  We report our discovery of an extremely rare, low mass, quadruple-lined
spectroscopic binary BD-22 5866 (=NLTT 53279, integrated spectral type = M0 V),
found during an ongoing search for the youngest M dwarfs in the solar
neighborhood. From the cross-correlation function, we are able to measure
relative flux levels, estimate the spectral types of the components, and set
upper limits on the orbital periods and separations. The resulting system is
hierarchical composed of K7 + K7 binary and a M1 + M2 binary with semi-major
axes of asini_{A}<=0.06 AU and asini_{B}<=0.30 AU. A subsequent search of the
SuperWASP photometric database revealed that the K7 + K7 binary is eclipsing
with a period of 2.21 days and at an inclination angle of 85 degrees. Within
uncertainties of 5%, the masses and radii of both components appear to be equal
(0.59 Msun, 0.61 Rsun). These two tightly orbiting stars (a = 0.035 AU) are in
synchronous rotation causing the observed excess Ca II, Halpha, X-ray and UV
emission. The fact that the system was unresolved with published adaptive
optics imaging, limits the projected physical separation of the two binaries at
the time of the observation to d_{AB} < 4.1 AU at the photometric distance of
51 pc. The maximum observed radial velocity difference between the A and B
binaries limits the orbit to asini_{AB}<=6.1 AU. As this tight configuration is
difficult to reproduce with current formation models of multiple systems, we
speculate that an early dynamical process reduced the size of the system such
as the interaction of the two binaries with a circumquadruple disk. Intensive
photometric, spectroscopic and interferometric monitoring as well as a parallax
measurement of this rare quadruple system is certainly warranted.
