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

¹ Institut de Ciències de l'Espai (CSIC- IEEC), Campus UAB – Facultat de Ciències, Torre C5 – parell 2, 08193 Bellaterra, Catalunya, Spain e-mail: girart@ieec.cat
² Department of Physics and Astronomy, University College London, London WC1E 6BT, UK

Received: 24 August 2006
Accepted: 10 May 2007

Abstract

Aims.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.

Methods.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.

Results.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.