Tennessee State University will build a dedicated spectrograph for robotically tracking changes in the chromospheric activity of stars like the Sun. The Sun has a zone in its upper atmosphere, called the chromosphere, which is formed and heated by magnetic fields. The amount of emission of the hot gases in the chromosphere tells us how much magnetic field the Sun is generating in its internal dynamo. The magnetic field, and the resulting emission, varies on an 11-year cycle, but longer cycles have been documented. Space-based observations have shown that the Sun's total brightness changes somewhat over this 11-year cycle; historical data suggest it can change a great deal more over the longer cycle.
The observations made with the new spectrograph will document magnetic cycles in about 300 stars chosen to approximate conditions of the Sun in the past, present, and near future. In combination with precise photometry already being collected on TSU telescopes for these same stars, the new data will define the way magnetic activity changes the luminosity of Sun-like stars and predict how much the Sun itself should vary. The combined spectroscopic and photometric results will ultimately determine whether old stars like the Sun are cyclically variable and just what kind of magnetic cycles these old dwarf stars typically have, hence how typical is the Sun itself. They will determine how prevalent times of very low magnetic activity, such as the Sun's Maunder minimum of the 17th century, are in these stars. These observations will further define how the history of solar magnetism may have affected development of life on the Earth.
The spectrograph is designed with few moving parts and to be integrated into an existing 2-meter, automatic telescope. The spectrograph will measure chromospheric emission of ionized calcium in the near ultraviolet spectra of stars to about V=8 magnitude. Observing robotically, without human telescope operators, will make it possible to obtain more observations per star and to maintain the program more easily into the future. It should be possible to follow these stars for decades.
These data from TSU will ultimately give us a deep understanding of the level and timescales of changes in the Sun's output of total energy and magnetic field. This is crucially important for understanding just how much the Sun affects our climate and thereby our economy. The development of this instrument at TSU ,a small, historically black university, will advance ethnic diversity in science and engineering by involving African-American students in development and use of state-of-the-art instrumentation.
