Showing papers by "Charles H. Townes published in 2002"
TL;DR: The Herbig Ae/Be star LkHα 101 has been imaged at high angular resolution at a number of wavelengths in the near-infrared (from 1 to ~3 μm), using the Keck I Telescope, and also observed in the mid-indrared (11.15 μm) using the UC Berkeley Infrared Spatial Interferometer (ISI) as mentioned in this paper.
Abstract: The Herbig Ae/Be star LkHα 101 has been imaged at high angular resolution at a number of wavelengths in the near-infrared (from 1 to ~3 μm), using the Keck I Telescope, and also observed in the mid-infrared (11.15 μm), using the UC Berkeley Infrared Spatial Interferometer (ISI). The resolved circular disk with a central hole or cavity reported by Tuthill, Monnier, & Danchi is confirmed. This is consistent with an almost face-on view (inclination of 35°) onto a luminous pre-main-sequence or early main-sequence object surrounded by a massive circumstellar disk. With a multiple-epoch study spanning almost 4 years, relative motion of the binary companion has been detected, together with evidence of changes in the brightness distribution of the central disk/star. The resolution of the LkHα 101 disk by ISI mid-infrared interferometry constitutes the first such measurement of a young stellar object in this wavelength region. The angular size was found to increase only slowly from 1.6 to 11.15 μm, inconsistent with standard power-law temperature profiles usually encountered in the literature, supporting instead models with a hot inner cavity and relatively rapid transition to a cool or tenuous outer disk. The radius of the dust-free inner cavity is consistent with a model of sublimation of dust in equilibrium with the stellar radiation field. Measurements from interferometry have been combined with published photometry, enabling an investigation of the energetics and fundamental properties of this prototypical system.
66 citations
TL;DR: The Herbig Ae/Be star LkHalpha 101 has been imaged at high angular resolution at a number of wavelengths in the nearinfrared (from 1 to 3 microns) using the Keck 1 Telescope, and also observed in the mid-infrared using the U.C. Berkeley Infrared Spatial Interferometer (ISI).
Abstract: The Herbig Ae/Be star LkHalpha 101 has been imaged at high angular resolution at a number of wavelengths in the near-infrared (from 1 to 3 microns) using the Keck 1 Telescope, and also observed in the mid-infrared (11.15 microns) using the U.C. Berkeley Infrared Spatial Interferometer (ISI). The resolved circular disk with a central hole or cavity reported in Tuthill et al. (2001) is confirmed. This is consistent with an almost face-on view (inclination < 35 deg) onto a luminous pre- or early-main sequence object surrounded by a massive circumstellar disk. With a multiple-epoch study spanning almost four years, relative motion of the binary companion has been detected, together with evidence for changes in the brightness distribution of the central disk/star. The resolution of the LkHalpha 101 disk by ISI mid-infrared interferometry constitutes the first such measurement of a young stellar object in this wavelength region. The angular size was found to increase only slowly from 1.6 to 11.15 microns, inconsistent with standard power-law temperature profiles usually encountered in the literature, supporting instead models with a hot inner cavity and relatively rapid transition to a cool or tenuous outer disk. The radius of the dust-free inner cavity is consistent with a model of sublimation of dust in equilibrium with the stellar radiation field. Measurements from interferometry have been combined with published photometry enabling an investigation of the energetics and fundamental properties of this prototypical system.
49 citations
TL;DR: In this article, it is shown that Rayleigh scattering by molecules provides more intensity than does Raman and can allow path length corrections over distances of a few hundred meters to somewhat more than a kilometer with a fractional accuracy as good as 10-6 of the total atmospheric delay.
Abstract: Adaptive optics provides a method for improving telescope imaging affected by atmospheric seeing distortions, but the differences in path length fluctuations through the atmosphere to two or more separate telescopes continues to limit the quality of stellar interferometry, and unfortunately is not ameliorated by adaptive optics. Some corrections to such fluctuations can be made by atmospheric density measurements near the ground, particularly since in some cases a substantial fraction of path length fluctuations occur in the atmosphere within 20-30 m of ground level. It is shown that more extensive corrections can be made by measurements of backscattered lidar radiation sent along the direction of the telescopes' observation. It is proposed that Rayleigh or Raman backscattering be used to measure changes in atmospheric density or index of refraction. Rayleigh scattering by molecules provides more intensity than does Raman and can allow path length corrections over distances of a few hundred meters to somewhat more than a kilometer with a fractional accuracy as good as 10-6 of the total atmospheric delay. Such measurements can substantially assist stellar interferometry. Details of how this might be done, and of likely errors and difficulties, are discussed quantitatively.
8 citations
01 Jan 2002
TL;DR: In this article, it was shown that more extensive corrections can be made by measurements of backscattered lidar radiation sent along the direction of the direction in which a substantial fraction of path length is affected by atmospheric seeing distortions within 20¨30 m of ground level.
Abstract: Adaptive optics provides a method for improving telescope imaging aUected by atmospheric seeing distortions, but the diUerences in path length —uctuations through the atmosphere to two or more separate telescopes continues to limit the quality of stellar interferometry, and unfortunately is not ameliorated by adaptive optics. Some corrections to such —uctuations can be made by atmospheric density measurements near the ground, particularly since in some cases a substantial fraction of path length —uctuations occur in the atmosphere within 20¨30 m of ground level. It is shown that more extensive corrections can be made by measurements of backscattered lidar radiation sent along the direction
8 citations
01 Jan 2002
TL;DR: The U.C. Berkeley Infrared Spatial Interferometer ( ISI) as discussed by the authors is a two-to-three telescope stellar interferometer operating in the 9-12 micron atmospheric window, utilizing heterodyne detection with CO2 laser local oscillators.
Abstract: The U.C. Berkeley Infrared Spatial Interferometer is a two telescope stellar interferometer operating in the 9-12 micron atmospheric window, utilizing heterodyne detection with CO2 laser local oscillators. Science with the ISI has been focused on the measurements of the spatial distribution of dust and molecules around mass-losing late type stars, and more recently precision measurements of stellar diameters in the mid-infrared avoiding molecular lines. Also during the past few years, a NSF sponsored program of expansion from two to three telescopes has been underway. This expansion will allow the ISI to make visibility observations on three simultaneous baselines and a measure a closure phase. The third telescope was completed last year and shipped to Mt. Wilson, and more recently a Central Control Facility and Master Laser Oscillator Facility were also completed and recently shipped to Mt. Wilson. In this talk we report progress on this program and highlight some of the most recent astrophysical results.
1 citations