A Chemical Study of the PDR around Mon R2

摘要

Around one of its IR sources, Mon R2 contains the nearest ultra-compact H ii region. Here we report the results of an observational campaigncarried out with the IRAM 30 m radiotelescope. We have detected reactive ions(CO~+and HOC~+) small hydrocarbons (c-C_3H_2and 2H) arising from theinterface between the ionized gas and the dense cold envelope. This interfaceis chemically identified as a Photo-dissociation Region (PDR), where we havedetermined the physical conditions and abundances of several species. The emis-sion lines associated to the PDR are remarkably narrow, which may indicate thatit is made of thin layers of excited gas. This region would be an excellent targetfor future studies using the ALMA facility, because of the small angular scale(less than 4") and the nearly-equatorial declination.