Detection of N^15NH⁺in L1544

Context. Excess levels of 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 -bearing molecules, thus we have searched for variants of the 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 telescope we have obtained deep integrations of the line at .Results. The line has been detected toward the dust emission peak of L1544. The abundance ratio in resulted , very close to the protosolar value of , 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.