Empirical determination of the lithium 6707.856 Å wavelength in young stars

TY - UNPB

T1 - Empirical determination of the lithium 6707.856 Å wavelength in young stars

AU - Campbell-White, Justyn

AU - Manara, Carlo F.

AU - Sicilia-Aguilar, Aurora

AU - Frasca, Antonio

AU - Nielsen, Louise D.

AU - Schneider, P. Christian

AU - Nisini, Brunella

AU - Bayo, Amelia

AU - Ercolano, Barbara

AU - Ábrahám, Péter

AU - Claes, Rik

AU - Fang, Min

AU - Fedele, Davide

AU - Gameiro, Jorge Filipe

AU - Gangi, Manuele

AU - Kóspál, Ágnes

AU - Maucó, Karina

AU - Petr-Gotzens, Monika G.

AU - Rigliaco, Elisabetta

AU - Robinson, Connor

AU - Siwak, Michal

AU - Tychoniec, Lukasz

AU - Venuti, Laura

N1 - ©ESO2023 Funded by the European Union under the European Union’s Horizon Europe Research & Innovation Programme 101039452 (WANDA). JCW and ASA were supported by the STFC grant number ST/S000399/1 ("The Planet-Disk Connection: Accretion, Disk Structure, and Planet Formation"). JCW also acknowledges funding from the SUPA Saltire grant. AF, BN, and MG acknowledge support by the PRIN-INAF 2019 STRADE (Spectroscopically TRAcing the Disk dispersal Evolution) and by the Large Grant INAF YODA (YSOs Outf low, Disks and Accretion). AB acknowledges partial funding by the Deutsche Forschungsgemeinschaft Excellence Strategy- EXC 2094- 390783311 and the ANID BASAL project FB210003. This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme under grant agreement No 716155 (SACCRED). JFG was supported by fundação para a Ciência e Tecnologia (FCT) through the research grants UIDB/04434/2020 and UIDP/04434/2020.

PY - 2023/3/8

Y1 - 2023/3/8

N2 - 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.

AB - 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.

KW - Stars: atmospheres

KW - Stars: pre-main sequence

KW - Stars: variables

KW - T Tauri

KW - Herbig Ae/Be

U2 - 10.48550/arXiv.2303.03843

DO - 10.48550/arXiv.2303.03843

M3 - Preprint

BT - Empirical determination of the lithium 6707.856 Å wavelength in young stars

PB - arXiv

CY - Cornell University

ER -