The Sun

Jeff Kuhn

Solar Oblateness

Jeff Kuhn works from the Institute for Astronomy on Maui. His solar research focuses on global solar properties determined from space observations, and solar and coronal magnetism measurements obtained from infrared spectropolarimetry, particularly by using the Daniel K. Inouye Solar Telescope (DKIST) and the cryonirsp instrument which he is responsible for delivering to the telescope for first-light measurements.

Dr. Kuhn uses precise space solar astrometry to measure the solar oblateness, and to understand its implications for the solar cycle. More recently his group on Maui showed that the solar radiative flux can slow down the solar rotation in the outer 100km of the photosphere. This “photon drag” affects the near-surface magnetism also and has implications for the helioseismically derived solar interior rotation. The figure below shows exaggerated measurements of waves observed by the Solar Dynamics Observatory/Helioseismic and Magnetic Imager that reveal the near-surface slowdown caused by Poynting-Robertson, “photon-drag”

Shadia Habbal

Solar Eclipses

Shadia Habbal has continued to lead eclipse expeditions with her team, the Solar Wind Sherpas, since joining the IfA in early 2005. The 2006 eclipse in Libya, led to the first image of the corona in Fe XI 789.2 nm emission. It led to the discovery of the importance of coronal forbidden lines, not only for the inference of the distribution of the electron temperature in the corona, but also to the realization that these lines provided very rich diagnostic tools for exploring the physics of the corona. One of the tools that has been recently implemented in a comprehensive manner by Graduate Student Ben Boe, is the first empirical inference of the freeze-in distance of ions in the inner corona.
The observations carried out by her team consist of imaging in broadband white light, and in narrow band filters centered on the wavelengths of known coronal emission lines. In 2015, the group successfully acquired high resolution spectra of the coronal emission spanning a field of view spanning 2 Solar Radii in the E-W direction, and 6 Solar Radii in the N-S direction. The observations led to the detection of Doppler shifts exceeding 1000 km/s associated with a coronal mass ejection (CME) front. More importantly, the spectra also revealed the presence of cool inclusions (at 10^4 to 10^5 K) emission of material characteristic of prominences streaming away from the Sun, in tandem with the hot CME material. This discovery resolved the puzzling finding of neutrals and low-ionization state ions in interplanetary space. The 2017 eclipse spectroscopic observations also detected two CME fronts, with cool inclusions as well, thus not only confirming the 2015 results, but more importantly indicating that cool inclusions of prominence material escaping from the Sun within a CME front, are rather common.

The Solar Wind Sherpas team is the only one world-wide that continues to yield unique coronal data, untenable from any other platform currently available, whether from the ground or space. The team’s observations are currently playing a major role in the planning of the upcoming first light observations with DKIST.

Xudong Sun

Magnetic Field and Space Weather

Xudong Sun studies the magnetic field of our own star, the Sun. By combining state-of-the-art remote-sensing observations and numerical models, he and his collaborators are trying to understand its complex dynamics to fine details. As magnetic field directly powers solar storms, their results will help improve the predicting capability of space weather disturbances.

Institute for Astronomy