Lunming Yuen

Spitzer Space Telescope Infrared Imaging and Spectroscopy of the Crab Nebula

We present 3.6, 4.5, 5.8, 8.0, 24, and 70 μm images of the Crab Nebula obtained with the Spitzer Space Telescope IRAC and MIPS cameras, low- and high-resolution Spitzer IRS spectra of selected positions within the nebula, and a near-infrared ground-based image made in the light of [Fe II] 1.644 μm. The 8.0 μm image, made with a bandpass that includes [Ar II] 7.0 μm, resembles the general morphology of visible Hα and near-IR [Fe II] line emission, while the 3.6 and 4.5 μm images are dominated by continuum synchrotron emission. The 24 and 70 μm images show enhanced emission that may be due to line emission or the presence of a small amount of warm dust in the nebula on the order of less than 1% of a solar mass. The ratio of the 3.6 and 4.5 μm images reveals a spatial variation in the synchrotron power-law index ranging from approximately 0.3 to 0.8 across the nebula. Combining this information with optical and X-ray synchrotron images, we derive a broadband spectrum that reflects the superposition of the flatter spectrum of the jet and torus with the steeper spectrum of the diffuse nebula. We also see suggestions of the expected pileup of relativistic electrons just before the exponential cutoff in the X-ray. The pulsar, and the associated equatorial toroid and polar jet structures seen in Chandra and Hubble Space Telescope images (Hester et al. 2002), can be identified in all of the IRAC images. We present the IR photometry of the pulsar. The forbidden lines identified in the high-resolution IR spectra are all double due to Doppler shifts from the front and back of the expanding nebula and give an expansion velocity of ≈1264 km s-1.

58 x 62 Si:As IBC detector arrays on PMOS multiplexers for astronomy

Four 58 X 62-element Si:As impurity-band-conduction (IBC) detector arrays produced by the Hughes Technology Center were tested to evaluate their usefulness for space- and ground- based astronomical observations. PMOS circuitry was used in the multiplexers to improve low-temperature noise performance. Laboratory tests at background levels simulating those expected on space-based observing platforms were combined with ground-based telescope IR observations. The devices have shown read noise levels below 120 rms e-, dark currents below 10 e-/s, and detective quantum efficiencies of 20%.

Measuring the water vapor above the SOFIA Observatory

The SOFIA airborne observatory flies in the lower stratosphere above more than 99.9% of the Earths water vapor. As low as this residual water vapor is, it will still affect SOFIAs infrared and sub-millimeter astronomical observations. As a result, a heterodyne instrument operating at 183 GHz will be used to measure the integrated water vapor overburden in flight. The accuracy of the measured precipitable water vapor must be 2 microns or better, 3 sigma, and measured at least once a minute. This presentation will cover the design and the measured laboratory performance of this instrument, and will discuss other options for determining the water vapor overburden during the SOFIA Early Science shared-risk period.

The NASA - Arc 10/20 micron camera

A new infrared camera (AIR Camera) has been developed at NASA - Ames Research Center for observations from ground-based telescopes. The heart of the camera is a Hughes 58 x 62 pixel Arsenic-doped Silicon detector array that has the spectral sensitivity range to allow observations in both the 10 and 20 micron atmospheric windows.

SOFIA water vapor monitor design

The SOFIA Water Vapor Monitor (WVM) is a heterodyne radiometer designed to determine the integrated amount of water vapor along the telescope line of sight and directly to the zenith. The basic technique that was chosen for the WVM uses radiometric measurements of the center and wings of the 183.3 GHz rotational line of water to measure the water vapor. The WVM reports its measured water vapor levels to the aircraft Mission Controls and Communication System (MCCS) while the SOFIA observatory is in normal operation at flight altitude. The water vapor measurements are also available to other scientific instruments aboard the observatory. The electrical, mechanical and software design of the WVM are discussed.