Non-Periodic Phenomena in Variable Stars 

                                 IAU Colloquium, Budapest, 1968



             HD 160202 - AN EARLY-TYPE FLARE STAR 

                        GUSTAV A. BAKOS
                      University of Waterloo 
                    Waterloo, Ontario, Canada


  In the course of a search for variable stars in the galactic cluster NGC 
6405 (M6) it was found that the brightest star of the cluster displayed what 
might be described as a flare.
  On July 3, 1965, in the course of a five-hour continuous observing with 
the image orthicon system of the Organ Mountain Station, about 20 minutes 
after the start the star brightened by about two magnitudes followed by another
outburst of seven magnitudes 30 minutes later. After the flare subsided the 
star remained at its pre-flare brightness for the rest of the observing period.
A graphical representation of the phenomenon is shown in Fig. 1. In this 
diagram a straight line was drawn between points of observations taken at 
five-minute intervals.
  There might be some uncertainty in the brightness of the second flare since 
it represents an extrapolation of the calibration curve over a range of five 
magnitudes. The photometric properties of the image orthicon tube indicate, 
however, that this uncertainty should not exceed +-1 magnitude.
  After the discovery of the flare an investigation showed that the following 
facts are known about the star:
  The cluster, including the flare star, was observed photoelectrically by 
Rohlfs, Schrick and Stock in 1957 and again in 1960 and 1961 by Eggen and 
Talbert respectively. During this period the star showed a small variation in 
brightness as seen from the following tabulation:

       1957, Rohlfs, etc. V = 6.76 mag   B - V = 0.04 mag
       1960, Eggen            6.63              -0.03
       1961, Talbert          6.75              -0.01

  In 1962 the cluster was observed by means of the image orthicon tube 
at Organ on two nights, namely on May 10 and August 13. On both nights 
the star appeared at a brightness of V = 6.75 mag. On the other hand, in 
1963 fluctuations were observed as follows:

             June 18, 1963         V = 7.25 mag
             June 24                   9.50
             July 2                    6.75
             July 14                   8.00

The estimated mean error of these observations is 0.25 mag. During 1964 and 
1965 the brightness of the star fluctuated between 8th and 9th magnitude except 
for the brief flare-up on July 3, 1965. It is remarkable, however, that after 
the flare the star remained at a constant brightness of 8th mag for 4 1/2 hours 
of observing time.




                             Fig. 1


  Recent photoelectric observations of the star by the writer made in 
July and August of 1968 showed a constant brightness of V = 6.75 on 14 
nights.
  The spectral type of HD 160202 is found in the literature to vary from 
B1ne to B5 and B8. Apparently there are no high dispersion spectrograms 
available.
  Although flares of the type described are not common among early 
type stars, as an hypothesis it is suggested that the star, because of its ne 
characteristic, might be a shell-producing star whose shell, or its part, gets 
occasionally blown off. If this process is periodic at all, the periodicity might
be of the order of 5-6 years.