2011ApJ...728..101T

We have observed dense gas around the Very Low Luminosity Objects (VeLLOs) L1521F-IRS and IRAM 04191+1522 in carbon-chain and organic molecular lines with the Nobeyama 45 m telescope. Toward L1521F-IRS, carbon-chain lines of CH₃ CCH (5₀-4₀), C₄H (-), and C₃H₂(2₁₂-1₀₁) are 1.5-3.5 times stronger than those toward IRAM 04191+1522, and the abundances of the carbon-chain molecules toward L1521F-IRS are 2-5 times higher than those toward IRAM 04191+1522. Mapping observations of these carbon-chain molecular lines show that in L1521F the peak positions of these carbon-chain molecular lines are different from each other and there is no emission peak toward the VeLLO position, while in IRAM 04191+1522 these carbon-chain lines are as weak as the detection limits, except for the C₃H₂line. The observed chemical differentiation between L1521F and IRAM 04191+1522 suggests that the evolutionary stage of L1521F-IRS is younger than that of IRAM 04191+1522, consistent with the extent of the associated outflows seen in the ¹³CO (1-0) line. The non-detection of the organic molecular lines of CH₃ OH (6_–2-7_–1 E) and CH₃ CN (6₀-5₀) implies that the warm (∼100 K) molecular-desorbing region heated by the central protostar is smaller than ∼100 AU toward L1521F-IRS and IRAM 04191+1522, suggesting the young age of these VeLLOs. We propose that the chemical status of surrounding dense gas can be used to trace the evolutionary stages of VeLLOs.