The AMBRE Project: Line-broadening and stellar rotation of ESO/FEROS archived spectra

TL;DR

This work targets the gap in large, homogeneous rotational catalogs by deriving the line-broadening parameter $V_{ m broad}$ for FGKM stars from ESO/FEROS spectra parameterised by AMBRE. The method relies on cross-correlation with AMBRE binary masks and a calibrated coupling between rotation and cross-correlation width, with $m{V_{ m broad} = A \, ext{sqrt}(\,\sigma_{CCF}^{2} - \, \sigma_{0}^{2}\,)}$ and a separately determined $m{\sigma_{0}}$ from non-rotating synthetic spectra; the constant $A$ is calibrated using synthetic rotating spectra and Monte Carlo resampling. The resulting catalogue provides $V_{ m broad}$ (with uncertainties or upper limits) for 2{,}584 AMBRE/FEROS stars, with a high-quality subset (roughly 1{,}900 stars) displaying median relative uncertainties below 8%, enabling robust assessment of rotational properties across FGKM types. Validation against Gaia DR3, GG2005, GALAH DR4, APOGEE DR17, and de Medeiros shows generally good agreement (differences ~3–4 km s$^{-1}$) and highlights the influence of macro-turbulence, binarity, and chromospheric activity on low-$V_{ m broad}$ measurements. The public AMBRE/FEROS $V_{ m broad}$ catalogue thus provides a valuable, homogeneous resource for studies of stellar rotation, evolution, and gyrochronology, with planned expansion to HARPS and UVES data to further increase the statistical power for high-resolution spectra.

Abstract

Stellar rotation is a fundamental parameter in stellar studies. However, large homogeneous catalogues of rotational velocities derived from high-resolution stellar spectra are still lacking. The main objective of this work is to determine the line-broadening parameter (Vbroad), a proxy for the stellar rotational velocity, in a large sample of FGKM stars based on their ESO/FEROS spectra, previously parameterised by the AMBRE Project. Vbroad was estimated by cross-correlating the FEROS spectra with AMBRE binary masks. This methodology also relies on a specific calibration of a coupling constant between the rotational velocity and the width of the cross-correlation function. This fundamental step was performed by adopting the AMBRE grid of synthetic spectra. The derived Vbroad were then validated using data from the literature, ground-based spectroscopic surveys, and Gaia/RVS. After analysing more than 5,000 FEROS spectra (including repeated spectra for several stars), we obtained the line-broadening coefficients for 2,584 stars covering the FGKM spectral types, any stellar gravity, and metallicities between the metal-poor up to sub-solar regimes. The mean Vbroad relative uncertainty of this sample was found to be smaller than 8%. As expected, most stars were found to be slow rotators (below a few km/s), in particular, cool dwarfs and giants. However, several hot dwarfs and high-luminosity stars with high-Vbroad rates were identified, most of them not previously classified as fast rotators and/or affected by large macro-turbulent effects. The measured rotational broadening values are of high-quality and verified on the basis of literature comparisons. We publicly provide this catalogue of Vbroad parameters, including stellar atmospheric and quality parameters, for the analysed AMBRE/FEROS sources.

Figures (10)

• Figure 1: Coupling constant of Eq. \ref{['equ:vb']} for the Solar spectrum and a mask having exactly the same parameters (FEROS-like spectrum with a wavelength sampling of 0.003 nm). The $A$-value and its uncertainty are reported in the upper-left corner.
• Figure 2: Comparison of the AMBRE/FEROS $V_{\rm broad}$ upper limits with the measurements of Fremat2023, derived from Gaia/RVS DR3 spectra. The horizontal red and blue dashed lines refer to the F23 measurement limit and to their low-$V_{\rm broad}$ domain, where overestimated values are suspected (5 and 12 km/s, respectively). The colour coding represents the F23 $V_{\rm broad}$ relative uncertainty. The inset focuses on low-rotating F23 stars having a $V_{\rm broad}$ relative uncertainty lower than 20%.
• Figure 3: Same as Fig. \ref{['Fig:ValidGaia']} but considering only AMBRE stars with a fully derived $V_{\rm broad}$ (i.e. excluding upper limits) and high-quality measurements in both catalogues ($V_{\rm broad}$ relative uncertainty less than 20%). The black-dashed line denotes the one-to-one relation for visual reference. For clarity, six extreme F23 stars with $V_{\rm broad}$>50 km/s are not shown (see text for details, including a discussion about the bias and dispersion associated to this comparison).
• Figure 4: Comparison of the AMBRE/FEROS upper limits $V_{\rm broad}$ with the measurements of GG2005.
• Figure 5: Same as Fig. \ref{['Fig:ValidGG05']} but excluding the AMBRE/FEROS upper limits, and only considering AMBRE/FEROS high-quality measurements (relative uncertainties less than 20%; see the colour coding). The black-dashed line denotes the one-to-one relation for visual reference. See the text for a discussion about the bias and dispersion associated to this comparison.