We present an extended ultraviolet-blue ( 850-4700 Å ) library of theoretical stellar spectral energy distributions ( SEDs ) computed at high resolution , \lambda / \Delta \lambda = 50 000 .
The Uvblue grid , as we named the library , is based on LTE calculations carried out with Atlas9 and Synthe codes developed by R. L. Kurucz and consists of nearly 1800 entries that cover a large volume of the parameter space .
It spans a range in T _ { \mathrm { eff } } from 3000 to 50 000 K , the surface gravity ranges from \log { g } = 0.0 to 5.0 with \Delta \log { g } = 0.5 dex , while seven chemical compositions are considered : [ M/H ] = -2.0 , -1.5 , -1.0 , -0.5 , +0.0 , +0.3 and +0.5 dex .
For its coverage across the H-R diagram , this library is the most comprehensive one ever computed at high resolution in the short-wavelength spectral range , and useful application can be foreseen both for the study of single stars and in population synthesis models of galaxies and other stellar systems .

We briefly discuss some relevant issues for a safe application of the theoretical output to ultraviolet observations , and a comparison of our LTE models with the NLTE ones from the Tlusty code is also carried out .
NLTE spectra are found , in average , to be slightly “ redder ” compared to the LTE ones for the same value of T _ { \mathrm { eff } } , while a larger difference could be detected for weak lines , that are nearly wiped out by the enhanced core emission component in case of NLTE atmospheres .
These effects seem to magnify at low metallicity ( typically [ M/H ] \lesssim - 1 ) .

A match with a working sample of 111 stars from the IUE atlas , with available atmosphere parameters from the literature , shows that Uvblue models provide an accurate description of the main mid- and low-resolution spectral features for stars along the whole sequence from the B to \sim G5 type .
The comparison sensibly degrades for later spectral types , with supergiant stars that are in general more poorly reproduced than dwarfs .
As a possible explanation of this overall trend , we could partly invoke the uncertainty in the input atmosphere parameters to compute the theoretical spectra .
In addition , one should also consider the important contamination of the IUE stellar sample , where the presence of binary and variable stars certainly works in the sense of artificially worsening the match between theory and observations .