Raman Scattered HeII 6545 in the Young and Compact Planetary Nebula NGC 6790

Abstract

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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• The BOES spectropolarimeter for Zeeman measurements of stellar magnetic fields
• Angular dimensions of planetary nebulae
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• The Discovery of Raman Scattering in HII Regions
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• A D'-type symbiotic binary in the planetary nebula SMP LMC 88
• Line Formation of Raman-Scattered He II $\lambda$ 4851 in an Expanding Spherical H I Shell in Young Planetary Nebulae
• Discovery of Raman-scattered He II $\lambda$6545 in the Planetary Nebulae NGC 6886 and NGC 6881
• Distribution and Kinematics of H I through Raman He II Spectroscopy of NGC 6302