标题： NGC 5253中的局部化学污染再研究：深部阶梯光谱测光结果 显示英文标题

标题： The localized chemical pollution in NGC 5253 revisited: Results from deep echelle spectrophotometry

摘要： 我们提供了蓝致密矮星系（BCDG）NGC 5253的阶梯光谱测光数据。 数据是在3100到10400埃的范围内使用甚大望远镜UVES阶梯光谱仪获得的。 我们在星系中心部分的四个区域测量了大量允许和禁戒发射线的强度。 特别是，我们检测到了微弱的C II和O II复合线（RLs）。 这是首次在矮星暴星系中明确检测到这些线条。 通过大量不同的线强度比值推导了电离气体的物理条件。 按照标准方法确定了He、N、O、Ne、S、Cl、Ar和Fe的化学丰度。 此外，C^{++}和O^{++}的丰度是从纯RLs中推导出来的。 这些丰度大于从碰撞激发线（CELs）得到的丰度（对于C^{++}从0.30到0.40 dex，对于O^{++}从0.19到0.28 dex）。 这一结果与温度波动参数（t^2）在0.050到0.072之间是一致的。 我们确认了之前的结果，表明在星系中心的某些区域存在局部的氮富集。 此外，我们的结果还表明在同一区域可能存在轻微的氦过量。 这种富集模式符合由沃尔夫-拉叶（WR）阶段大质量恒星喷出物污染所预期的模式。 为了产生观测到的过量物质，所需的富集物质数量与星暴中估计的WR星数量损失的质量一致。 最后，我们讨论了在H II区域中从RLs和CELs推导出的丰度差异的可能原因，发现基于超新星喷出物包含物延迟富集的最近假设似乎无法解释观测到的特征。 显示英文摘要

摘要： We present echelle spectrophotometry of the blue compact dwarf galaxy (BCDG) NGC 5253. The data have been taken with the Very Large Telescope UVES echelle spectrograph in the 3100 to 10400 angstroms range. We have measured the intensities of a large number of permitted and forbidden emission lines in four zones of the central part of the galaxy. In particular, we detect faint C II and O II recombination lines (RLs). This is the first time that these lines are unambiguously detected in a dwarf starburst galaxy. The physical conditions of the ionized gas have been derived using a large number of different line intensity ratios. Chemical abundances of He, N, O, Ne, S, Cl, Ar, and Fe have been determined following the standard methods. In addition, C^{++} and O^{++} abundances have been derived from pure RLs. These abundances are larger than those obtained from collisionally excited lines, (CELs) (from 0.30 to 0.40 dex for C^{++} and from 0.19 to 0.28 dex for O^{++}). This result is consistent with a temperature fluctuations parameter (t^2) between 0.050 and 0.072. We confirm previous results that indicate the presence of a localized N enrichment in certain zones of the center of the galaxy. Moreover, our results also indicate a possible slight He overabundance in the same zones. The enrichment pattern agrees with that expected for the pollution by the ejecta of massive stars in the Wolf-Rayet (WR) phase. The amount of enriched material needed to produce the observed overabundance is consistent with the mass lost by the number of WR stars estimated in the starbursts. Finally, we discuss the possible origin of the difference between abundances derived from RLs and CELs in H II regions, finding that a recent hypothesis based on the delayed enrichment by SNe ejecta inclusions seems not to explain the observed features.