Six-Channel uvby–Hβ Photometer at the Danish 0.5-m
The Six-Channel uvby–Hβ Photometer was mounted at the Cassegrain focus of the Danish 0.5-metre telescope at La Silla Observatory. It was designed for simultaneous measurement of all uvbyβ indices — the Strömgren four colour system (u, v, b and y) and the Hβ index developed by David Crawford.
The Six-Channel uvby–Hβ Photometer replaced the previous Four-Channel uvby Photometer in 1987. The production of four-channel uvby photometers began in the late 1960s, notably at the Brorfelde Observatory, where the development of photoelectric instrumentation received a major impulse with Strömgren’s return to Denmark in 1967. The uvbyβ system was mainly designed to investigate stars and their basic astrophysical characteristics in an accurate way, and can be used to estimate interstellar extinction and reddening.
The four-channel photometer used a filter-set acquired from Kitt Peak with transmission curves fairly close to those used in the original uvby system. The edges of the passbands were defined by slots cutting the spectrum produced by the photometer grating at positions where the filters transmission was less than 8% of maximum.
The Hβ index was developed in 1958 at Kitt Peak National Observatory by Crawford, where Strömgren also continued his uvby observations. It is a parameter basically free from the effects of interstellar reddening and line blanketing, used to derive effective temperatures and absolute magnitudes.
On La Silla, the Stromgren uvby and Hβ system was realised in two ways: the single channel photometers on the ESO 0.5-metre and 1-metre telescopes, with a purely filter-defined system, and the two six-channel spectrophotometers on the Danish 1.5-metre and 0.5-metre telescopes, using a combination of filters and spectral slots to define the passbands.
Six-Channel uvby-Hβ Photometer
This table lists the global capabilities of the instrument.