COMMISSION 27 OF THE I. A. U.
          INFORMATION BULLETIN ON VARIABLE STARS
                      Number 2694

                                    Konkoly Observatory
                                    Budapest
                                    26 March 1985

                                    HU ISSN 0374 - 0676


        HD 22403 : A NEW VARIABLE WITH CaII H AND K EMISSION


   HD 22403 (BD + 25d580) is a single-lined spectroscopic binary with strong
Ca II H and K emission. The orbital period is ~ 1.93 days and the spectral
type of the visible component is close to G2V (Carquillat et al., 1979). This
object was included in a photometric programme on late type emission binaries
to search for the type of photometric variability exhibited by most of the
binaries with G-K spectra with Ca II H and K emission.
   Observations of HD 22403 were made with the 34-cm Cassegrain reflector
of the Kavalur Observatory on 18 nights through standard B and V filters
during the period from 1980 November to 1981 February. All the measurements
were made with respect to the comparison star HD 22269 (BD + 27d529). As a
check on the constancy of the comparison, HD 22145 (BD + 26d572) was also
observed on all the nights of variable star observation. The mean differential 
magnitude and colour of the comparison with respect to the check star
(in the sense HD 22 145 - HD 22 269) obtained by us are DeltaV=1.010 +- 
0.003 and Delta(B-V) = -0.801 +- 0.002 .
   The photometric data collected by us showed a scatter of ~0.10 mag both
in V and B indicating that HD 22404 is definitely a variable. The Julian
days of the observations were converted into orbital phases using the 
following ephemeris:

          J.D.244 1926.590 + 1.9299395d E

where the initial epoch corresponds to the time of the periastron passage
and the period is the spectroscopic orbital period (Carquillat et al., 1979).
The differential magnitude and colour (in the sense HD 22 403 - HD 22 269) are
plotted against the orbital phases thus computed in Figure 1. Each point is
an average of 3-4 independent observations. The probable errors of the 
differential magnitude and colour are 0.012 and 0.010, respectively. Even though
the observations are spread over about 47 orbital periods, the data obtained
define a coherent light curve with little scatter. This implies that the
photometric period is either equal or very close to that of the binary orbital
period. As seen in Figure 1 the light curve is very asymmetric and the total

                               [FIGURE 1]

amplitude in V is ~ 0.09 mag. The Delta(B-V) values do not show any significant
correlation with the light variation but appear scattered about the mean
Delta(B-V) = -0.384 +- 0.002. From our photometric data we derived a mean (B-V) =
0.70 +- 0.01 for HD 22 403, consistent with the spectral type G2V assigned to
it by Carquillat et al. (1979).
  The nature of the light curve rules out geometrical eclipses as the cause
of the observed light variation. Probably, in HD 22 403 we are seeing the type
of 'activity' exhibited by the well known RS Canum Venaticorum and BY Draconis
variables, where the photometric variation is attributed to the presence of
'starspots' which rotationally modulate the observed flux.


                A.V. RAVEENDRAN, S. MOHIN and M.V. MEKKADEN
                   Indian Institute of Astrophysics
                     Bangalore - 560 034, India


Reference:

Carquillat, J.M., Nadal, R., Ginestel, N., Pedoussaut, A., 1979, Astron.
   Astrophys., 74, 113. [BIBCODE 1979A&A....74..113C ]