Recent Stellar Occultation Observations Using High‐Speed, Portable Camera Systems

We have recently constructed six observing systems identified as POETS (Portable Occultation Eclipse and Transit System[1]). These systems are optimized for (i) high‐speed, high signal‐to‐noise observations at visible wavelengths and (ii) easy transport, to allow mounting on telescopes worldwide. The Andor iXon cameras have e2v CCD97 (frame transfer) sensors: a $512×512$ array of 16‐micron pixels, back illuminated, with peak quantum efficiency $>90%.$ The maximum readout rate is 32 full frames per second, while binning and subframing can increase the cadence to a few hundred frames per second. Read noise in conventional modes goes below 6 electrons per pixel. Further, an electron‐multiplying mode can effectively reduce the read noise to sub‐electron levels, at the expense of dynamic range. The cameras are operated via a desktop computer that contains a 3 GHz Pentium 4 processor, 2 GB memory, and a 10,000 rpm hard disk. Images are triggered from a GPS receiver and have an approximately 50 nanosecond timing uncertainty. Each POETS can be transported as carry‐on luggage. Here, we present instrument details, along with recent results from their use in stellar occultation observations by small bodies in the outer solar system. Occultations can produce data of the highest spatial resolution for any Earth‐based observing method; therefore, they play a key role in determining diameters of distant solar‐system bodies and probing the structure of atmospheres at the microbar level. We discuss POETS deployments in 2005–2007 to observe stellar occultations by Charon and Pluto (on 0.6‐ to 6.5‐m telescopes) and future work on occultations by Kuiper Belt objects.