Step 1: Formula / Definition}
\[
a^2 = \cos^2 \alpha, b^2 = \sin^2 \alpha, e^2 = 1 + \frac{b^2}{a^2} = 1 + \tan^2 \alpha = \sec^2 \alpha
\]
Step 2: Calculation / Simplification}
\(a = \cos \alpha, e = \sec \alpha\)
Foci: \((\pm ae, 0) = (\pm \cos \alpha \sec \alpha, 0) = (\pm 1, 0)\)
Abscissa of foci = \(\pm 1\), independent of \(\alpha\).
Step 3: Final Answer
\[
\text{Abscissa of foci}
\]