IRC +10216的四十年：使用MMT自适应光学器件和MIRAC4在10微米处解析富碳尘壳的演变
Four Decades of IRC +10216: Evolution of a Carbon Rich Dust Shell Resolved at 10 microns with MMT Adaptive Optics and MIRAC4
摘要：
演化出的富含碳的AGB恒星IRC +10216（CW Leo）是太阳系外最明亮的中红外光源，也是最接近演化恒星失去质量的例子之一。它在近红外波段的小尺度上具有复杂多变的星周结构，而中红外波段的干涉测量则揭示了一个动态尘埃形成区。我们已经获得了IRC +10216在6.5m MMT的N波段（~8-13微米）的衍射极限成像和棱镜光谱。这些新的观测结果表明，在过去的二十年里，IRC +10216周围的尘埃壳层发生了变化，这可以通过在11微米处的SiC光谱特征的表观形状的变化和在13微米处的连续体的减少来说明。正如预期的那样，我们的衍射有限的空间信息显示了一个扩展的拱星包络。我们还证明，灰尘信封似乎是约30%的SiC功能的波长，可能是由于增加SiC的不透明度。物体的去卷积FWHM从波长< 10微米的0.43”（~56 AU）增加到11.8微米处的0.58”（~75 AU），然后在12.7微米处减小到0.5”（~65 AU）。我们对IRC +10216大小的估计使我们能够将过去12.5年光谱的变化与尘埃拱星包层以12-17公里/秒的速度演化联系起来。
英文摘要：
The evolved carbon-rich AGB star IRC +10216 (CW Leo) is the brightest mid-infrared source outside the solar system, as well as one of the closest examples of an evolved star losing mass. It has a complex and variable circumstellar structure on small scales in the near-IR, and mid-IR interferometry has revealed a dynamic dust formation zone. We have obtained diffraction limited imaging and grism spectroscopy of IRC +10216 at the 6.5m MMT in the N-band (~8-13 microns). These new observations show that a change has occurred in the dust shell surrounding IRC +10216 over the last two decades, which is illustrated by a change in the apparent shape of the well known SiC spectral feature at ~11 microns and a reduction in the continuum at 13 microns. As expected, our diffraction limited spatial information shows an extended circumstellar envelope. We also demonstrate that the dusty envelope appears to be ~30% larger at the wavelengths of the SiC feature, likely due to the increased opacity of SiC. The deconvolved FWHM of the object increases from 0.43" (~56 AU) for wavelength < 10 microns to 0.58" (~75 AU) at 11.8 microns, then decreases to 0.5" (~65 AU) at 12.7 microns. Our estimates of IRC +10216's size allow us to plausibly tie the change in the spectrum over the last 12.5 years to the evolution of the dusty circumstellar envelope at speeds of 12-17 km/sec.
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