Detection of HCO+ emission toward the planetary nebula K3-35

Abstract

We report the detection, for the first time, of HCO+(J = 1 → 0) emission, as well as marginal CO(J = 1 → 0) emission, toward the planetary nebula (PN) K3-35 as a result of a molecular survey carried out toward this source. We also report new observations of the previously detected CO(J = 2 → 1) and water maser emission, as well as upper limits for the emission of the SiO, H13CO+, HNC, HCN, HC3OH, HC 5N, CS, HC3N, 13CO, CN, and NH3 molecules. From the ratio of CO(J = 2 → 1) to CO(J = 1 → 0) emission we have estimated the kinetic temperature of the molecular gas, obtaining a value of ≃20 K. Using this result we have estimated a molecular mass for the envelope of ≃0.017 M⊙ and an HCO+ abundance relative to H2 of 6 × 10-7, similar to the abundances found in other PNe.K3-35 is remarkable because it is one of the two PNe reported to exhibit water maser emission, which is present in the central region, as well as at a distance of ≃5000 AU from the center. The presence of molecular emission provides some clues that could help in understanding the persistence of water molecules in the envelope of K3-35. The HCO+ emission could be arising in dense molecular clumps, which may provide the shielding mechanism that protects water molecules in this source. © 2007. The American Astronomical Society. All rights reserved.