论文标题
可变星云IC 4997的物理条件和化学丰度
Physical Conditions and Chemical Abundances of the Variable Planetary Nebula IC 4997
论文作者
论文摘要
行星星云（PN）IC 4997是少数几个快速发展的物体之一，其亮度可变，并且围绕氢恒星周围发射。在这项研究中，我们使用碰撞激发线（CELS）（CELS）和光学重组线（ORL）确定了该物体的物理条件和化学丰度，并根据2014年7月在La Palma opvatoration的北欧光望远镜上使用纤维喂养的Échelle光谱仪进行的中分辨率光谱测量。我们得出了$ \ gtrsim的电子密度3 \ times 10^4 $ cm $^{ - 3} $，以及$ \ gtrsim 14,000 $ k的电子温度分别从helium and Helium and Helium and Heluim and heluim and helium and helium and helium and heluim and helium and themeement elempls ofer cels $ \ gtrsim 14,000 $ k。从CELS指向[O/H] $ \ Lesssim-0.75 $的金属贫困祖细胞的元素丰度，而ORL丰度略高于太阳金属性，[O/H] $ \约0.15 $。我们的丰度分析表明，该PN的丰度差异因子（ADFS $ \ equiv $ ORLS/CELS）相对较大：ADF（O $^{2+}）\ GTRSIM 8 $和ADF（N $^{2+}）\ GTRSIM 7 $ 7 $。需要进一步的研究来找出该对象中如何形成ADF和可变排放，以及它们是否与二元伴侣或非常晚的热脉冲相关。
The planetary nebula (PN) IC 4997 is one of a few rapidly evolving objects with variable brightness and nebular emission around a hydrogen-deficient star. In this study, we have determined the physical conditions and chemical abundances of this object using the collisionally excited lines (CELs) and optical recombination lines (ORLs) measured from the medium-resolution spectra taken in July 2014 with the FIbre-fed Échelle Spectrograph on the Nordic Optical Telescope at La Palma Observatory. We derived electron densities of $\gtrsim 3 \times 10^4$ cm$^{-3}$ and electron temperatures of $\gtrsim 14,000$ K from CELs, whereas cooler temperatures of $\sim 11,000$ and $\sim 7,000$ K were obtained from helium and heavy element ORLs, respectively. The elemental abundances deduced from CELs point to a metal-poor progenitor with [O/H]$\lesssim-0.75$, whereas the ORL abundances are slightly above the solar metallicity, [O/H]$\approx 0.15$. Our abundance analysis indicates that the abundance discrepancy factors (ADFs$\equiv$ORLs/CELs) of this PN are relatively large: ADF(O$^{2+})\gtrsim 8$ and ADF(N$^{2+})\gtrsim 7$. Further research is needed to find out how the ADFs and variable emissions are formed in this object and whether they are associated with a binary companion or a very late thermal pulse.
