Products and Models for "Mapping the SO2 Shoreline in Gas Giant Exoplanets"

JWST has revealed sulfur chemistry in the atmospheres of gas giant exoplanets. Molecules such as SO2 may be sensitive tracers of high-altitude photochemistry, atmospheric metallicity, and of planet formation & migration. To ascertain the conditions that determine whether (or how much) SO2, H2S, and other sulfur-bearing species are present in exoplanet atmospheres, we present a series of model grids of planetary atmospheres covering metallicities from 0.3–1000× Solar and temperatures from 250–2050 K. With these models we map out the “SO2 shoreline,” the region of metallicity and irradiation for which SO2 (the most easily detected sulfur tracer) may be sufficiently abundant to be detectable. A key conclusion is that for a given temperature, SO2 abundance is an extremely sensitive indicator of metallicity (robust to all the other factors; mixing, plausible C/O ratios, UV irradiation). Expected SO2 abundances also depend strongly on overall temperature and C/O ratio; the SO2 abundance depends surprisingly weakly on XUV irradiation, also weakly on Kzz (for Teq ≳ 600 K), and is essentially independent of internal temperature. Despite its detection in a growing number of giant planets, SO2 is never the dominant sulfur-bearing molecule: depending on temperature and metallicity, H2S, S2, NS, SO, SH, and even S8 or atomic S are frequently as common (or more so) as SO2. Nonetheless SO2 remains the most easily detectable sulfur-bearing species, followed by H2S, though perhaps SO and SH could be detectable in some gas giants. Aside from a pressing need for additional observational constraints on sulfur, we also identify the need for future work to account for the effects of clouds and hazes, fully self-consistent atmospheric models, 2D and 3D models, a wider range of planetary masses and radii, and studies to measure and refine reaction rates and molecular opacities of sulfur-bearing species. The atmospheric grid and associated models used in the paper arepresented here. An example directory name isMTgrid_XUV1,00_Kzz7.0_Tint100_TP_helios_1000K_SNCHO_1.0x_z83_C1.0_N1.0_O1.0_S1.0_where the name is formatted as"MTgrid_XUV{xuv}_Kzz{kzz}_Tint{tint}_TP_helios_{teq}K_SNCHO_{met}_z83_C{cmet}_N{nmet}_O{omet}_S{smet}_" Table 1 and Section 2 of the paper provide further details on therelevant parameters and how they are used in the subsequent modelingprocess. The values are: xuv - scaling from nominal HAT-P-26 XUV stellar spectrum kzz - log10 of Kzz value [cgs units: cm^2/s] tint - internal temperature [K] (for T-P profile calculation) teq - planet temperature [K] met - metallicity used for T-P profile calculation, relative to Solar cmet - enhancement of C/H relative to the Solar value (for chemistry calculation) nmet - enhancement of N/H relative to the Solar value (for chemistry calculation) omet - enhancement of O/H relative to the Solar value (for chemistry calculation) smet - enhancement of S/H relative to the Solar value (for chemistry calculation) Each directory contains several files: (1) cfg_mtgrid_helios.txt (2) mtgrid_helios.vul (3) mtgrid_helios_vertical_profiles.csv (4) mtgrid_helios_vertical_mmr_profiles.csv (5) mtgrid_helios_transmission.csv (1) cfg_mtgrid_helios.txt The VULCAN control file used for the run. See https://github.com/exoclime/VULCAN and Tsai et al. (2021) - https://ui.adsabs.harvard.edu/abs/2021ApJ...923..264T - for more details. (2) mtgrid_helios.vul The VULCAN output file. This is a Python pickle object. See https://github.com/exoclime/VULCAN and Tsai et al. (2021) - https://ui.adsabs.harvard.edu/abs/2021ApJ...923..264T - for more details. (3) mtgrid_helios_vertical_profiles.csv A machine-readable CSV file with vertical profiles extracted from the VULCAN output: pressure, temperature, Kzz, MMW (mean molecular weight), and volume mixing ratios of a subset of the molecules used in the VULCAN photochemistry calculation. (4) mtgrid_helios_vertical_mmr_profiles.csv A machine-readable CSV file with vertical profiles extracted from the VULCAN output: pressure, temperature, Kzz, MMW (mean molecular weight), and mass mixing ratios (MMR) of a subset of the molecules used in the VULCAN photochemistry calculation. (5) mtgrid_helios_transmission.csv A machine-readable CSV file with the synthetic transmission (transit) spectrum calculated using petitRadTrans from the associated VULCAN output file. The first two colums are 'wave' (wavelength in microns) and 'rprs2' (the transit depth, i.e. [Rp/Rs]^2). Subsequent columns such as 'rprs2_only_CO2' and 'rprs2_no_CO2' are transmission spectra containing (respectively) only the specified absorber, and all other absorbers except the specified absorber.詹姆斯·韦伯空间望远镜（JWST）首次揭示了系外气态巨行星大气中的硫化学机制。诸如二氧化硫（SO₂）这类分子可作为高海拔光化学过程、大气金属丰度以及行星形成与迁移过程的灵敏示踪剂。为明确决定系外行星大气中是否存在二氧化硫（SO₂）、硫化氢（H₂S）及其他含硫物种，以及其丰度水平的相关条件，本研究构建了一系列行星大气模型网格，其覆盖的金属丰度范围为0.3~1000倍太阳丰度，温度范围为250~2050开尔文。借助上述模型，我们绘制出了“SO₂海岸线”——即金属丰度与辐照水平的参数区间，在此区间内作为最易探测的含硫示踪剂的SO₂丰度足以被观测到。核心结论之一为：在固定温度下，SO₂丰度是金属丰度的极强灵敏指示器（对其他所有因素，包括混合过程、合理碳氧比、紫外辐照均保持稳健）。预期SO₂丰度同样强烈依赖于整体温度与碳氧比；但出人意料的是，SO₂丰度对极紫外（XUV）辐照的依赖极弱，在平衡温度（T_eq ≳ 600开尔文）下对涡动扩散系数Kzz的依赖也较弱，且基本与内部温度无关。尽管在越来越多的巨行星中已探测到SO₂，但它始终不是占主导地位的含硫分子：根据温度与金属丰度的不同，硫化氢（H₂S）、双硫分子（S₂）、一硫化氮（NS）、一氧化硫（SO）、硫氢自由基（SH）甚至八硫环（S₈）或单质硫（S）的丰度往往与SO₂相当，甚至更高。尽管如此，SO₂仍是最易被探测的含硫物种，其次为H₂S；不过部分气态巨行星中或可探测到SO与SH。除了亟需更多关于硫元素的观测约束外，本研究还指出未来研究需考虑云与霾的影响、构建完全自洽的大气模型、开展二维与三维模拟、覆盖更广范围的行星质量与半径区间，以及开展测量并优化含硫物种反应速率与分子不透明度的相关工作。 本文所用的大气模型网格与相关模型已在此公开。示例目录名称为`MTgrid_XUV1,00_Kzz7.0_Tint100_TP_helios_1000K_SNCHO_1.0x_z83_C1.0_N1.0_O1.0_S1.0_`，其命名格式为：`MTgrid_XUV{xuv}_Kzz{kzz}_Tint{tint}_TP_helios_{teq}K_SNCHO_{met}_z83_C{cmet}_N{nmet}_O{omet}_S{smet}_` 本文的表1与第2节详细说明了相关参数及其在后续建模流程中的使用方式。各参数含义如下： - xuv：基于标准HAT-P-26恒星极紫外（XUV）光谱的缩放因子 - kzz：涡动扩散系数Kzz值的以10为底的对数（单位为厘米·克·秒制：cm²/s） - tint：用于温度-压强（T-P）廓线计算的内部温度（单位：开尔文） - teq：行星平衡温度（单位：开尔文） - met：用于T-P廓线计算的、相对于太阳丰度的金属丰度 - cmet：用于化学计算的、相对于太阳值的碳氢比（C/H）增强因子 - nmet：用于化学计算的、相对于太阳值的氮氢比（N/H）增强因子 - omet：用于化学计算的、相对于太阳值的氧氢比（O/H）增强因子 - smet：用于化学计算的、相对于太阳值的硫氢比（S/H）增强因子 每个目录包含以下文件： 1. `cfg_mtgrid_helios.txt`：本次运行所用的VULCAN控制文件。详细信息可参考https://github.com/exoclime/VULCAN 与Tsai等人2021年的研究（https://ui.adsabs.harvard.edu/abs/2021ApJ...923..264T）。 2. `mtgrid_helios.vul`：VULCAN的输出文件，为Python pickle序列化对象。详细信息可参考https://github.com/exoclime/VULCAN 与Tsai等人2021年的研究（https://ui.adsabs.harvard.edu/abs/2021ApJ...923..264T）。 3. `mtgrid_helios_vertical_profiles.csv`：可机读的CSV格式文件，包含从VULCAN输出中提取的垂直廓线数据：压强、温度、Kzz、平均分子质量（MMW），以及VULCAN光化学计算中所用部分分子的体积混合比。 4. `mtgrid_helios_vertical_mmr_profiles.csv`：可机读的CSV格式文件，包含从VULCAN输出中提取的垂直廓线数据：压强、温度、Kzz、平均分子质量（MMW），以及VULCAN光化学计算中所用部分分子的质量混合比（MMR）。 5. `mtgrid_helios_transmission.csv`：可机读的CSV格式文件，包含基于关联VULCAN输出文件、通过petitRadTrans计算得到的合成透射（凌星）光谱。前两列分别为`wave`（波长，单位：微米）与`rprs2`（凌星深度，即[R_p/R_s]^2）。后续列如`rprs2_only_CO2`与`rprs2_no_CO2`分别代表仅包含指定吸收体、以及除指定吸收体外所有其他吸收体的透射光谱。