COMMISSION 27 OF THE I. A. U.
        INFORMATION BULLETIN ON VARIABLE STARS
                     NUMBER 326


                                Konkoly Observatory
                                Budapest
                                1969 February 7


         PROPOSALS TO FLARE STAR OBSERVERS


      With the rapid increase in both the number of 
observers and the quantity of flare observations which has
taken place in the last few years, several problems of
standardisation and homogenisation of observational data
have revealed themselves. It has become clear that the
existing, various ways of observing and of publishing
results cannot provide data suitable for future statistical
investigations.
      Drawing from the accumulated experience of many
observers, the 'Working group on flare stars' of Commission
27 would like to suggest that further work on UV Ceti-type
stars be based on the following considerations.
      1) Photoelectric monitoring should be carried out
in one of the standard UBV spectral bands (c.f. Johnson, H.L.
1955, Ann.d'ap., 18, p. 292) within a closely-matched photometric
system. Multi-colour observations of flares are most
desirable, but continuous monitoring should be done bearing
in mind that the effectiveness of flare detection increases
towards shorter wavelengths.
      2) In order to study the slow (secondary) and
possibly secular light variations it is necessary to 
determine differential magnitudes and colours of the flare
stars with respect to one, or better two comparison stars
in the proximity. It is felt that this additional information
on secondary variation is well worth the slight loss
of monitoring time. The following comparison stars are 
suggested to improve the combining of results from different
observers.

      YZ CMi  Stars a and c (BD +3d1783) in I.B.V.S.
           No. 265, 1968.
      AD Leo   Companion star at 1.7' N. See I.B.V.S.
           No. 307, 1968.
      UV Cet Stars d and e in Ap.J. Vol. 109, p. 534, 1949.
  V 1216 Sag Stars d and e in I.B.V.S. No. 273, 1968.


Whilst the colours of some of these comparison stars do not
closely match the flare stars the possible variability of
the redder stars makes them somewhat less suitable. Details
of mirror-photomultiplier-filter combinations, and 
transformation equations from instrumental to standard system,
when applied, should be stated.

      3) Data on monitoring should include, whenever
possible:

      a) The date and Universal time of the star and end
of effective coverage given in tabular form, noting all 
interruptions of more than one minute.

      b) The standard deviation of random noise fluctuations,
typical of the night or series of nights, given in
magnitude form,

             sigma (mag) = -2.5 log (abs(sigma)/I_0)

where I_0 is the intensity deflection (less sky) of the
quiet star.

      The sampling time interval for sigma should be that
used throughout for the detection of small flares. The 
detection criterion is normally given by the 3-sigma rule.

      c) A limiting magnitude for flare detection in the
UBV spectral bands, defined with sufficient accuracy by,

             m_lim = m_0 - 2.5 log ((abs(3 sigma))/I_0)

                 = m_0 + sigma(mag) - 1.19


where m_0 is the mean apparent magnitude of the quiet star
in the UBV system for the night or series of nights, for
each filter.

      4) The following standardised data on flares is
also requested:
      a) The date and Universal time of flare maximum.
      b) The durations before and after maximum in the
spectral band used for monitoring for all flares exceeding
3sigma deviation at maximum. Difficulties are frequently 
experienced here and individual treatment is almost inevitable.
It is suggested that pre-flares be omitted and that
the duration on the primary rising branch be given. The
greatest difficulty is met with on the descending branch,
particularly when the star does not return to normal brightness.
It should be stressed that the quoted duration after
maximum need only be an indication, and cannot be a 
satisfactory time scale for large and small flares alike, and
for flares of differing forms.

     c) The standard deviations (as 3b) near all flares
in each spectral band in which the flare is observed, using
the same sampling procedure as in the general detection.

     d) The maximum intensity in the magnitude scale
approximately in the UBV system, in each spectral band if
possible, as defined by,


      m_f = m_0 - 2.5  log (I_0+f - I_0)/I_0

where I_0+f is the total intensity deflection (less sky) of
star plus flare at maximum. It should be noted that statistical
investigations in which the valued Delta m have been used
may be strongly affected by the observational selection;
therefore it is desirable to express the measured fluxes of
flares in stellar magnitude (or in absolute units).

     e) The integrated intensity (in minutes) of each
flare over the total duration, including pre-flare if 
present, as given by,

            P = Integral (I_0+f - I_0) /I_0 dt

     f) The light curves in relative intensity units (as
indicated in the integral or all observed flares. 
Sufficient time resolution should be employed to retain all
reasonable detail as dictated by the study of standard 
deviations and the time constant of the equipment.
     g) The air mass (or secant of zenith distance) at
the time of all flares, together with remarks on sky 
conditions including seeing and moonlight, to aid in the
weighting of suspected flares.


     A.D. ANDREWS       P.F. CHUGAINOV, R.E. GERSHBERG
  Armagh Observatory       Crimean Observatory

                 V.S. OSKANIAN
               Burakan Observatory