2020/10/29 by Bo-Eun Choi, Hee-Won Lee, Hee‐Won Lee
Physics and Astronomy · #Astronomy #Astronomy and Astrophysical Research #Astrophysics #Astrophysics and Star Formation Studies #Asymptotic giant branch #Galaxy #Optics #Physics #Planetary nebula #Raman spectroscopy #Redshift #Spectral line #Spectrograph #Spectroscopy #Stars #Stellar, planetary, and galactic studies #astro-ph.GA #astro-ph.SR
paper · pdf · doi:10.3847/2041-8213/abc559
7 pages, 3 figures, 1 table, accepted for publication in ApJL
arxiv created 2020/10/29 · openalex publication_date 2020/11/01 · openalex created_date 2020/11/09 · arxiv updated 2020/11/18 · openalex updated_date 2026/08/05
Abstract Young planetary nebulae (PNe) retain a large amount of neutral material that was shed in the previous asymptotic giant branch stage. The thick H i region in young PNe can be effectively probed by illuminating far-UV radiation that may be inelastically scattered to appear in the optical region. Raman-scattered features are unique spectroscopic tracers of neutral regions that can be used to investigate the mass-loss process in young PNe. We conduct high-resolution spectroscopy of young PNe using the Bohyunsan Observatory Echelle Spectrograph (BOES) and report the discovery of a Raman-scattered He ii feature at 6545 Å in NGC 6886 and NGC 6881. The Raman-scattered He ii features have been found in only five PNe so far, and in particular, it is the first direct detection of an H i component in NGC 6881. The Raman He ii λ 6545 features in the two PNe are observed to be redshifted with respect to He ii λ 6560, indicating that the neutral regions are expanding. We perform line profile analyses using the grid-based Monte Carlo code “STaRS” by assuming a neutral hydrogen region in the shape of a partial spherical shell expanding radially. The profiles are well fitted with the model parameters of covering factor CF = 0.3, H i column density N HI = 5 × 10 20 cm −2 , and expansion speed for NGC 6886 and CF = 0.6, N HI = 3 × 10 20 cm −2 , and for NGC 6881, respectively.