年轻致密行星状星云NGC 6790中的拉曼散射HeII 6545
Raman Scattered HeII 6545 in the Young and Compact Planetary Nebula NGC 6790
摘要：
本文报道了用宝贤山光学天文台的阶梯光栅摄谱仪获得的年轻致密星云NGC 6790的高分辨光谱，并报道了在该天体中发现的拉曼散射He Ⅱ 6545。这条线的特征是形成在一个厚厚的中性区域周围的热中心的恒星，在那里的He II 1025线光子被非弹性散射的氢原子。采用Monte Carlo方法计算了一个简单的几何模型下的谱线轮廓，其中中性区是一个从中心恒星向外扩展的圆柱壳。根据我们的谱线轮廓分析，HI区的膨胀速度在V_exp = 15- 19 Km/s范围内。对HI柱密度N_HI和覆盖因子C的限制不太严格，拉曼He II 6545的总通量与N_HI和C的乘积一致，即CN_HI约为0.5 × 10^20 cm^-2。稳态辐射模型的Monte Carlo分布在机翼部分表现出亏损。当He II发射区被假定为以~ 18 Km/s的转速缓慢旋转的环形时，得到了更好的拟合。简要讨论了质量损失过程和未来的观测。
英文摘要：
We present the high resolution spectra of the youn and compact planerary nebula NGC 6790 obtained with the echelle spectrograph at Bohyunsan Optical Astronomy Observatory and report the discovery of Raman scattered He II 6545 in this object. This line feature is formed in a thick neutral region surrounding the hot central star, where He II 1025 line photons are scattered inelastically by hydrogen atoms. A Monte Carlo technique is adopted to compute the line profile with a simple geometric model, in which the neutral region is in the form of a cylindrical shell that is expanding from the central star. From our line profile analysis, the expansion velocity of the HI region lies in the range V_exp = 15- 19 Km/s. Less stringent constraints are put on the HI column density N_HI and covering factor C, where the total flux of Raman He II 6545 is consistent with the product of N_HI and C being CN_HI ~ 0.5 X 10^20 cm^-2. The Monte Carlo profiles from stationary emission models exhibit deficit in the wing parts. A much better fit is obtained when the He II emission region is assumed to take the form of a ring that slowly rotates with a rotation speed ~ 18Km/s. Brief discussions are presented regarding the mass loss processes and future observations.
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