Galactic cold cores:<i>Herschel</i>study of first<i>Planck</i>detections

<i>Context. <i/> We present the first results from the project Galactic cold cores, where the cold interstellar clouds detected by the <i>Planck<i/> satellite are studied with <i>Herschel<i/> photometric observations. The final <i>Planck<i/> catalogue is expected to contain several thousand sources. The <i>Herschel<i/> observations during the science demonstration phase provided the first glimpse into the nature of these sources.<i>Aims. <i/>The main goal of the project is to derive the physical properties of the cold core population revealed by <i>Planck<i/>. We examine three fields and confirm the <i>Planck<i/> detections with <i>Herschel<i/> data, which we also use to establish the evolutionary stage of the identified cores.<i>Methods. <i/>We study the morphology and spectral energy distribution of the sources using the combined wavelength coverage of <i>Planck<i/> and <i>Herschel<i/>. The dust colour temperatures and emissivity indices are determined. The masses of the cores are determined with distance estimates which are taken from the literature and are confirmed by kinematic and extinction information. <i>Results. <i/>The observations reveal extended regions of cold dust with dust colour temperatures down to <i>T<i/><sub>dust<sub/> ~ 11 K. The fields represent different evolutionary stages ranging from a quiescent, cold filament in Musca to regions of active star formation in Cepheus. <i>Conclusions. <i/>The <i>Herschel<i/> observations confirm that the all-sky survey of <i>Planck<i/> is capable of making a large number of new cold core detections. Our results suggest that many of the sources may already have left the pre-stellar phase or are at least closely associated with active star formation. High-resolution <i>Herschel<i/> observations are needed to establish the true nature of the <i>Planck<i/> detections.