2. Data

For this work, we selected 23 frames, namely nine for the U-domain, seven for V and seven for R (Table 2). The plates were then calibrated by means of ESO's ETA-wedge spectra (see Paper VII). This gives relative intensities of the night sky (including all the atmospheric and zodiacal light effects). Parallel to these exposures simultaneous, photoelectric measurements were made by one of us (TSK) with the 61 cm Bochum telescope at La Silla, which then were used to determine atmospheric extinctions, colour transformations, zero points of absolute intensities and airglow values for different zenith distances. All plates were digitized using the PDS machine of the Astronomisches Institut der Westfälischen Wilhelms-Universität at Münster. The diaphragm was , corresponding to about in the sky. Special care was taken to reveal possible time-dependent sensitivity changes of the scanning system, which, however, proved to be of excellent stability. The paper strip chart records of the photoelectric measurements were processed by means of a standard digitizer table commercially available for personal computers.

   

Plate Date(1971) I_A0(S10) C²

U28 Mar.26/27 32^*) 0.970^**) 98^**)

U29 26/27 51 0.970 98

U31 26/27 60 0.970 98

U32 26/27 72 0.970 98

U33 27/28 40 0.970 98

U36 27/28 52 0.970 98

U55 Apr.01/02 130 0.970 98

U56 Apr.01/02 65 0.970 98

U57 Apr.01/02 70 0.970 98

V14 Mar.23/24 120 0.970 99

V17 23/24 120 0.970 98

V19 23/24 180 0.966 108

V49 Mar.31/Apr.01 140 0.963 118

V53 Mar.31/Apr.01 175 0.958 117

V95 Apr.26/27 150 0.972 88

V96 26/27 150 0.973 88

R27 Mar.25/26 532 0.979 69

R73 Apr.17/18 533 0.965 115

R79 19/20 533 0.965 115

R82 21/22 760 0.950 165

R88 23/24 577 0.975 81

R89 23/24 577 0.975 81

R107 28/29 532 0.979 69

^*) all photoelectric zenith airglows multiplied by a factor of 0.43 to allow for cut-off of emission lines in the photographic system
^**) Parameter C² and effective height of emission layer set to average 0.970 resp. 98 km (U-band only)