Four-Channel Photometer at the Danish 1.54-m

The Four-Channel uvby Photometer was mounted on the instrument adaptor at the Cassegrain focus of the Danish 1.54-metre telescope in 1979. The adapter housed a field viewer with a field of 3.5 × 3.5 arcminutes² and an integrating TV system. The TV system was also used via a periscope system for centring the star in the photometer diaphragm.

The Four-Channel uvby Photometer was designed for simultaneous measurements in the Strömgren four colour system, u, v, b, y.

The light from a star, after passing through a diaphragm wheel, was collimated and dispersed by a Littrow mounted grating. Six diaphragms with different diameters (110, 32, 16, 10, 7 and 4 arcseconds) were available. The light then reached four photomultipliers, each preceded by a slot in the camera focal plane which defined the passband. No wavelength defining filters were used in this system. The passbands defined by the slots were as follows: u = 335.8–366.0 nm, v = 402.4–421.3 nm, b = 456.1–479.5 nm and y = 531.95–560.6 nm.

In order to carry out photometry on bright standard stars, an optional neutral density filter (≃10% transmission) could be mounted in front of the diaphragm wheel. Other neutral filters could be mounted in front of the v (≃ 50% transmission) and b (≃50% transmission) channels as these normally had the highest signal. Furthermore, an optional depolariser (90% transmission) could be mounted in front of the diaphragm wheel.

The brightness limit for this photometer without the use of a neutral-density filter was a V=6.5.

The data output was saved on paper tape in ASCII.

The Four-Channel uvby Photometer was decommissioned in the 1980s.