An Infrared Multiplicity Survey of Class I/Flat-Spectrum Systems in the ρ Ophiuchi and Serpens Molecular Clouds

Abstract

We present new near- and mid-IR observations of 19 Class I/flat-spectrum young stellar objects in the nearby ρ Oph (d = 125 pc) and Serpens (d = 310 pc) dark clouds. These observations are part of a larger systematic infrared multiplicity survey of Class I/flat-spectrum objects in the nearest dark clouds. We find 7/19 (37% ± 14%) of the sources surveyed to be multiple systems over a separation range of ~150–1800 AU. This is consistent with the fraction of multiple systems found among older pre–main-sequence stars in each of the Taurus, ρ Oph, Chamaeleon, Lupus, and Corona Australis star-forming regions over a similar separation range. However, solar-type main-sequence stars in the solar neighborhood have a fraction approximately one-third that of our Class I/flat-spectrum sample (11% ± 3%). This may be attributed to evolutionary effects or environmental differences. An examination of the spectral energy distributions (SEDs) of the SVS 20 and WL 1 binaries reveals that the individual components of each source exhibit the same SED classifications, similar to what one typically finds for binary T Tauri star (TTS) systems, where the companion of a classical TTS also tends to be of the same SED type.