Period analysis of the Hα equivalent width in P Cygni
The
large
data
set
of
Halpha
equivalent
width
measurements
(almost
23
years)
enables
an
analysis
of
its (quasi)-periodic
behavior
(see
fig.
below). The
data
set
is
a
compilation
of
professional
data
(Markova
&
Scuderi)
and
amateur
data,
gotten
with
partly
very
different
spectrographs.
Fig.
1:
Hα-EW
time
behavior
Fig.
2:
Periodogram
Fig. 3:
Phase
plot
The
Scargle-periodogram
shows
a
main
period
of
approx.
1200
days.
This
is
fairly
close to
the
period
of
the
visual
brightness
of
1300
days,
which
has
been
often
assumed /
discussed in
the past,
and
confirms
a
certain
connection
between
both,
as
it
has
been
found
in
our
international
campaign
"Photometry
and
Spectroscopy"
and
has
been
published
in
AAVSO
newsletter.
The
other
small
periods
between
500
to
900
days
are
caused
probably
by
sampling
effects
(alias
periods)
