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Issue A&A
Volume 414, Number 3, February II 2004
Page(s) L53 - L56
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:20031766



A&A 414, L53-L56 (2004)
DOI: 10.1051/0004-6361:20031766

Letter

L1521E: The first starless core with no molecular depletion

M. Tafalla and J. Santiago

Observatorio Astronómico Nacional, Alfonso XII 3, 28014 Madrid, Spain
(Received 20 November 2003 / Accepted 22 December 2003)

Abstract
L1521E seems unique among starless cores. It stands out in a distribution of a ratio (R) that we define to asses core evolution, and which compares the emission of the easily-depleted C 18O molecule with that of the hard to deplete, late-time species N 2H +. While all cores we have studied so far have R ratio lower than 1, L1521E has an R value of 3.4, which is 8 times the mean of the other cores. To understand this difference, we have modeled the C 18O and N 2H + abundance profiles in L1521E using a density distribution derived from 1.2 mm continuum data. Our model shows that the C 18O emission in this core is consistent with constant abundance, and this makes L1521E the first core with no C 18O depletion. Our model also derives an unusually low N 2H + abundance. These two chemical peculiarities suggest that L1521E has contracted to its present density very recently, and it is therefore an extremely young starless core. Comparing our derived abundances with a chemical model, we estimate a tentative age of ${\le} 1.5 \times 10^5$ yr, which is too short for ambipolar diffusion models.


Key words: ISM: abundances -- ISM: clouds -- ISM: molecules -- stars: formation -- ISM: individual: L1521E

Offprint request: M. Tafalla, m.tafalla@oan.es

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