Empirical Determination of the Lithium 6707.856 Å Wavelength in Young Stars

Abstract

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 Å 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 Å, with a standard error of 0.002 Å (0.09 km/s) and a weighted standard deviation of 0.026 Å (1.16 km/s). The observed spread in measured positions spans 0.145 Å, 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 Å, are actually more blueshifted than previously thought, this then favours a disk wind as the origin for such emission in young stars.

Accepted for publication in A&A

References in corpus (24)

• Molecfit: A general tool for telluric absorption correction. I. Method and application to ESO instruments
• Molecfit: A general tool for telluric absorption correction II. Quantitative evaluation on ESO-VLT X-Shooter spectra
• X-Shooter spectroscopy of young stellar objects in Lupus: Accretion properties of class II and transitional objects
• Tracing Slow Winds from T Tauri Stars via Low Velocity Forbidden Line Emission
• Connection between jets, winds and accretion in T Tauri stars: the X-shooter view
• X-Shooter spectroscopy of young stellar objects: V - Slow winds in T Tauri stars
• PENELLOPE: the ESO data legacy program to complement the Hubble UV Legacy Library of Young Stars (ULLYSES) I. Survey presentation and accretion properties of Orion OB1 and $\sigma$-Orionis
• A multiwavelength radial velocity search for planets around the brown dwarf LP 944-20
• The Gaia-ESO Survey: Lithium depletion in the Gamma Velorum cluster and inflated radii in low-mass pre-main-sequence stars
• The rotation - Lithium depletion correlation in the beta Pictoris association and LDB age determination
• GIARPS High-resolution Observations of T Tauri stars (GHOsT). IV. Accretion properties of the Taurus-Auriga young association
• The interpretation of protoplanetary disc wind diagnostic lines from X-ray photoevaporation and analytical MHD models
• The Gaia-ESO Survey: Calibrating the lithium-age relation with open clusters and associations. I. Cluster age range and initial membership selections
• The ODYSSEUS Survey. Motivation and First Results: Accretion, Ejection, and Disk Irradiation of CVSO 109
• The Effects of Starspots on Spectroscopic Mass Estimates of Low-mass Young Stars
• Gaia-ESO Survey: Role of magnetic activity and starspots on pre-main sequence lithium evolution
• X-shooter spectroscopy of young stellar objects in Lupus: Lithium, iron, and barium elemental abundances
• New insights on the near-infrared veiling of young stars using CFHT/SPIRou data
• The Gaia-ESO Survey: Lithium measurements and new curves of growth
• Non-detection of ${}^6$Li in Spite plateau stars with ESPRESSO
• [OI] 6300Å emission as a probe of external photoevaporation of protoplanetary discs
• The STAR-MELT Python package for emission line analysis of YSOs
• The role of FUV Pumping in exciting the [Oi] lines in Protostellar Disks and Winds
• Accretion variability in RU Lup

Cited by in corpus (3)

• PENELLOPE IV. A comparison between optical forbidden lines and ${\mathrm{H}}_2$ UV lines in the Orion OB1b and $\sigma$-Ori associations
• Multi-wavelength detection of an ongoing FUOr-type outburst on a low-mass YSO
• Evidence of a Disk-wind Origin for Fluorescent H${}_2$ in Classical T Tauri Stars