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We present the high resolution spectra of the youn and compact planerarynebula NGC 6790 obtained with the echelle spectrograph at Bohyunsan OpticalAstronomy Observatory and report the discovery of Raman scattered He II 6545 inthis object. This line feature is formed in a thick neutral region surroundingthe hot central star, where He II 1025 line photons are scattered inelasticallyby hydrogen atoms. A Monte Carlo technique is adopted to compute the lineprofile with a simple geometric model, in which the neutral region is in theform of a cylindrical shell that is expanding from the central star. From ourline profile analysis, the expansion velocity of the HI region lies in therange V_exp = 15- 19 Km/s. Less stringent constraints are put on the HI columndensity N_HI and covering factor C, where the total flux of Raman He II 6545 isconsistent with the product of N_HI and C being CN_HI ~ 0.5 X 10^20 cm^-2. TheMonte Carlo profiles from stationary emission models exhibit deficit in thewing parts. A much better fit is obtained when the He II emission region isassumed 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 andfuture observations.

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