6 Data format and public access

The spectra are stored in HFA in the form of FITS files containing 4 extensions (Grøsbol et al. 1988):

The first extension is a 1D image header data unit (HDU) containing the spectra calibrated in wavelength expressed in the rest-frame of each star and sampled between 410 and 680 nm. The high resolution version is normalized with a step between the sampling points of 0.005 nm and the low resolution version is given in physical flux with a step of 0.020 nm.

Another image HDU (EXTNAME=NOISE), with the same sampling, contains the noise attached to the values in the primary HDU (in the unit of this spectra). Pixels are independent.

The other extensions are the flux calibration relations which enable to convert the instrumental flux into physical or normalized flux. They are binary table extensions and the relations are coded as spline representations. The details are given in the Pleinpot user's manual, and the conversions can be done on-the-fly with the pipeline attached to HFA.

The physical flux calibration (EXTNAME=FCAPHY) and the normalized flux relation (EXTNAME=FCANOR) have a spectral resolution of about 2 nm.

Each header, which includes the keywords created during the observations and TACOS reduction, have been completed with useful information on the star: spectral type, Tycho-2 V and B-V, absolute magnitude M_V and ( $T_{\rm eff}$, $\log~g$, [Fe/H]) with their reliability flag, and $v_{\rm r}$. The nominal FWHM of the spectrum can also be retrieved in the header.

In addition to the spectra of the stars, the archive contains the different intermediate files used along the data processing. They are described in the electronic version of the paper.