In memory of Robert Alexander Rankin, 27.X.1915Rankin, 27.X. -27.I.2001 0. Introduction. In [5] we gave a partial solution to a problem of Rankin [8] on the behaviour of the Fourier coefficients of a special family of cusp-forms introduced by Hecke. Our purpose in this paper is to extend and refine the methods of [5]. One consequence of this will be a complete solution of Rankin's problem. To explain our new results we adhere to the notation and terminology of [5]. Let K be a number field, [K : Q] = κ, 2 ≤ κ < ∞, and let χ be a normalised Grössencharakter of K. For n ∈ N let T (n, χ) = χ(a), the sum being over all integral ideals a in K with absolute norm N a = n. In the present context, the most important result in [5] is the asymptotic formulaHere β is any fixed positive number, while A(χ, β), c(χ, β) and γ(χ, β) are positive constants depending only on χ and β. In fact, we showed that (0.1) holds with γ(χ, β) ≥ min{1, β/2}; in §1 this will be improved to γ(χ, β) ≥ min{1, β}. Unfortunately we were not able in [5] to give an explicit expression for c(χ, β), although we were able to prove the existence of a unique upper-semicontinuous probability distribution functionHere M (0−, χ) = 0 and M (κ 2 , χ) = 1. In particular M (t, χ) is compactly supported, and so, by classical Hausdorff moment theory [2], it is uniquely determined if, for example, we know the values c(χ, k) for all k ∈ N, or even just for a subset of k ∈ N with k −1 = ∞.