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

Abstract

We establish an empirical effective temperature calibration of main sequence, luminosity class V to III B-type stars for the Delta 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 5200A. However, this system provides the index (g1-y) which shows an excellent correlation with (B-V) as well as (b-y) and can be used as an indicator of the effective 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 Delta 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 uvbybeta, Geneva 7-color and Johnson UBV systems, a polynomial fit of third degree for the averaged effective temperatures to the individual (g1-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 238K which is sufficient to investigate the HRD of distant galactic open clusters as well as extragalactic aggregates in the future.

arXiv comment7 pages, 5 figures, accepted by A&A

References in corpus (6)

• Be-star rotation: how close to critical?
• On the detection of chemically peculiar stars using Delta a photometry
• The status of Galactic field lambda Bootis stars in the post-Hipparcos era
• The 5200A flux depression of chemically peculiar stars: I. Synthetic Delta a photometry - the normality line
• Theoretical isochrones for the Delta a photometric system
• On the incidence of chemically peculiar stars in the Large Magellanic cloud

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