On the Effect of Fraunhofer Lines on u, b, V Measurements.

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• Burbidge, E. M.
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• Sandage, A. R.
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• Burbidge, G. R.

Abstract

The effect on the observed U, B, and V magnitudes of the removal of the Fraunhofer lines from the spectra of Peg (F7 V), SO And (F8 V), the center of the solar disk (GO V), and RD 19445 (sdF) is assessed by the measurement on direct-intensity microphotometer tracings of the energy abstracted from the continuum by the absorption lines. The star 70 Vir (GS V) has also been measured in part, but it was impossible to place the continuum in the ultraviolet region by empirical means because of the extreme crowding of the lines. The effect on the colors caused by (1) blocking of the radiation by the Fraunhofer lines and (2) the back-warming effect due to radiation back-scattered into the photo sphere is considered. The slopes of the blanketing vectors in the U - B, B - V diagram are determined as a function of their B - V intersection with the Hyades relation. From the slopes, a family of curves has been constructed which allow corrections A(B - V), A(U - B), and V to be applied to any weak-lined star to reduce the U, B, and V observations to those for stars with as strong metal lines as the Hyades stars. These corrections, given in Table 4, are a function of the observed B - V and the observed ultraviolet excess (U - B) alone. Previous conclusions that most mild subdwarfs are explicable in terms of line blanketing are preserved.