We report the discovery of a low-mass ( 0.26 \pm 0.02 , 0.15 \pm 0.01 { M } _ { \odot } ) pre-main-sequence eclipsing binary with a 5.3 { day } orbital period .
JW 380 was detected as part of a high-cadence time-resolved photometric survey ( the Monitor project ) using the 2.5 { m } Isaac Newton Telescope and Wide Field Camera for a survey of a single field in the Orion Nebula Cluster ( ONC ) region in V and i bands .
The star is assigned a 99 per cent membership probability from proper motion measurements , and radial velocity observations indicate a systemic velocity within 1 \sigma of that of the ONC .
Modelling of the combined light and radial velocity curves of the system gave stellar radii of 1.19 ^ { +0.04 } _ { -0.18 } { R } _ { \odot } and 0.90 ^ { +0.17 } _ { -0.03 } { R } _ { \odot } for the primary and secondary , with a significant third light contribution which is also visible as a third peak in the cross-correlation functions used to derive radial velocities .
The masses and radii appear to be consistent with stellar models for 2 - 3 { Myr } age from several authors , within the present observational errors .
These observations probe an important region of mass-radius parameter space , where there are currently only a handful of known pre-main-sequence eclipsing binary systems with precise measurements available in the literature .