2007A&A...470..633G

We present SEST observations of the molecular environment ahead of the southern Herbig-Haro object 188 (HH 188), associated with the low-mass protostar Re 4 IRS. We have also used the SuperCosmos Hα survey to search for Hα emission associated with the Re 4 IRS - HH 188 region. The aim of the present work is to study the properties of the molecular gas and to better characterize this southern star forming region. We mapped the HCO⁺ 3-2 and H¹³CO⁺ 1-0 emission around the YSO and took spectra of the CH₃OH 2₀-1₀ A⁺ and 2_–1-1_–1 E and SO 6₅-5₄ towards the central source. Column densities are derived and different scenarios are considered to explain the origin of the molecular emission. HCO⁺ arises from a relatively compact region around the YSO; however, its peak emission is displaced to the south following the outflow direction. Our chemical analysis indicates that a plausible scenario is that most of the emission arises from the cold, illuminated dense gas ahead of the HH 188 object. We have also found that HH 188, a high excitation object, seems to be part of a parsec scale and highly collimated HH system. Re 4 IRS is probably a binary protostellar system, in the late Class 0 or Class I phase. One of the protostars, invisible in the near-IR, seems to power the HH 188 system.