About
Overview
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The PEGASUS webtool identifies a generalized high resolution (Δλ < 0.01 Å) synthetic extreme ultraviolet (EUV; 100-1000 Å) spectrum for a searched target exoplanet host star (M or K spectral type) from a grid of ~1,500 PHOENIX spectra with Teff = 2500 - 5044 K, log(g) = 4.45 - 5.32 cm/s2, and M = 0.08 - 0.89 Msun.
Required inputs for returning a spectrum are Teff, log(g), mass, radius, distance, and GALEX FUV and NUV flux densities.
Teff, log(g), and mass are used for two purposes:
- To select a PHOENIX photosphere model that is used for subtracting out the star's photospheric contribution from the GALEX flux densities The photosphere model grid is sampled as such: Teff = 2500 - 5100 K (ΔTeff = 10 K), log(g) = 4.35 - 5.35 cm/s2 (Δlog(g) = 0.01), M = 0.08 - 0.9 Msun (ΔM = 0.1))
- To select a subgrid of closest matching spectral subtype from which to identify the best representative model for the searched star
Radius and distance are used to scale the GALEX fluxes to the stellar surface. The PHOENIX models are similarly scaled to the stellar surface and have no photospheric contribution included.
GALEX FUV and NUV flux densities are used to identify the best representative model of the star. A χ2 minimization is done to identify the model with the closest matching (photospheric-flux-corrected) FUV and NUV fluxes to the target star.
The downloadable data product from the main search function is a PHOENIX spectrum (EUV - IR; 100 Å to 100 μm) in FITS file format. The wavelengths (given in Å) are in vacuum and the wavelength grid has a resolution of <0.1 Å. Please note that the wavelength grid is not uniformly spaced. The flux densities (given in ergs/cm2/s/Å) are that at the stellar surface and are scalable to a distance D via (R_star/D)2.
NOTE: The data product is a general representation of the star, tailored to predict the EUV wavelengths. Wavelengths longer than 1000 Å may not match observed spectra of the star due to the model having slightly a different temperature, gravity, and/or mass from the searched target star.
Notes if utilizing our built-in search function
The PEGASUS webtool queries the NExSci catalog for Teff, log(g), mass, radius, and distance. Please confirm that the values you select are correct for your target. Clicking on the NExSci hyperlink on the modal with returned values will navigate you to that star's NASA Exoplanet Archive Summary page, which may provide additional options for stellar parameters.
The PEGASUS webtool queries GALEX catalog 6/7 for FUV and NUV flux densities. It queries the catalog by RA and dec, which have been corrected for proper motion via the values returned by the GAIA EDR3 catalog.
Citation
If you make use of the synthetic spectra downloaded from the PEGASUS webtool, please cite Peacock et al. (2023).
Data Products
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The data file naming convention is as follows:
PEGASUS.<SpT>.Teff=<Teff>.logg=<logg>.TRgrad=<TRgrad>.cmtop=<cmtop>.cmin=<cmin>.fits
Where
<SpT> = Spectral subtype of the model
<Teff> = Effective Temperature of the model in K
<logg> = Log of the surface gravity of the model in cm s2
<TRgrad> = Log of the temperature gradient in the transition region in K dyne-1 cm2
<cmtop> = Log of the column mass at the top of the chromosphere (absolute value) in g cm-2
<cmin> = Log of the column mass at the temperature minimum (absolute value) in g cm-2
Data Access
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Python Script to Run
from astropy.io import fits
import matplotlib.pyplot as plt
spec = fits.getdata('PEGASUS.M0.Teff=3850.logg=4.78.TRgrad=8.5.cmtop=6.5.cmin=3.5.fits',1)
plt.plot(spec['WAVELENGTH'],spec['FLUX'])
plt.suptitle('Synthetic EUV spectrum for <STAR>')
plt.xlabel('Wavelength (Å)')
plt.ylabel('Flux Density (erg/cm2/s/Ang)')
plt.xrange(100,1000)
plt.show()