Ultrahigh-resolution images of the solar chromosphere and corona using coordinated rocket and balloon observations

摘要

In 1989, we were selected by NASA to develop a comprehensive solar observatory, the Ultra-High Resolution XUV Spectroheliograph (UHRXS) for flight on space station Freedom. The principal UHRXS instruments were to be ten (10) multilayer Ritchey-Chretien telescopes able to obtain images in selected line multiplets, excited over the full range of temperatures present in the chromosphere and corona (4,500 K $LS T $LS 20,000,000 K), permitting the corona and chromosphere to be imaged with resolution approximately 0.1 arc second over fields of several arc minutes, and five (5) grating spectrographs able to resolve line profiles on spatial scales of 1 - 2 arc seconds. Over the past two years, fiscal constraints have caused NASA to defer the development of the UHRXS indefinitely, and to cancel or defer all the other planned high resolution solar space observatories, including the Orbiting Solar Laboratory. With the prospects for new initiatives limited to Small Explorers for the foreseeable future, we have explored the possibility of obtaining simultaneous ultra high resolution coronal and chromospheric observations by deploying coordinated rocket and balloon observatories simultaneously. We discuss the scientific objectives that can be addressed by simultaneous coronal/chromospheric observations with our rocket borne observatory, the Multi-Spectral Solar Telescope Array (MSSTA), and a new balloon borne observatory, which we call the Ultra-High Resolution Vacuum Ultraviolet Spectroheliograph (UHRVS). High altitude balloons can maintain payloads at altitudes of 40 - 45 kilometers for a period of several weeks. Such flights are practical from the Antarctic. It is possible to make observations from balloons over the spectral range from approximately 1850 angstroms - 3300 angstroms unimpeded by the atmosphere. This spectral range includes a number of chromospheric lines of great interest, including Mg II and Si III. We describe the proposed UHRVS observatory which will incorporate two instruments, a 65 cm aperture telescope with narrow band filters for high resolution photographic and photoelectric spectroheliograms; and a very high resolution ($lambda@/$delta$lambda $APGR 3 $MUL 10$+4$/) spectrograph which uses a 40 cm aperture telescope. The spectrograph and a large balloon gondola are already available. We also briefly review the capabilities of the MSSTA, and the joint UHRVS/MSSTA observing program that we envision.