A Protocometary Cloud around HR 4796A?
A Protocometary Cloud around HR 4796A?
复制标题
HR 4796A 周围的原彗星云？
DOI：
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发表时间：
1998
期刊：
影响因子：
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通讯作者：
R. Fisher
中科院分区：
文献类型：
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作者：
M. Jura;M. Malkan;Russel J. White;C. Telesco;R. Piña;R. Fisher
我们报告了宽双星HR 4796的ROSAT观测和地基10.8 μm成像，它由一颗主序星A型星星和大量的星周尘埃组成，HR 4796 A，以及一颗主序前M型伴星HR 4796 B，距离为7.″7。从ROSAT的数据中，我们发现X射线发射集中在HR 4796 B上，LX/Lbol = 3 × 10-4。来自HR 4796 A的10.8 μm通量显示出超过光球辐射0.08 ± 0.02 Jy，这一结果与之前将12 μm ≤ λ ≤ 100 μm波长范围内的星周尘埃辐射表征为110 K黑体的结果一致。依巴谷的数据可以用来证明亮星星表中的三颗LIR/Lbol > 10-3的主序星A型星（HR 4796 A、β Pic和49 Cet）都有低光度的颜色。我们认为，大约20%的A型恒星经历了一个早期阶段，在这个阶段，它们拥有的星周尘埃量与HR 4796 A或β Pic周围的尘埃量相当。为了解释颗粒辐射可以用110 K黑体近似的结果，我们提出星周颗粒主要由典型半径接近100 μm的冰粒组成，当它们距离HR 4796 A超过~35 Au时，它们迅速升华。这群冰粒可能是一个原彗星云。
We report both ROSAT observations and ground-based 10.8 μm imaging of the wide binary HR 4796, which consists of a main-sequence A-type star with a large amount of circumstellar dust, HR 4796A, and, at a separation of 7.″7, a pre-main-sequence M-type companion, HR 4796B. From the ROSAT data, we find that the X-ray emission is centered on HR 4796B, with LX/Lbol ≈ 3 × 10-4. The 10.8 μm flux, which arises from HR 4796A, displays an excess over the photospheric emission of 0.08 ± 0.02 Jy, a result consistent with the previous characterization of the emission from the circumstellar dust in the wavelength range 12 μm ≤ λ ≤ 100 μm as a 110 K blackbody. The Hipparcos data can be used to argue that the three main-sequence A-type stars in the Bright Star Catalogue with LIR/Lbol > 10-3 (HR 4796A, β Pic, and 49 Cet) all have low luminosities for their colors. We argue that approximately 20% of all A-type stars pass through an early phase where they possess an amount of circumstellar dust comparable to that found around HR 4796A or β Pic. In order to explain the result that the grain emission can be approximated by a 110 K blackbody, we propose that the circumstellar grains are largely composed of ice particles with a typical radius near 100 μm, and that they sublimate rapidly when they are closer than ~35 AU to HR 4796A. This swarm of ice particles might be a protocometary cloud.