分类： 天文学 >> 天文学 提交时间： 2023-02-19
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 Robinson
摘要： Absorption features in stellar atmospheres are often used to calibrate photocentric velocities for kinematic analysis of further spectral lines. The Li feature at $\sim$ 6708 {\AA} 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 6707.856 {\AA}, with a standard error of 0.002 {\AA} (0.09 km/s) and a weighted standard deviation of 0.026 {\AA} (1.16 km/s). The observed spread in measured positions spans 0.145 {\AA}, or 6.5 km/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 [O i] 6300 {\AA}, are actually more blueshifted than previously thought, this then favours a disk wind as the origin for such emission in young stars.
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