High-Precision Near-Infrared Abundances of Solar Analogs in the YJ Bands

Abstract

We present a near-infrared abundance analysis of 46 solar analogs with known ages, observed with the WINERED WIDE-mode spectrograph at a resolution of $λ/Δλ= 28,000$. Using an empirically calibrated, line-by-line approach in the $YJ$ bands (0.976--1.089 and 1.182--1.319~{$μ$}m), we derive abundances for 16 elements. Despite the intrinsic weakness of near-infrared phosphorus diagnostics, the combination of five P\,{\sc i} lines yields a typical uncertainty half-width of $\sim$0.04~dex, providing an estimate of the internal precision over the solar-analog sample. For other elements, the internal precision ranges from $\sim$0.01~dex for Fe and Si to over 0.05--0.14~dex for elements with only a couple of lines available. The resulting per-object abundances for various elements are consistent with previous measurements using high-precision optical spectra with residuals of 0.03--0.2~dex depending on the element. The inferred age--[X/Fe] relations reproduce known trends for the thin disk, while extending them to elements difficult to access in the optical, including P and K. We find the slope of the age--[P/Fe] relation is steeper than that for $α$ elements, which provides an empirical constraint for future modeling of Galactic phosphorus evolution. In addition, we publish a high signal-to-noise (S/N 500--1000) reference spectrum constructed by combining solar-analog spectra, together with the spectra of individual stars, and an empirically calibrated line list with per-line zero-point corrections, for future near-infrared spectroscopic studies.

Figures (13)

• Figure 1: Examples of residual curves. Panels (a,b) show the curves for Fe I 10611.69 Å and Fe I 10555.65 Å measured in solar-analog calibrators. Panels (c,d) show the target-stage combined residual curves for HIP 114328: Fe i in (c) and P i in (d). Gray curves are individual residual curves, while the thick blue/green curves are the combined residual curves. All curves are normalized to their minima for illustration.
• Figure 2: Distributions of per-line zero-point offsets $\Delta_\mathrm{line}$ and half-widths $\sigma_\mathrm{line}$ for candidate lines taken from VALD (blue) and those from MB99 (orange). Left: histograms of $\Delta_\mathrm{line}$. Center: histograms of $\sigma_\mathrm{line}$. Right: $|\Delta_\mathrm{line}|$ versus $\sigma_\mathrm{line}$. Most lines cluster around small offsets and narrow widths, while several lines were rejected due to large offsets ($|\Delta_\mathrm{line}|>0.5$) or half-widths ($\sigma_\mathrm{line}>0.25$).
• Figure 3: Bootstrap test using Fe i VALD combined curves for solar-analog stars. Gray and orange lines show, respectively for individual calibrators (ages 3--7 Gyr) and non-calibrators, the robust $\sigma$([Fe/H]) and median half-width versus subset size $M$; blue curves show the median over all stars; red curves are $\alpha/\sqrt{M}$ fits. Both metrics decline approximately as expected from statistical averaging.
• Figure 4: Residuals between our VALD abundances and literature values for Fe i, Si i, and Mg i, plotted versus literature [X/H]. Error bars indicate our 1$\sigma$ intervals, and the horizontal line marks zero residual.
• Figure 5: Five P i lines we selected. Observed spectra are shown in blue and the best-fitting synthetic spectra are shown in red for two solar analogs, HIP 4909 (upper) and HIP 117367 (lower). The solid vertical line marks the line center, and the dashed vertical lines indicate the fitting range (corresponding to $\pm 30$ km s$^{-1}$).