LIME: Semiautomated line measurement and identi cation from stellar spectra

Abstract

We present LIME (Line Measurements from ECHELLE Spectra), an IDL-based code, as a powerful toolfor semiautomated stellar line measurement and identi cation. Interactively selected line positions (i.e. wavelengths)are compared with a master line list of the user\'s selections. Each unknown line that the user interactively chooses isdisplayed with potential identi cations provided by the code in the vicinity of the selected line. The best identi cationis evaluated on the basis of several criteria (e.g., atomic/molecular line information, wavelength displacement, andtheoretical equivalent width for solar atmospheric values). We examined the identi cations by LIME in the spectra ofpost-red supergiant star HD 179821 over a range of signal-to-noise values and wavelength ranges. We found that theresults obtained by LIME show virtually complete agreement with the manual identi cations for which the conventionaland also tedious approach is to use a revised multiplet table as an initial guide and perform a systematic search thatmakes use of the lower excitation potential and gf-values. Comparison to previous identi cations for HD 179821 in theliterature revealed not only lines that were unmeasurable and/or blended but also misidenti cations. While a manualidenti cation process takes a relatively longer time to be accomplished by an experienced spectroscopist, LIME canprovide a rapid extraction of line information in a few hours with moderate user interaction.