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首页> 外文学位 >A Spitzer study of the mass-loss and infrared variability properties of Asymptotic Giant Branch stars in the Magellanic Clouds.
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A Spitzer study of the mass-loss and infrared variability properties of Asymptotic Giant Branch stars in the Magellanic Clouds.

机译：Spitzer研究麦哲伦星云中渐近巨分支恒星的质量损失和红外变异性。

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摘要

The Asymptotic Giant Branch (AGB) is one of the most interesting, and least understood, phases of stellar evolution. The fate of approximately solar mass stars as they exhaust their nuclear fuel for the final time, these stars are also one of the universe's primary sources for many heavy elements, such as carbon and oxygen. We have assembled a sample of ∼30,000 AGB stars in the Large Magellanic Cloud (LMC) with multi-wavelength data ranging from the ultraviolet to the mid-infrared, and multi-epoch data spanning 5 years. This dataset allows us to probe the variability and mass-loss properties of AGB stars at population scales, a valuable contribution to studies of stellar evolution and the mass budget of the interstellar medium (ISM).;We combine variability information from the MAssive Compact Halo Objects (MACHO; Alcock et al. 1997) microlensing survey with infrared photometry from the Spitzer Space Telescope legacy program Surveying the Agents of Galaxy Evolution (SAGE; Meixner et al. 2006) to determine the infrared period-magnitude relationships for three evolutionary classes of AGB stars at 8 different wavelengths. We find that the most evolved AGB stars are pulsating in the fundamental and first overtone, while less evolved stars are concentrated in higher-overtone modes. We show that the slope of the period-magnitude relationship becomes steeper for more evolved stars, at all wavelengths.;Using a grid of radiative transfer models of circumstellar dust shells (GRAMS; Sargent et al. 2011; Srinivasan et al. 2011) and photometry in 12 bands ranging from the ultraviolet to the infrared, we calculated individual bolometric luminosities and dust mass-loss rates for each AGB star in the LMC. This allowed us to calculate the total dust injection to the interstellar medium from these stars via direct summation. We find that the total mass injection rate (gas and dust) from AGB stars into the ISM of the LMC is ∼5x10 --3 M⊙ yr--1, and that carbon-rich AGB stars and oxygen-rich AGB stars contribute equal amounts of total mass. The carbon-rich stars dominate the dust injection rate by a factor of two and half, however. We show that all AGB stars pulsating in the first overtone or fundamental mode are producing measurable amounts of dust.;Using the warm mission of the Spitzer Space Telescope, we have taken 4 epochs of observations of the densest stellar regions of both Magellanic Clouds at 3.6 & 4.5 mum to investigate the infrared variability of sources not visible at the optical wavelengths explored by ground-based surveys. By comparing the brightness of every source in each pair of epochs, we identify 3660 variable sources in the LMC and 1283 such sources in the SMC. Comparing our dataset to other surveys such as OGLE and MACHO, 2741 of our variables have no currently known counterpart in these studies.
机译：渐近巨人分支（AGB）是恒星演化中最有趣，最鲜为人知的阶段之一。大约有太阳质量的恒星在最后一次耗尽核燃料时的命运，这些恒星也是宇宙中许多重元素（如碳和氧）的主要来源之一。我们在大麦哲伦星云（LMC）中收集了约30,000个AGB恒星的样本，其多波长数据范围从紫外线到中红外，以及跨历时5年的数据。该数据集使我们能够在人口规模上探究AGB恒星的变异性和质量损失特性，这对恒星演化和星际介质（ISM）的质量预算研究具有重要意义。;我们结合了MAssive Compact Halo的变异性信息斯皮策太空望远镜遗留程序“测量银河系演化的媒介”（SAGE； Meixner等人，2006）用红外光度法对物体（MACHO； Alcock等人，1997）进行微透镜测量，以确定三种星系演化等级的红外周期-量级关系。 AGB在8个不同波长下恒星。我们发现，发展最快的AGB恒星在基本和第一泛音中脉动，而发展较少的恒星则集中在高泛音模式中。我们发现，在所有波长下，对于更多演化的恒星来说，周期量级关系的斜率变得更陡;使用星尘壳辐射传递模型的网格（GRAMS; Sargent等人2011; Srinivasan等人2011）以及在从紫外线到红外的12个波段中进行光度测定，我们计算了LMC中每个AGB恒星的辐射强度和粉尘质量损失率。这使我们能够通过直接求和来计算从这些恒星向星际介质注入的总尘埃。我们发现，从AGB恒星向LMC的ISM注入的总质量（气体和粉尘）约为5x10 -3 M＆odot； yr--1，而富含碳的AGB星和富含氧的AGB星贡献了相等的总质量。但是，富含碳的恒星在粉尘喷射速率中占主导地位的比例是原来的二分之一。我们显示出所有以第一泛音或基波模式脉动的AGB恒星都在产生可测量的尘埃。;使用Spitzer太空望远镜的温暖任务，我们对麦哲伦星云中最密集的恒星区进行了4个观测，分别为3.6 ＆4.5妈妈调查地面调查所探测的在光学波长不可见的光源的红外可变性。通过比较每对纪元中每个光源的亮度，我们确定了LMC中的3660个可变光源和SMC中的1283个此类光源。将我们的数据集与其他调查（例如OGLE和MACHO）进行比较，这些研究中目前尚无对应的2741个变量。

著录项

  • 作者

    Riebel, David.;

  • 作者单位

    The Johns Hopkins University.;

  • 授予单位 The Johns Hopkins University.;
  • 学科 Physics Astrophysics.
  • 学位 Ph.D.
  • 年度 2012
  • 页码 148 p.
  • 总页数 148
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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