A star’s extreme ultraviolet (EUV) radiation, located at 100 to 1000 Å, affects the evolution, atmospheric stability, and habitability of close-orbiting planets. However, it is currently impossible to take stellar EUV measurements directly.
The current beta version of the Phoenix EUV Grid and Stellar UV Spectra (PEGASUS) web tool allows users to input the name or coordinates of an exoplanet host star (M or K spectral type) and identifies a generalized high resolution (Δλ < 0.01 Å) synthetic spectrum from a grid of ~1,500 PHOENIX models. PHOENIX is an established code for modeling stellar atmospheres, and has been identified as the next best option when observed UV spectra are not available.
PEGASUS is a collaboration between team members from NASA’s Goddard Space Flight Center, the University of Maryland, and the University of Arizona’s Lunar and Planetary Lab. A full version of the web tool is currently in the works.
The PEGASUS Point of Contact is Sarah Peacock.
What Are Stellar Spectra?
A star’s spectrum is the pattern of light emitted by a star across different wavelengths, which shows the absorption of light by different elements within the star’s atmosphere. This reveals star properties such as chemical composition, temperature, and surface gravity.
The characteristics of a star’s outer layer are particularly important to exoplanet researchers. While scientists are still investigating how planets form, the properties of the host star are thought to play a significant role in the creation and evolution of exoplanets. Stellar atmospheres can have a huge impact on a planet’s composition, size, climate, and suitability for life.
Some wavelengths in a stellar spectrum are easier to observe than others. In particular, the extreme ultraviolet (EUV) part of most stellar spectra is impossible to measure directly with Earth-orbiting space telescopes because these wavelengths cannot pass through the dust and gas of the interstellar medium. PEGASUS uses models to help users get a complete stellar spectrum, including the unobservable EUV wavelengths.
When users search for a target star in the PEGASUS web tool, the application automatically fills in the required inputs based on existing NASA data catalogs. The properties needed to produce a spectrum are:
- The star’s effective temperature Teff, surface gravity log(g), mass, radius, and distance from Earth, which the search tool pulls from the NASA Exoplanet Science Institute (NExSci) archive.
- The star’s far ultraviolet (FUV) and near ultraviolet (NUV) flux densities, which the search tool pulls from NASA’s Galaxy Evolution Explorer (GALEX) catalog 6/7.
Users can also search for non-exoplanet host stars. However, the required inputs must be entered manually, because the NExSci archive only has information about exoplanet host stars.
The downloadable data product from the main search function is a PHOENIX spectrum (EUV - IR; 100 Å to 100 μm) in FITS file format.
PEGASUS was made possible by the following institutions and archives.
Team Member Affiliations:
- University of Maryland, Baltimore County
- NASA Goddard Space Flight Center
- University of Arizona, Lunar and Planetary Lab
- High Performance Computing Centers:
- NASA Center for Climate Simulation
- University of Arizona High Performance Computing (HPC)
- University of Arizona Planetary Atmospheres Computing and Modeling Analysis (PACMAN)
Archives:
- NASA Exoplanet Archive
- Mikulski Archive for Space Telescopes (MAST)
- Galaxy Evolution Explorer (GALEX)
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