2010MNRAS.401..455C

We present submillimetre observations of the J = 3 ⟶ 2 rotational transition of ¹²CO, ¹³CO and C¹⁸O across over 600arcmin² of the Perseus molecular cloud, undertaken with the Heterodyne Array Receiver Programme (HARP), a new array spectrograph on the James Clerk Maxwell Telescope. The data encompass four regions of the cloud, containing the largest clusters of dust continuum condensations: NGC 1333, IC348, L1448 and L1455. A new procedure to remove striping artefacts from the raw HARP data is introduced. We compare the maps to those of the dust continuum emission mapped with the Submillimetre Common-User Bolometer Array (SCUBA; Hatchell et al.) and the positions of starless and protostellar cores (Hatchell et al.). No straightforward correlation is found between the masses of each region derived from the HARP CO and SCUBA data, underlining the care that must be exercised when comparing masses of the same object derived from different tracers. From the ¹³CO/C¹⁸O line ratio the relative abundance of the two species ([¹³CO]/[C¹⁸O] ∼ 7) and their opacities (typically τ is 0.02-0.22 and 0.15-1.52 for the C¹⁸O and ¹³CO gas, respectively) are calculated. C¹⁸O is optically thin nearly everywhere, increasing in opacity towards star-forming cores but not beyond τ₁₈∼ 0.9. Assuming the ¹²CO gas is optically thick, we compute its excitation temperature, T_ex(around 8-30K), which has little correlation with estimates of the dust temperature.