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Chemical abundances in the old LMC globular cluster Hodge 11

机译:旧的LMC球状星团Hodge 11中的化学丰度

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Context. The study of globular clusters is one of the most powerful ways to learn about a galaxy’s chemical evolution and star formation history. They preserve a record of chemical abundances at the time of their formation and are relatively easy to age date. The most detailed knowledge of the chemistry of a star is given by high resolution spectroscopy, which provides accurate abundances for a wide variety of elements, yielding a wealth of information on the various processes involved in the cluster’s chemical evolution. Aims. We studied red giant branch (RGB) stars in an old, metal-poor globular cluster of the Large Magellanic Cloud (LMC), Hodge?11 (H11), in?order to measure as many elements as possible. The goal is to compare its chemical trends to those in the Milky?Way halo and dwarf spheroidal galaxies in order to help understand the formation history of the LMC and our own Galaxy. Methods. We have obtained high resolution VLT/FLAMES spectra of eight RGB?stars in?H11. The spectral range allowed us to measure a variety of elements, including?Fe, Mg, Ca, Ti, Si, Na, O, Ni, Cr, Sc, Mn, Co, Zn, Ba, La, Eu and?Y. Results. We derived a mean [Fe/H]?= ?2.00 ±? 0.04, in?the middle of previous determinations. We found low [α/Fe]?abundances for our targets, more comparable to values found in dwarf spheroidal galaxies than in the Galactic halo, suggesting that if?H11 is representative of its ancient populations then the?LMC does not represent a good halo building block. Our?[Ca/Fe]?value is about?0.3?dex less than that of halo stars used to calibrate the Ca?IR?triplet technique for deriving metallicity. A?hint of a?Na?abundance spread is observed. Its?stars lie at the extreme high?O, low?Na end of the Na:O?anti-correlation displayed by Galactic and LMC?globular clusters.
机译:上下文。球状星团的研究是了解星系化学演化和恒星形成历史的最有力方法之一。它们在形成时会保留化学丰度的记录,并且相对容易老化。高分辨率光谱学提供了有关恒星化学的最详细知识,它可以为各种元素提供准确的丰度,并提供有关星团化学演化所涉及的各种过程的大量信息。目的为了研究尽可能多的元素,我们研究了大型麦哲伦星云(LMC),霍奇11(H11)的一个旧的,金属贫乏的球状星团中的红色巨星(RGB)星。目的是将其化学趋势与银河系晕圈和矮球状星系中的化学趋势进行比较,以帮助了解LMC和我们自己的银河系的形成历史。方法。我们已经获得了?H11中八颗RGB?星的高分辨率VLT / FLAMES光谱。光谱范围使我们能够测量各种元素,包括铁,镁,钙,钛,硅,钠,氧,镍,铬,,锰,钴,锌,钡,镧,Eu和?。结果。我们得出平均值[Fe / H]?=?2.00±? 0.04,在先前确定的中间。我们发现目标的[α/ Fe]丰度低,与矮球状星系中的值相比,比银河系光环中的值更可比,这表明如果H11代表其古代种群,那么LMC并不代表良好的光环积木。我们的[Ca / Fe]α值比用于校准Ca?IR?triplet技术以获取金属性的晕星的值小约0.3?dex。观察到Na丰度分布的提示。它的星位于银河系和LMC球状星团所显示的Na:O反相关的极高O,低Na末端。

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