Volume 575, March 2015
|Number of page(s)||38|
|Section||Interstellar and circumstellar matter|
|Published online||16 February 2015|
Tables A.1 and A.2 provide a detailed list of the observationally derived physical parameters of the cores for each transition separately. The method for extracting these values is described in Sects. 3 and 4. For the spectra that have two velocity components, the derived properties based on both components are listed. The integrated intensities are listed only for the transitions that were used to derive column densities.
Line parameters and physical parameters of cores in Cha I.
Line parameters and physical parameters of cores in Cha III.
For the calculation of critical densities we use the Einstein A-coefficients, the collisional rate coefficients, and energies from the Leiden Atomic and Molecular Database (LAMDA4).
The critical density is the density at which the rate of spontaneous emission is equal to the rate of collisional de-excitation,(B.1)where Aul is the Einstein coefficient for spontaneous emission (s-1), Cul = nH2γul the collision coefficient (collision de-excitation rate, s-1), and γul the collision rate (cm3 s-1). The critical densities we derive are listed in Table B.1 for various molecular transitions.
C18O 2–1 was observed toward all 60 cores in Cha I and C17O 2−1 toward 32. We estimate the optical depth of the C18O 2–1 transition for this sample of 32 cores. We assume an isotopic ratio [18O]/[17O] of ~4.11, as was found for the nearby (140 pc) low-mass star forming cloud ρ Ophiuchus (Wouterloot et al. 2005), to derive the opacity of C18O 2−1 with the relation (C.1)where IC18O and IC17O are the integrated intensities of the two transitions, τC18O and τC17O their opacities, and τC17O = τC18O/4.11. Table C.1 lists the opacity estimates for the sample of 32 cores in Cha I. Approximately half of them are somewhat optically thick (4.2 >τC18O ≥ 1) in C18O 2–1.
We can only calculate the C18O 2–1 opacities for the two cores in Cha III that were also observed in C17O 2–1, Cha3-C1 and Cha3-C4. Cha3-C1 is borderline optically thick/thin with an opacity of ~ 1, while Cha3-C4 is optically thin (Table C.2). They are both optically thin in C17O 2–1.
C18O 2–1 and C17O 2–1 opacities of the Cha I cores.
We assume an isotopic ratio of [32S]/[34S] ~ 22 (Frerking et al. 1980) to calculate the opacity of the CS 2–1 line in Cha I. All 57 CS 2–1 spectra feature detections and 23 out of the 57 are detected in C34S 2–1. We follow the same method as above to estimate the CS 2–1 opacities toward the 23 cores that are detected in both transitions. The results are given in Table C.3.
For the remaining 34 spectra we calculate upper limits for the CS 2–1 opacity by using the ratio of the CS 2–1 integrated intensity to the value of 3 × rms of the C34S 2–1 spectra. The opacity upper limits are listed in Table C.4. All 23 cores that have detections in C34S 2–1 are optically thick in CS 2–1, with opacities ranging from ~2–10.
Two cores in Cha III are detected in C34S 2−1 and their CS 2−1 opacity is listed in Table C.5. Both have CS 2−1 opacities greater than one, while they are optically thin in C34S 2−1. CS 2−1 is detected toward all remaining cores, for which we calculate upper limits (Table C.6) in the same way as for the Cha I cores.
C18O 2–1 and C17O 2–1 opacities of the Cha III cores.
CS 2–1 and C34S 2–1 opacities of the Cha I cores.
CS 2–1 upper limit opacities of the Cha I cores.
CS 2–1 and C34S 2–1 opacities of the Cha III cores.
CS 2–1 upper limit opacities of the Cha III cores.
For the conversion of hydrogen densities to free-particle densities and vice versa we use the mean molecular weight per free-particle, μ ~ 2.37 (see Appendix A.1 in Kauffmann et al. 2008). The cosmic mass ratio of hydrogen to the total mass of matter is ~ 0.71, while that of helium is ~0.27 (Cox 2000). The total hydrogen density, nH, is equivalent to (D.1)which gives (D.2)with nfp the free-particle density.
Spectra obtained with APEX and the Mopra telescope toward the Cha I and III sources listed in Table 7, displayed in main-beam temperature scale. Spectra that were rescaled to fit in the figure have their scaling factor indicated on the right. The vertical dashed line marks the systemic velocity as derived from a Gaussian fit to the CH3OH 20–10 A+ transition, except for sources Cha1-C6, Cha1-C24, Cha1-C27, Cha1-C35, and Cha3-C10 for which the C18O 2–1 transition was used.
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© ESO, 2015
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