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Showing papers by "Charles H. Townes published in 2007"


Journal ArticleDOI
TL;DR: In this article, three-telescope interferometric observations from the Infrared Spatial Interferometer (ISI) are reported at spatial frequencies that resolve the size and shape of the star Betelgeuse (α Ori) at a wavelength of 11.15 μm with a bandwidth of 0.18 cm-1.
Abstract: Three-telescope interferometric observations from the Infrared Spatial Interferometer (ISI) are reported at spatial frequencies that resolve the size and shape of the star Betelgeuse (α Ori) at a wavelength of 11.15 μm with a bandwidth of 0.18 cm-1. The data include closure phase measurements, the first such measurements of a stellar disk in the mid-infrared. The data indicate a clear asymmetry of the stellar surface at these wavelengths. Mechanisms for generating the observed asymmetry via an elliptical shape or a hot spot near the southern limb of the star are discussed.

24 citations


Journal ArticleDOI
TL;DR: Asymmetries and motions in the dust shell surrounding Mira A (o Ceti) are reported in this paper, where fits are made to the visibility and closure phase curves, which are then used to create one-dimensional profiles of the dust shells.
Abstract: Asymmetries and motions in the dust shell surrounding Mira A (o Ceti) are reported. Measurements were taken with the UC Berkeley Infrared Spatial Interferometer (ISI), a three-element interferometer operating at 11.15 μm. At the time of these observations, it was in a linear, east-west configuration with a maximum baseline of 12 m and thus had a resolution of better than 100 mas. Three years of data (2003-2005) are presented and permit observation of the movement of dust shells over time. Fits are made to the visibility and closure-phase curves, which are then used to create one-dimensional profiles of the dust shells. Asymmetries in the circumstellar dust have been observed, and several possible explanations for these asymmetries are explored.

16 citations


Journal ArticleDOI
TL;DR: In this article, measurements and analysis of large-scale turbulent irregularities in the atmosphere are reported, based on precision measurement of atmospheric temperature fluctuations at 24 and 70 feet above ground for a variety of wind velocities at the Mount Wilson Observatory.
Abstract: Measurements and analysis of large-scale turbulent irregularities in the atmosphere are reported. Results were obtained from precision measurement of atmospheric temperature fluctuations at 24 and 70 feet above ground for a variety of wind velocities at the Mount Wilson Observatory. Measurements were made as wind blew air past detectors, at frequencies of 0.01-10 Hz, corresponding to distances in the atmosphere between about 1 and 250 m. Analysis shows that large-scale turbulences fit the Greenwood-Tarazano model well, and notably better than the von Karman model of turbulence.

10 citations


Journal ArticleDOI
07 Jun 2007-Nature

10 citations


Journal ArticleDOI
TL;DR: In this article, the authors interpreted an ejection of approximately 10-6 M☉ of material in 1990 that has subsequently expanded and dissipated, at a rate of 75 km s-1, much larger than previous observations.
Abstract: Interferometric observations of α Herculis at a wavelength of 11.15 μm over the period 1989-2004 show large visibility variations. These variations are interpreted as an ejection of approximately 10-6 M☉ of material in 1990 that has subsequently expanded and dissipated. The expansion rate is approximately 75 km s-1, much larger than previous observations. No substantial material has been emitted during the subsequent 14 years.

8 citations


Journal ArticleDOI
TL;DR: In this paper, three-baseline interferometry data from a linear array of telescopes is used to create a one-dimensional image of the star and circumstellar dust, which yields some insight into the two-dimensional structure of IRC +10216.
Abstract: The unusual source IRC +10216 is the brightest stellar object at mid-infrared wavelengths in the northern hemisphere. Adding to its distinctiveness, the dust around IRC +10216 almost completely enshrouds the star and has an extremely complex distribution. We report the imaging of IRC +10216 at 11.15 μm with three telescopes and the closure phase at two different stellar phases. Three-baseline interferometry data from a linear array of telescopes is used to create a one-dimensional image of the star and circumstellar dust. The two epochs over which data have been taken provide information at different position angles, which yields some insight into the two-dimensional structure of IRC +10216. Specifically, we observe two areas of peaked intensity. The first is 66 ± 4 mas to the west and 160 ± 51 mas to the south of the star, and the second is 227 ± 8 mas to the east and 94 ± 57 mas to the south. These two features can explain most of the observed asymmetry.

8 citations


Proceedings ArticleDOI
TL;DR: The infrared stellar interferometer (ISI) as mentioned in this paper is an interferometry system that operates at mid-infrared wavelengths with three movable telescopes and heterodyne detection with CO 2 laser local oscillators.
Abstract: The ISI (Infrared Stellar Interferometer), an interferometer operating at mid-infrared wavelengths will be discussed, including both the instrumentation and results of stellar measurements. The ISI operates in the 10 micron wavelength region using three movable telescopes and heterodyne detection with CO 2 laser local oscillators. Phase closure allows rather complete imaging of stars and their dust shells, including measurement of asymmetries. Measurements have been conducted of the emission of material from stars, some ejected at very high velocity, the size and change of size of some stars, stellar ellipticity, and stellar asymmetry. Material blown off from stars is often emitted in periodic shells, and frequently asymmetric.

1 citations