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Bowen fluorescence is a mechanism that produces emission lines from ionized atoms like - oxygen, carbon, and nitrogen, in diffuse nebulae. It happens when very hot stars or accretion disks emit copious amounts of extreme ultraviolet radiation and excites these ions. The excited ions return to their ground state by emitting a series of photons. When it emits, it creates an emission line.[1] Bowen’s work explained the strong green emission lines observed in nebulae, which were previously attributed to a hypothetical element called “nebulium.”[2]
Background
editIt happens when EUV radiation from hot stars, typically those whose temperatures exceeds 30,000 K - excites ions of carbon (C III) and nitrogen (N III) in surrounding gas clouds. This EUV radiation, specially at a wavelength of 30.4 nm, is absorbed by these ions. As these excited ions return to their ground states, they emit photons at specific wavelengths of emission lines around 464-465 nm.[1][3]
Observational evidence
editBowen fluorescence is a process where ultraviolet photons, specially from helium ions, excite oxygen ions, emits specific spectral lines. This phenomenon is observed in both planetary nebulae and symbiotic stars.
- Planetary nebulae: In planetary nebulae, Bowen fluorescence is often observed through the emission lines of doubly ionized oxygen (O III). Studies have shown that the O III lines are produced by the excitation of the 2p3d ( 3Po ) level of O III by the Lyα line of He II at 303.78 Å. It emits several prominent lines, includes those at 3133 Å and 3444 Å.[3]
- Symbiotic stars: Observations have identified the presence of O III and N III lines, which are excited by the same mechanism as in planetary nebulae. For example, a study by Pereira et al. (1999) analyzed spectroscopic data from eight type-D symbiotic systems and was shown the presence of O III lines formed by the Bowen process.[3]
Importance
editSpectroscopy involves dispersing light from an astronomical source into its component wavelengths. So, we can identify specific emission lines corresponding to different elements and ions. For Bowen fluorescence, the key lines to look for are those of O III and N III in the ultraviolet and optical regions.[4]
By examining the intensity and ratios of these emission lines, astronomers can infer different physical properties of the emitting region, such as electron temperature, density, and ionization state.[4] For instance, the ratio of certain O III lines can indicate the efficiency of the Bowen mechanism and the conditions under which it operates.[5] The profiles of these lines can also provide information about the kinematics of the gas, such as its velocity and turbulence.[4]
Bowen fluorescence is an important mechanism in astrophysics, particularly for in nebulae and the processes occurring in hot stars. Like -
- Diagnostics of nebulae: Bowen fluorescence lines are strong emission lines which can be observed at the spectra of nebulae. By analyzing these lines, scientists can infer the physical conditions within nebulae.[5]
- Processes in hot stars: In hot stars, the intense ultraviolet radiation can excite helium ions, which then transfer energy to oxygen ions through Bowen fluorescence. Mapping the distribution of different elements and understanding the energy transfer mechanisms in the stellar atmosphere become easy.[5]
References
edit- ^ a b "Bowen fluorescence".
{{cite journal}}: Cite journal requires|journal=(help) - ^ "I.S. Bowen | Cosmic Microwave Background, Radio Astronomy & Astrophysics | Britannica".
{{cite journal}}: Cite journal requires|journal=(help) - ^ a b c Liu, Xiao-Wei; Danziger, John (1993). "Observations of the Bowen Fluorescence Mechanism and Charge Transfer in Planetary Nebulae I". Symposium - International Astronomical Union. 155: 190. doi:10.1017/S0074180900170524.
- ^ a b c https://astrobites.org/guides/spectroscopy-and-spectral-lines/.
{{cite journal}}: Cite journal requires|journal=(help); Missing or empty|title=(help) - ^ a b c https://academic.oup.com/mnras/article/309/4/1074/1085694.
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