The origin of the molecular emission around the southern hemisphere Re 4 IRS - HH 188 region

Abstract

We present SEST observations of the molecular environment ahead of the southern Herbig-Haro object 188 (HH188), associated with the low-mass protostar Re4 IRS. We have also used the SuperCosmos Halpha survey to search for Halpha emission associated with the Re4 IRS - HH188 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 2(0)-1(0)A+ and 2(-1)-1(-1)E and SO 6(5)-5(4) 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 HH188 object. We have also found that HH188, a high excitation object, seems to be part of a parsec scale and highly collimated HH system. Re4 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 HH188 system.