[论文解读] Resolving the cold debris disc around a planet-hosting star . PACS photometric imaging observations of q<SUP>1</SUP> Eridani (HD 10647, HR 506)

R. Liseau, C. Eiroa+33 more|arXiv (Cornell University)|Jan 1, 2010

Stellar, planetary, and galactic studies参考文献 14被引用 31

一句话总结

利用赫歇尔空间望远镜PACS的测光成像，本研究首次在亚毫米波段解析了围绕系外行星宿主恒星q1 Eri的冷尘埃盘，揭示了一条约40 AU宽、位于约85 AU处的狭窄环状结构，其表面密度分布与环状结构一致。该环是系外行星系统中首个类柯伊伯带的观测类比，暗示可能存在一颗额外的、尚未探测到的行星q1 Eri c。

ABSTRACT

Context. About two dozen exo-solar debris systems have been spatially resolved. These debris discs commonly display a variety of structural features such as clumps, rings, belts, excentric distributions and spiral patterns. In most cases, these features are believed to be formed, shaped and maintained by the dynamical influence of planets orbiting the host stars. In very few cases has the presence of the dynamically important planet(s) been inferred from direct observation. Aims. The solar-type star q(1) Eri is known to be surrounded by debris, extended on scales of less than or similar to 30 ''. The star is also known to host at least one planet, albeit on an orbit far too small to make it responsible for structures at distances of tens to hundreds of AU. The aim of the present investigation is twofold: to determine the optical and material properties of the debris and to infer the spatial distribution of the dust, which may hint at the presence of additional planets. Methods. The Photodetector Array Camera and Spectrometer (PACS) aboard the Herschel Space Observatory allows imaging observations in the far infrared at unprecedented resolution, i.e. at better than 6 '' to 12 '' over the wavelength range of 60 mu m to 210 mu m. Together with the results from ground-based observations, these spatially resolved data can be modelled to determine the nature of the debris and its evolution more reliably than what would be possible from unresolved data alone. Results. For the first time has the q(1) Eri disc been resolved at far infrared wavelengths. The PACS observations at 70 mu m, 100 mu m and 160 mu m reveal an oval image showing a disc-like structure in all bands, the size of which increases with wavelength. Assuming a circular shape yields the inclination of its equatorial plane with respect to that of the sky, i > 53 degrees. The results of image de-convolution indicate that i likely is larger than 63 degrees, where 90 degrees corresponds to an edge-on disc. Conclusions. The observed emission is thermal and optically thin. The resolved data are consistent with debris at temperatures below 30 K at radii larger than 120 AU. From image de-convolution, we find that q(1) Eri is surrounded by an about 40 AU wide ring at the radial distance of similar to 85 AU. This is the first real Edgeworth-Kuiper Belt analogue ever observed.

研究动机与目标

• 确定围绕q1 Eri这颗系外行星宿主恒星的尘埃盘的光学与物质特性。
• 利用空间分辨的亚毫米波段数据推断盘中尘埃的空间分布。
• 检验观测到的盘结构是否与未见行星的引力动力雕刻作用一致。
• 将该盘表征为太阳系柯伊伯带的潜在类比。
• 利用高灵敏度、高分辨率的PACS观测，改进对盘物理特性的约束。

提出的方法

• 在赫歇尔空间望远镜上使用PACS测光成像，波长分别为70 µm、100 µm和160 µm，角分辨率分别为6′′、7′′和11.5′′。
• 采用斩波-调制（chop-nod）和扫描地图（scan-map）观测模式，以优化信噪比并最小化扩展源成像中的条纹噪声。
• 使用最大熵法（MEM）进行图像反卷积，采用从α Boo获得的点扩散函数（PSF），以增强结构细节。
• 在反卷积前，从100 µm扫描图中减去恒星光球通量（100 µm处为8 mJy），以分离盘的辐射。
• 沿主轴和副轴建模表面亮度分布，以推断盘的倾角、径向范围和表面密度分布。
• 将观测通量与理论模型进行比较，包括单温度黑体模型和环带复合模型。

实验结果

研究问题

• RQ1 在亚毫米波段，q1 Eri周围冷尘埃盘的空间结构和径向范围如何？
• RQ2 观测到的盘形态是否与环状结构一致？其物理参数是什么？
• RQ3 图像反卷积技术能否揭示盘中如窄环或带状结构等亚结构？
• RQ4 盘的结构是否暗示存在一颗已知行星q1 Eri b之外的额外、尚未探测到的行星？
• RQ5 该盘的热辐射与冷而扩展的尘埃盘模型相比如何？

主要发现

• q1 Eri周围的尘埃盘在70 µm、100 µm和160 µm波段均被解析，显示出随波长增加而扩大的椭圆形亮度分布。
• 该盘最适宜被描述为一个约40 AU宽的窄环或带状结构，中心位于恒星约85 AU处。
• 图像反卷积揭示了一个约2%深度的中心凹陷和一个展宽的平台，与环状结构而非光滑盘的特征一致。
• 从反卷积图像中，盘的倾角被约束为i > 63°，最佳拟合模型建议i ≈ 70°，与光学散射光观测所推断的边缘朝向几何结构一致。
• 在半径大于120 AU处，尘埃温度低于30 K，表明存在一个冷的外层尘埃盘。
• 观测到的盘结构是系外行星系统中首个直接类比柯伊伯带的结构，暗示在较小半径处可能存在一颗额外的行星q1 Eri c。