It is shown how erroneous results can occur using some period-finding methods, such as Fourier analysis, on data containing closely spaced frequencies. The frequency spacing accurately resolvable with data of length T is increased from the standard value of about lIT quoted in the literature to approximately 1.5/T.
A search for small-amplitude variability among members of old stellar populations reveals no variability >0 ,?1 01 among 15 metal-deficient or high-velocity F-and G-type subdwarfs, 13 old-disk main-sequence F stars, four cluster blue stragglers, and seven blue horizontal-branch field stars. Variability was detected in two A-type stars: A metal-deficient main-sequence A star, BDS 1269A = HD 15165 is shown to have 8 Scuti-like variability, and the variability of the high-velocity field blue straggler HD 100363 reported by Eggen (1971) is confirmed. The high-velocity sdAp star GD-210, a suspected variable, showed no amplitude > 0 ,p 017 for three hours.T eff and logg of ten high-velocity, short-period variables are similar to those of the 8 Scuti stars with Uff ^ 7800° K, although the low-mass variables in the sample probably do not share the same evolutionary history as the higher-mass field blue stragglers.
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