Multiple stellar systems are formed during the early stages of star formation, and fragmentation is widely agreed to be the main formation mechanism. However, it is still debated when fragmentation occurs and if all multiple protostars form and evolve contemporaneously. To address this question, the coevality, i.e. the relative evolutionary stages of components in multiple protostars, must be determined. Since age isochrones are not useful at this stage of star formation, the coevality is determined through another method: the spectral energy distribution (SED).
Reference: Murillo, N. M., van Dishoeck, E. F., Tobin, J. J. and Fedele, D., 2016, A&A, 592, 56