Sensor performance analysis

The theory is described and the equations required to design are developed and the performance of electro-optical sensor systems that operate from the visible through the thermal infrared spectral regions are analyzed. Methods to compute essential optical and detector parameters, signal-to-noise ratio, MTF, and figures of merit such as NE delta rho and NE delta T are developed. A set of atmospheric tables are provided to determine scene radiance in the visible spectral region. The Planck function is used to determine radiance in the infrared. The equations developed were incorporated in a spreadsheet so that a wide variety of sensor studies can be rapidly and efficiently conducted

APM 08279+5255: Keck Near- and Mid-IR High-Resolution Imaging

We present Keck high-resolution near-IR (2.2 microns; FWHM~0.15") and mid-IR (12.5 microns; FWHM~0.4") images of APM08279+5255, a z=3.91 IR-luminous BALQSO with a prodigious apparent bolometric luminosity of 5x10^{15} Lsun, the largest known in the universe. The K-band image shows that this system consists of three components, all of which are likely to be the gravitationally lensed images of the same background object, and the 12.5 micron image shows a morphology consistent with such an image configuration. Our lens model suggests that the magnification factor is ~100 from the restframe UV to mid-IR, where most of the luminosity is released. The intrinsic bolometric luminosity and IR luminosity of APM08279+5255 are estimated to be 5x10^{13} Lsun and 1x10^{13} Lsun, respectively. This indicates that APM 08279+5255 is intriniscally luminous, but it is not the most luminous object known. As for its dust contents, little can be determined with the currently available data due to the uncertainties associated with the dust emissivity and the possible effects of differential magnification. We also suggest that the lensing galaxy is likely to be a massive galaxy at z~3.Comment: 32 pages, 4 tables, 11 figures; Accepted for publication in Ap

Mid-infrared Imaging of a Circumstellar Disk Around HR 4796: Mapping the Debris of Planetary Formation

We report the discovery of a circumstellar disk around the young A0 star, HR 4796, in thermal infrared imaging carried out at the W.M. Keck Observatory. By fitting a model of the emission from a flat dusty disk to an image at lambda=20.8 microns, we derive a disk inclination, i = 72 +6/-9 deg from face on, with the long axis of emission at PA 28 +/-6 deg. The intensity of emission does not decrease with radius as expected for circumstellar disks but increases outward from the star, peaking near both ends of the elongated structure. We simulate this appearance by varying the inner radius in our model and find an inner hole in the disk with radius R_in = 55+/-15 AU. This value corresponds to the radial distance of our own Kuiper belt and may suggest a source of dust in the collision of cometesimals. By contrast with the appearance at 20.8 microns, excess emission at lambda = 12.5 microns is faint and concentrated at the stellar position. Similar emission is also detected at 20.8 microns in residual subtraction of the best-fit model from the image. The intensity and ratio of flux densities at the two wavelengths could be accounted for by a tenuous dust component that is confined within a few AU of the star with mean temperature of a few hundred degrees K, similar to that of zodiacal dust in our own solar system. The morphology of dust emission from HR 4796 (age 10 Myr) suggests that its disk is in a transitional planet-forming stage, between that of massive gaseous proto-stellar disks and more tenuous debris disks such as the one detected around Vega.Comment: 9 pages, 4 figures as LaTex manuscript and postscript files in gzipped tar file. Accepted for publication in Astrophysical Journal Letters. http://upenn5.hep.upenn.edu/~davidk/hr4796.htm

Thermal Model Calibration for Minor Planets Observed with Wide-Field Infrared Survey Explorer/Neowise

With the Wide-field Infrared Survey Explorer (WISE), we have observed over 157,000 minor planets. Included in these are a number of near-Earth objects, main-belt asteroids, and irregular satellites which have well measured physical properties (via radar studies and in situ imaging) such as diameters. We have used these objects to validate models of thermal emission and reflected sunlight using the WISE measurements, as well as the color corrections derived in Wright et al. for the four WISE bandpasses as a function of effective temperature. We have used 50 objects with diameters measured by radar or in situ imaging to characterize the systematic errors implicit in using the WISE data with a faceted spherical near-Earth asteroid thermal model (NEATM) to compute diameters and albedos. By using the previously measured diameters and H magnitudes with a spherical NEATM model, we compute the predicted fluxes (after applying the color corrections given in Wright et al.) in each of the four WISE bands and compare them to the measured magnitudes. We find minimum systematic flux errors of 5%-10%, and hence minimum relative diameter and albedo errors of ~10% and ~20%, respectively. Additionally, visible albedos for the objects are computed and compared to the albedos at 3.4 μm and 4.6 μm, which contain a combination of reflected sunlight and thermal emission for most minor planets observed by WISE. Finally, we derive a linear relationship between subsolar temperature and effective temperature, which allows the color corrections given in Wright et al. to be used for minor planets by computing only subsolar temperature instead of a faceted thermophysical model. The thermal models derived in this paper are not intended to supplant previous measurements made using radar or spacecraft imaging; rather, we have used them to characterize the errors that should be expected when computing diameters and albedos of minor planets observed by WISE using a spherical NEATM model

