论文标题
在Tailless Oort-Cloud Comet C/2020 T2（Palomar）的灰尘上
On the dust of tailless Oort-cloud comet C/2020 T2 (Palomar)
论文作者
论文摘要
我们报告了我们对Oort-Cloud Comet C/2020 T2（Palomar）（T2）的新分析，在2.06 au处从太阳（相位角为28.5 ver）观察到，大约在围围院前两周。 T2在散落的光线下缺乏明显的灰尘尾巴，在整个幻影中显示出昏迷的强烈中央凝结，让人联想到所谓的Manx彗星。它的偏光光的光谱斜率分别在J（1.25 um）和H（1.65 um）带中增加并减小，与观察到的活性彗星的红色极性颜色在类似的落球体上观察到的红色极性颜色相比，总体负（蓝色）斜率（-0.31 +/- 0.14％UM^-1）。 H频段的J和2.75 +/- 0.16％的T2的平均极化度为2.86 +/- 0.17％。 Given that near-infrared wavelengths are sensitive to the intermediate-scale structure of cometary dust (i.e., dust aggregates), our light-scattering modeling of ballistic aggregates with different porosities and compositions shows that polarimetric properties of T2 are compatible with low-porosity (~66 %), absorbing dust aggregates with negligible ice contents on a scale of 10--100 um (density of 〜652 kg m^-3）。这是由T2的昏迷形态支持的，T2的昏迷形态具有<〜10^-4的可行β（太阳辐射压力在灰尘上的相对重要性）。 T2从档案数据中的R波段活性的世俗演变表明，其亮度的增加加速了约2.4 au pre-Perihelion，其总体灰尘产量速度比Active Oort-Cloud Comets小的100倍。我们还发现，T2和Manx彗星的明显浓度朝向黄道轨道。本文强调了Oort-Cloud Comets的异质性质，可以在不久的将来对其尘埃特征进行专门研究。
We report our new analysis of Oort-cloud comet C/2020 T2 (Palomar) (T2) observed at 2.06 au from the Sun (phase angle of 28.5 deg) about two weeks before perihelion. T2 lacks a significant dust tail in scattered light, showing a strong central condensation of the coma throughout the apparition, reminiscent of so-called Manx comets. Its spectral slope of polarized light increases and decreases in the J (1.25 um) and H (1.65 um) bands, respectively, resulting in an overall negative (blue) slope (-0.31+/-0.14 % um^-1) in contrast to the red polarimetric color of active comets observed at similar geometries. The average polarization degree of T2 is 2.86+/-0.17 % for the J and 2.75+/-0.16 % for the H bands. Given that near-infrared wavelengths are sensitive to the intermediate-scale structure of cometary dust (i.e., dust aggregates), our light-scattering modeling of ballistic aggregates with different porosities and compositions shows that polarimetric properties of T2 are compatible with low-porosity (~66 %), absorbing dust aggregates with negligible ice contents on a scale of 10--100 um (density of ~652 kg m^-3). This is supported by the coma morphology of T2 which has a viable beta (the relative importance of solar radiation pressure on dust) range of <~10^-4. Secular evolution of the r-band activity of T2 from archival data reveals that the increase in its brightness accelerates around 2.4 au pre-perihelion, with its overall dust production rate ~100 times smaller than those of active Oort-cloud comets. We also found an apparent concentration of T2 and Manx comets toward ecliptic orbits. This paper underlines the heterogeneous nature of Oort-cloud comets which can be investigated in the near future with dedicated studies of their dust characteristics.
