Abstract:
We utilize the data from the Apache Point Observatory Galactic Evolution Experiment-2 in the fourteenth data release of the Sloan Digital Sky Survey, and select 22 old open clusters of age larger than 1 Gyr from the Milky Way open cluster catalog of Kharchenko, and derive their structural and kinematic parameters, the intrinsic total luminosity in K_s band ($L_{K_s}$)， the line-of-sight velocity dispersion ($\sigma_{1D}$), and the half-number radius ($R_{50}$).  There is a robust monotonically increasing correlation between luminosity and radius.  The fundamental plane is built for the old open clusters, based on the $L_{K_s}$, the $\sigma_{1D}$, and the $R_{50}$. There is an age dependence of the open clusters on the fundamental plane with older clusters lying closer to the plane.  The fundamental plane expressed as,  $L_{K_s}\propto\sigma_{1D}^{0.7\pm0.3}\cdot r_{50}^{2.2\pm0.6}$, is tilted from the virial plane significantly. The strong tidal field of the Galactic disk, such as the molecular cloud encounters and the spiral arm pertubation, might be reasons for the tilt of old OCs.