Detection of HCO2+ toward the low-mass protostar IRAS 04368+2557 in L1527

The millimeter-wave rotational emission lines (4(04)-3(03) and 5(05)-4(04)) of protonated carbon dioxide, HCO2+ (HOCO+), have been detected toward the low- mass Class 0 protostar IRAS 04368+2557 in L1527 with the IRAM 30 m telescope. This is the first detection of HCO2+ except for the Galactic center clouds. The column density of HCO2+ averaged over the beam size (29'') is determined to be 7.6 x 10(10) cm(-2), assuming a rotational temperature of 12.3 K. The fractional abundance of gaseous CO2 relative to H-2 is estimated from the column density of HCO2+ with the aid of a simplified chemical model. If the HCO2+ emission only comes from the evaporation region of CO2 near the protostar (T greater than or similar to 50 K), the fractional abundance of CO2 is estimated to be higher than. This is comparable to the elemental abundance of carbon in interstellar clouds, and hence, 6.6 x 10(-4) the direct evaporation of CO2 from dust grain is unrealistic as a source of gaseous CO2 in L1527. A narrow line width of HCO also supports this. On the other hand, the fractional abundance of CO2 is estimated to be if the source size is comparable to the beam size. These results indicate that gaseous CO2 is abundant 2.9 x 10(-7) even in the low-mass star-forming region. Possible production mechanisms of gaseous CO2 are discussed.