[Paper Review] RAVE: Results and Updates from Data Release 4

G. Kordopatis|arXiv (Cornell University)|Oct 15, 2014

Astrophysics and Star Formation Studies3 citations

TL;DR

RAVE Data Release 4 presents stellar atmospheric parameters, abundances, radial velocities, proper motions, and distances for over 400,000 stars using improved spectral analysis pipelines and Bayesian distance modeling. Key results include constraints on the Milky Way’s kinematics, chemo-dynamical evolution, and evidence against radial migration as the primary driver of thick disc formation, with implications for Galactic archaeology and synergy with Gaia.

ABSTRACT

The RAdial Velocity Experiment (RAVE) published in November 2013 its fourth data release with the stellar atmospheric parameters, abundances, distances, radial velocities, proper motions and spectral morphological flags of more than 480,000 targets. With that, a plethora of papers ranging from the mass of the Milky Way to the mapping of the Diffuse Interstellar Band, and from the chemo-dynamical history and properties of the disc to the Galaxy's bar pattern speed have also been published. Being one of the largest spectroscopic surveys in the magnitude range of Gaia, RAVE has helped to pave the way for the exploitation of the Gaia catalogs. Here, we review some of these results and present some perspectives about future RAVE data releases.

Motivation & Objective

• To provide a comprehensive, high-precision spectroscopic catalog of stellar parameters and kinematics for over 400,000 stars in the Milky Way’s disk and halo.
• To improve metallicity calibration and reduce spectral degeneracies using high-resolution spectroscopy of cluster stars and photometric priors from 2MASS and APASS.
• To enable detailed chemo-dynamical modeling of the Milky Way’s evolution, including the formation of the thick disc and radial migration.
• To prepare the community for Gaia by establishing a robust, large-scale spectroscopic reference sample in Gaia’s magnitude range.

Proposed method

• Applied a new spectral parameterization pipeline based on a reduced-dimensional synthetic grid, excluding the core of the Ca triplet lines and incorporating 2MASS photometry to reduce degeneracies.
• Improved chemical abundance pipeline to derive six-element abundances (Mg, Al, Si, Ti, Fe, Ni) using full-spectrum fitting techniques.
• Employed two independent distance estimation methods: one based on isochrone projection with mild evolutionary priors, and another using a Bayesian framework with a Galactic model including disk and halo stellar distributions.
• Validated distances against Hipparcos and cluster members, achieving median uncertainties below 10% for typical RAVE targets.
• Used kinematic and chemical data to infer velocity dispersion profiles, circular speed, and solar motion, and to trace radial migration via metallicity-velocity correlations.
• Incorporated high-precision APASS photometry and future benchmark star data to refine metallicity calibration, especially at the metal-rich end.

Experimental results

Research questions

• RQ1 What are the chemo-dynamical properties of the Milky Way’s thin and thick discs, and how do they constrain formation mechanisms?
• RQ2 To what extent does radial migration shape the metallicity and velocity distribution of the Galactic disc?
• RQ3 What is the kinematic signature of metal-weak thick disc stars, and what does it imply about their formation?
• RQ4 How do the velocity dispersion and [Mg/Fe] abundance ratios of metal-poor stars relate to the Galaxy’s merger history?
• RQ5 Can extended tidal debris and halo stars around globular clusters be identified in RAVE data, suggesting accretion of dwarf spheroidal galaxies?

Key findings

• The radial velocity dispersion profile of the thick disc has a smaller radial scale length than the thin disc, indicating distinct formation histories.
• The velocity distribution of stars in the solar neighborhood exhibits non-Gaussian features, with the velocity ellipsoid shape and orientation varying with location.
• A kinematic signature of thick disc stars is detected down to [M/H] ≈ −2 dex, with ∂Vφ/∂[M/H] ≈ −50 km s⁻¹ dex⁻¹, suggesting radial migration was not the dominant formation mechanism.
• Metal-poor, α-enhanced stars (with [Mg/Fe] > 0.4 dex) show a decrease in velocity dispersion, consistent with radial migration from the inner Galaxy.
• Evidence for radial migration is also found in the super-solar metallicity end of the thin disc, where stars with high [Fe/H] show kinematic trends consistent with inward migration.
• Tidal debris from ω Centauri are detected in radial velocity histograms around globular clusters NGC 1851 and NGC 3201, with a peak at 230 km s⁻¹, indicating extended halo structures.