Empirical determination of the lithium 6707.856 Å wavelength in young stars

Justyn Campbell-White, Carlo F. Manara, Aurora Sicilia-Aguilar, Antonio Frasca, Louise D. Nielsen, P. Christian Schneider, Brunella Nisini, Amelia Bayo, Barbara Ercolano, Péter Ábrahám, Rik Claes, Min Fang, Davide Fedele, Jorge Filipe Gameiro, Manuele Gangi, Ágnes Kóspál, Karina Maucó, Monika G. Petr-Gotzens, Elisabetta Rigliaco, Connor RobinsonMichal Siwak, Lukasz Tychoniec, Laura Venuti

Research output: Working paper/PreprintPreprint

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Abstract

Absorption features in stellar atmospheres are often used to calibrate photocentric velocities for kinematic analysis of further spectral lines. The Li feature at ∼6708Å is commonly used, especially in the case of young stellar objects for which it is one of the strongest absorption lines. However, this is a complex line comprising two isotope fine-structure doublets. We empirically measure the wavelength of this Li feature in a sample of young stars from the PENELLOPE/VLT programme (using X-Shooter, UVES and ESPRESSO data) as well as HARPS data. For 51 targets, we fit 314 individual spectra using the STAR-MELT package, resulting in 241 accurately fitted Li features, given the automated goodness-of-fit threshold. We find the mean air wavelength to be 6707.856Å, with a standard error of 0.002Å (0.09km/s) and a weighted standard deviation of 0.026Å (1.16km/s). The observed spread in measured positions spans 0.145Å, or 6.5km/s, which is up to a factor of six higher than typically reported velocity errors for high-resolution studies. We also find a correlation between the effective temperature of the star and the wavelength of the central absorption. We discuss how exclusively using this Li feature as a reference for photocentric velocity in young stars could potentially be introducing a systematic positive offset in wavelength to measurements of further spectral lines. If outflow tracing forbidden lines, such as [Oi]6300Å, are actually more blueshifted than previously thought, this then favours a disk wind as the origin for such emission in young stars.
Original languageEnglish
Place of PublicationCornell University
PublisherarXiv
Number of pages14
DOIs
Publication statusPublished - 8 Mar 2023

Keywords

  • Stars: atmospheres
  • Stars: pre-main sequence
  • Stars: variables
  • T Tauri
  • Herbig Ae/Be

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