1994A&A...288..165A

We present 1-3.4µm near-IR array images of ESO Hα 279, the optical emission line star proposed to be the exciting source of the bipolar Herbig-Haro complex HH106/107 in Serpens. These images show the presence of a close, bright infrared stellar companion to ESO Hα 279 located 8.2" due south. At 2µm, no other sources are seen within ∼1' of these stars suggesting that ESO Hα 279 and its companion may form a pre-main sequence (PMS) binary. Our NIR photometry has shown that the optical emission line star, ESO Hα 279a, is a young, PMS object possessing a strong thermal excess beyond 2µm. Additionally, 2µm spectroscopy has revealed that ESO Hα 279a possesses very strong CO bandhead emission from 2.29-2.45µm indicative of the presence of an active accretion disk and/or molecular outflow. The companion source, ESO Hα 279b, was found to be extremely red with a J-K∼7. Spectroscopy showed that it possesses strong CO bandhead absorption. From both the relative strengths of the dereddened spectral features and evidence provided by the near-IR photometry, we suggest that ESO Hα 279b is likely not a PMS companion to ESO Hα 279a, but rather it is a highly reddened (A_V=30-40) background M5 III giant. This result emphasizes the extreme care that needs to be taken when using infrared imaging data to study the frequency of binaries amongst PMS stars.