Line shift, line asymmetry, and the 6Li-7Li isotopic ratio determination - AstrophysicsReport as inadecuate




Line shift, line asymmetry, and the 6Li-7Li isotopic ratio determination - Astrophysics - Download this document for free, or read online. Document in PDF available to download.

Abstract: Context: Line asymmetries are generated by convective Doppler shifts instellar atmospheres, especially in metal-poor stars, where convective motionspenetrate to higher atmospheric levels. Such asymmetries are usually neglectedin abundance analyses. The determination of the 6Li-7Li isotopic ratio is proneto suffering from such asymmetries, as the contribution of 6Li is a slightblending reinforcement of the red wing of each component of the corresponding7Li line, with respect to its blue wing. Aims: The present paper studies thehalo star HD 74000 and estimates the impact of convection-related asymmetrieson the Li isotopic ratio determination. Method: Two methods are used to meetthis aim. The first, which is purely empirical, consists in deriving a templateprofile from another element that can be assumed to originate in the samestellar atmospheric layers as Li I, producing absorption lines of approximatelythe same equivalent width as individual components of the 7Li I resonance line.The second method consists in conducting the abundance analysis based on NLTEline formation in a 3D hydrodynamical model atmosphere, taking into account theeffects of photospheric convection. Results: The results of the first methodshow that the convective asymmetry generates an excess absorption in the redwing of the 7Li absorption feature that mimics the presence of 6Li at a levelcomparable to the hitherto published values. This opens the possibility thatonly an upper limit on 6Li-7Li has thus far been derived. The second methodconfirms these findings. Conclusions: From this work, it appears that asystematic reappraisal of former determinations of 6Li abundances in halo starsis warranted.



Author: Roger Cayrel GEPI, Matthias Steffen AIP, Hum Chand IAP, Piercarlo Bonifacio GEPI, CIFIST, INAF - OAT, Monique Spite GEPI, Fran├žo

Source: https://arxiv.org/







Related documents