The NASA Galaxy Evolution Explorer ( \it GALEX ) satellite has obtained simultaneous near and far ultraviolet light curves of the ROTSE-I Catalog RR Lyrae type ab variable star J143753.84+345924.8 .
A series of 38 \it GALEX Deep Imaging Survey observations well distributed in phase within the star ’ s 0.56432 d period shows an AB = 4.9 mag variation in the far UV ( 1350 - 1750 Å ) band and an AB = 1.8 mag variation in the near UV ( 1750 - 2750 Å ) band , compared with only a 0.8 mag variation in the broad , unfiltered ROTSE-I ( \approx 4500 - 10000 Å ) band .
These \it GALEX UV observations are the first to reveal a large RR Lyrae amplitude variation at wavelengths below 1800 Å .
We compare the \it GALEX and ROTSE-I observations to predictions made by recent Kurucz stellar atmosphere models .
We use published physical parameters for the comparable period ( 0.57433 d ) , well-observed RR Lyrae star WY Antliae to compute predicted FUV , NUV , and ROTSE-I light curves for J143753.84+345924.8 .
The observed light curves agree with the Kurucz predictions for [ Fe/H ] = -1.25 to within AB = 0.2 mag in the GALEX NUV and ROTSE-I bands , and within 0.5 mag in the FUV .
At all metallicities between solar and one hundredth solar , the Kurucz models predict 6 - 8 mag of variation at wavelengths between 1000 - 1700 Å .
Other variable stars with similar temperature variations , such as Cepheids , should also have large-amplitude FUV light curves , observable during the ongoing \it GALEX imaging surveys .