Astron. Astrophys. 335, 605-621 (1998)
3. The light curves of the LBVs
Since the microvariations depend on the phase of the star during
its moderate variations, we show the lightcurves of the program stars
from Spoon et al. (1994) in Fig. 1. Below we briefly review the
photometric variablity in V of the stars during the last
decades, i.e. the time interval over which we study the
Fig. 1. The light curves of the program stars over periods of about 12 to 25 years (data collected by Spoon et al. 1994). Different symbols refer to data from different photometric systems (see Spoon et al.). The horizontal bars indicate the time intervals in which we found periodicity of the microvariations.
The data consists of intervals with frequent measurements
alternated with intervals of no available measurements. For each star
we selected time intervals of the lightcurve that contained enough
data points to allow a meaningful search for periodicities. These time
intervals have a length of 50 to 500 days, except for R 127 which has
an interval of 800 days. These intervals were chosen on visual
inspection of the lightcurve. We also searched for periodicities in
other intervals. However, we only found periodic variations in the
intervals which were originally selected. This does not imply
that the visual magnitude is not varying periodically outside the
selected intervals. It means that there are insufficient data to find
a periodicity with any degree of reliability. The selected regions in
which we found a periodic behaviour are indicated in Fig. 1 by
R 71 : From 1975 until half 1979 the visual magnitude has
dropped from about to 10.8, where it stayed
until 1995. We studied the microvariations halfway down the descending
branch and at six intervals during the faint phase.
HR Car : The star has varied in visual magnitude between 7.4
and 8.4 mag. Between 1982 and 1985 and between 1985 and 1989 the
visual magnitude went through a dip. Thereafter the star brightened,
reaching V=7.4 mag in 1993. We studied the microvariations during 5
intervals at V between 8.0 and 8.4.
164 G Sco : The star showed a slow decrease in visual
brightness from to 6.8 between 1980 and 1985.
The star remained faint at between 1985 and
1995. This star has been showing microvariations during the complete
observational period from 1974 until half 1994 (van Genderen et al.
1997b). We studied the microvariations in two intervals at
S Dor : Intense observations started just before S Dor begun
its moderate variation. Its visual brightness decreased from 1982 to
1985 from to 10.2, but it increased again from
10.2 to 9.0 between 1985 to 1989. After 1989 the magnitude decreased
again, reaching a visual minimum in 1993 from which it is now
recovering. We studied the microvariations in two intervals, close to
R 127 : The star has slowly been rising to visual maximum
from in 1983 to 8.8 around 1990. From 1990 to
1994 it has slowly become fainter. We studied the microvariations in
two intervals at and 8.9.
AG Car : The lightcurve of this star showed a huge dip
during the time of observations. AG Car varied from
to 8.0 between 1982 and 1985. Between 1985 and
1990, when the star was in this minimum, it showed clear
microvariations. In late 1989 the star started to become brighter
again. In early 1994 it had reached again. We
studied the microvariations in three intervals during visual minimum.
The intervals chosen for the study of the microvariations are
listed in Table 3. Column 2 gives the interval-number that will
be used later to indicate the interval. Column 3 gives the duration of
the interval. The mean absolute visual magnitude in the interval is
listed in Column 4. Column 5 gives the number of photometric
observations in each interval.
Table 3. Intervals of microvariations
© European Southern Observatory (ESO) 1998
Online publication: June 18, 1998