Dynamic range

Observations of the binary $\alpha$ Herculis were also obtained on the night of 2003 May 13. The brighter primary component saturated the detector, but it was possible to perform exposure selection on the faint companion (typically three magnitudes fainter, depending on the variable brightness of the primary component), as shown in Figure 3.36. The absence of significant scattered light from the bright companion emphasises the potential to perform high-dynamic range imaging given suitable camera performance. There is no evidence that the primary component is a $190$ $mas$ binary as suggested by McAlister et al. (1989), but this cannot be ruled out due to the detector saturation.

Figure 3.36: Lucky Exposures image of $\alpha$ Her using the faint component as the reference star. The best $1\%$ of exposures were selected, giving a Strehl of ratio of $0.24$ for the reference star. The bright component was saturated in the individual short exposures.