To obtain more information about the variations of the continuum light in the
different episodes during the long time scale variations of HD 45677 we have
constructed the spectral energy distribution (SED), from the UV to the infrared
wavelength ranges, for several V magnitudes. An attempt
was made to use as much simultaneous measured data as possible in these SEDs,
but simultaneous blue and optical photometry and UV spectrophotometric
data were available for a few dates only. Data measured at slightly different
times, but at the same stellar brightness were therefore combined into one
SED. The SEDs were corrected for interstellar and circumstellar extinction by
comparing the observed fluxes to the theoretically observed flux
(
) at earth in a photometric system:
In this formula 
is the flux emitted by the star per surface
unit, 
is the stellar radius, d is the stellar distance,
is the total extinction at a given wavelength (in magnitudes)
and 
is the transmission function (normalized to unity) of the
photometric filter. 
was taken from the
Kurucz (1991) model for
a B2 V star, assuming solar abundance. 
was obtained from the
extinction laws by Steenman & Thé (1991),
using the relation
= 
, with 
the ratio of total to selective
extinction. A best value of this 
, according to the 
test,
was determined using a trial and error method. Since 
and d are
not accurately known we fitted the parameter (
to the observed
fluxes for each value of 
. The results of the fit procedure are listed
in Table 4 (click here) and a typical resulting SED fit is shown in Fig. 11 (click here). In this
figure we notice a very good fit to the theoretical Kurucz model in the
ultraviolet and in the optical, with a large amount of excess radiation above
photospheric levels in the infrared. The presence and appearance of this
infrared excess once again indicates the existence of circumstellar dust
around HD 45677.
From the SED, we also computed the scaled stellar luminosity using the following formula:
with 
the Kurucz model flux, fitted to the
extinction-corrected SED. These scaled stellar luminosities are also listed
in Table 4 (click here).
Again using Eq. (5), we also computed the total luminosity of the
infrared excess of HD 45677 by taking 
from a 
-spline fitted
to the extinction-corrected SED of HD 45677 minus the corresponding Kurucz
model flux. Beyond the last wavelength at which we have observational data,
this model was extrapolated with a Planckian curve of 900 K,
smoothly joined to the
slope of the last spline curve. The resulting scaled luminosity of the
infrared excess (
) turns out to be about 0.26 
, or about 28% of the stellar luminosity. When we also compute the fraction of
the stellar luminosity absorbed by dust in the blue and ultraviolet
(
) by taking
the difference between the luminosities of the Kurucz model fitted to the
extinction-corrected SED and a version of this model reddened with the
parameters listed in Table 4 (click here), we typically obtain values like 82% of the
stellar luminosity. The ratio 
.
The fact that 
suggests that either we are seeing a star/disk system
at a small inclination angle, or that 
of the star's total
extinction must be interstellar rather than circumstellar as 
is necessary to produce the re-radiated light as 
. In view of the
discussion in the previous sections, the first possibility seems more likely.