JOP156 Multi-Spectral Solar Telescope Array III D. Martinez-Galarce, P. Scherrer, P. Boerner Coordinated campaign with TRACE, SoHO, the MSSTA rocket, and ground-based observatories Received: March 14, 2002 --GOALS-- The Multi-Spectral Solar Telescope Array rocket is scheduled for launch on 10 April, 2002. The MSSTA is an observatory that uses an array of multilayer telescopes to probe the structure and dynamics of the solar atmosphere. The flight configuration consists of 12 telescopes, each of which will image the full solar disk with spatial resolution of ~1 arc-second. Each instrument's bandpass is tuned to one or more strong emission lines. The MSSTA will produce a powerful dataset of high-resolution full-disk spectroheliograms. The expected dataset is summarized below: Wavelength Ion T_Formation Resolution 57.9 Mg X 1.0 MK 5 arc-sec 98.3 Ne VIII 0.5 MK 5 arc-sec 131 Fe VIII/Fe XX 0.7MK/8MK 5 arc-sec 150.1 O VI/NiXII/XIII 0.4MK/1.3MK 1 arc-sec 171 Fe IX/X 1 MK 2 arc-sec 180 Fe XI 1.2 MK 2 arc-sec 195 Fe XII 1.5 MK 1 arc-sec 211 Fe XIV 2 MK 1 arc-sec 256 He II 0.08 MK 1 arc-sec 1216 H Ly a 0.02 MK 1 arc-sec 1550 C IV/UV cont 0.1 MK/4000 K 1 arc-sec (* 93.9 Fe XVIII 6.5 MK 5 arc-sec*) All images will be recorded on photographic film, allowing the field of view to span from the center of the solar disk out to 5-15 solar radii. All will be photometrically calibrated. While the spectral resolution of the MSSTA telescopes is insufficient to measure velocities or most line ratios, the MSSTA data will allow modeling of local and global emission measure as well as cross-calibration of other EUV observatories (especially TRACE and EIT). --PLAN-- TRACE In order to maximize the utility of the MSSTA data in cross-calibration with TRACE, we would like full-disk mosaics taken in as many as possible of TRACE's EUV bandpasses, as well as 1216 and 1550, within a few hours of flight. During flight, we would like high-cadence 171 Ê observations of a prominent active region, with images of the same region in all bandpasses before and after the start of the high-cadence observations. We would also like a series of deep observations of a quiet region in multiple bands taken as close to the flight window as other requirements allow. EIT: Full disk images in 304, 284, 171 and 195 before, during and after flight. MDI (added by SOHO SOC): Full disk magnetograms and dopplergrams at a one minute cadence. Yohkoh: Full-disk SXT images, or partial-frame images of bright active region. CDS: CDS will coordinate with TRACE and perform a raster with good spectral information over a square region during the flight. OTHER Observatories: The dataset's relevance to the chromosphere and photosphere would be enhanced by obtaining full-disk ground based observations in white light, H alpha, and Ca K, as well as full-disk magnetograms, as close to the time of flight as possible. --PROPERTIES OF MSSTA DATA-- Spatial Resolution: Using the 3500mm focal length Ritchey-Chretien systems and high-resolution 649 film, the MSSTA is, in principle, capable of spatial resolution around 0.3 arc-seconds across the solar disk. The shorter-focus telescopes and coarser-grained XUV-100 film are still capable of imaging at around 1 arc-second resolution. Our past experience with the MSSTA suggests that the low signal-to-noise ratio at high spatial frequencies limits the useful resolution to a few (5-10) arc-seconds, although we hope to achieve sub-arc-second resolution with at least some of the MSSTA instruments. Spectral Resolution: The 9 EUV telescopes will have narrowband multiplayer coatings applied by Troy Barbee of Lawrence Livermore National Labs. The FWHM of the coating bandpasses varies (tending to increase with higher central wavelengths), but we expect values ~5 Ê, or E/dE ~ 30. This is generally sufficient to ensure that the image formed by each telescope is dominated by a single emission line (and thus that each image shows the distribution of plasma at a particular temperature). Notable exceptions are the 131 Ê Herschelian and the 150 Ê Ritchey-Chretien telescope. These bandpasses are centered on transition region lines (T ~ 400,000 or 600,000 K), but allow for a significant contribution from lines of highly-ionized nickel or iron on either side of the peak. The resulting spectroheliogram should be dominated by TR emission over most of the solar surface, with strong emission from the hot lines appearing over the active regions. Filtering the two components of the image, by subtraction of an Fe XII image (Fe XII emission should be highly correlated with Ni XI and XII emission) for example, may be possible. The FUV telescope optics and filters were prepared by the Acton Research Corporation; as a system (both mirror coatings and filters contribute to narrowing the bandpass) they have E/dE ~ 200. However, because there is a strong continuum in the neighborhood of the C IV line, the resulting spectroheliogram will be dominated by the emission of material much cooler than C IV. We do not have provisions to perform any continuum subtraction of the sort described by Handy et al for "purifying" TRACE C IV images. Time Resolution: The MSSTA data will more closely resemble portraits than movies. Because of the relatively modest aperture and low detector QE of the MSSTA instruments, exposure times of up to 200 seconds will be necessary to achieve high signal-to-noise spectroheliograms. This fact, coupled with the limit of ~350 seconds of useful observing time in flight, makes it difficult to attempt any high-cadence observations. Energy Calibration: Detailed calibration of all instruments will not be completed until after the flight. Based on our experience in calibrating the MSSTA telescopes and film at SSRL, we expect to be able to provide absolute flux calibration for all images accurate to ~25%. Field of View: The sensitivity of the MSSTA telescopes is sufficient to show some structure in the extended corona in longer exposures. Unlike in past MSSTA flights, each instrument will image onto a dedicated camera. Therefore, the unvignetted field of the telescopes ranges from 15 solar radii in diameter for the 1000 mm focal-length Herschelian telescopes to 4 solar radii for the 3500 mm Ritchey-Chretiens. However, the telescopes are optimized for recording the higher-flux emissions from on the disk.