|First detection of 15NH and the determination of the 14N-15N in the diffuse Interstellar Medium
|Understanding the origin of the elements in the Solar system is an outstanding question of modern astrophysics, cosmochemistry, and astrobiology. The origin of nitrogen, though amongst the five to six most abundant elements in our local Universe, remains poorly understood. This is due to the lack of observational constraints to nucleosynthesis models. Elemental isotopic ratio is an extremely powerful tool in this regard. A value of 440 for the 14N-15N ratio has been measured in the protosolar nebula. Similar values have been obtained in cold dense cores and in molecular clouds. Determinations of the 14N-15N ratio in the interstellar medium (ISM) are indirect and are based on abundance ratios of N-bearing molecules and their 15N isotopologues. Hence the interpretation in term of 14N-15N depends on chemical fractionation processes. Chemical models indicate that these processes strongly affect nitriles, and recent observations suggest that ammonia is probably not a reliable tracer for the 14N-15N ratio. Nonetheless, reliable methods to determine the 14N-15N ratio in cold and dense gas seem to emerge. The same is unfortunately not true for the diffuse ISM where very little is known regarding the nitrogen isotopic ratio, which should be representative of the nucleosynthesis products. One measurement in the diffuse interstellar medium (ISM) led to the small value of 240. However, this determination is based on the nitriles HCN and HC15N, and the translation into 14N-15N is strongly model-dependent. Chemical considerations show that the NH molecule is not fractionated in the diffuse gas such that the 14NH-15NH abundance ratio is the best proxy for the 14N-15N ratio. The NH molecule has been detected by Herschel-HIFI in several diffuse clouds and offers a unique opportunity to determine the 14N-15N ratio in the diffuse ISM. The proposed observations aim at the first detection of 15NH in the ISM which will allow the first ro...bust determination of the 14N-15N isotopic ratio in the diffuse ISM.
|Far-infrared study of tracers of oxygen chemistry in diffuse clouds . Wiesemeyer H. et al. . Astronomy & Astrophysics, Volume 585, id.A76, 18 pp. . 585 . 10.1051/0004-6361/201526473 . 2016A&A...585A..76W ,
|Herschel was launched on 14 May 2009! It is the fourth 'cornerstone' mission in the ESA science programme. With a 3.5 m Cassegrain telescope it is the largest space telescope ever launched. It is performing photometry and spectroscopy in approximately the 55-671 µm range, bridging the gap between earlier infrared space missions and groundbased facilities.
|Publisher And Registrant
|European Space Agency
|European Space Agency, 2013, OT2_philybla_3, SPG v14.1.0. https://doi.org/10.5270/esa-k0svmih