COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                     Number 1975

                                   Konkoly Observatory
                                   Budapest
                                   1981 June 15

                                   HU ISSN 0374-0676


         ON THE PHOTOMETRIC PERIOD OF HD 81410


  HD 81410 is a single lined spectroscopic binary with K1 III
spectrum displaying strong CaII H and K emission and 'filled
Balmer lines' (Bidelman and MacConnell 1973, Eggen 1978). 
Photometric observations by Eggen (1973) in 1971 and 1972 confirmed
the suspected light variability of HD 81410. He quotes a 
photometric period of 25.4 day which satisfies the observations of
each season separately.
  HD 81410 was included in our photometric programme on late
type emission binaries mainly because very little is known about
this system. Observations were made with the 34-cm reflector of
the Kavalur Observatory on 34 nights, during 1981 January 3-March
14, through standard B and V filters. All measurements were made
with respect to the comparison HD 81904. As a check on the 
constancy of the comparison, HD 80991 was also observed. An 
unrefrigerated 1P21 together with the conventional d.c. setup was
used throughout.
  It was immediately understood that the present set of observations 
does not follow the period derived by Eggen. Our observations
indicated a period around 12.7 day. We tried a number of trial
periods and find that P = 12.86833 day fits the present as well
as Eggen's observations well. In the figure the visual magnitude
difference, HD 81410-HD 81904, is plotted against the photometric
phase computed using the above period. The time of the first
observation is taken as the initial epoch. We find that the light
curve has changed drastically since Eggen obtained the first light
curve during 1971-72. The amplitude of light variation has decreased
to ~ 0.15 from ~ 0.45 mag and the mean light level of the system has gone
up by ~ 0.10 mag.

                        [FIGURE 1]

  It appears that HD 81410 is a member of the RS CVn group of
binaries proposed by Hall (1976), where the photometric variation 
is attributed to the presence of 'starspots' which rotationally
modulate the observed flux. A detailed analysis of all the available
information, both spectroscopic and photometric, is in progress
and will be published elsewhere.

                     A.V. RAVEENDRAN, M.V. MEKKADEN
                            S. MOHIN
                     Indian Institute of Astrophysics
                     Bangalore 560034
                     India




References:
Bidelman, W.P. and MacConnell., D.J., 1973, Astr. J., 78, 687. [BIBCODE 1973AJ.....78..687B ]
Eggen, O.J., 1973, Publ.astr. Soc. Pacif., 85, 42. [BIBCODE 1973PASP...85...42E ]
Eggen, O.J., 1978, I.B.V.S. No. 1426.
Hall, D.S., 1976, IAU Colloquium No. 29. (Review papers) p. 287 [BIBCODE 1976ASSL...60..287H ]