河外HII区的Keck HIRES谱学：来自电离线的C和O丰度
Keck HIRES Spectroscopy of Extragalactic HII Regions: C and O Abundances from Recombination Lines
摘要：
我们提出了非常深的分光光度法的14个明亮的河外HII地区属于螺旋形，不规则，和蓝色的紧凑星系。13个物体的数据是用凯克一号望远镜上的HIRES阶梯光栅摄谱仪拍摄的。我们已经测量了10个对象中的CII复合线和8个对象中的OII复合线。我们从几种离子的谱线比，特别是低电离势离子的谱线比测定了电子温度。我们发现Te（[NII]）和Te（[OIII]）之间存在一个相当紧密的线性经验关系。我们发现OII线总是比[OIII]线给出更大的丰度。此外，两个O++丰度测定的差异-所谓的丰度差异因子-在所有天体中非常相似，平均值为0.26+/-0.09 dex，与HII区域和母星系的性质无关。利用观测到的复合线，我们测定了3个旋涡星系M33、M101和NGC 2403的O、C和C/O径向丰度梯度，发现C丰度梯度总是比O的更陡，在银盘上产生负的C/O梯度。这一结果与在银河系中发现的结果相似，并对化学演化模型和C的核合成具有重要意义。
英文摘要：
We present very deep spectrophotometry of 14 bright extragalactic HII regions belonging to spiral, irregular, and blue compact galaxies. The data for 13 objects were taken with the HIRES echelle spectrograph on the Keck I telescope. We have measured CII recombination lines in 10 of the objects and OII recombination lines in 8 of them. We have determined electron temperatures from line ratios of several ions, specially of low ionization potential ones. We have found a rather tight linear empirical relation between Te([NII]) and Te([OIII]). We have found that OII lines give always larger abundances than [OIII] lines. Moreover, the difference of both O++ abundance determinations --the so-called abundance discrepancy factor-- is very similar in all the objects, with a mean value of 0.26+/-0.09 dex, independently of the properties of the HII region and of the parent galaxy. Using the observed recombination lines, we have determined the O, C, and C/O radial abundance gradients for 3 spiral galaxies: M33, M101, and NGC2403, finding that C abundance gradients are always steeper than those of O, producing negative C/O gradients accross the galactic disks. This result is similar to that found in the Milky Way and has important implications for chemical evolution models and the nucleosynthesis of C.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
