COMMISSION 27 OF THE I. A. U.
             INFORMATION BULLETIN ON VARIABLE STARS
                         Number 1927

                                	Konkoly Observatory
                                       	Budapest
                                 	1981 February 26

                                	HU ISSN 0374-0676



               HD 175742: A NEW RS CVn VARIABLE


  The 8.4m SB1 binary HD 175742 is known to display strong Ca II H & K
emission lines (Joy and Wilson 1949, Fekel 1980) and to have a variable
radial velocity (Wilson and Joy 1950). A spectroscopic orbital solution
recently has been published by Imbert (1979), who gives the period as
2.879395d, the primary spectral type as K0 V, and the secondary spectral
type between K5 V and M2 V. He also predicts the possibility of a partial
eclipse.
  The author observed HD 175742 photoelectrically on ten nights with
the 0.6 meter reflector at Dyer Observatory to look for optical variability.

	Hel. J.D.      Phase       DeltaV        DeltaB
      (2,444,500+)

	35.5800         0.1651p      0.229m      -0.556m
	36.5346          .4966        .156
	38.5914          .2109        .222
	45.5311          .6210        .153       -0.653
	49.5138          .0042        .217       -0.566
	50.5014          .3472        .218
	54.5072          .7384        .162
	55.5569          .1029        .233
	56.5096          .4338        .210
	69.4874         0.9410       0.204

BD +23d3497 was observed as a comparison star. The table gives nightly
means of the three differential magnitudes obtained each night.  Correction
has been made for differential extinction and transformation to the UBV
system, and Delta is in the sense variable minus comparison. The standard
deviation of the nightly measures was usually +-0.005m or less.  Phases
were computed with the ephemeris
	JD(hel.) = 2,443,677.045+ 2.879395d E,
where the epoch is Imbert's time of conjunction with the cooler star
in front.

                         [FIGURE 1]

   The nightly means in V are plotted versus orbital phase in the
figure and fit with the truncated Fourier series
   l = A_0 + A_1 cos Theta + A_2 cos 2Theta + B_1 sin Theta.
The resulting sine curve has an amplitude (maximum to minimum) of
DeltaV = 0.079m +- 0.012m and a minimum at phase 0.165p +- 0.023p.
   This roughly sinusoidal light variation is clearly evident with its
0.08m amplitude and is typical of the wave seen in most RS CVn binaries.
There is, however, no evidence of an eclipse near Imbert's time of
conjunction.     
   Further photometry is being planned to determine the photometric
period more precisely (to check for any migration of the wave through
the light curve) and to look for variations in the wave amplitude.
   The author acknowledges that this work was supported in part by
N.A.S.A. research grant NSG-7543.



                        GREGORY W. HENRY

                        Dyer Observatory
                      Vanderbilt University
                     Nashville, Tennessee 37235


References:

Fekel, F.C. 1980, private communication.
Imbert, M. 1979, A. A. Suppl. 38, 401. [BIBCODE 1979A&AS...38..401I ]
Joy, A.H. and Wilson, R.E. 1949, Ap. J. 109, 231. [BIBCODE 1949ApJ...109..231J ]
Wilson, R.E. and Joy, A.H. 1950, Ap. J. 111, 221. [BIBCODE 1950ApJ...111..221W ]