The Balmer discontinuities of O9 - B2 supergiants.

New energy distributions of supergiants at 50 A resolution from AA3200-8000 show that the Balmer discontinuities are poorly correlated with spectral types. A particularly good example is E Ori, whose Balmer discontinuity is 0.1 mag larger than other 09.5 Ia and B0.5 Ia supergiants. Analysis of available four-color and Hfl photometry shows that whereas Hfl correlates well with luminosity as indicated by MK luminosity class, the Balmer discontinuity does not. Our energy distributions show that several 09.5-B0.5 Ia supergiants have Balmer discontinuities in emission on the Palomar system of absolute calibration. They appear to be continuous across the Balmer discontinuity on the calibration of Hayes. Subject headings: atmospheres, stellar - early-type stars - luminous stars - spectrophotometry