An empirical temperature calibration for the △a photometric system -: I.: The B-type stars

We establish an empirical effective temperature calibration of main sequence, luminosity class V to III B-type stars for the. a photometric system which was originally developed to detect magnetic chemically peculiar objects of the upper main sequence ( early B-type to early F-type) at 5200 angstrom. However, this system provides the index (g(1) - y) which shows an excellent correlation with (B-V) as well as (b-y) and can be used as an indicator of the e.ective temperature. This is supplemented by a very accurate color-magnitude diagram, y or V versus ( g1 - y), which can be used, for example, to determine the reddening, distance and age of an open cluster. This makes the. a photometric system an excellent tool to investigate the Hertzsprung-Russell-Diagram (HRD) in more detail. Using the reddening-free parameters and already established calibrations within the Stromgren uvby beta, Geneva 7-color and Johnson UBV systems, a polynomial fit of third degree for the averaged e.ective temperatures to the individual (g(1) - y)(0) values was derived. For this purpose, data from the literature as well as new observations were taken resulting in 225 suitable bright normal B-type objects. The statistical mean of the error for this sample is 238 K which is sufficient to investigate the HRD of distant galactic open clusters as well as extragalactic aggregates in the future.