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Up: Photographic surface photometry

1. Introduction

In 1971, about one hundred photographs of the Southern Milky Way were taken at La Silla with the Bochum Super-Wide-Angle Camera (Schlosser & Schmidt-Kaler 1978; Schlosser et al. 1975). The majority of the frames were exposed in spectral passbands with filter/emulsion combinations, which matched as closely as possible Sandage & Smith's (1963) photoelectric UBVR system. While these U, B, and V passbands are quite similar to the Johnson (1955) system and thus could be transformed into that standard system by linear colour equations, things are different with the red passband. Sandage & Smith employed a red spectral region, which contains Htex2html_wrap_inline1029. This we did not consider as an appropriate base for stellar work, since Htex2html_wrap_inline1029 from dispersed interstellar hydrogen is practically omnipresent in the night sky and makes stellar aggregates "looking older" than they really are. Therefore this hydrogen line was omitted and the R-band was restricted to wavelengths above tex2html_wrap_inline1035 656.3 nm. The finally adopted photographic system U, V, and R (excluding Htex2html_wrap_inline1029) is given in Table 1 (click here).


Passband U V R
Filter/Schott UG1 GG475 RG665
Emulsion/Kodak IIaO 103aG 103aF
tex2html_wrap_inline1059nm 356 534 681
FWHM/nm 52.5 83.5 21.5
tex2html_wrap_inline1045nm 350 555 690
Table 1: Photographic Colour System. tex2html_wrap_inline1045 taken from Johnson (1955) (U and V), and Sandage & Smith (1963) (R)


Additionally we used the following colour equations to transform our photoelectric magnitudes (index "pe") to the Johnson standard system:


Although our R-photometry has been calibrated using stellar colours from Tereshchenko & Kharitonov (1977), one should always remember that - in a strict sense - our R-map of the Southern Milky Way (Figs. 1c, 4) represents a colour system of its own.

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