用神经网络分析太阳类星化学成分，发现太阳更稀有且存在银河系子结构。
Signatures of planets and Galactic subpopulations in solar analogs. Precise chemical abundances with neural networks
- 用神经网络自动解析高精度光谱，获得99颗太阳类星的精确大气参数与20种元素丰度。
- 太阳在难熔元素上比91%同类星更贫乏，与无行星系统恒星相比显著（9.5σ）。
- 揭示太阳类星中可能存在铜富集、铜贫化及钠贫化三类子群体，暗示银河盘层精细结构。
本研究旨在通过自动获取太阳孪生星和类太阳星的精确大气参数与化学丰度，寻找系外行星的踪迹，并评估太阳在银河系中的独特性，以及分析银河系薄盘可能存在的细微结构。我们开发了一种基于Python的神经网络算法，对来自哈勃望远镜高分辨率光谱仪（HARPS）的99颗太阳类星进行分析，其分辨率R ≈ 115,000，信噪比S/N > 400。成功获得了有效温度、表面重力、铁氢比[Fe/H]以及微湍流、宏湍流和投影自转速度等参数，与文献结果一致：平均差异为(2 ± 27) K（T_eff）、(0.00 ± 0.06) dex（log g）、(0.00 ± 0.02) dex（[Fe/H]）、(-0.01 ± 0.05) km s⁻¹（微湍流）、(0.02 ± 0.08) km s⁻¹（宏湍流）、(-0.12 ± 0.26) km s⁻¹（v sin i）。对20种元素（Li, C, O, Na, Mg, Al, Si, S, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Y, Ba）的丰度比[ X/Fe ]也实现高精度测量，多数元素与文献值偏差小于0.02 dex。通过校正银河系化学演化影响，并结合元素冷凝温度（T_cond），检验难熔元素是否相对挥发性元素贫乏。结果表明，太阳在难熔元素上的贫化程度高于所研究星体的89%，与无系外行星的恒星相比具有9.5σ显著性。此外，还发现了三类子群体：铜富集型、铜贫化型，以及稍老且钠贫化的类型。
原文摘要 · Abstract (English)
The aim of this work is to obtain precise atmospheric parameters and chemical abundances automatically for solar twins and analogs to find signatures of exoplanets, as well as to assess how peculiar the Sun is compared to these stars and to analyze any possible fine structures in the Galactic thin disk. We developed a neural network (NN) algorithm using Python to obtain these parameters for a sample of 99 solar twins and solar analogs previously studied in the literature from normalized high-quality spectra from HARPS, with a resolving power of R $\sim$ 115000 and a signal-to-noise ratio S/N > 400. We obtained precise atmospheric parameters and abundance ratios [X/Fe] of 20 chemical elements (Li, C, O, Na, Mg, Al, Si, S, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Y, and Ba). The results are in line with the literature, with average differences and standard deviations of $(2 \pm 27)$ K for T$_{\rm eff}$, $(0.00 \pm 0.06)$ dex for log g, $(0.00 \pm 0.02)$ dex for [Fe/H], $(-0.01 \pm 0.05)$ km s$^{-1}$ for microturbulence velocity, $(0.02 \pm 0.08)$ km s$^{-1}$ for the macro turbulence velocity, and $(-0.12 \pm 0.26)$ km s$^{-1}$ for the projected rotational velocity (vsin$i$). Regarding the chemical abundances, most of the elements agree with the literature within 0.01 - 0.02 dex. The abundances were corrected from the effects of the Galactic chemical evolution and analyzed with the condensation temperature (T$_{\rm cond}$) to verify whether the stars presented depletion of refractories compared to volatiles. We found that the Sun is more depleted in refractory elements compared to volatiles than 89% of the studied solar analogs, with a significance of 9.5$σ$ when compared to the stars without detected exoplanets. We also found the possible presence of three subpopulations in the solar analogs: one Cu-rich, one Cu-poor, and the last one slightly older and poor in Na.
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