2016/05/10 by Ajay Mishra, Aigen Li, B. W. Jiang
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysics and Star Formation Studies #Asymptotic giant branch #Feature (linguistics) #Giant star #Milky Way #Planetary nebula #Radiative transfer #Stars #Stellar evolution #Stellar, planetary, and galactic studies #astro-ph.SR
paper · pdf · doi:10.3847/0004-637x/825/1/68
36 pages, 8 figures, 7 tables; accepted for publication in The Astrophysical Journal
arxiv created 2016/05/10 · openalex created_date 2016/06/24 · openalex publication_date 2016/06/29 · arxiv updated 2016/07/06 · openalex updated_date 2026/08/05
ABSTRACT Over two decades ago, a prominent, mysterious emission band peaking at ∼20.1 μ m was serendipitously detected in four preplanetary nebulae (PPNe; also known as “protoplanetary nebulae”). To date, this spectral feature, designated as the “21 μ m” feature, has been seen in 27 carbon-rich PPNe in the Milky Way and the Magellanic Clouds. The nature of its carriers remains unknown although many candidate materials have been proposed. The 21 μ m sources also exhibit an equally mysterious, unidentified emission feature peaking at 30 μ m. While the 21 μ m feature is exclusively seen in PPNe, a short-lived evolutionary stage between the end of the asymptotic giant branch (AGB) and planetary nebula (PN) phases, the 30 μ m feature is more commonly observed in all stages of stellar evolution from the AGB through PPN to PN phases. We derive the stellar mass-loss rates ( ) of these sources from their infrared (IR) emission, using the “2-DUST” radiative transfer code for axisymmetric dusty systems which allows one to distinguish the mass-loss rates of the AGB phase ( ) from that of the superwind ( ) phase. We examine the correlation between or and the fluxes emitted from the 21 and 30 μ m features. We find that both features tend to correlate with , suggesting that their carriers are probably formed in the AGB phase. The nondetection of the 21 μ m feature in AGB stars suggests that, unlike the 30 μ m feature, the excitation of the carriers of the 21 μ m feature may require ultraviolet photons which are available in PPNe but not in AGB stars.