Showing papers by "Charles H. Townes published in 1986"

C II forbidden-line 158 micron mapping in Sagittarius A Rotation curve and mass distribution in the galactic center

Abstract: Based on data obtained with the NASA Kuiper Airborne Observatory 91.4 cm telescope, the 158-micron fine structure line emission of C(+) is mapped near the galactic center. The strongest emission comes from a 10-pc FWHM diameter disk centered on Sgr A West whose dominant motion is rotation. Extended C(+) emission is also found from the +50 km/s galactic center molecular cloud, and a second cloud at v(LSR) of about -35 km/s. The rotation curve and mass distribution within 10 pc of the galactic center are derived, and the C(+) profiles show a drop-off of rotation velocity between 2 and 10 pc. A mass model is suggested with 2-4 million solar masses in a central point mass, and a M/L ratio of the central stellar cluster of 0.5 solar masses/solar luminosities, suggesting a large abundance of giants and relatively recent star formation in the center.

Long Baseline Spatial Interferometer For The IR

Abstract: Two high-precision and movable telescopes of 65 inch aperture are being constructed for long baseline infrared spatial interferometry (1). The telescopes are of novel design and emphasize the control of optical pathlengths and of telescope positions to a precision of about one micron. This will allow the relative phase of interference fringes to be determined over rather large angles of the sky and over some period of time, so that high precision astrometry as well as aperture synthesis can be done at wavelengths near 10 microns.

Collision cross sections for ammonia in its ground vibrational manifold

Abstract: Rates for inelastic collision‐induced transitions between rotation–inversion states are measured for the NH3 molecule colliding with He atoms and with N2 molecules. An infrared–microwave double resonance method is used to determine differences within pairs of collisional transition rates connecting different inversion pairs in the ground (ν2=0) vibrational manifold of NH3. The measured rates are analyzed for parity, and J and k selection rules. The results are consistent with Oka’s saturation experiments on NH3, but in some respects inconsistent with theoretical calculations of collisional transition rates.

A High Precision Telescope Pointing System

Abstract: A novel method of telescope pointing has been developed based on He-Ne laser interferometric measurements of mirror position. We have applied this technique to a Pfund-type telescope, which consists of a fixed parabolic mirror illuminated by a flat mirror which rotates in altitude and azimuth. If the parabolic mirror is stationary the angle of pointing depends only on the change of orientation of the flat mirror with respect to the parabolic mirror. The relative angles of mirrors with radius of 1 meter are measured to a precision of ~.05 arcsec. Fluctuations in the index of refraction of the atmosphere between the mirrors are the primary source of this limit; however, changes in pointing position involving only a gradient in the index of refraction perpendicular to the optic axis are largely compensated by this pointing technique. Conversion of interference fringe counts to precise angle of pointing involves solutions of equations of modest complexity, but is easily handled by a small computer.

Diffraction-Limited 10 µm Imaging With 3 Meter Telescopes

Abstract: We have constructed an infrared imaging system that achieves diffraction-limited spatial resolution (about 0.8 arc seconds) at 10 um on 3 meter ground-based telescopes. The system uses a linear array of sensitive HgCdTe photodiodes, scanned in the direction perpendicular to the array axis, to form two-dimensional images. Scans are completed rapidly enough to freeze atmospheric fluctuations. Individual detectors are small compared to the diameter of the Airy disk, and images are oversampled heavily in the scan direction. This method has a number of advantages for studying small fields with very high spatial resolution, and has been applied successfully to the problem of directly imaging faint circumstellar dust shells.