CESAR at Poker Flat

Abstract:

The Compact Echelle Spectrograph for Aeronomic Research (CESAR) has been sited at Poker Flat Research Range since November 2013, collecting data over two seasons of the nightglow and the aurora. CESAR has operated with a field of view of seven degrees in the zenith direction, with a resolution of 5000, although a resolution three times greater is available. So far, data collection times have been in the range of 20 minutes, while the wavelength range used has been 500-1050 nm. Detailed studies of a number of optical features have been carried out.

1) It is demonstrated that the v = 2 level of the O₂(b) state is best studied by using the weak b-X 2-1 band near 697 nm, it being free of auroral contamination.

2) Similarly, the best uncontaminated feature of the N₂⁺ Meinel system is the complex A-X 0-1 band, which has been accurately simulated for the first time [Dubowsky and McCall, private communication, 2014].

3) The N(²P-²D) quartet of lines near 1040 nm is an important auroral feature, being the N-atom equivalent of the oxygen green line. These lines are uncontaminated in many of our spectra. For lower altitude auroral excitation, there may be some overlap with the N₂ First Positive 0-0 band [Pendleton et al, 1989].

4) Time series on the O⁺(²P-²D) lines near 732-733 nm have been studied, showing variable background emission in this region depending on auroral type.

Information on OH Meinel band lines is available throughout the region studied, and there is substantial evidence from sky spectra (Keck, VLT) that the attempt to extract kinetic temperatures from OH intensity distributions is strongly influenced by non-LTE effects [Cosby and Slanger, 2007; Noll et al, 2014].