Long Slit Spectroscopy In The Ten Micron Infrared As A Tool For Remote Sensing

Long slit spectroscopy in the ten micron atmospheric window has confirmed its usefulness as a ground-based astronomical tool. For example, it has been used recently to resolve the circumstellar shell of Betelgeuse, the bright red star in the Orion Constellation. The angular size of the circumstellar shell is approximately a second of arc (arcsec), as measured near ten microns with a 2.3 meter telescope with no compensation for atmospheric turbulence. For comparison, the angular diameter of the star's photosphere found interferometrically by Michaelson is 45 milliarcsec. The success in resolving Betelgeuse at 10 microns is in part due to the instantaneous recording of all spectral and spatial elements that is possible with a long slit spectrometer and two-dimensional detector array. Also, the detection of extension was possible only with an analysis tool with which program and reference star data are compared. The aim here is to explore the capabilities of an earth-viewing platform using similar instrumentation and analysis techniques. Long slit data Long slit data is in the form of a twodimensional numerical array, with one axis corresponding to wavelength and the other to the distribution of radiation along the spectrograph slit. Contour plots of such data will indicate pronounced extension of the program source relative to the reference source. For more subtle levels of extension, a plot of the width of the one-dimensional radiation profile against wavelength (spatiogram) is the preferred alternative to a contour plot. The spectral properties of an extended radiation source can then be distinguished from those of the blur resulting from atmospheric turbulence and telescopic diffraction. This is true even for a mildly extended source, if the spatial extent varies with wavelength. Astronomical results In order to interpret differences in the spatiograms of Betelgeuse and the reference star Aldebaran, we consider their stellar radiation properties and the atmospheric transmission that give rise to the spectrum observed from the ground. Figure 1 shows spectra in the ten Figure 1. Spectral Flux (Watt cm-2 pm-')