The characteristics of the O-2 Herzberg II and Chamberlain bands observed with VIRTIS/Venus Express

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 O-2 and to further study its vertical distribution, in particular the (0-v '' with v '' = 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 v '' = 7-11, are inferred from the recorded spectra. The resulting values lie in the range of 84-116 kR at the altitudes of maximum intensity, which are found to lie in the range of 93-98 km. Three bands of the Chamberlain system, centered at 560 nm, 605 nm, and 657 nm have been identified as well. Their emission peak is located at about 100 km, 4 km higher than the Herzberg II bands. For the first time, the O-2 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 O-2(a(1)Delta g-X-3 Sigma(-)(g)) bands. An airglow model, proposed by Gerard et al. (Gerard, 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 O-2 systems.