EPoS Contribution
EPoS Contribution
Mid-Infrared Observations of Class I/Flat-Spectrum Systems in Six Nearby Molecular Clouds

Karl Haisch
Utah Valley State College, Orem, USA
We present the results of new mid-infrared observations of 64 Class I/flat-spectrum objects in the Perseus, Taurus, Chamaeleon I and II, Rho Ophiuchi, and Serpens dark clouds. These objects represent a subset of the young stellar objects (YSOs) from our previous near-infrared multiplicity surveys. We detected 45/48 (94%) of the single sources, 16/16 (100%) of the primary components, and 12/16 (75%) of the secondary/triple components of the binary/multiple objects surveyed. While the composite spectral energy distributions for all of our sample YSOs are either Class I or flat-spectrum, the individual source components typically display Class II, or in one case Class III, spectral indices, and frequently display mixed pairings; Class I objects paired with a flat-spectrum source, or a flat-spectrum source paired with a Class II YSO. Such behavior is not consistent with what one typically finds for T Tauri stars (TTS), where the companion of a classical TTS also tends to be a classical TTS, although other mixed pairings have been previously observed among Class II YSOs. Based on an analysis of the spectral indices of the individual binary components, there appears to be a higher proportion of mixed Class I/Flat-Spectrum systems (70-80%) than that of mixed Classical/Weak Lined T Tauri systems (25-40%), demonstrating that the envelopes of Class I/Flat-Spectrum systems are rapidly evolving during this evolutionary phase, although they may still be coeval if Class I and Flat-Spectrum systems are intrinsically similar, but different geometric orientations are responsible for producing different spectral energy distributions (SEDs). Finally, the source ISO-Cha I 97, with a spectral index of alpha > 3.9, is a member of a rare class of very steep spectral index YSOs, those with alpha > 3.