We describe the synthetic photometry algorithm and its general usefulness in a wide range of applications.

The use of calculated colour indices, based on model stellar atmospheres, is discussed. It is concluded that such synthetic photometry has a variety of interesting applications, well worth further exploration and systematic utilization.

Synthetic photometry must be used to accurately define the passbands which characterize a photometric system. On the one hand, the colour indices of the stars must be coherent with their absolute spectrophotometry; on the other hand, direct comparisons of model atmospheres with observations must be carried out without resorting to arbitrary transformations. A systematic evaluation procedure could be applied to various photometric systems.

Observed stellar energy distributions are used in synthetic photometry to evaluate the accuracy of the response functions and to determine the transformation coefficients. The characteristics required of a catalog of energy distributions to be used for synthetic photometry are discussed, and the catalogs found in the literature are reviewed.

We are working hard to improve model atmospheres because existing models have numerical errors, an unphysical treatment of convection, an inadequate or non-existant treatment of statistical equilibrium, an arbitrarily chosen microturbulent velocity, an arbitrarily chosen helium abundance, and a greatly underestimated line opacity for iron group elements.

The combined Scientific Instruments (SIs) on the Hubble Space Telescope (HST) feature an extensive wavelength coverage in both photometric and spectrophotometric modes with an overall dynamic range of more than twenty-five magnitudes. We demonstrate how synthetic photometry techniques are to be used to establish and maintain their calibration. This approach makes efficient use of limited HST observing time by taking full advantage of pre-launch knowledge on the SI sensitivity functions and calibration targets.

At the meeting, Calibration of Fundamental Stellar Quantities, IAU Symposium No. III held in Como, Italy in May, 1984, Philip and Egret (1985) suggested that the facilities of the Strasbourg Data Center be used to construct a microfiche of standard stars and other stars for which fundamental data have been obtained. A start had been made on this idea in Egret and Philip (1979) who published a microfiche, “Photometric Systems and Standard Stars” as part of the proceedings of the workshop “Problems of Calibration of Multicolor Photometric Photometry”. Now the plan is to expand this idea to cover standard stars in many systems and other stars for which fundamental data have been obtained.

Color indices of solar analogs in the Vilnius seven-color photometric system are discussed. The physical parameters (effective temperatures, radii and luminosities) for solar analogs with reliable spectrophotometric and photometric data were obtained by means of infrared fluxes. The effective temperatures of 16 Cyg A and B, which are considered to be the closest solar analogs are 5854 and 5664 K, respectively. The radii of both stars are in the range of 1 Ro < R < 1.4 Ro and luminosities 1.2Lo < L < 2.1 Lo for 16 Cyg A and Lo < L < 1.7 Lo for 16 Cyg B depending on different evaluations of the distances. We find that the relative solar energy distribution in the 0.33 – 1.25 μm range determined by Neckel and Labs (1984) is reliable enough, however the absolute fluxes are slightly too low at the maximum of energy distribution.

In 1984 Neckel and Labs (1984) published improved absolute solar radiation data which followed from an absolute calibration of the Fourier-transform-spectra (FTS) obtained by J. Brault at Kitt Peak. Fig. 1 shows two pages of that special solar spectrum atlas which served to derive the diverse published spectral data. The upper spectrum concerns the disk-center, the lower one the disk-averaged intensity. Both spectra are plotted in the same absolute scale (numbers on the left ordinate axis). The right ordinate axis refers to the full disk spectrum only; it yields the solar irradiance at 1 AU. These spectra, which extend from 3300 to 12500 Å and are stored on magnetic tape, allow an easy derivation of any desired spectral data; e. g. of the spectral averages for successive, rectangular passbands (10, 20 or 50 Å wide) or for any arbitrary passbands used by other observers. The maxima in successive passbands can be used to localize the level of the ‘continuum’ (dashed lines in Fig. 1).

Nearly all of the exciting discoveries in radio astronomy have come from new instruments or techniques which have provided new frequencies, high sensitivity, higher spatial or time resolution, or improved image quality. Since the last General Assembly a number of major new radio telescopes have been completed while construction of others have only just begun. At the same time telescopes of the more distant future are still in the conceptual stage. This paper summarizes a full-day meeting of Commission 40 on recently completed radio telescopes, new radio telescopes now under construction, and radio telescopes of the future.

Whereas the I.A.U. standard values of the constants Ro, ⊙o, A, and B, differ from those currently considered best, the errors of current determinations are still rather large. Although the means of recent determinations lead to a fairly consistent set of values for the four main constants, the agreement may be largely coincidental. However, a case can be made for agreeing on a new pair of standard values for Ro and ⊙o as a matter of practical convenience.