Two Embedded Young Stellar Objects in NGC 2264 with FU Orionis Characteristics

Abstract

We report the discovery of two young stars in the NGC 2264 star-forming molecular cloud whose physical and morphological characteristics are similar to FU Orionis objects. The objects form a close pair and exhibit a curved reflection nebula in the near-IR. The brighter of the two stars, AR 6A, is optically visible but considerably reddened, has a small 3 μm IR excess, shows pronounced 2.294 μm CO overtone band head absorption, and is the brightest near-IR object in the region. The fainter star, AR 6B, located 28 south, has a much larger thermal IR excess and shows considerably deeper CO band head absorption identical to that seen in several known FU Orionis stars (FUors). Both stars therefore resemble FUors in terms of thermal excess, near-IR spectral features, and morphology. Here we discuss the characteristics of AR 6A and AR 6B in relation to the FUor population and propose that both stars are likely additional members of this class of young stellar outburst objects. We speculate that the simultaneous appearance of two FUor–like objects in a binary system, which would be highly unlikely if unrelated, could be caused by orbital evolution in a newly formed hierarchical quadruple system.