In cycle 6, UV spectra were obtained with the HST (program number 6539). The galaxies were observed with the GHRS and the G140L grating, which has a nominal dispersion of 0.57 Å/diode, using the Large Science Aperture (LSA, 1.7411#111.74 arcsec). The acquisition of the targets was done with the FOS blue side detector, then the LSA was pointed to the peak of the UV surface brightness. Two different wavelength settings were used for each galaxy, covering 1175-1462 Å and 1314-1600 Å for NGC 7130, 1162-1449 Å and 1313-1600 Å for NGC 5135, and 1162-1449 Å and 1301-1587 Å for IC 3639. These ranges provide about 148 Å of overlap between the spectra. The total integration times were 1461 s, 1448 s and 2898 s (split in two equal integrations) in the blue spectral range for NGC 7130, NGC 5135 and IC 3639, respectively. In the red spectral range, the total integration times (split into two integrations) were 2628 s and 2652 s for NGC 7130 and NGC 5135, respectively. For IC 3639 it was 5204 s, split into four integrations.
The instrumental spectral resolution for a point source observed through the LSA is 0.8 Å, but for an extended object it depends on the size of the UV source. Using the Galactic CII 1#11335 interstellar absorption line we determine that the instrumental resolution is < 2.819#190.5 Å and < 2.119#190.3 Å for the blue and the red spectra of NGC 7130, < 2.719#190.2 Å and < 2.519#190.2 Å for the blue and red spectra of NGC 5135, and < 1.919#190.1 Å for IC3639 (equal for the blue and red spectra). Thus, the instrumental resolution is of order of 500 km s-1. Note that this CII line falls in the overlap wavelength region of the blue and red spectra.
The center of the Galactic CII 1#11335 line (assuming a gaussian profile) is 1333.919#190.1 Å and 1333.619#190.1 Å for the blue and the red spectra of NGC 7130, 1333.819#190.1 Å and 1334.119#190.1 Å for the blue and the red spectra of NGC 5135, and 1334.7019#190.05 Å for IC 3639. These give a correction to the zero point wavelength calibration of -0.6 Å and -0.9 Å for NGC 7130, -0.7 Å and -0.4 Å for NGC 5135, and 0.2 Å for IC 3639. We have corrected the nominal wavelength scale, assuming that this apparent shift (of order of 100 km s-1) is due to errors in centering the targets within the LSA aperture.
After standard pipeline processing, the spectra were combined into a single spectrum for each galaxy covering 1175-1600 Å, 1162-1600 Å and 1162-1587 Å for NGC 7130, NGC 5135 and IC 3639, respectively.
Finally, the spectra were corrected for redshift with the values given in Table 1.