S-PLUS: Beyond Spectroscopy IV. Stellar Parameters and Elemental-abundance Ratios for Six Million Stars from DR4 and First Results for the Magellanic Clouds

Abstract

We combine narrow/medium-band filter photometry from the Southern Photometric Local Universe Survey (S-PLUS) DR4 with ultra broad-band filter photometry from Gaia EDR3 to derive fundamental stellar parameters ($T_{\rm eff}$, $\log g$, [Fe/H], ages) and elemental-abundance ratios ([C/Fe] and [$α$/Fe]) for 5.4 million stars in the Galaxy (4.9 million dwarfs and 0.5 million giants), as well as for over 0.7 million red giant stars in the Large and Small Magellanic Clouds (LMC and SMC). The precisions of the abundance estimates range from 0.05-0.10 dex for metallicity in the relatively metal-rich range ([Fe/H] $> -1.0$) to 0.10-0.30 dex in the metal-poor regime ([Fe/H] $<-1.0$), 0.10-0.20\,dex for [C/Fe], and 0.05 dex for [$α$/Fe]. The stellar parameters for LMC and SMC member stars are somewhat less precise than those from the S-PLUS main survey, primarily because of the effect of high reddening. The use of both metallicity- and carbon-sensitive filters provides unbiased measurements of both [Fe/H] and [C/Fe], of particular importance for very low-metallicity ([Fe/H] $< -2.0$) stars, where carbon enhancement can lead to systematically high estimates of [Fe/H] when only a single metallicity-sensitive filter is employed. Furthermore, multiple narrow-band filters enable metallicity estimates down to [Fe/H] $\sim -4.0$ with an accuracy of around 0.3 dex, exceeding the precision typically achieved by low/medium-resolution spectroscopy. This extensive photometric dataset, combined with the other three datasets in this series, will serve as a valuable legacy resource for Milky Way and Magellanic Clouds studies.

Figures (15)

• Figure 1: Histograms of the training sets in metallicity ([Fe/H]) for dwarfs (blue) and giants (red).
• Figure 2: Distributions of stars in the training sample: [$\alpha$/Fe] in the [$\alpha$/Fe]–[Fe/H] plane (top panels) and [C/Fe] in the [C/Fe]–[Fe/H] plane (bottom panels). The left panels correspond to dwarf stars, while the right panels show giant stars. In the bottom panels, the red-dashed lines mark [C/Fe] $= +0.7$, a commonly adopted criterion for defining carbon-enhanced metal-poor (CEMP) stars. For the present analysis, we report the measured [C/Fe] values without applying evolutionary corrections. The blue-dashed lines in each panel indicate the Solar ratios.
• Figure 3: Comparisons between photometric and spectroscopic metallicities (top panels) for dwarf stars (left column) and giant stars (right column) in the training sample. The photometric metallicities are derived from multiple colors constructed by combining S-PLUS DR4 and $Gaia$ EDR3 magnitudes using the KPCA technique (see text). The lower panels show the abundance differences (photometric minus spectroscopic), as a function of the spectroscopic values. Blue dots and error bars indicate the median and dispersion of the differences within each bin. The blue-dashed lines mark the one-to-one relations, and the color bars at the top indicate the number of stars in each bin.
• Figure 4: Similar to Figure \ref{['fig:training_res1']}, but for [$\alpha$/Fe] (top panels) and [C/Fe] (bottom panels).
• Figure 5: Left panel: Density distribution of the [Fe/H] quality flag flg$_{\rm [Fe/H]}$, as a function of $r$-band magnitude. A color bar representing the numbers of stars is provided at the top of the panel. Right panel: Comparisons of the photometric metallicity and the SDSS/SEGUE spectroscopic metallicity for different ranges of the [Fe/H] quality flag (as marked in the top-left corner of each sub-panel). The blue-dashed lines are the one-to-one lines. The total number of stars used in the comparison is marked in the bottom-right corner of each sub-panel.