SEDs of cores located at the center of a spherical filament with a total central extinction A_V = 8   mag (left-hand figure) and A_V = 64   mag (right-hand figure). The filaments are embedded in a medium with p_ext/k = 2  ×  10⁴   K/cm³ (top) or 10⁶   K/cm³ (bottom) and are heated by an unattenuated interstellar radiation field (grey solid line). The derived dust re-emission spectrum is shown as a solid black line, the radiation heating the core as a long dashed line, and the attenuated emission leaving the core as a dashed-dotted line. Also given is the emission produced by photons scattered inside the core (black dotted lines). The grey dotted lines show the individual components of multiply scattered photons. The top curve shows singly scattered emission, the curves below emission scattered twice and so on. The dust emission spectrum is fitted to a modified black-body function (short dashed line).