标题： 哈勃太空望远镜光谱学中的螺旋星系中的碳 显示英文标题

标题： Carbon in Spiral Galaxies from Hubble Space Telescope Spectroscopy

摘要： 我们利用哈勃空间望远镜上的 faint object spectrograph（Faint Object Spectrograph，FOS）的紫外线光谱，测量了旋涡星系M101和NGC 2403中的六个H II区域的气相C/O丰度比。 在这两个星系中，C/O比值都随着O/H的增加而系统性地增大，从log O/H = -4.0时的log C/O ≈ -0.8增加到log O/H = -3.4时的log C/O ≈ -0.1。C/N比值与O/H之间没有相关性。 由于不确定紫外消光定律以及金属丰度对尘埃耗尽的依赖性，C/O比值增长的速率存在一定的不确定性。然而，C/O随O/H增加的趋势非常明显，证实并扩展了之前从不规则星系观测中得到的C/O趋势。 我们的数据表明，旋涡星系中C/H的径向梯度比O/H的径向梯度更陡峭。将数据与旋涡星系的化学演化模型进行比较后发现，那些假设大质量恒星的产率不随金属丰度变化的模型预测出的径向C/O梯度比观测到的梯度平坦得多。 目前最可能的假设是，大质量恒星的星风对元素产率以及碳和氧丰度的演化有重要影响。 迄今为止确定的旋涡星系外盘中的C/O和N/O丰度比与矮星不规则星系中的非常相似。这意味着旋涡星系的外盘具有比内盘年轻得多的平均恒星年龄。 显示英文摘要

摘要： We present measurements of the gas-phase C/O abundance ratio in six H II regions in the spiral galaxies M101 and NGC 2403, based on ultraviolet spectroscopy using the Faint Object Spectrograph on the Hubble Space Telescope. The C/O ratios increase systematically with O/H in both galaxies, from log C/O approximately -0.8 at log O/H = -4.0 to log C/O approx. -0.1 at log O/H = -3.4. C/N shows no correlation with O/H. The rate of increase of C/O is somewhat uncertain because of uncertainty as to the appropriate UV reddening law, and uncertainty in the metallicity dependence on grain depletions. However, the trend of increasing C/O with O/H is clear, confirming and extending the trend in C/O indicated previously from observations of irregular galaxies. Our data indicate that the radial gradients in C/H across spiral galaxies are steeper than the gradients in O/H. Comparing the data to chemical evolution models for spiral galaxies shows that models in which the massive star yields do not vary with metallicity predict radial C/O gradients that are much flatter than the observed gradients. The most likely hypothesis at present is that stellar winds in massive stars have an important effect on the yields and thus on the evolution of carbon and oxygen abundances. C/O and N/O abundance ratios in the outer disks of spirals determined to date are very similar to those in dwarf irregular galaxies. This implies that the outer disks of spirals have average stellar population ages much younger than the inner disks.