利用哈勃、斯皮策、ZTF、凯克、APO和GROWTH可见光和红外成像和光谱对活动过渡半人马座、P/2019 LD2（ATLAS）的初步表征
Initial Characterization of Active Transitioning Centaur, P/2019 LD2 (ATLAS), using Hubble, Spitzer, ZTF, Keck, APO and GROWTH Visible & Infrared Imaging and Spectroscopy
摘要：
我们展示了临时木星共轨彗星P/2019 LD $_2$的可见光和中红外图像和测光，这些图像是用HST/WFC3，Spitzer/IRAC，GROWTH望远镜网络拍摄的，来自Keck/LRIS的可见光谱和2019年4月至2020年8月期间拍摄的ZTF观测档案。我们的观测结果表明，LD $_2$的核半径在0.2 - 1.8 km之间，假设0.08倍正入射角，彗发主要由$\sim$ 100 $μ$ m尺度的尘埃以$\sim$ 1 m/s的速度喷出，$\sim$ 1 "喷流指向西南方向。从2019年4月9日至2019年11月8日，LD $_2$经历了$\sim$ 10 $^8$ kg的总粉尘质量损失，损失率为$\sim$ 6 kg/s，Af $ρ$/横截面在$\sim$ 85 cm/125 km $^2$和$\sim$ 200 cm/310 km $^2$之间变化。如果Af $ρ$/横截面的增加保持不变，这意味着LD $_2$的活动开始于$\sim$ 2018年11月，当时距离太阳4. 8 au，这意味着H $_2$ O升华的开始。我们从我们的4.5 $μ$ m Spitzer观测测量$\lesssim$ 10 $^{27}$ mol/s/$\lesssim$ 10 $^{26}$ mol/s的CO/CO $_2$气体产生，从GROWTH观测$g$-$r$ = 0.59 $\pm$ 0.03，$r$-$i$ = 0.18 $\pm$ 0.05，$i$-$z$ = 0.01 $\pm$ 0.07，$_2$ O的$\lesssim$的气体产量80 kg/s，由我们从Keck/LRIS光谱估计的$Q_{C_2}\lesssim$ 7.5 $\times10^{24}$ mol/s的$C_2$产量换算。我们确定LD $_2$的长期轨道类似于木星家族彗星，在$\sim$ 3 y的最后一次$\sim$ 0.5 Hill半径内与木星近距离相遇，在$\sim$ 9 y的0.8 Hill半径内与木星近距离相遇。此外，在$1 \times 10^{6}$年内，我们的轨道克隆中有78.8个$\%$被从太阳系中抛出，动力学半衰期为3.4 $\times 10^5$年。
英文摘要：
We present visible and mid-infrared imagery and photometry of temporary Jovian co-orbital comet P/2019 LD$_2$ taken with HST/WFC3, Spitzer/IRAC, the GROWTH telescope network, visible spectroscopy from Keck/LRIS and archival ZTF observations taken between 2019 April and 2020 August. Our observations indicate that the nucleus of LD$_2$ has a radius between 0.2-1.8 km assuming a 0.08 albedo and a coma dominated by $\sim$100$μ$ m-scale dust ejected at $\sim$1 m/s speeds with a $\sim$1'' jet pointing in the SW direction. LD$_2$ experienced a total dust mass loss of $\sim$10$^8$ kg at a loss rate of $\sim$6 kg/s with Af$ρ$/cross-section varying between $\sim$85 cm/125 km$^2$ and $\sim$200 cm/310 km$^2$ from 2019 April 9 to 2019 Nov 8. If the increase in Af$ρ$/cross-section remained constant, it implies LD$_2$'s activity began $\sim$2018 November when within 4.8 au of the Sun, implying the onset of H$_2$O sublimation. We measure CO/CO$_2$ gas production of $\lesssim$10$^{27}$ mol/s /$\lesssim$10$^{26}$ mol/s from our 4.5 $μ$m Spitzer observations, $g$-$r$ = 0.59$\pm$0.03, $r$-$i$ = 0.18$\pm$0.05, $i$-$z$ = 0.01$\pm$0.07 from GROWTH observations, H$_2$O gas production of $\lesssim$80 kg/s scaling from our estimated $C_2$ production of $Q_{C_2}\lesssim$7.5$\times10^{24}$ mol/s from Keck/LRIS spectroscopy. We determine that the long-term orbit of LD$_2$ is similar to Jupiter family comets having close encounters with Jupiter within $\sim$0.5 Hill radius in the last $\sim$3 y, within 0.8 Hill radius in $\sim$9 y. Additionally, 78.8$\%$ of our orbital clones are ejected from the Solar System within $1 \times 10^{6}$ years having a dynamical half-life of 3.4 $\times 10^5$ years.
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