We report the discovery of an L dwarf companion to the A3V star \textbeta Circini .
VVV J151721.49-585131.5 , or \textbeta Cir B , was identified in a proper motion and parallax catalogue of the Vista Variables in the Vía Láctea survey as having near infrared luminosity and colour indicative of an early L dwarf , and a proper motion and parallax consistent with that of \textbeta Cir .
The projected separation of \sim 3.6 \arcmin corresponds to 6656 au , which is unusually wide .
The most recent published estimate of the age of the primary combined with our own estimate based on newer isochrones yields an age of 370 - 500 Myr .
The system therefore serves as a useful benchmark at an age greater than that of the Pleiades brown dwarfs and most other young L dwarf benchmarks .
We have obtained a medium resolution echelle spectrum of the companion which indicates a spectral type of L1.0 \pm 0.5 and lacks the typical signatures of low surface gravity seen in younger brown dwarfs .
This suggests that signs of low surface gravity disappear from the spectra of early L dwarfs by an age of \sim 370 - 500 Myr , as expected from theoretical isochrones .
The mass of \textbeta Cir B is estimated from the BHAC15 isochrones as 0.056 \pm 0.007 M _ { \odot } .