Infrared Spatial Interferometer (ISI)
Operating in the mid-IR, ISI studies circumstellar dust around evolved stars and finds that half emit dust episodically in outbursts separated by decades or centuries. These include aOri, a Sco, and a Her, with dust at a mean distance of 38 R*, and Mira variables, with dust at < 6 R•. ISI is now monitoring some 30 stars for changes in their surrounding dust from which the stellar distances can be found.

ISI found the diameter of Mira to be 47.8 ± 0.5 mas, at pulsation phase 0.9, substantially larger than previously expected, with a systematic variation of ±13% over its ~ 330 day period. With its three telescopes, ISI can measure “closure phase” to check for departures from circular symmetry. While such stars as a Her and a Sco were found to be symmetric sources, at least seven Miras show varying degrees of asymmetry.

• Mid-Infrared Interferometry on Dust Shells around 4 Late Type Stars~T, S.Tevousjan, J. Weiner, K. S. Abdeli, D. D. S. Hale, C. H. Townes, ApJ, Vol 611, 466 (2004)
• The Asymmetrical Dust Environment of IK Tau~T, J. Weiner, K. Tatebe, D. D.S. Hale, C. H. Townes, J. Monnier, M. Ireland, P. Tuthill, R. Cohen, R. K. Barry, J. Rajagopol, W. C. Danchi, Ap.J. 636-1067 (2006)
• Low Frequency Behavior of Turbulent Fluctuations at Mt. Wilson Observatory~T, A. Wheelon, N. Short, and C. Townes, to be submitted to ApJ. 172, 720 (2007)
• Changes in Apparent Size of Giant Stars with Wavelength Due to Electron-Hydrogen Collisions~T, K. Tatebe and C. H. Townes, ApJ ApJ 644, 1145 (2006)
• Characteristication of Dust Shell Dynamics and Asymmetry for 6 Mira-Type Stars, K. Tatebe, A.A. Chandler, D.D.S. Hale, and C.H. Townes, ApJ. 652, 666 (2006)
• The Radiative Pattern and Asymmetry of IRC+10216 at 11 Microns with Interferometry and Closure Phase, A.A. Chandler, K. Tatebe, D.D.S. Hale, and C.H. Townes, ApJ.657, 1042 (2007)
• Observation of a Burst of High-Velocity Dust from - Herculis~T, K. Tatebe, D.D.S. Hale, E.H. Wishnow, and C.H. Townes, ApJ. Letters 658, L103 (2007)
• Asymmetries and Outflows in the Circumstellar Dust of Mira A~T, A.A. Chandler, K. Tatebe, E.H. Wishnow, D.D.S. Hale, and C.H. Townes, Ap.J. 670 (2007)
• The Nonspherical Shape of Betelgeuse in the Mid-Infrared ~T, K Tatebe, A.A Chandler, E.H. Wishnow, D.D.S. Hale, C.H. Townes, Ap.J. 670, L21 (2007)