Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006dps....38.2611s&link_type=abstract
American Astronomical Society, DPS meeting #38, #26.11; Bulletin of the American Astronomical Society, Vol. 38, p.526
Astronomy and Astrophysics
Astronomy
Scientific paper
Radiative recombination is a major source of atomic oxygen emission in the 3p-3s multiplets at 7772-5 Å and 8446 Å at non-auroral latitudes in the terrestrial atmosphere. This is known from a study of a wide range of O-atom Rydberg lines made with intensity-calibrated sky spectra from the Keck telescopes [Slanger et al., 2004]. We have observed that the I(7774)/I(8446) intensity ratio is approximately constant throughout most of the night with a value near 2.3, although both emissions fall rapidly in intensity. However, late at night the ratio plunges by a factor of 5-10, indicating that the 8446 Å source is still present, while the 7774 Å source turns off.
This behavior is explained by noting that the 3d-2p triplet transition of atomic oxygen is in close energy coincidence with the solar hydrogen Lyman-beta line at 1025.572 Å. It is therefore to be expected that the oxygen 3d-2p transition will be excited in the high atmosphere, leading to a cascading sequence - 3d-3p(1.13 μm)->3p-3s(8446 Å) ->3s-2p(1304-06 Å) [Meier et al., 1987]. This process is an example of Bowen fluorescence, and because the oxygen ground state is a triplet, only triplet transitions can be generated in this manner, thus excluding quintet 3p-3s 7774 Å production. Therefore, when the radiative recombination process dies away as charged particles are neutralized, Lyman-beta pumping continues.
Because of comparable [O+] and [Ne] [Fox, 1996], radiative recombination will proceed at similar rates in the Venus and terrestrial atmospheres, leading to similar intensities of 7774 and 8446 Å radiation. However, the Bowen fluorescence process at Venus may be more pronounced because of proximity to the sun. In the Mars atmosphere, both sources will be substantially weaker. Support for this work comes from NASA Planetary Astronomy and NSF Atmospheric Sciences (Aeronomy), as well as the NSF REU program.
Cosby Philip C.
O'Neill E. R.
Sharpee Brian D.
Slanger Tom G.
No associations
LandOfFree
Measurement of the Thermospheric Oxygen Atom I(7774)/I(8446) Intensity Ratio, and Expectations for Venus and Mars does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Measurement of the Thermospheric Oxygen Atom I(7774)/I(8446) Intensity Ratio, and Expectations for Venus and Mars, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Measurement of the Thermospheric Oxygen Atom I(7774)/I(8446) Intensity Ratio, and Expectations for Venus and Mars will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-999480