  We have discovered that the Halpha emission line star Haro 5-2, located in
the 3-6 Myr old Ori OB1b association, is a young quadruple system. The system
has a 2+2 configuration with an outer separation of 2.6 arcseconds and with
resolved subarcsecond inner binary components. The brightest component, Aa,
dominates the A-binary, it is a weakline T Tauri star with spectral type
M2.5pm1. The two stars of the B component are equally bright at J, but the Bb
star is much redder. Optical spectroscopy of the combined B pair indicates a
rich emission line spectrum with a M3pm1 spectral type. The spectrum is highly
variable and switches back and forth between a classical and a weakline T Tauri
star. In the near-infrared, the spectrum shows Paschen beta and Brackett gamma
in emission, indicative of active accretion. A significant mid-infrared excess
reveals the presence of circumstellar or circumbinary material in the system.
Most multiple systems are likely formed during the protostellar phase,
involving flybys of neighboring stars followed by an in-spiraling phase driven
by accretion from circumbinary material and leading to compact sub-systems.
However, Haro 5-2 stands out among young 2+2 quadruples as the two inner
binaries are unusually wide relative to the separation of the A and B pair,
allowing future studies of the individual components. Assuming the components
are coeval, the system could potentially allow stringent tests of PMS
evolutionary models.
