  (abridged) Spectral energy distributions (SEDs) were constructed for a sample
of 477 classical cepheids (CCs). The SEDs were fitted with a dust radiative
transfer code. Four stars showed a large mid- or far-infrared excess and the
fitting then included a dust component. These comprise the well-known case of
RS Pup, and three stars that are (likely) Type-II cepheids (T2Cs), AU Peg, QQ
Per, and FQ Lac.
  The remainder of the sample was fitted with a stellar photosphere to derive
the best-fitting luminosity and effective temperature. Distance and reddening
were taken from the literature. The stars were plotted in a Hertzsprung-Russell
diagram and compared to evolutionary tracks for cepheids and theoretical
instability strips. For the large majority of stars, the position in the HRD is
consistent with the instability strip for a CC or T2C. About 5% of the stars
are outliers in the sense that they are much hotter or cooler than expected. A
comparison to effective temperatures derived from spectroscopy suggests in some
cases that the photometrically derived temperature is not correct and that this
is likely linked to an incorrectly adopted reddening.
  In this work the presence of a small NIR excess, as has been proposed in the
literature for a few well-known cepheids, is investigated. Firstly, this was
done by using a sample of about a dozen stars for which a mid-infrared spectrum
is available. Secondly, the SEDs of all stars were fitted with a dust model to
see if a statistically significant better fit could be obtained. The results
were compared to recent work. Eight new candidates for exhibiting a NIR excess
are proposed, solely based on the photometric SEDs. Obtaining mid-infrared
spectra would be needed to confirm this excess. Finally, period-bolometric
luminosity and period-radius relations are presented for samples of over 370
fundamental-mode CCs.
