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Pluto/Triton occultations Young et al. Pluto and Triton: observing their evolving atmospheres with stellar occultations: Facilities and Equipment Laboratory Southwest Research Institute in Boulder has an optics lab suitable for maintaining the Portable High-speed Occultation Telescope (PHOT) systems we propose to use. Clinical: Not applicable Animal: Not applicable Computer: Southwest Research Institute provides all of the computer equipment and support needed to conduct the intended research. Office Southwest Research Institute provides all of the library facilities and staff support needed to conduct the intended research, and a clean, safe area in which to store the two PHOT systems in use at SwRI Boulder. Other Not applicable MAJOR EQUIPMENT 1. Summary The Boulder office in Southwest Research Institute and with Lowell Observatory have been funded by NSF Major Research Instrumentation (MRI) to build four lightweight, portable 14" occultation systems that can be easily deployed to sites around the world. The Project Description is self-contained, and includes a summary of these systems. We repeat and elaborate on that description here. (Note that without the duplicated tables, the sum of the Project Description and this description of Major Instrumentation is still within 15 pages.) Our occultation systems will use high-speed, low-noise CCDs suitable for high-frame rate occultation observations. Our acronym for these systems is PHOT, for Portable High-speed Occultation Telescope. Development is underway; we received shipment of our cameras on November 11, 2003, on schedule for a useable system by summer of 2004. We expect the PHOT systems to have a useful lifespan of at least ten years. Facility and Equipment-1 Pluto/Triton occultations Young et al. 2. Performance The PHOT systems are being developed by Eliot Young (SwRI), Leslie Young (SwRI), and Ted Dunham (Lowell), each of who has helped design and operate stellar occultation systems for more than a decade, and understand the unique requirements that stellar occultations place on telescopes and cameras. The requirements on a stellar occultation system are summarized in Table 1. Table 1: System performance of the Portable High-speed Occultation Telescopes (PHOT) Component Frame rate Dead time Full field of view Pixel scale Subframe size Timing knowledge Storage capacity Deployability Ease of setup Sensitivity Requirements 1-20 Hz (5-1000 ms/frame) < 10% of frame rate 1-20 arcmin 0.5-1.0 arcsec/pixel 30-200 pix 1 ms > 10 Gb Worldwide, <3 weeks lead time Observe < 1 h after 1st star acquisition Pluto: SNR=16 at 5 Hz KBO: SNR=10 at 1 Hz Centaur: SNR = 10 at 20 Hz Designed performance of PHOT 0.4-200 Hz <0.01% of frame rate 6 arcmin 0.75 arcsec/pixel 1-512 pix < 0.001 ms 20 Gb 2 week lead time typical 20 min setup typical Pluto at V< 14.3 KBO at V<17.4 Centaur atV<14.2 High frame rates are needed in order to derive vertical profiles of temperature and pressure from an atmospheric occultation or to resolve narrow features like jets. We determined the frame rate achievable on the Roper Instruments 512BFT camera with the existing WinView software is 7 Hz for a 64 x 64 subframe. Our planned and budgeted custom software will require the minimum number of parallel and serial shifts and will be limited by the digitization rate. We will achieve frame rates of 25 Hz for a 64 x 64 box at the slow digitization rate of 100 kHz (with 3.1 electron read noise), and over 200 Hz frame rate at the fast digitization rate of 1 MHz (11.8 electron read noise). The pixel smear caused by image rotation with our alt-az mount is less than 1/10 of a pixel if we maintain frame rates faster than 0.4 Hz. Dead time needs to be minimized for photometric fidelity. Atmospheric occultations are often characterized by "spikes," or local refocusing of the stellar flux by small density fluctuations in the occulting atmosphere. If the dead time is larger than 10%, then these spikes may not get recorded, degrading the photometric interpretation of the occultation lightcurve. The dead time per frame is dominated by the serial transfer rate, and is only 600 ns to shift all 512 rows to the serial register. The full field of view should be relatively large to help identify star fields. Pixel scales of 0.5 -1.0 arcsec are a good compromise: much larger pixels lead to object confusion and excessive background contamination, while much smaller pixels give unnecessarily large read noise and data volumes. Occultations are typically run with small sub frames sizes to increase frame rates. Typical subframes range from 30x30 pixels to 200x200 pixels, and are sized to allow good subtraction of sky background. The full field of view for the 6.7-mm area of the 512BFT array is 6.4 arcmin for the 3.556 meter focal length of the Meade 14" LX200-GPS telescope, and the pixel scale for the 512BFT's 13-micron pixels is 0.75 arcsec. Both the existing WinView and planned PVCam software will allow the specification of multiple subframes of any size from a single pixel to the full array, surpassing our requirement of subframes ranging from 30 to 200 pixels. Facility and Equipment-2 Pluto/Triton occultations Young et al. To know the timing of a given frame to 20% at the fastest frame rate (5 ms/frame) requires a timing knowledge of 1 ms. The timing knowledge of the 1 PPS - 1 million PPS (pulse per second) output of the Trak 8821A GPS is specified to be within one microsecond of Coordinated Universal Time (UTC). The computer needs enough storage capacity for an event's data, to ensure data is archived properly. A 30-minute occultation at 20 Hz will produce 36000 frames. For 128x128 pixel subframes (32 kilobytes per frame), this requires 1.1 gigabytes of storage. Test runs will be made for each