We report the detection , for the first time , of HCO ^ { + } ( J = 1 \rightarrow 0 ) emission as well as marginal CO ( J = 1 \rightarrow 0 ) emission toward the planetary nebula ( PN ) K 3-35 as a result of a molecular survey carried out toward this source .
We also report new observations of the previously detected CO ( J = 2 \rightarrow 1 ) and water maser emission , as well as upper limits for the emission of the SiO , H ^ { 13 } CO ^ { + } , HNC , HCN , HC _ { 3 } OH , HC _ { 5 } N , CS , HC _ { 3 } N , ^ { 13 } CO , CN , and NH _ { 3 } molecules .
From the ratio of CO ( J = 2 \rightarrow 1 ) to CO ( J = 1 \rightarrow 0 ) emission we have estimated the kinetic temperature of the molecular gas , obtaining a value of \simeq 20 K. Using this result , we have estimated a molecular mass for the envelope of \simeq 0.017 M _ { \odot } , and an HCO ^ { + } abundance relative to H _ { 2 } of 6 \times 10 ^ { -7 } , similar to the abundances found in other PNe .
K 3-35 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 \simeq 5000 AU away from the center .
The presence of molecular emission provides some clues that could help to understand the persistence of water molecules in the envelope of K 3-35 .
The HCO ^ { + } emission could be arising in dense molecular clumps , that may provide the shielding mechanism which protects water molecules in this source .