Chemical abundances of 11 bulge stars from high-resolution, near-IR spectra
Chemical abundances of 11 bulge stars from high-resolution, near-IR spectra
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高分辨率近红外光谱中 11 颗核球星的化学丰度
DOI：
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发表时间：
2009
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通讯作者：
M. Zoccali
中科院分区：
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作者：
N. Ryde;B. Gustafsson;B. Edvardsson;J. Meléndez;A. Alves;M. Asplund;B. Barbuy;V. Hill;H. Kaufl;D. Minniti;S. Ortolani;A. Renzini;M. Zoccali
上下文人们争论银河系的核球是否具有更类似于经典核球的特征，而不是伪核球。详细的核球星丰度研究在研究核球的起源、历史和分类时非常重要。这些研究提供了恒星形成历史，初始质量函数和恒星种群之间的差异的限制。由于大的距离和高度可变的视觉消光沿着视线朝向隆起，没有太多类似的研究已经完成。因此，近红外研究可以提供上级结果。目标。对已经用光学光谱研究过的核球巨星，通过近红外光谱研究核球的起源和核球的化学丰度。光谱还提供了恒星的参数，这是非常重要的，目前的研究。特别是，重要的CNO元素在近红外波段得到了更精确的测定。氧和其他α元素对研究恒星形成历史具有重要意义。C和N的丰度对于确定巨星的演化阶段和核球中C的来源具有重要意义。方法.使用安装在甚大望远镜上的CRIRES光谱仪记录了H波段的高分辨率近红外光谱。CNO丰度由观察到的波长范围内的众多分子谱线确定。α元素Si、S和Ti的丰度也由近红外光谱确定。结果丰度比[O/Fe]、[Si/Fe]和[S/Fe]提高到至少[Fe/H] =-0.3的金属丰度，之后它们下降。这表明，银河系核球经历了一个快速和早期爆发的星星形成类似的经典核球。然而，隆起趋势和局部厚盘趋势之间的相似性似乎是存在的。这种相似性表明，隆起可能有一个假隆起的起源。碳和氮的丰度表明，我们的巨星是第一个上升的红巨星或丛星，而测量到的氧丰度是恒星诞生时的氧丰度。我们的[C/Fe]趋势并没有显示出随[Fe/H]的增加而增加，如果W-R星对C丰度有很大的贡献，这是可以预期的。在我们观测到的丰度趋势周围，没有“宇宙散射”可以追踪到：考虑到观测的不确定性，测量到的散射是预期的。
Context. It is debated whether the Milky Way bulge has characteristics more similar to those of a classical bulge than those of a pseudobulge. Detailed abundance studies of bulge stars are important when investigating the origin, history, and classification of the bulge. These studies provide constraints on the star-formation history, initial mass function, and differences between stellar populations. Not many similar studies have been completed because of the large distance and high variable visual extinction along the line-of-sight towards the bulge. Therefore, near-IR investigations can provide superior results. Aims. To investigate the origin of the bulge and study its chemical abundances determined from near-IR spectra for bulge giants that have already been investigated with optical spectra. The optical spectra also provide the stellar parameters that are very important to the present study. In particular, the important CNO elements are determined more accurately in the near-IR. Oxygen and other alpha elements are important for investigating the star-formation history. The C and N abundances are important for determining the evolutionary stage of the giants and the origin of C in the bulge. Methods. High-resolution, near-infrared spectra in the H band were recorded using the CRIRES spectrometer mounted on the Very Large Telescope. The CNO abundances are determined from the numerous molecular lines in the wavelength range observed. Abundances of the alpha elements Si, S, and Ti are also determined from the near-IR spectra. Results. The abundance ratios [O/Fe], [Si/Fe], and [S/Fe] are enhanced to metallicities of at least [Fe/H] = -0.3, after which they decline. This suggests that the Milky Way bulge experienced a rapid and early burst of star formation similar to that of a classical bulge. However, a similarity between the bulge trend and the trend of the local thick disk seems to be present. This similarity suggests that the bulge could have had a pseudobulge origin. The C and N abundances suggest that our giants are first-ascent red-giants or clump stars, and that the measured oxygen abundances are those with which the stars were born. Our [C/Fe] trend does not show any increase with [Fe/H], which is expected if W-R stars contributed substantially to the C abundances. No "cosmic scatter" can be traced around our observed abundance trends: the measured scatter is expected, given the observational uncertainties.