event, which increases the storage requirements by a factor of roughly 10. The storage capacity of the Latitude C840 computer is 20 Gb, providing room for programs and system files, and 10 Gb of data storage. The new system will be designed easy deployability, since frequent use provides a large scientific return on the investment of hardware. Since salaries associated with travel and preparation are a major factor in the cost of observing occultations with current occultation systems, decreasing the preparation time allows more occultations to be observed on the same budget. The lead time for preparing and shipping the PHOT systems should be typically less than two weeks, based on our recent experiences and our plans to include a local expert on import/export regulations. Ease of setup will increase the number of occultations observed. Many occultations occur at difficult observing circumstances: shortly after sunset, shortly after the object has risen above the horizon, or during breaks in cloudy weather. In these cases, the ability to set up the telescope and acquire the field soon after stars are detectable can make the difference between an excellent data set and a complete loss of the event. The setup time for the Meade LX200-GPS systems is notoriously short, and we conservatively estimate 20 minutes between acquiring the first bright star and taking data on the occultation objects. The sensitivity requirements depend on the scientific goal. The required SNR and frame rates for each type of occultation were discussed above in the context of Pluto, KBO or centaur occultations. We recap these SNR requirements here for the three cases, and discuss the expected number of events per year by sufficiently bright stars. Compared with the PCCD system. The PHOT system allows our science goals to be met with stars that are 1.4 mags fainter (3.6 times fainter) for observing Pluto's changing atmosphere and 1.1 mags fainter (2.7 times fainter) for measuring KBO shapes and sizes. The importance of low read noise is most evident in the highspeed observations of centaurs, where the PHOT systems can go 2.2 mags fainter (7.6 times fainter) than the PCCD systems. This dramatically increases the number of events observable. 3. Design Table 2 summarizes the planned PHOT system. The telescope will be a 14" with a computercontrolled Alt-Az mount. The detector is a high-speed, low-noise frame transfer array with an active area of 512 x 512 pixels. This CCD is run from a laptop, and probably will include a dock to house a full-size PCI card to control the CCD. A GPS-referenced clock will generate an accurate external time sync to trigger the CCD. This GPS unit may be a PCMCIA card in the laptop, although our default choice is a stand-alone unit from Trak that produces accurate 1 Hz and 1 MHz pulses. Facility and Equipment-3 Pluto/Triton occultations Young et al. Table 2. Baseline design of PHOT Manufacturer Meade Roper Scientific Dell Computer Trak National Instruments Clear Night Products Various Atlas Cases Component Telescope Camera Laptop GPS clock Timing card Wind screen Field kit Shipping cases Items(s) 14" LX200GPS MicroMAX-512BFT Latitude C840 8821A-12 NI PXI-6602 Teledome Various 3 custom cases Newer telescopes have higher throughput than the Celestron 14 inch telescopes used for PCCD, especially with high transmission coatings. Also, most observers have stories about close calls or missed occultations that could have been averted with help from a GPS-assisted, computer-controlled mount. Of the half-dozen CCD vendors we contacted, only Roper Scientific has frame-transfer detectors that had low read noise, thermo-electric cooling of the CCDs, and PCI-card connections to the host laptop computer that can handle the necessary frame rates. We have purchased the "512BFT" CCD from Roper Scientific, where B means "back illuminated" and FT means "frame transfer." The array has 1024 rows and 512 columns, but only a 512 x 512 area is used for imaging; the other 512 x 512 region is used for reading out the previous image while an exposure is taking place. Tests at SwRI Boulder show this camera has a readnoise of 3.1 electrons at 100 KHz, much lower than the read noise of around 12 to 15 electrons per pixel for the decade-old PCCD occultation camera. The Roper Scientific CCDs can be triggered from an external TTL signal generated by the 1-MHz output of a GPS receiver, processed by counters on a timing card. For use in the field, we will use a windscreen to decrease windshake (a problem, for example, with the Chillagoe observations of T176). A field kit will include tools and materials needed for assembly and minor repairs. We have asked Atlas Case Corporation (http://www.atlascases.com) for quotes on foam-filled cases made of 1/4" ply/fiberglass laminate cases for the Optical Tube Assembly (OTA), the fork mount, and the CCD camera and electronics (3 separate cases). Not only will the cases facilitate safe air transit of equipment, they will permit two observers to load each case into rental cars or vans. OTHER RESOURCES: For this program to be feasible, we must be able to get the equipment to the desired location. Since the events of Sept. 11th, shipping or traveling with certain technologies has been restricted, and is prohibited to some destinations. Advance planning is necessary to get the correct licenses and documentation, in order to prevent transportation delays. To address these concerns, we have an SwRI consultant available to evaluate and classify our equipment, and then to review the import/export restrictions on the equipment prior to making travel plans. For each occultation we will review the planned destination against the most current government regulations (since the restrictions are constantly changing with world events). Facility and Equipment-4