Evidence for supernova-induced star formation in the monoceros OB2 association

Abstract

The Monoceros ring, a circular optical nebulosity ~3°.5 in diameter and centred at R.A.=6^h37^m, Dec.=6°30' (l^II=205°.5, b^II=0°.2) is in good structural agreement with radio observations. A neutral hydrogen shell is also accurately projected on the ring. These observations are consistent with the Monoceros ring being a supernova remnant 90-100 pc in diameter expanding at about 45 km s⁻¹ and having an age of the order of a million years. Bright HII regions containing early-type stars (e.g., galactic cluster NGC 2244 in the Rosette nebula) and extremely young stars of the OB association Mon OB2 lie at the edges of the ring. The positional and temporal coincidence of the Mon OB2 association with a supernova remnant suggests that probably the star formation in this region is induced or speeded up by the passage of a supernova shock wave through the clumpy interstellar medium.