LOREN W. ACTON Research Professor Office: Cobleigh Hall 418 Telephone: (406)994-6072 Fax: (406)994-4452 acton@physics.montana.edu

Dr. Loren Acton Department of Physics Montana State University PO BOX 173840 Bozeman, MT 59717-3840

The Sun provides an excellent astrophysical "laboratory" as it is a star like other stars -- only much closer. In many ways it is a "Rosetta Stone" of astronomy because what we learn from it provides a key to the understanding of much of cosmic physics. The sun is also the ultimate source of all of the life-giving energy on earth. The variability and activity of this star are responsible for terrestrial effects from the northern lights to climatic change. These matters are important for us to understand.

Dr. Acton oversees the solar physics group, which carries on an active research program under NASA support. They are actively involved in day-to-day operation and scientific utilization of the Japan/US/UK Yohkoh mission for studies of high-energy solar physics. This satellite carries a solar x-ray telescope, prepared under the leadership of Dr. Acton, for the study of high-energy processes, such as solar flares, on the sun. The primary emission of the extremely hot outer atmosphere of the sun, the solar corona, is at x-ray wavelengths and the extended duration, high resolution x-ray imagery from Yohkoh are being analyzed in an effort to learn why the sun has a corona at all and why it varies in intensity so strongly in response to the 11 year sunspot cycle.

Dr. Acton is also a co-investigator on the NASA Transition Region and Coronal Explorer (TRACE) mission which is scheduled for launch in 1997. This battery of 4 ultraviolet telescopes will provide new and detailed observations of the thin and dynamic interface region at the base of the corona. This region is also the source of much of the ionizing radiation that determines the properties of the upper atmosphere of the earth such as the ionosphere and ozone layer.

Recent Publications

"Nitric Oxide Abundance in the Mesosphere/Lower Thermosphere Region: Roles of Solar Soft X Rays, Suprathermal N(4S) Atoms, and Vertical Transport", P. K. Swaminathan, D. F. Strobel, D. G. Kupperman, C. Krishna Kumar, L. Acton, R. DeMajistre, J. -H. Yee, L. Paxton, D. E. Anderson and D. J. Strickland, accepted by JGR(Space Physics), (1997).

"The Nature of the Heating Mechanism for the Diffuse Corona", E.R. Priest, T. D. Arber, C. A. Foley, J. Heyvaerts, J. L. Culhane and L. W. Acton, submitted to Nature (1997).

"Yohkoh Soft X-ray Determination of Plasma Parameters in a Polar Coronal Hole", C. A. Foley, J. L. Culhane, and L. W. Acton, ApJ, in press for the December 20, 1997, issue.

"X-ray network flares of the quiet sun", S. Krucker, A. O. Benz, T. S. Bastian, and L. W. Acton, accepted for publication in ApJ, 1997.

"Fine Structure of the X-ray and Radio Emissions of the Quiet Solar Corona", A. O. Benz, S. Krucker, L. W. Acton, and T. S. Bastian, Astron. & Astrophys., 320, 993-1000, (1997).

"Coronal Heating and the Vertical Temperature Structure of the Quiet Corona", M. S. Wheatland, P. A. Sturrock, and L. W. Acton, submitted to Astrophys. J. (Sept 1996).

"Comparison of Yohkoh X-ray and Other Solar Activity Parameters for November 1991 to November 1995," L.W. Acton, Proc. of Ninth Coostar Workshop, Florence, Italy, 3-6 October 1995 (1996) Preprint

"Coronal Structures, Local and Global," L.W. Acton, Proc. IAU Colloquium 153 on Magnetodynamic Phenomena in the Solar Atmosphere -- Prototypes of Stellar Magnetic Activity, Y. Uchida, H. Hudson, T. Kosugi, eds., Kluwer, pp 1-12 (1996)

"YOHKOH Soft X-ray Telescope Images of the Diffuse Solar Corona," P.A. Sturrock, M.S. Wheatland, and L.W. Acton, Astrophys. J. (Letters), 461, L1-L100 (1996)

"A Long-duration Solar Flare with Mass Ejection and Global Consequences," H.S. Hudson, L.W. Acton, and S.L. Freeland, to be published in the Astrophysical Journal (1996)

"Spectral Averaging of the Point Spread Function for Yohkoh's SXT," D.C. Weston and L.W. Acton, to be published in Solar Physics (1996) Preprint

"Solar Identification of Solar-Wind Disturbances Observed at Ulysses," J.R. Lemen, L.W. Acton, D. Alexander, A.B. Galvin, K.L. Harvey, J.T. Hoeksema, X. Zhao, and H.S. Hudson, to be published in Proceedings of Solar Wind 8, Dana Pt., CA, June 25-30, 1995

"The Point Spread Function of the Soft X-ray Telescope Aboard Yohkoh", P.C. Martens, L.W. Acton and J.R. Lemen, Solar Physics 157, 141-168 (1995).

"Correlated Brightness Variations in Solar Radiative Output from the Photosphere to the Corona", J.L. Lean, J.T. Mariska, K.T. Strong, H.S. Hudson, L.W. Acton, G.J. Rottman, T.N. Woods, and R.C. Willson, Geophys. Res. Ltrs. 22, 655-658 (1995).

"The 1991 October 24 Flare: A Challenge for Standard Models", J. de La Beaujardiere, R.C. Canfield, H.S. Hudson, J.-P. Wuelser, L.W. Acton, T. Kosugi, and S. Masuda, Astrophys J. 440, 386-393 (1995).

"The Band of Solar Wind Variability at Low Heliographic Latitudes Near Solar Activity Minimum: Plasma Results From the Ulysses Rapid Latitude Scan", J.T. Gosling, S.J. Bame, W.C. Feldman, D.J. McComas, J.L. Phillips, B. Goldstein, M. Neugebauer, J. Burkepile, A.J. Hundhausen, and L. Acton, Geophys. Res. Letters 22, 3329-3332 (1995). Abstract

"Morphology of Active Region Transient Brightenings with the YOHKOH Soft X-ray Telescope", T. Shimizu, S. Tsuneta, L. Acton, J. Lemen, Y. Ogawara, and Y. Uchida, ApJ, 422, 906-911, 1994.

"The Morphology of the 10(7) K Plasma: I. Nonimpulsive flares", U. Feldman, J. Selly, G. Doschek, K. Strong, L. Acton, Y. Uchida, and S. Tsuneta, Ap. J. 424, 444-458, 1994.

"Multispectral Observations of Chromospheric Evaporation in the 1991 November 15 X-Class Solar Flare", J.-P. Wuelser, R.C. Canfield, L.W. Acton, J.L. Culhane, A. Phillips, A. Fludra, T. Sakao, S. Masuda, T. Kosugi, S. Tsuneta, Astrophys. J., 424, 459 (1994).

Awards and Honors

Back to Physics Homepage Back to Faculty Directory To Solar Physics Research Page

Questions and/or comments can be addressed to: www@solar.physics.montana.edu
Last Updated: 13 November 1999