Carbon-Enhanced Metal-Poor Star Candidates in the Milky Way from J-PLUS and S-PLUS

TL;DR

This study leverages photometric estimates from the J-PLUS and S-PLUS surveys to assemble a large catalog of CEMP candidates and test the photometric recovery of established CEMP subclasses. It uses Gaussian Mixture Models on corrected carbon abundances $A(C)_{ m c}$ to identify subgroups corresponding to CEMP-no, CEMP-$s$, and Group IV, adopting $A(C)_{ m c}=7.15$ to separate CEMP-no from CEMP-$s$ for direct comparison with spectroscopic work. The resulting catalog of ~104,941 CEMP candidates across ~6.40 million stars reveals metallicity-dependent trends and distinct Galactic-region frequencies, with CEMP-no stars dominating at the lowest metallicities and Group IV contributing notably to the counts. The work provides independent photometric validation of spectroscopic results and delivers a rich target set for future high-/medium-resolution follow-up to constrain the origins of CEMP subgroups and the early evolution of the Milky Way.

Abstract

Recent large-scale multi-band photometric surveys now enable elemental-abundance estimates for millions of stars with accuracies approaching those of low- to medium-resolution spectroscopy. Using [Fe/H] and [C/Fe] estimates derived from the Javalambre Photometric Local Universe Survey (J-PLUS) DR3 and the Southern Photometric Local Universe Survey (S-PLUS) DR4, which together cover $\sim$6,200 deg$^2$ of the sky, we identify large numbers of carbon-enhanced metal-poor (CEMP) stars in the Milky Way. After applying data-quality cuts and evolutionary corrections to the carbon-abundance estimates, we construct a combined J/S-PLUS sample of $\sim$6.40 million stars and identify $\sim$104,900 CEMP candidates, roughly twice the number of CEMP candidates identified from Gaia XP spectra by Lucey et al. We photometrically confirm that the absolute carbon abundance $A$(C) separates CEMP stars into two primary groups, CEMP-no and CEMP-$s$ stars, consistent with previous spectroscopic studies. We also recover CEMP morphological Groups I-III in the Yoon-Beers diagram, as well as the recently proposed Group IV, and show that it is statistically distinct even in photometric data. A cumulative frequency analysis confirms that the CEMP fraction increases toward lower metallicity and that CEMP-no stars dominate in the most metal-poor regime. By comparing frequencies with and without Group IV stars, we assess their relation to CEMP-no and CEMP-$s$ stars, and examine CEMP distributions across different Galactic components. The resulting catalog provides a substantial sample for future spectroscopic follow-up, in particular to constrain the likely origin(s) of the Group IV stars.

Figures (11)

• Figure 1: Distribution of $G$ magnitudes for the combined J/S-PLUS sample and the L25 SDSS and LAMOST samples. Unfilled black and blue histograms represent the total J/S-PLUS and L25 samples, respectively, while filled histograms show the distributions of the CEMP stars in the J/S-PLUS and L25 samples. The number of stars in each sample is indicated in the top-left corner.
• Figure 2: Distribution of [C/Fe]$_{\rm c}$, as a function of [Fe/H], for the combined J/S-PLUS sample. From left to right are all the samples in this study, the dwarf stars, and the giant stars, respectively. The total number of stars is shown in the top-right, and the number density is color-coded on a logarithmic scale. The dashed-black line marks [C/Fe]$_{\rm c}$$= +0.7$, and the white box indicates the CEMP candidate region. The number of CEMP candidates is shown in the top-left corner.
• Figure 3: The $A$(C)$_{\rm c}$ distribution of the combined J/S-PLUS CEMP sample with [Fe/H] $< -2.5$, after applying flag cuts of 0.85. The sample size is indicated in the upper-right corner. The dashed-blue and dashed-red curves represent the GMM fits for CEMP-$s$ and CEMP-no candidates, respectively, while the solid-purple curve indicates the sum of the Gaussian fits. The intersection of the two Gaussians is marked by a vertical dashed-black line at $A$(C)$_{\rm c} = 7.44$.
• Figure 4: Distribution of $A$(C)$_{\rm c}$, as a function of [Fe/H], for the combined J/S-PLUS sample. The solid-green line represents [C/Fe]$_{\rm c}= +0.7$. The red, blue, orange, and magenta ellipses represent subgroups of CEMP stars, corresponding to Groups I, II, III, and IV, respectively. The left-most panel shows the SDSS and LAMOST DR6 sample from L25, and the second through fourth panels show the J/S-PLUS sample with data-quality flag cuts of 0.85, 0.90, and 0.95, respectively. The total number of stars in each sample is indicated at the top of each panel.
• Figure 5: The $A$(C)$_{\rm c}$ distribution of the combined J/S-PLUS CEMP sample with [Fe/H] $\leq -2.0$, after applying flag cuts of 0.85. The [Fe/H] ranges for each panel are displayed in the top-right corner along with the sample size. The dashed-blue, dashed-red, and dashed-green curves represent the GMM fits for each component, while the solid-purple curve denotes the fit for the sum of all components. The intersections of the Gaussians, representing the separation between Groups II, III, and IV, are marked by vertical dashed-black lines at $A$(C)$_{\rm c} =$ 6.73 and 7.78.