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

Journal article, 2007

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, (HCO+)-C-13, HNC, HCN, HC3OH, HC5N, CS, HC3N, (CO)-C-13, 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 similar or equal to 20 K. Using this result we have estimated a molecular mass for the envelope of similar or equal to 0.017M(circle dot) and an HCO+ abundance relative to H-2 of 6 x 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 similar or equal to 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.