Friday, January 13, 2012

Entry #4: A method for blocking the light of a star for long-term exposures of a particular system

Capturing images of exoplanets has been a long, sought after goal for astronomers. Until very recently, when Rolf Olsen was able to capture a planet forming disc around a Beta Pictoris, the possibility of amateur astronomers being able to block out enough light from a star to capture any orbiting material had been extremely slight.  He followed a method described in a paper titled, "Observation of the Central Part of the Beta-Pictoris Disk with an Anti-Blooming CCD" as he notes,
"I followed the technique described in the paper above, which basically consists of imaging Beta and then taking another image of a similar reference star under the same conditions. The two images are subtracted from each other to eliminate the stellar glare, and the dust disc should then hopefully reveal itself."
This method, while producing an incredible result, has numerous flaws, including multiple unknown conditions that could produce a false result. As such, a method that is both relatively inexpensive, and accessible, is a necessity in going forward, with the ever-expanding archive of discovered exoplanets.
Two readily available technologies exist that include precision control and are able to pass incoming light.  These two considerations are obviously absolutely necessary for such a system but each method has considerable drawbacks that must be considered carefully.

Method 1 - DLP: DLP chips operate by actuating microscopic mirrors to direct of deflect light. A high resolution chip may be used in place of a right-angle mirror piece.  Once attached to a computer, a simple image application may be used to control the device.
+ :  very high contrast, obvious placement in optical assembly, does not diminish the final picture
 - :  requires an expensive high resolution chip, possibly limited angular resolution

Method 2 - LCD: LCD panels pass light through opposing polarizing filters by twisting the light path through a liquid crystal cell. If the cell remains untwisted, the polarizing filters will block most of the light from passing.  Using a high resolution panel in front of the primary objective would allow precise control over the light which is blocked.
+ :  potentially cheaper option
 - :  likely to be heavier/more invasive, lower contrast potential, screen door effect is likely to diminish visual quality and produce numerous artifacts