Dominated by a single , large-amplitude pulsation mode , the rapidly-pulsating hot subdwarf B star CS 1246 is a prime candidate for a long-term O-C diagram study .
We collected nearly 400 hours of photometry with the PROMPT telescopes over a time span of 14 months to begin looking for secular variations in the pulse timings .
Interestingly , the O-C diagram is dominated by a strong sinusoidal pattern with a period of 14.1 days and an amplitude of 10.7 light-seconds .
Underneath this sine wave is a secular trend implying a decrease in the 371.7-s pulsational period of \dot { P } = -1.9 \times 10 ^ { -11 } , which we attribute to the evolution of the star through the H-R diagram .
The sinusoidal variation could be produced by the presence of a low-mass companion with m \sin i \simeq 0.12 M _ { \sun } orbiting the subdwarf B star at a distance of 20 R _ { \sun } .
Analysis of the combined light curve reveals the presence of a low-amplitude first harmonic to the main pulsation mode .