SIMBAD references

We have used the IRAM 30 m telescope to map some targets with HCO⁺ (1-0) and H¹³CO⁺ (1-0) lines in order to search for evidence of gas infall in clumps. In this paper, we report the mapping results for 13 targets. All of these targets show HCO⁺ emissions, while H¹³CO⁺ emissions are observed in 10 of them. The HCO⁺ integrated intensity maps of 10 targets show clear clumpy structures, and nine targets show clumpy structures in the H¹³CO⁺ maps. Using the RADEX radiative transfer code, we estimate the column density of H¹³CO⁺, and we determine the abundance ratio [H¹³CO⁺]/[H₂] to be approximately 10^–12-10^–10. Based on the asymmetry of the HCO⁺ line profiles, we identify 11 targets that show blue profiles, while six clumps have evidence of global infall. We use the RATRAN and two-layer models to fit the HCO⁺ line profiles of these infall sources, and analyze their spatial distribution of the infall velocity. The average infall velocities estimated by these two models are 0.24-1.85 km s^–1 and 0.28-1.45 km s^–1, respectively. The mass infall rate ranges from approximately 10^–5 to 10^–2M_⊙ yr^–1, which suggests that intermediate- or high-mass stars may be forming in the target regions.