We obtained N-band observations of the Apollo asteroid 2002~NY40 during its close Earth fly-by in August 2002 with TIMMI2 at the ESO 3.6 m telescope .
The photometric measurement allowed us to derive a radiometric diameter of 0.28 \pm 0.03 km and an albedo of 0.34 \pm 0.06 through the near-Earth asteroid thermal model ( NEATM ) and a thermophysical model ( TPM ) .
The values are in agreement with results from radar data , visual and near-IR observations .
In this first comparison between these two model approaches we found that the empirical NEATM beaming parameter \eta = 1.0 corresponds to a thermal inertia values of about 100 \mathrm { J m ^ { -2 } s ^ { -0.5 } K ^ { -1 } } for a typical range of surface roughness , assuming an equator-on viewing angle .
Our TPM analysis indicated that the surface of 2002~NY40 consists of rocky material with a thin or no dust regolith .
The asteroid very likely has a prograde sense of rotation with a cold terminator at the time of our observations .
Although both model approaches can fit the thermal spectra taken at phase angles of 22 ^ { \circ } and 59 ^ { \circ } , we did not find a consistent model solution that describes all pieces of photometric and spectroscopic data .
In addition to the 2002~NY40 analysis , we discuss the possibilities to distinguish between different models with only very few photometric and/or spectroscopic measurements spread over a range of phase angles .