The characteristics of the O2 Herzberg II and Chamberlain bands observed with VIRTIS/Venus Express

Abstract

The oxygen Venus nightglow emissions in the visible spectral range have been known since the early observations from the Venera spacecraft. Recent observations with the VIRTIS instrument on board Venus Express allowed us to re-examine the Herzberg II system of O2 and to further study its vertical distribution, in particular the (0–ν″ with ν″=7–13) bands. The present work describes the vertical profile of the observed bands and relative intensities from limb observation data. The wavelength-integrated intensities of the Herzberg II bands, with ν″=7–11, are inferred from the recorded spectra. The resulting values lie in the range of 84–116kR at the altitudes of maximum intensity, which are found to lie in the range of 93–98km.Three bands of the Chamberlain system, centered at 560nm, 605nm, and 657nm have been identified as well. Their emission peak is located at about 100km, 4km higher than the Herzberg II bands.For the first time, the O2 nightglow emissions were investigated simultaneously in the visible and in the IR spectral range, showing a good agreement between the peak position for the Herzberg II and the O2(a1Δg–X3Σg-) bands. An airglow model, proposed by Gérard et al. (Gérard, J.C., Soret, L., Migliorini, A., Piccioni, G. [2013]. Icarus.) starting from realistic O and CO2 vertical distributions derived from Venus-Express observations, allows reproduction of the observed profiles for the three O2 systems.