Detection of N15NH+ in L1544

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 N2H+ 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 30m 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. © ESO 2010.