The Peton photometric system

Basic Reference

Peton A., Bigay J.H., Garnier R., Paturel G. 1972, A&A 17, 47


Comparisons between B and Be stars having the same intrinsic index (U-B)o, show that the Be stars do not follow the B sequence. There are two causes which explain this:

  1. an emission in the external shell of the star, with a corresponding shift of the point in the (alpha, (U-B)o) and (beta, (U-B)o) diagrams.

  2. the external shell causes a displacement of the (U-B)o index toward the red which is underestimated. Narrow band photometry for emission measurements can only be used with Be stars for the emission is much greater than the absorption by the envelope.
Direct photoelectric measurements of Balmer decrements are compared with those obtained by conventional spectroscopy. The photoelectric indices E(alpha) and E(beta) increase with the stars temperature. They are proportional to the equivalent widths W(alpha) and W(beta), measured by spectroscopy. The variation of the emission amplitude increase with the temperature of the star. The ratios E(alpha) / E(beta) and Halpha / Hbeta are proportional, the scatter in the data are larger than can be explained by the precision of measurements.


Access to the data and references

Indices and Parameters

alpha, beta


  Filter     Width   Position 

    1          29     Hbeta
    2         112     Hbeta
    3         158     Halpha
    4          89     6645 Å
    5         164     6350 Å


beta = m(1) - m(2)
alpha = m(3) - 1/2 (m(4) + m(5))


EMI trialcali, sensitive from 3000 Å to 8000 Å
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Last update: 21 May 1996