Other
Scientific paper
Apr 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008apj...677l..75s&link_type=abstract
The Astrophysical Journal, Volume 677, Issue 1, pp. L75-L75.
Other
1
Scientific paper
We missed referring to a paper by B. E. Turner, R. Terzieva, & E. Herbst (ApJ, 675, L89 [2008]), reporting observations of HCO+2 in a few cold starless clouds. So our detection of HCO+2 is not the first case for molecular clouds besides Galactic center clouds, but for star-forming regions. Here we correct the Abstract, the last two sentences in the second paragraph of § 1, and the last paragraph of § 3. Since our purpose is to explore the behavior of HCO+2 in star-forming regions, these corrections do not change our major conclusions.
The Abstract should be read as follows:
The millimeter-wave rotational emission lines (404-303 and 505-404) of protonated carbon dioxide, HCO+2(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 HCO+2 in star-forming regions besides the Galactic center clouds. The column density of HCO+2 averaged over the beam size (29") is determined to be 7.6×1010 cm-2, assuming a rotational temperature of 12.3 K. The fractional abundance of gaseous CO2 relative to H2 is estimated from the column density of HCO+2 with the aid of a simplified chemical model. If the HCO+2 emission only comes from the evaporation region of CO2 near the protostar (T>~50 K), the fractional abundance of CO2 is estimated to be higher than 6.6×10-4. This is comparable to the elemental abundance of carbon in interstellar clouds, and hence the direct evaporation of CO2 from dust grains is unrealistic as a source of gaseous CO2 in L1527. The narrow line width of HCO+2 also supports this. On the other hand, the fractional abundance of CO2 is estimated as 2.9×10-7, if the source size is comparable to the beam size. These results indicate that gaseous CO2 is abundant even in low-mass star-forming regions. Possible production mechanisms of gaseous CO2 are discussed.
The last two sentences in the second paragraph of § 1 should be read as follows:
However, HCO+2 has never been detected in any star-forming region except for the Galactic center clouds such as Sgr B2 and Sgr A (Thaddeus et al. 1981; DeFrees et al. 1982; Minh et al. 1991) and a few starless clouds [B. E. Turner, R. Terzieva, & E. Herbst (ApJ, 675, L89 [2008])]. It has been thought that HCO+2 is efficiently produced under specific conditions in the Galactic center region, where shock chemistry would play an important role (e.g., Minh et al. 1988; Charnley & Kaufman 2000).
The last paragraph of § 3 should be read as follows:
The present result shows the existence of HCO+2 in the low-mass star-forming core. The column density of HCO+2 in L1527 is less than those toward Sgr B2 and Sgr A (e.g., Minh et al. 1988; Deguchi et al. 2006) by almost 3 orders of magnitude. On the other hand, the HCO+2 lines were not detected in star-forming cores such as Orion KL and B335 in spite of extensive searches (Minh et al. 1988). One possible explanation of the nondetection is insufficient sensitivity of the previous observations. In fact, the column density of HCO+2 in L1527 is lower than the upper limits reported by Minh et al. (1988) (~1012 cm-2).
Aikawa Yuri
Sakai Nami
Sakai Takeshi
Yamamoto Satoshi
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