This directory contains 31,500 seconds of Keck HIRES data of the BAL quasar Q08279+5255 obtained in April/May 1998. These data are available for general public use by ftp on the understanding that anyone using the spectra will include the following acknowledgements in any published work which uses them. Firstly, the Keck Observatory must be acknowledged with the following statement "Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation." Secondly, please reference Ellison, S. L., Lewis, G. F., Pettini, M., Sargent, W. L. W., Chaffee, F. H., Foltz, C. B., Rauch, M., & Irwin, M. J. 1999,. PASP, submitted, which presents the full spectrum. See also the paper by Ellison et al. (1999) astro-ph/9903063. The data in this directory are the result of S/N weighted co-addition of 13 individual exposures with varying echelle settings so as to achieve almost complete wavelength coverage from 4400-9250 A. The data have a resolution of approximately 6 km/s and the individual spectra were re-dispersed to a scale of 0.04 A/pix before being co-added. The spectra were wavelength calibrated by reference to a Th-Ar hollow cathode lamp and mapped onto a linear wavelength scale. There are 3 wavelength sections for the APM08279+5255 spectral data available in fits format with their corresponding one sigma error arrays. q0827_blue.fits 4400 - 5499 A data. q0827_blue.sig.fits " " sigma q0827_purple.fits 5500 - 5899 A data q0827_purple.sig.fits " " sigma q0827_red.fits 5900 - 9250 A data q0827_red.sig.fits " " sigma After co-addition and averaging, the 3 sections have the following effective exposure times: blue - 2700 seconds purple - 3000 seconds red - 3000 seconds No flux calibration has been applied and the data are not normalised. Standard star spectra are also to be found in this directory in 2D format (i.e. echelle orders not combined) so that flux calibration can be carried out if desired. The standards are as follows Flux-128-L.fits Feige 34 300 seconds Flux-007-L.fits SAO62257 20 seconds Flux-021-L.fits BD+28 4211 300 seconds Flux-047-L.fits Feige 34 300 seconds Flux-054-L.fits SAO 62257 20 seconds Flux-071-L.fits BD+28 4211 400 seconds Flux-120-L.fits SAO 62257 20 seconds Flux-117-L.fits Feige 34 300 seconds Flux-017-L.fits Feige 34 300 seconds Flux-018-L.fits Feige 34 300 seconds Alternatively, the fluxed low dispersion spectrum of APM08279+5255 can be used to calibrate these data. It is included in this directory as lores.asc as an ascii file. Also included in this directory are 4 postscript (gzipped) files containing plots of the data over the full wavelength range - plot1.ps.gz - plot4.ps.gz. Finally, we note that there are some apparent `glitches' in the final spectrum. As part of the reduction process, the cosmic ray hits were cleaned from the raw data, but inevitabley in the complicated process of joining the many orders and many spectra together some cosmetic `blips' have crept in. We have removed all of the major blemishes but in order to avoid too much interference with the original spectrum we leave it to the discretion of the individual as to how much they wish to alter the data we provide here.