The millimeter-wave rotational emission lines ( 4 _ { 04 } -3 _ { 03 } and 5 _ { 05 } -4 _ { 04 } ) of protonated carbon dioxide , HCO _ { 2 } ^ { + } ( HOCO ^ { + } ) , has 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 _ { 2 } ^ { + } except for the Galactic Center clouds .
The column density of HCO _ { 2 } ^ { + } averaged over the beam size ( 29 ^ { \prime \prime } ) is determined to be 7.6 \times 10 ^ { 10 } cm ^ { -2 } , assuming the rotational temperature of 12.3 K. The fractional abundance of gaseous CO _ { 2 } relative to H _ { 2 } is estimated from the column density of HCO _ { 2 } ^ { + } with an aid of a simplified chemical model .
If the HCO _ { 2 } ^ { + } emission only comes from the evaporation region of CO _ { 2 } near the protostar ( T > \sim 50 K ) , the fractional abundance of CO _ { 2 } is estimated to be higher than 6.6 \times 10 ^ { -4 } .
This is comparable to the elemental abundance of carbon in interstellar clouds , and hence , the direct evaporation of CO _ { 2 } from dust grain is unrealistic as a source of gaseous CO _ { 2 } in L1527 .
A narrow line width of HCO _ { 2 } ^ { + } also supports this .
On the other hand , the fractional abundance of CO _ { 2 } is estimated to be 2.9 \times 10 ^ { -7 } , if the source size is comparable to the beam size .
These results indicate that gaseous CO _ { 2 } is abundant even in the low-mass star-forming region .
Possible production mechanisms of gaseous CO _ { 2 } are discussed .