The determination of physical parameters such as effective temperature and superficial gravity can be done through the Strömgren photometric
data reduced to the standard system for B-F stars, once corrected for interstellar extinction. This procedure has been done previously by the
authors for scuti variables and for stars in open cluster which lie
within these spectral; its description can be found in Peniche et al.
(1990), for example.
We must emphasize that for these fast pulsators, some of which are
multi-periodic or with unexplained light curve variations, the data gathered in
the present work has the advantage that it need not be adjusted in phase as it
would have been with a one-channel photometer. This also allows an extensive
time coverage along the cycle, in particular if the star is faint. On the other
hand, the simultaneous measurements in the different filters that define the
Strömgren system let us avoid problems due to interpolation which worsen if
more than one frequency is present since it is well known (Breger 1998) that
many high amplitude Scuti stars (HADS) are double mode radial
pulsators. Hence, the analysis of the photometry presented in the current
work shows the
real variation of the physical characteristics of the stars along their
pulsation cycles.
If the photometric system is well-defined and calibrated, it will
provide an efficient way to investigate physical conditions. A comparison
with theoretical models, such as those of Relyea & Kurucz (1978), allows
a direct comparison with intermediate or wide band photometry measured from
the stars with those obtained theoretically for early type stars. Relyea &
Kurucz (1978) calculated grids for stellar atmospheres for G, F, A, B and
O stars for the solar abundance in a temperature range
from 5500 K up to 50 000 K. They also considered abundances of 0.1 and
0.001. A comparison of the photometric unreddened indexes (b-y)0 and
c0 obtained for each star with such models permits the determination of
the effective temperature Te and superficial gravity
along the
cycle of pulsation. Therefore, the research goals for
Scuti stars
should be to try to determine not only the frequency content but also the
maximum number of physical characteristics of as many stars as possible,
along each star's cycle variation. Furthermore, there still exists the
question of the real physical differences between the
Scuti
stars and Dwarf Cepheids; Breger (1980) stated that the majority of dwarf
Cepheids mimic Pop I
Scuti stars in basically all aspects, except
for a few stars in the subgroup of Dwarf Cepheids known as the SX Phe that
show low metallicity, high space velocities and low luminosities and that
do not conform the theoretical period gravity relation in the direction of
low mass. Hence motivation of the present work.
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