The Serpens Star-Forming Region in HCO+, HCN, and N2H+
  This poster presents single-dish and aperture-synthesis observations of the J=1-0 (lambda~3 mm) transitions of HCO+, HCN, and N2H+ towards the Serpens star-forming region. Jets driven by young stars affect the structure and the chemistry of their surrounding cloud, and this work aims to assess the extent to which the emission of these three molecular lines is dominated by such processes. In Serpens I find that N2H+ 1-0 traces the total amount of material, except in two regions slightly ahead of shocks. In contrast, the HCO+ and, especially, HCN emission is dominated by regions impacted by outflows. One previously unknown, strongly shocked region is located ~0.1 pc northwest of the young stellar object SMM 4. There is a marked spatial offset between the peaks in the HCN and the N2H+ emission associated with shocked regions. I construct a simple, qualitative chemical model where the N2H+ emission increases in the magnetic precursor of a C-type shock, while N2H+ is destroyed deeper in the shock as the neutrals heat up and species like HCN and water are released from icy grain mantles. I conclude that N2H+ is a reliable tracer of cloud material, and that unresolved observations of HCO+ and HCN will be dominated by material impacted by outflows. 
Michiel R. Hogerheijde (Steward Observatory)