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Gaia mapping the stars of the Milky Way


Stellar chemistry from photometric narrow-band imaging

Project duration Jul 2020 - Jul 2022

Strong metallic absorption lines can absorb a significant fraction of continuum flux in a stellar atmosphere. Because of this, its metallic content can be inferred from a contrast between fluxes in narrow-band images centered on and off of these lines. This classical idea has been hindered by unknown values of stellar parameters, which also influence line strengths.

Both the luminosity and effective temperature of a star depend on its mass and age, and to a smaller extent, its chemical composition. Even luminosities of dwarf stars increase over time, so effects of chemistry cannot be separated from age. This is even more pertinent for stellar multiplicity, where binary stars are brighter than single ones but with an approximate color of the brighter component. This means that the position of a field star in the luminosity-temperature plane is not enough to infer its metallic content.

Gaia results published last spring accurately determine stellar temperatures and luminosities. Yet chemistry composition remains unknown for the majority of stars.

Photometric chemical measurements

In this project, we use a theoretical example to demonstrate the feasibility of photometric chemical measurements under new circumstances, noting that this approach is much less time-consuming than spectroscopy. By implementing an observational pilot study, we will check whether this approach can be used to recover a vital part of the missing chemical information for the majority of stars observed by Gaia, as well as for many PLATO mission exoplanet hosts and for future Gaia-IR mission targets (for which no on-board spectroscopy is planned).

We will infer a star's chemistry by measuring its brightness in 3 specific photometric filter bands centered on and off of the prominent metallic lines.

Detailed chemical abundances, which are being determined by spectroscopic ground-based surveys, will be used to calibrate relations between narrowband photometric indices and chemistry across the parameter space and across the Galaxy.


  • Faculty of mathematics and Physics, University of Ljubljana
  • European Space Agency (ESA)

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