Effective temperatures derived using 
can be also compared
with those obtained using the Infrared Flux Method (IRFM hereafter) and
spectrophotometric methods. Although the lack of
common observations between this paper and the papers quoted in this section
prevents us from repeating the same tests done with the photometric calibrations,
the similarity between 
and MD85 found in Fig. 4.2 (click here) allows us
to establish
comparisons by using MD85 instead of 
.
Blackwell & Lynas-Gray (1994) (Bl94, hereafter) constitutes one of the most recent works on the determination of effective temperatures using IRFM. They recalculated the values given in Blackwell et al. (1990) (Bl90, hereafter) by using the newest version of the Kurucz models (1990, 1991, 1992) characterized by providing more accurate determinations of blanketing and ultraviolet flux than the older versions.
Figure 5.1 (click here) compares, for the sample of stars given in Bl94, the
values of 
calculated with the MD85 calibration and the IRFM.
As suggested by Bl94, an error of 
has been adopted in the IRFM values, whereas an error of
has been adopted for MD85. These
errors have to be understood from the point of view that the
error associated to the IRFM is ``absolute" in the sense that it is the result of
errors in the adopted values of gravity, metallicity and interstellar extinction
as well as errors in Kurucz models, especially those concerned with
convection inhomogeneities and non-LTE assumptions, whereas the error
of MD85 is an internal error caused by indetermination
in the photometric indices which do not include errors due to the models or to the
physical parameters of the stars considered as standards.
In Fig. 5.1 (click here) we see how the IRFM gives values which are 
systematically lower than MD85. Some authors (Mégessier 1988; Napiwotzki
et al. 1993; Smalley 1993) have found similar results
suggesting two possible sources of errors: the infrared calibrations and the
flux models employed. To quantify the influence of the calibration as well as
the importance of the models in our range of temperatures, we have plotted in
Figs. 5.1 (click here)c and 3d the 
values of those stars in common to Bl94
and Bl90: whereas Bl94 used the new version of Kurucz models
(1990-1992) together with Cohen et al. calibration
(1992), the MARCS code of Guftasson et al. (1975) and the Dreiling
& Bell (1980) calibration were employed in Bl90. The difference of
(
) between Bl90 and Bl94 can be explained in terms of
blanketing: if blanketing increases at short wavelengths (as it happens with
the new Kurucz models) the total flux conservation will make the infrared flux
to be higher and, following the IRFM, the temperature lower.
The series of papers by Malagnini et al. (1982, 1985,
1986) and Morossi & Malagnini (1985) constitute
one of the most extensive works in the calculation of 
using spectrophotometric methods. In Fig. 5.1 (click here) we have compared
the values of 
given in Malagnini et al.
(1986) (Mal86, hereafter) and Morossi & Malagnini
(1985) (Mor85, hereafter) with those values obtained from the
MD85 calibration. The average difference between MD85 and Mal86 is 
and between MD85 and Mor85 it is 
. A possible explanation of the differences between the two
samples found in Fig. 5.1 (click here)b could be the adopted color excess: in
the Mor85 sample, the reported values of 
depend on
E(B-V) since the reddening modifies both the shape and the absolute
level of the flux distribution. The color excess was measured according
to the values of 
adopted by Fitzgerald
(1970). These have an associated error of 0.02 mag. which
corresponds to an error in 
of 
. To produce the
systematic difference of 132 K found in Fig. 5.1 (click here)b
a deviation of 
would be enough. Hence, we see how a slight
difference in the definition of the intrinsic colors could explain the trend
found in Fig. 5.1 (click here)b. This problem is not present in Mal86 since in this case
the sample is formed of bright stars with 
.