The Mid-Infrared Instrument for the James Webb Space Telescope, VII: The MIRI Detectors

The MIRI Si:As IBC detector arrays extend the heritage technology from the Spitzer IRAC arrays to a 1024 x 1024 pixel format. We provide a short discussion of the principles of operation, design, and performance of the individual MIRI detectors, in support of a description of their operation in arrays provided in an accompanying paper (Ressler et al. (2015)). We then describe modeling of their response. We find that electron diffusion is an important component of their performance, although it was omitted in previous models. Our new model will let us optimize the bias voltage while avoiding avalanche gain. It also predicts the fraction of the IR-active layer that is depleted (and thus contributes to the quantum efficiency) as signal is accumulated on the array amplifier. Another set of models accurately predicts the nonlinearity of the detector-amplifier unit and has guided determination of the corrections for nonlinearity. Finally, we discuss how diffraction at the interpixel gaps and total internal reflection can produce the extended cross-like artifacts around images with these arrays at short wavelengths, ~ 5 microns. The modeling of the behavior of these devices is helping optimize how we operate them and also providing inputs to the development of the data pipeline

The Compact Nucleus of the Deep Silicate Absorption Galaxy NGC 4418

High resolution, Hubble Space Telescope (HST) near-infrared and Keck mid-infrared images of the heavily extinguished, infrared luminous galaxy NGC 4418 are presented. These data make it possible to observe the imbedded near-infrared structure on scales of 10-20 pc, and to constrain the size of the mid-infrared emitting region. The 1.1-2.2 um data of NGC 4418 show no clear evidence of nuclear star clusters or of a reddened active galactic nucleus. Instead, the nucleus of the galaxy consists of a ~100-200 pc linear structure with fainter structures extending radially outward. The near-infrared colors of the linear feature are consistent with a 10-300 Myr starburst suffering moderate levels (few magnitudes) of visual extinction. At 7.9-24.5 um, NGC 4418 has estimated size upper limits in the range of 30-80 pc. These dimensions are consistent with the highest resolution radio observations obtained to date of NGC 4418, as well as the size of 50-70 pc expected for a blackbody with a temperature derived from the 25 um, 60 um, and 100 um flux densities of the galaxy. Further, a spectral energy distribution constructed from the multi-wavelength mid-infrared observations show the strong silicate absorption feature at 10 um, consistent with previous mid-infrared observations of NGC 4418. An infrared surface brightness of 2.1x10^13 L_sun kpc^-2 is derived for NGC 4418. Such a value, though consistent with the surface brightness of warm ultraluminous infrared galaxies (ULIGs: L_IR [8-1000 um] >~ 10^12 L_sun) such as IRAS 05189-2524 and IRAS 08572+3915, is not large enough to distinguish NGC 4418 as a galaxy powered by an Active Galactic Nucleus (AGN), as opposed to a lower surface brightness starburst.Comment: LaTex, 7 pages, including 2 jpg figures and 3 postscript figures, AJ, in press (May, 2003

High Resolution Infrared Imaging of the Compact Nuclear Source in NGC4258

We present high resolution imaging of the nucleus of NGC4258 from 1 micron to 18 microns. Our observations reveal that the previously discovered compact source of emission is unresolved even at the near-infrared resolution of about 0.2 arcsec FWHM which corresponds to about 7 pc at the distance of the galaxy. This is consistent with the source of emission being the region in the neighborhood of the purported 3.5*10^7 M_sun black hole. After correcting for about 18 mags of visual extinction, the infrared data are consistent with a F_nu \propto nu^(-1.4+/-0.1) spectrum from 1.1 micron to 18 micron, implying a non-thermal origin. Based on this spectrum, the total extinction corrected infrared luminosity (1-20 micron) of the central source is 2*10^8 L_sun. We argue that the infrared spectrum and luminosity of the central source obviates the need for a substantial contribution from a standard, thin accretion disk at these wavelengths and calculate the accretion rate through an advection dominated accretion flow to be Mdot \sim 10^(-3) M_sun/yr. The agreement between these observations and the theoretical spectral energy distribution for advection dominated flows provides evidence for the existence of an advection dominated flow in this low luminosity AGN.Comment: 21 pages, 5 figures, Appearing in Mar 2000 ApJ vol. 53