We present deep spectrophotometry of several Hii regions in the nearby low-mass spiral galaxies NGC 300 and M33. The data have been taken with UVES and OSIRIS spectrographs attached to the 8m VLT and 10.4m GTC telescopes, respectively. We have derived precise values of the physical conditions for each object making use of several emission line-intensity ratios. In particular, we have obtained direct determinations of the electron temperature in all the observed objects. We detect pure recombination lines (RLs) of Cii and Oii in several of the Hii regions, permitting to derive their C/H and C/O ratios. We have derived the radial abundance gradient of O for each galaxy making use of collisionally excited lines (CELs) and RLs, as well as the C and N gradients using RLs and CELs, respectively. We obtain the first determination of the C/H gradient of NGC 300 and improve its determination in the case of M33. In both galaxies, the C/H gradients are steeper that those of O/H, leading to negative C/O gradients. Comparing with similar results for other spiral galaxies, we find a strong correlation between the slope of the C/H gradient and M_V. We find that some Hii regions located close to the isophotal radius (R_25) of NGC 300 and M33 show C/O ratios more similar to those typical of dwarf galaxies than those of Hii regions in the discs of more massive spirals. This may be related to the absence of flattening of the gradients in the external parts of NGC 300 and M33. Finally, we find very similar N/H gradients in both galaxies and a fair correlation between the slope of the N/H gradient and M_V comparing with similar data for a sample of spiral galaxies.
Adsorption energies of carbon, nitrogen, and oxygen atoms on the low-temperature amorphous water ice: A systematic estimation from quantum chemistry calculations
Carbon and hydrogen radio recombination lines from the cold clouds towards Cassiopeia A
我们使用低频阵列对仙后座A视线方向上的低频33-78 MHz频谱进行系统的高光谱分辨率调查。我们补充说，这与304-386兆赫韦斯特博克综合射电望远镜观测。在这第一篇论文中，我们专注于碳放射性复合线。我们探测到Cn $α$线在-47和-38公里秒$^{-1}$在吸收量子数n=438-584和在发射n=257-278与高信噪比。这些线与英仙座旋臂部分的冷云有关。在n=257-278的发射中检测到Hn条$α$线。此外，我们还探测到了与猎户臂相关的0 km s $^{-1}$处的Cn $α$谱线，并分析了这些跃迁的光学深度和谱线宽度。我们的模型表明，在英仙座臂的碳线组件是最好的拟合与电子温度85 K和电子密度0.04 cm $^{-3}$，可以限制在15\%。电子压力被限制在20%以内。我们认为，这些碳无线电复合线出现在CO-暗的分子云的表面层，其中大部分的碳离子化，但氢已从原子到分子的过渡。氢谱线显然与碳谱线发射云有关，但低频上限表明它们可能不是同一种气体。结合氢和碳的结果，我们得出了宇宙射线电离率的一个确定下限，即2.5 $\times$ 10 $^{-18}$ s $^{-1}$，但实际值可能要大得多。
CHAOS V: Recombination Line Carbon Abundances in M101
CHAOS项目正在建立附近旋涡星系LBT H II区光谱的大型数据库，以使用直接丰度更好地确定金属丰度随星系半径变化的分散度。在这里，我们提出了混沌LBT观测的C II $λ$ 4267发射检测在10 H II地区的M 101，并使用一个新的光电离模型为基础的电离校正因子，我们将这些测量到总碳丰度。与文献中M101 C II复合线观测结果的比较显示出极好的一致性，我们测量到一个相对陡峭的log（C/H）梯度为-0.37 +/-0.06 dex/R_e。C/N观测结果与log（C/N）= 0.84的恒定值一致，离散度仅为0.09 dex，考虑到C和N的不同核合成来源，理解这一点具有挑战性。我们还注意到，当绘制N/O与O/H的关系图时，所有检测到CII $λ$ 4267的H II区域在O/H的给定值下，N/O的散射最小时呈现N/O丰度。如果探测微弱复合线所需的高表面亮度被解释为H II区年轻的指标，那么这可能表明最年轻的H II区缺乏氮污染。在未来，我们预计混沌项目将显着增加在河外H II地区的C II $λ$ 4267测量的总数。
Modeling Nitrogen Fractionation in the Protoplanetary Disk around TW Hya: Model Constraints on Grain Population and Carbon-to-Oxygen Elemental Abundance Ratio
Exploring the Milky Way stellar disk. Carbon, nitrogen, oxygen, sulphur, potassium, and copper abundances for 714 F- and G-type dwarf stars in the solar neighbourhood
Understanding molecular ratios in the carbon and oxygen poor outer Milky Way with interpretable machine learning
Leiden University（莱顿大学）；SURF；University of Bonn（波恩大学）；University College London（伦敦大学学院）；INAF - Osservatorio Astrofisico di Arcetri（INAF-阿雷特里天文台）；PSL Research University（巴黎综合理工研究大学）
Molecular diagnostics for the mid-infrared emission of planet-forming disks. Carbon and oxygen elemental abundances
Kapteyn Astronomical Institute, Rijksuniversiteit Groningen（格罗宁根大学卡普坦天文研究所）；Leiden Observatory, Leiden University（莱顿大学莱顿天文台）；Max-Planck Institut für Extraterrestrische Physik (MPE)（马克斯·普朗克地外物理研究所）；Space Research Institute, Austrian Academy of Sciences（奥地利科学院空间研究所）；University Observatory, Faculty of Physics, Ludwig-Maximilians-Universität München（慕尼黑大学物理学院大学天文台）；Department of Physics and Astronomy, University of Exeter（埃克塞特大学物理与天文学系）；Department of Astronomy, University of Michigan（密歇根大学天文学系）；Université Paris-Saclay, CNRS, Institut d’Astrophysique Spatiale（巴黎萨克雷大学、法国国家科学研究中心、空间天体物理学研究所）
