of the deficit can not be explained with current CIA opacity calculations .
The infrared portion of the LHS 1126 spectral energy distribution is best-fit with a power law index of - 1.99 ; identical to a Rayleigh-Jeans spectrum .
This argues that the deficit may be due to an unrecognized grey-like opacity source in the infrared .