Advanced Technology Solar Telescope
Presiding: D G Socker, Naval Research Laboratory; M Weber, Harvard-Smithsonian Center for Astrophysics
SP34A-01 15:30h
Overview and Status Report on the Advanced Technology Solar Telescope
The ATST is a 4-m aperture, off-axis solar telescope with integrated adaptive optics, low-scattered light, infrared, coronagraphic, and polarimetric capabilities. It will resolve the essential, fine-scale magnetic features and their dynamics that dictate the varying release of energy from the Sun's atmosphere. The ATST design is optimized in terms of throughput, scattered light, and instrumental polarization properties to perform precision vector magnetic field measurements down to its diffraction limit (0.03 arcsec at 500 nm) and throughout the solar atmosphere. Its collecting area, which is a factor of 16 greater than today's solar telescopes, will provide the sensitivity to measure both weak fields and rapidly evolving stronger fields. It has a factor of 64 greater collecting area than the largest existing coronagraph, and will provide the sensitivity and coronagraphic capability needed to measure the weak, fine-scale coronal magnetic fields. With adaptive optics and a set of facility class instrumentation the ATST will be the worlds leading resource for studying solar magnetism. ATST will be the successor to the solar telescopes built in the 1960s and 1970s, and is a natural complement to planned space missions. Starting in late 2001, ATST began a design and development phase. To date the D&D phase has produced and refined a science requirements document and a conceptual design that would meet those requirements. A conceptual design review was held in August of 2003. Following the review, a construction proposal, including a complete work breakdown structure and cost, was submitted in early 2004 and was successfully peer reviewed. NSF astronomy is now in the process of submitting ATST to the NSF Major Research Equipment and Facilities Construction program review process. During the D&D phase, a thorough site survey was also conducted resulting in Haleakala as the site best able to fulfill the ATST science requirements. We present a brief overview of the ATST program, how it fits into the broader picture of solar facilities and capabilities, and discuss the current status of the ATST project and plans for constructing and commissioning the ATST.
http://atst.nso.edu
SP34A-02 15:45h
Design of the Advanced Technology Solar Telescope
The ATST is a 4-m aperture, off-axis solar telescope with integrated adaptive optics, low-scattered light, infrared, coronagraphic, and polarimetric capabilities. We present an overview of the ATST design. The ATST design has progressed in to the point where the project is ready to lead contracts for construction of major subsystems. These subsystems include the enclosure, the telescope mount assembly, and the primary and secondary mirror assemblies. We summarize the design concepts of the major telescope components. Thermal control of telescope structure and optical components to ambient temperature has been a major design focus. Where applicable, the conditions at the selected site, Haleakala, have been worked into the designs. The design of the wavefront control system that integrates telescope alignment functions, active control of the primary and high order adaptive optics will be summarized. A vigorous systems engineering approach has been implemented to ensure that the telescope will deliver the diffraction limited imaging performance specified in the Science Requirements Document.
http://atst.nso.edu
SP34A-03 16:00h
First-Light Instrumentation for the Advanced Technology Solar Telescope
The 4m Advanced Technology Solar Telescope (ATST) is the next generation ground based solar telescope. In this paper we provide an overview of the ATST post-focus instrumentation. The majority of ATST instrumentation is located in an instrument Coude lab facility, where a rotating platform provides image de-rotation. A high order adaptive optics system delivers a corrected beam to the Coude lab facility. Alternatively, instruments can be mounted at the Nasmyth focus. For example, instruments for observing the faint corona preferably will be mounted at Nasmyth where maximum throughput is achieved. In addition, the Nasmyth focus has minimum telescope polarization and minimum stray light. We give an overview of the initial set of first generation instruments: the Visible-Light Broadband Imager (VLBI), the Visible Spectro-Polarimeter (ViSP), the Near-IR Spectro-Polarimeter (NIRSP), which includes a coronal module, and the Visible Tunable Filter. We also discuss the unique and efficient approach to the ATST instrumentation, which builds on the use of common components such as detector systems, polarimetry packages and various opto-mechanical components. For example, the science requirement for polarimetric sensitivity (10-5 relative to intensity) and accuracy (5'10-4 relative to intensity) place strong constraints on the polarization analysis and calibration units. Consequently, these systems are provided at the facility level, rather than making it part of the requirement for each instrument.
http://atst.nso.edu/
SP34A-04 16:15h
The ATST Site Survey
The Advanced Technology Solar Telescope (ATST) will be the world's largest aperture solar telescope, and is being designed for high resolution, IR, and coronal research. It must be located at a site that maximizes the scientific return of this substantial investment. We present the instrumentation, analysis and results of the ATST site survey. Two instrumentation sets were deployed at each of six sites to measure seeing as a function of height, and sky brightness as a function of wavelength and off-limb position. Analysis software was developed to estimate the structure function Cn2 as a function of height near the ground, and the results were verified by comparison with in-situ measurements. Additional software was developed to estimate the sky brightness. The statistics of the conditions at the sites were corrected for observing habits and the annualized hours of specific observing conditions were estimated. These results were used to identify three excellent sites suitable to host the ATST: Haleakala, Big Bear and La Palma. Among them, Haleakala is proposed as the optimal location of the ATST, La Palma and Big Bear being viable alternative sites.
http://atst.nso.edu/site/
SP34A-05 16:30h
Triple Fabry-Perot Imaging Interferometer for High Resolution Solar Spectroscopy using the ATST
We present a telecenrically mounted triple Fabry-Perot imaging interferometer for the NSOs Advanced Technology Solar Telescope (ATST). It consists of three Fabry-Perot etalons and the feed and imaging optics. This system provides high throughput, flexibility and breadth of operation when compared to other spectroscopic imaging systems. It can operate in four distinct modes: as a spectro-polarimeter, a filter-vector magnetograph, an intermediate-band imager, and broadband high-resolution imager. In the proposed telecentric mount configuration, the transmittance of the etalon system is not a function of position in the field, so that instantaneous spectroscopic measurements can be performed across the entire field of view; however, the transmission peak of the interferometer is broadened. Mitigation of this broadening requires a low F&35; image at the etalons. Together with the requirement that the field of view be large enough to observe large-scale processes in the solar atmosphere, this limitation dictates that the diameter of the etalons have a large aperture. Specifically, for a spectrographic passband full-width at half-maximum (FWHM) of around 2 pm, and entrance pupil diameter of 4 m, and a field of view of 35", the required etalon diameter is around 200 mm. This is beyond the size of current Fabry-Perot etalons and near the current projected limit of manufacturability. The development of this instrument will bring these large etalons to realization and take Fabry-Perot imaging interferometry to the next level of operational capability within telescopes of large aperture. This instrument will provide spectral, spatial, and temporal resolution which is not currently available to large aperture solar astronomy, but which is necessary, in conjunction with the new class telescopes, to the continuing discovery of laws that govern the dynamics of the sun and the earth-sun connection. The resolution afforded by higher aperture telescopes and instrumentation will give scientists new insight into the magnetohydrodynamic processes occurring on the Sun via simultaneous spectral and spatial measurements across the entire field of view. We will describe the optical train supporting the filter system and the expected imaging performance. We will analyze the effects of spectral resolution of the instrument due etalon spacing parameters, optical configuration, and the plate defect finesse. We present calculations of the pupil apodization for three modes of operation and the consequences for the imaging and spectroscopic performance of the system; and a treatment of noise contributions from the parasitic off-band spectral orders and ghost images arising from multiple reflections within the etalon system.