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We have observed dense gas around the Very Low-Luminosity Ob jects (VeLLOs)L1521F-IRS and IRAM 04191+1522 in carbon-chain and organic molecular lines withthe Nobeyama 45 m telescope. Towards L1521F-IRS, carbon-chain lines of CH3CCH(50-40), C4H (17/2-15/2), and C3H2 (212-101) are 1.5 - 3.5 times stronger thanthose towards IRAM 04191+1522, and the abundances of the carbon-chain moleculestowards L1521F-IRS are 2 to 5 times higher than those towards IRAM 04191+1522.Mapping observations of these carbon-chain molecular lines show that in L1521Fthe peak positions of these carbon-chain molecular lines are different fromeach other and there is no emission peak towards the VeLLO position, while inIRAM 04191+1522 these carbon-chain lines are as weak as the detection limitsexcept for the C3H2 line. The observed chemical differentiation between L1521Fand IRAM 04191+1522 suggests that the evolutionary stage of L1521F-IRS isyounger than that of IRAM 04191+1522, consistent with the extent of theassociated outflows seen in the 13CO (1-0) line. The non-detection of theorganic molecular lines of CH3OH (6-2-7-1 E) and CH3CN (60-50) implies that thewarm (~ 100 K) molecular-desorbing region heated by the central protostar issmaller than ~ 100 AU towards L1521F-IRS and IRAM 04191+1522, suggesting theyoung age of these VeLLOs. We propose that the chemical status of surroundingdense gas can be used to trace the evolutionary stages of VeLLOs.

Carbon-Chain and Organic Molecules around Very Low-Luminosity Protostellar Objects of L1521F-IRS and IRAM 04191+1522