采用基于LOCI的背景减除技术对HR 8799行星系的M波段成像
M-band Imaging of the HR 8799 Planetary System Using an Innovative LOCI-based Background Subtraction Technique
摘要：
对系外行星大气的多波长观测/光谱学是比较系外行星学这一令人兴奋的新兴领域的基础。HR 8799行星系是一个理想的实验室，可以研究我们目前在大质量场棕矮星和寒冷的5-Gyr年龄的太阳系行星之间的知识差距。到目前为止，HR 8799行星的成像是在J-到L-波段，只有上限在M-波段。在这里，我们提出了深高对比度凯克II自适应光学M波段的观测，显示成像检测的4个目前已知的HR 8799行星。这样的检测之所以成为可能，是因为开发了一种创新的基于LOCI的背景减除方案，该方案比经典的Keck II AO数据的中值背景减除效率高3倍，代表望远镜时间的增益高达9倍。这些M波段探测器将宽波段光度覆盖范围扩展到约5微米，并提供了在4.5微米处的强CO基本吸收带。新的M波段测光显示HR 8799行星位于L/T型矮过渡附近，与其他研究发现的相似。我们还确认，最好的大气拟合与低表面重力，尘埃和非平衡CO/CH 4化学模型是一致的。
英文摘要：
Multi-wavelength observations/spectroscopy of exoplanetary atmospheres are the basis of the emerging exciting field of comparative exoplanetology. The HR 8799 planetary system is an ideal laboratory to study our current knowledge gap between massive field brown dwarfs and the cold 5-Gyr old Solar system planets. The HR 8799 planets have so far been imaged at J- to L-band, with only upper limits available at M-band. We present here deep high-contrast Keck II adaptive optics M-band observations that show the imaging detection of 3 of the 4 currently known HR 8799 planets. Such detections were made possible due to the development of an innovative LOCI-based background subtraction scheme that is 3 times more efficient than a classical median background subtraction for Keck II AO data, representing a gain in telescope time of up to a factor of 9. These M-band detections extend the broad band photometric coverage out to about 5 microns and provide access to the strong CO fundamental absorption band at 4.5microns. The new M-band photometry shows that the HR 8799 planets are located near the L/T-type dwarf transition, similar to what was found by other studies. We also confirm that the best atmospheric fits are consistent with low surface gravity, dusty and non-equilibrium CO/CH4 chemistry models.
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