  We present the results of an optical absorption study of NGC 7293, the Helix
planetary nebula (PN), designed to search for diffuse band (DIB) absorptions
perhaps arising in the carbon-rich circumstellar matter of the PN. We made high
resolution spectra of 8 stars located close to and behind the Helix. Through a
detailed analysis of the NaI and CaII lines, we find that two lines of sight
situated close to the PN as mapped in CO and HI exhibit very strong NaI
absorption. This absorption is due to the PN neutral or molecular material. No
corresponding CaII line is observed in agreement with the very high Ca
depletion often observed in PNs. No trace of any DIB features was found in
these two circumstellar lines of sight (shortened abstract).
