Warm water vapor envelope in Mira variables and its effects on the apparent size from the near-infrared to the mid-infrared
Warm water vapor envelope in Mira variables and its effects on the apparent size from the near-infrared to the mid-infrared
复制标题
米拉变星中的温暖水汽包络及其对近红外到中红外视尺寸的影响
DOI：
10.1051/0004-6361:20041207
复制
发表时间：
2004
影响因子：
6.5
通讯作者：
K. Ohnaka
中科院分区：
文献类型：
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作者：
K. Ohnaka
我们提出了一种可能的解释，解释了最近使用窄带通的干涉观测所揭示的从K波段到11 μ m区域的Mira变量的角直径增加（Weiner et al. 2003a,b）。先前的光谱观测已经揭示了Mira变量中存在的暖水蒸汽包层的两层简单模型，该模型可以重现红外空间干涉仪观测到的角直径以及在11µm区域获得的高分辨率TEXES光谱。热水蒸汽层在光学上很厚，因此，由于H2O的强吸收可以从这样一个致密的水蒸汽包层中得到。然而，吸收谱线被包络线延伸部分的发射所填充，这导致高分辨率的11µm光谱只表现出微弱的、精细的光谱特征，掩盖了致密的、温暖的水蒸气包络线的光谱证据。另一方面，与近红外测量结果相比，热水蒸气包层的存在表现为11 μ m区域的角直径更大。此外，将近红外波段（1.5 ~ 3.8µm）的能见度预测值与已有文献的观测结果进行比较，结果表明，我们的暖水蒸气包膜双层模型也能再现观测到的近红外波段的能见度和角直径，表明Mira变量在红外波段角尺寸的波长依赖性很大程度上反映了H2O的不透明度。在三个Mira变量中，当温度为1800-2000 K，水柱密度为（1 - 5）× 10 21 cm−2时，热水层的半径为1.5-1.7 r；当温度为1200-1400 K，水柱密度为（1 - 7）× 10 21 cm−2时，冷水层的半径为2.2-2.5 r。
We present a possible interpretation for the increase of the angular diameter of the Mira variables o Cet, R Leo, and χ Cyg from the K band to the 11 µm region revealed by the recent interferometric observations using narrow bandpasses where no salient spectral feature is present (Weiner et al. 2003a,b). A simple two-layer model consisting of hot and cool H2O layers for the warm water vapor envelope, whose presence in Mira variables was revealed by previous spectroscopic observations, can reproduce the angular diameters observed with Infrared Spatial Interferometer as well as the high-resolution TEXES spectra obtained in the 11 µm region. The warm water vapor layers are optically thick in the lines, and therefore, strong absorption due to H2O can be expected from such a dense water vapor envelope. However, the absorption lines are filled in by emission from the extended part of the envelope, and this results in the high-resolution 11 µm spectra which exhibit only weak, fine spectral features, masking the spectroscopic evidences of the dense, warm water vapor envelope. On the other hand, the presence of the warm water vapor envelope manifests itself as the larger angular diameters in the 11 µm region as compared to those measured in the near-infrared. Furthermore, comparison of the visibilities predicted in the near-infrared (1.5-3.8 µm) with observational results available in the literature demonstrates that our two-layer model for the warm water vapor envelope can also reproduce the observed near-infrared visibilities and angular diameters, and suggests that the wavelength dependence of the angular size of Mira variables in the infrared largely reflects the H2O opacity. The radii of the hot H2O layers in the three Mira variables are derived to be 1.5-1.7 Rwith temperatures of 1800-2000 K and H2O column densities of (1−5) × 10 21 cm −2 , while the radii of the cool H2O layers are derived to be 2.2-2.5 Rwith temperatures of 1200-1400 K and H2O column densities of (1−7) × 10 21 cm −2 .
DOI：
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发表时间：
2008
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影响因子：
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作者：
Tatsuya TAKAHARA;Osamu GOTO;Hirokazu YAMAMOTO;Tadatsugu TAI;Yukie SAITO
通讯作者：
Yukie SAITO
麻省理工学院/哈佛大学和史密森尼 CfA/佛罗里达大学（美国）
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