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Astron. Astrophys. 335, 605-621 (1998)

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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 microvariations.

[FIGURE] 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 horizontal bars.

  1. R 71 : From 1975 until half 1979 the visual magnitude has dropped from about [FORMULA] 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.

  2. 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.

  3. 164 G Sco : The star showed a slow decrease in visual brightness from [FORMULA] to 6.8 between 1980 and 1985. The star remained faint at [FORMULA] 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 [FORMULA].

  4. S Dor : Intense observations started just before S Dor begun its moderate variation. Its visual brightness decreased from 1982 to 1985 from [FORMULA] 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 the minimum.

  5. R 127 : The star has slowly been rising to visual maximum from [FORMULA] in 1983 to 8.8 around 1990. From 1990 to 1994 it has slowly become fainter. We studied the microvariations in two intervals at [FORMULA] and 8.9.

  6. AG Car : The lightcurve of this star showed a huge dip during the time of observations. AG Car varied from [FORMULA] 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 [FORMULA] 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

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© European Southern Observatory (ESO) 1998

Online publication: June 18, 1998