We report our discovery of an extremely rare , low mass , quadruple-lined spectroscopic binary BD –22 ^ { \circ } 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 a _ { \mathrm { A } } sin i _ { \mathrm { A } } \leq 0.06 AU and a _ { \mathrm { B } } sin i _ { \mathrm { B } } \leq 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 ^ { \circ } .
Within uncertainties of 5 % , the masses and radii of both components appear to be equal ( 0.59 M _ { \sun } , 0.61 R _ { \sun } ) .
These two tightly orbiting stars ( a = 0.035 AU ) are in synchronous rotation causing the observed excess Ca II , H \alpha , 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 _ { \mathrm { AB } } \lesssim 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 a _ { \mathrm { AB } } sin i _ { \mathrm { AB } } \leq 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 .