Detection of HCO{sub 2}{sup +} toward the Low-Mass Protostar IRAS 04368+2557 in L1527

Abstract

The millimeter-wave rotational emission lines (4{sub 04}-3{sub 03} and 5{sub 05}-4{sub 04}) of protonated carbon dioxide, HCO{sub 2}{sup +}(HOCO{sup +}), 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 HCO{sub 2}{sup +} except for the Galactic center clouds. The column density of HCO{sub 2}{sup +} averaged over the beam size (29{sup ''}) is determined to be 7.6 x 10{sup 10} cm{sup -2}, assuming a rotational temperature of 12.3 K. The fractional abundance of gaseous CO{sub 2} relative to H{sub 2} is estimated from the column density of HCO{sub 2}{sup +} with the aid of a simplified chemical model. If the HCO{sub 2}{sup +} emission only comes from the evaporation region of CO{sub 2} near the protostar (T {approx}> 50 K), the fractional abundance of CO{sub 2} is estimated to be higher than 6.6 x 10{sup -4}. This is comparable to the elemental abundance of carbon in interstellar clouds, and hence, the direct evaporation of CO{sub 2} from dust grain is unrealistic as a source of gaseous CO{sub 2} in L1527. A narrow line width of HCO{sub 2}{sup +} also supports this. On the othermore » hand, the fractional abundance of CO{sub 2} is estimated to be 2.9 x 10{sup -7}, if the source size is comparable to the beam size. These results indicate that gaseous CO{sub 2} is abundant even in the low-mass star-forming region. Possible production mechanisms of gaseous CO{sub 2} are discussed.« less