COMMISSION 27 OF THE I. A. U.
                    INFORMATION BULLETIN ON VARIABLE STARS
                                 Number 2479

                                                        Konkoly Observatory
                                                        Budapest
                                                        15 February 1984
                                                        HU ISSN 0374-0676



               ON THE PERIOD OF THE W UMa SYSTEM epsilon CrA


  Epsilon CrA was found to be a binary in 1950 by Cousins and Cox. Cousins (1964)
published a photographic light curve and reported a small variation of the
period. Knipe (1967) made observations with blue and yellow filters. (See
also measurements by Binnendijk, 1965.) The primary component of epsilon CrA is a
star of spectral class F5 and the secondary cooler component is of type G0.
This W UMa system is an A type one (transit at primary minimum).
  Since 1965, Tapia (1969) and Hernandez (1972) have published UBVRI 
observations obtained in 1967. Their observations are well represented by the 
following ephemeris:

         HJD_minI= 2,439,707.6619d + 0.5914264d E

Tapia concluded that the period had remained constant for 17 years.
 One of us carried out infrared observations of epsilon CrA at the ESO 1m 
telescope during the nights of July 2/3 and 3/4, 1982 (Lunel and Bergeat 1983).
The period of the system is somewhat over 14 hours. Hence a substantial part
of the cycle was covered each night, in a12 hours interval centered on the
meridian transit. The InSb photometer was used with a K-Band filter (2.2mu)
and gamma CrA was used as a comparison star. 140 individual observations were
obtained during the first night (of better photometric quality than the second
one). The observed minimum occured later than the epoch computed from Tapia`s
elements. We found

                     O-C = 0.0691d

Alternatively, the discrepancy could be explained if we accept for 1967-1982
a period larger than Tapia's, i.e. P = 0.5914345d.
  The difference is then 0.7s = 8*10^-6 d, well above the accuracy of +-10^-7 d
quoted by Tapia (1969). Here some doubt arises since his pinpointing of the
period on the 1950-1967 time basis relies on the early 1950 photographic 
observations published by Cousins (1964). Clearly more observations were needed.




  In 1983 uvby observations were made with the Danish 50 cm telescope at
ESO during the nights of June 22/23 and 23/24. Despite bad weather conditions
a primary minimum was determined from the observations in V, which confirm
the results of the infrared observations of 1982. The epoch of the minimum is
2,445,509.63d, resulting in

         O-C = 0.075d if Tapia's elements are used.

  Hence we are able to confirm the elements:


          HJD_minI  = 2,439,707.6619d + 0.5914345d E

as published by Lunel and Bergeat (1983).
  The authors' contention is that a period variation remains to be 
established. A regular monitoring of this system would be useful.





              J. MANFROID

              Institut d'Astrophysique
              B-4200 Cointe-Ougree
              Belgium

              M. LUNEL and J. BERGEAT
              Observatoire de Lyon
              F-69230 Saint-Genis-Laval
              France


              P. BOUCHET

              ESO
              Karl.-Schwarzschild-Strasse 2
              D-8046 Garching bei Munchen
              FRG





References:

Binnendijk L. 1965, 3rd Colloquium on Variable Stars, Bamberg, p. 36 [BIBCODE 1965VeBam..27...36B ]
Cousins A.W. and Cox A.N. 1950, MNASSA 9, 90 [BIBCODE 1950MNSSA...9...90C ]
Cousins A.W. 1964, MNASSA 23, 24 [BIBCODE 1964MNSSA..23...24C ]
Hernandez C.A. 1972, Astron.J. 77, 152 [BIBCODE 1972AJ.....77..152H ]
Knipe G.E. 1967, Rep.Obs.Johannesburg Circ. No. 7, 148 [BIBCODE 1967ROCi..126..148K ]
Lunel M. and Bergeat J. 1983, The Messenger 33, 19 [BIBCODE 1983Msngr..33...19L ]
Tapia S. 1969, Astron.J. 74, 533 [BIBCODE 1969AJ.....74..533T ]