Airglow

In these programs, COS airglow exposures were taken in parallel with STIS calibration observations.

Observations will be posted as they are released to the public.

Dr. Vincent Bourrier of Geneva Observatory and his team, used a recent set of COS observations of 55 Cnc to build observational templates of four airglow lines and used them successfully to decontaminate the observations, as outlined in High-energy environment of super-Earth 55 Cnc e. Bourrier et al. have graciously offered to share these templates with the greater astronomy community through STScI. They caution that the lines in the templates are not centered on their rest wavelengths and have an arbitrary flux scaling. Users wishing to make use of these templates should fit the position and amplitude of the templates according to their observations, as these properties are specific to a given observation that was obtained with the COS G130M grating at a central wavelength of 1291 Å with the Hubble Space Telescope.

The templates can be seen in the paper in the following figures: 

• OI line (rest wavelength 1304.8576 Å) in Fig. 4 
• OI line (rest wavelength 1306.0286 Å) in Fig. 4 
• OI line (rest wavelength 1302.1685 Å) in Fig. 5 
• HI line (rest wavelength 1215.6702 Å) in Fig. 6

The four tables follow the same structure. They contain three columns: 

1. The wavelength, in angstroms 
2. The flux of a given geocoronal emission line, in erg/cm²/Å/s 
3. The associated errors, in erg/cm²/Å/s

STScI and the COS Team have not tested these templates and while we encourage the astronomy community to make use of these products, we warn users to do so at their own risk.

Below is a table of FUV airglow lines which may be present in your COS observations. These lines are were compiled by Paul Feldman from FUSE and HUT observations*.

Additional Information:

• Lines grouped together may be blended;
• A range of wavelengths indicates multiple features at nearly the same wavelength;
• Only the Lyman series features will be strong during the night. However, if your observation is taken close to the bright earth limb, the strongest daytime airglow lines of other species may also be present.
• While COS has a similar resolution to FUSE, HUT had a resolution of about 2.5 Å;
• FUSE and HUT had much larger apertures than COS;

*Feldman et al. (2001, JGR, 106, 8119) present an extensive set of airglow spectra observed with FUSE

The subtractAirglow tool is an open-source Python code that can be used to fit airglow profiles of HI and OI lines to COS observations, subtract them, and reconstruct the underlying emission line of the source. The code is optimized for F, G, K, and M dwarf stars, but it can be used for other targets observed with COS G130M.

The code is described in this paper: Cruz Aguirre et al. 2023: Disentangling Stellar and Airglow Emission Lines from Hubble Space Telescope (HST) Cosmic Origins Spectrograph (COS) Spectra]. It is publicly available in the following GitHub repository: https://github.com/AstroAguirre/subtractAirglow. This tool has a user-friendly Graphics User Interface (GUI), and the repository contains basic instructions on operating the GUI.

The COS Team has tested this code and verified its usability and accuracy in a limited test data set. While we encourage the astronomy community to use this product, we warn users to do so at their own risk.