Skip to main content
SearchLoginLogin or Signup

Recovering Stellar Lyα and O I Emission from HST-COS Spectra: Separating Stellar and Geocoronal Signals

Presentation #102.213 in the session Poster Session.

Published onJun 20, 2022
Recovering Stellar Lyα and O I Emission from HST-COS Spectra: Separating Stellar and Geocoronal Signals

Lyα (1216 Å) and the O I triplet (1302, 1305, and 1306 Å) are bright stellar emission lines in the far-ultraviolet (FUV) that trace the stellar chromosphere. Lyα in particular is used to predict the flux in other high-energy wavelength regimes and serve as a backlight for probing the atmospheric escape of transiting exoplanets. In addition to absorption in the line core of Lyα by the interstellar medium (ISM), observations of stellar Lyα and O I are contaminated with geocoronal emission, or airglow. Airglow contamination is particularly strong with the Hubble Space Telescope’s (HST) most sensitive FUV spectrograph, the Cosmic Origins Spectrograph (COS), due to the instrument’s wide spectroscopic aperture. We have explored the stability of the Lyα and O I airglow emission profiles observed with the COS G130M grating for different lifetime and grating positions. This analysis demonstrates that the profiles are sufficiently stable to create airglow templates that can be used to remove contaminating airglow from stellar spectra observed by COS. We find that one O I template is sufficient across all G130M grating setups, whereas separate templates for specific grating setups are required for Lyα. We developed a graphical user interface (GUI) to implement the airglow subtraction on a sample of 172 F, G, K, and M-type dwarfs to recover airglow-free stellar emission lines. We investigate correlations between recovered stellar fluxes and several measures of stellar activity such as the R’HK index, stellar rotation, and other chromospheric and coronal tracers. The airglow subtraction results indicate that the recovery tool developed in this work can produce acceptable recovered spectra for late type stars.

Comments
0
comment

No comments here