We present a detailed analysis of the UV spectrum of the calibration star BD + 28 \arcdeg 4211 using high-quality spectra obtained with the HST and FUSE satellites .
To this aim , we compare quantitatively the observed data with model spectra obtained from state-of-the-art NLTE metal line-blanketed model atmospheres and synthetic spectra calculated with TLUSTY and SYNSPEC .
We thus determine in a self-consistent way the abundances of eleven elements with well-defined lines in the UV , namely those of C , N , O , F , Mg , Si , P , S , Ar , Fe , and Ni .
The derived abundances range from about solar to 1/10 solar .
We find that the overall quality of the derived spectral fits is very satisfying .
Our spectral analysis can be used to constrain rather tigthly the effective temperature of BD + 28 \arcdeg 4211 to a value of T _ { eff } = 82 , 000 \pm 5000 K. We also estimate conservatively that its surface gravity falls in the range log g = 6.2 _ { -0.1 } ^ { +0.3 } .
Assuming that the Hipparcos measurement for BD + 28 \arcdeg 4211 is fully reliable and that our model atmospheres are reasonably realistic , we can reconcile our spectroscopic constraints with the available parallax measurement only if the mass of BD + 28 \arcdeg 4211 is significantly less than the canonical value of 0.5 M _ { \odot } for a representative post-EHB star .