2004A&A...420..533T

Three prominent cold objects of the Taurus Molecular Ring (TMR) were revealed by our ISOPHOT 200 µm map of the south-eastern part of the Heiles Cloud 2 (HCL2) cloud complex. One corresponds to the cyanopolyyne peak region of the TMC-1 ridge, (TMC-1CP), one is the HCL2-E cloud, and one which we call HCL2-ES lies south of TMC-1. The 200/100µm colour temperatures and column densities of the three ISOPHOT cold clouds are ≃12K, and 1.2±0.7x10²²cm^–2 respectively, as calculated from ISO/IRAS surface brightnesses. As Nagoya-4m C¹⁸O (1-0) spectra show, these are dense molecular clouds with N(H)>10²¹cm^–2 column density peaks. The ISOPHOT 200µm surface brightness is well correlated with the C¹⁸O line intensity (corr. coef.≃70%). The large dust particle emissivity is found to be increased in the prototypical very dense core TMC-1CP. As the low linewidths (Δv=0.8±0.2 km/s) indicate, the level of turbulent energy density is 50% lower in these three clouds than in other clouds of HCL2. Dense cores were identified inside the C¹⁸O clouds by NH₃ measurements with the Effelsberg-100 m telescope and Nobeyama-45m H¹³CO⁺ data. The density of the dense cores is n≥1.1x10⁵cm^–3, and their kinetic temperatures are ≲10K, in good agreement with the FIR results. The total molecular gas mass in the gravitationally bound cloud cores of TMC-1CP and HCL2-E is about 21 M_☉ and 8 M_☉ respectively. The cores, TMC-1CPb and HCL2-Eab are associated with 3 low mass YSO candidate 2MASS point sources, while 35 other low mass YSO candidates are seen elsewhere in TMR south, which we consider as evidence for ongoing low mass star formation.