U - B - V photometry of the spectroscopic-visual triple HD 165590

Abstract

HD 165590 is a visual binary (dG0 + dG5,P = 20.y25,e = 0.96) whoseA component is an SB1 double (dG5 + dM:P = 0.d88,e≈0.0). TheA pair (Aa +Ab) undergoes partial eclipses. PhotoelectricUBV photometry from Lines and one of the Automatic Photoelectric Telescopes, andV photometry from Scarfe are examined here. The data are from the 1977, 1984, 1985, and 1986 observing seasons. The non-eclipse light variations are analyzed with a FORTRAN program which does a sinusoidal curve fitvia least squares repeatedly to obtain the best period. Periods found from each observing season and passband are consistent with Boydet al. (1985): the greatest variations seem to be produced by a rotating (∼0.d88), spotted, G0 star (theAa component). To the residuals from the first analysis a further curve fit is made to determine characteristics of the wave due to the ellipticity effect. An early limit on the spectral type of the unseenAb component, based on the primary eclpse depth and the upper limit on the depth of the unseen secondary eclipse, is K2. Eclipse depths and widths seen here suggest that theA pair's inclination = 74.09 ± 10, close to theA +B inclination of 82.07 ± 20 (Battenet al., 1979). TheA pair's orbital period does not appear to vary, appearing instead to be well-described by a new linear ephemeris (Hel. J.D. = 2443665.4568 + 0.d8795045E) which does, however, take into account a variable light-travel-times as theA component orbits theA +B center of mass with a 20.y25 period. The maximum light-travel-time O-C thus produced is + /−8.m4 = + /−0.d0059.