A far-infrared H-R diagram of young stellar objects

The observed spectral energy distributions from far-infrared (FIR) to millimeter wavelengths of young stellar objects (YSOs) fit a modified blackbody radiation with a peak around 100 m for both high-and low-mass YSOs. The spectra are nearly represented by the FIR colors made byIRAS flux densities at 60 and 100 m. UsingIRAS data, we make a FIR H-R diagram of cold YSOs, the parameters of which are the FIR color and the luminosity at 60 m. In each FIR H-R diagram of YSOs of three nearby star-forming regions, YSOs in early evolutionary phase form a fundamental sequence, along which they move with increasing of the luminosity while keeping the mass of FIR emitting envelope. We can predict the stellar masses of YSOs by using the H-R diagram.