Dust temperature in L1688, taken from Herschel Gould Belt Survey archive. The solid white contours show the coherent cores in the region (described later in Sect. 4.4). The vertical dotted line roughly separates the dark cloud (to the left of the line) from the molecular material affected by the external illumination, due to irradiation from HD147889 (Habart et al. 2003). The 1′ beam, which the data was convolved to, is shown in green in the bottom-left corner, and the scale bar is shown in the bottom-right corner.