L. Bizzocchi, P. Caselli, L. Dore
Abstract
Context. Excess levels of 15N isotopes which have been detected in primitive solar system materials are explained as a remnant of interstellar chemistry which took place in regions of the protosolar nebula.
Aims: Chemical models of nitrogen fractionation in cold clouds predict an enhancement in the gas-phase abundance of 15N-bearing molecules, thus we have searched for 15N variants of the N_2H^+ ion in L1544, which is one of the best candidate sources for detection owing to its low central core temperature and high CO depletion.
Methods: With the IRAM 30 m telescope we have obtained deep integrations of the N15NH+ (1-0) line at 91.2 GHz.
Results: The N15NH+ (1-0) line has been detected toward the dust emission peak of L1544. The 14N/15N abundance ratio in N15NH^+ resulted 446± 71, very close to the protosolar value of ˜ 450, higher than the terrestrial ratio of ~270, and significantly lower than the lower limit in L1544 found by Gerin et al. (2009, ApJ, 570, L101) in the same object using ammonia isotopologues.
Keywords
ISM: clouds – ISM: molecules – ISM: individual object: L1544 – radio lines: ISM
Astronomy & Astrophysics
Volume 510, Number of pages L5_1
2010 February
