DUSTY OB STARS IN THE SMALL MAGELLANIC CLOUD. II. EXTRAGALACTIC DISKS OR EXAMPLES OF THE PLEIADES PHENOMENON?
DUSTY OB STARS IN THE SMALL MAGELLANIC CLOUD. II. EXTRAGALACTIC DISKS OR EXAMPLES OF THE PLEIADES PHENOMENON?
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小麦哲伦云中布满灰尘的OB星。
DOI：
10.1088/0004-637x/771/2/112
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发表时间：
2013
期刊：
影响因子：
--
通讯作者：
Adams J
中科院分区：
文献类型：
--
作者：
Adams J
我们利用中红外斯皮策光谱和远红外赫歇尔光度测量方法，对小麦哲伦星云中20颗主序O9-B2星的强24μm超额进行了研究，以探讨中红外辐射的来源。无论是恒星周围的残骸圆盘，还是星际致密介质(ISM)照亮的斑块，都可能导致这种中红外辐射。在第一篇论文中，我们使用光学光谱学来证明这些源不太可能是经典的Be星或HerBig Ae/Be星。我们把重点放在碎片盘和卷云热点上。这些模型的本地原型天体是织女星周围的碎片圆盘和昂宿星团中环绕恒星的加热尘埃云，也被称为卷云热点。这两个案例预测了不同的尘埃质量、半径、来源和结构，但由于SMC距离较远，物理分辨率较差，因此失去了最干净的分类工具。我们还考虑了过渡盘，它将具有类似于碎片盘的可观察特性。我们通过测量可用的最高分辨率中红外图像的角度范围来开始分类。我们发现20颗恒星中有3颗显著延伸，使它们成为卷云热点。然后我们对红外光谱能量分布进行拟合，以确定尘埃温度和质量。分析得出最小颗粒尺寸、热平衡距离和由此产生的尘埃质量估计。我们发现SMC恒星中的尘埃质量比任何已知的碎片盘都要大。推论性质的差异是由于SMC恒星比已知的碎片盘宿主更热、更亮，而不是任何直接观察到的尘埃性质，所以这种反对碎片盘假说的证据是间接的。最后，我们通过交叉匹配广域红外巡天探测器(WISE)和依巴谷星表，创建了银河系明亮的中红外OB星的局部比较样本。我们发现，在MW中数以千计的附近(⩽1kpc)热星中，只有一小部分(几个百分比)与SMC星的高中红外光度相匹配。在适当的光度范围内，可以明确分类的所有此类局部恒星都是具有光学发射线的年轻恒星，或者由WISE进行空间分辨，其大小太大而不是可信的碎片盘候选者。我们的结论是，很强的中红外通量过剩最有可能被解释为卷云热点，尽管我们不能严格排除样本的一小部分由碎片盘或过渡盘组成。我们提出的证据表明，围绕失控恒星的弓激波加热可能是星际发射的一种贡献机制。这些源被解释为卷云热点，为低金属丰度环境中弥漫的星际尘埃提供了一个新的局部化探测器。
We use mid-infrared Spitzer spectroscopy and far-infrared Herschel photometry for a sample of 20 main sequence O9–B2 stars in the Small Magellanic Cloud (SMC) with strong 24 μm excesses to investigate the origin of the mid-IR emission. Either debris disks around the stars or illuminated patches of dense interstellar medium (ISM) can cause such mid-IR emission. In a companion paper, Paper I, we use optical spectroscopy to show that it is unlikely for any of these sources to be classical Be stars or Herbig Ae/Be stars. We focus our analysis on debris disks and cirrus hot spots. The local, prototype objects for these models are the debris disk around Vega and the heated dust cloud surrounding the stars in the Pleiades, also known as a cirrus hot spot. These two cases predict different dust masses, radii, origins, and structures, but the cleanest classification tools are lost by the poor physical resolution at the distance of the SMC. We also consider transition disks, which would have observable properties similar to debris disks. We begin classification by measuring angular extent in the highest resolution mid-IR images available. We find 3 out of 20 stars to be significantly extended, establishing them as cirrus hot spots. We then fit the IR spectral energy distributions to determine dust temperatures and masses. Analysis yields minimum grain sizes, thermal equilibrium distances, and the resultant dust mass estimates. We find the dust masses in the SMC stars to be larger than for any known debris disks. The difference in inferred properties is driven by the SMC stars being hotter and more luminous than known debris disk hosts and not in any directly observed dust properties, so this evidence against the debris disk hypothesis is circumstantial. Finally, we created a local comparison sample of bright mid-IR OB stars in the Milky Way (MW) by cross-matching the Wide-field Infrared Survey Explorer (WISE) and Hipparcos catalogs. We find that of the thousands of nearby (⩽ 1 kpc) hot stars in the MW that show a mid-IR excess, only a small fraction (few percent) match the high mid-IR luminosities of the SMC stars. All such local stars in the appropriate luminosity range that can be unambiguously classified are young stars with optical emission lines or are spatially resolved by WISE with sizes too large to be plausible debris disk candidates. We conclude that the very strong mid-IR flux excesses are most likely explained as cirrus hot spots, although we cannot rigorously rule out that a small fraction of the sample is made up of debris disks or transition disks. We present suggestive evidence that bow-shock heating around runaway stars may be a contributing mechanism to the interstellar emission. These sources, interpreted as cirrus hot spots, offer a new localized probe of diffuse interstellar dust in a low metallicity environment.
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DOI：
10.1088/0004-637x/720/1/887
发表时间：
2010-06
期刊：
The Astrophysical Journal
影响因子：
--
作者：
K. Pontoppidan;C. Salyk;G. Blake;R. Meijerink;J. Carr;J. Najita
通讯作者：
K. Pontoppidan;C. Salyk;G. Blake;R. Meijerink;J. Carr;J. Najita
DOI：
10.1007/s00159-013-0069-0
发表时间：
2003-10
影响因子：
3.5
作者：
J. Porter;T. Rivinius
通讯作者：
J. Porter;T. Rivinius
A 型和晚期 B 型恒星周围尘埃碎片的斯皮策中红外光谱：小行星带类似物和幂律尘埃分布
DOI：
--
发表时间：
2009
期刊：
影响因子：
--
作者：
F. Morales;M. W. Werner;G. Bryden;P. Plavchan;K. Stapelfeldt;G. Rieke;K. Su;C. Beichman;C.;K. Grogan;S. Kenyon;A. Moro;S. Wolf
通讯作者：
S. Wolf
HR 4796A 周围的原彗星云？
DOI：
--
发表时间：
1998
期刊：
影响因子：
--
作者：
M. Jura;M. Malkan;Russel J. White;C. Telesco;R. Piña;R. Fisher
通讯作者：
R. Fisher
类 Vega 系统的光学、红外和毫米波特性 - III。
DOI：
--
发表时间：
1997
期刊：
影响因子：
--
作者：
R. J. Sylvester;C. Skinner;M. Barlow
通讯作者：
M. Barlow