Gerald M. Lamb

Structure in the nucleus of NGC 1068 at 10 microns

New 8 to 13 micron array camera images of the central kiloparsec of Seyfert 2 galaxy NGC 1068 resolve structure that is similar to that observed at visible and radio wavelengths. The images reveal an infrared source which is extended and asymmetric, with its long axis oriented at P.A. 33 deg. Maps of the spatial distribution of 8 to 13 micron color temperature and warm dust opacity are derived from the multiwavelength infrared images. The results suggest that there exist two pointlike luminosity sources in the central regions of NGC 1068, with the brighter source at the nucleus and the fainter one some 100 pc to the northeast. This geometry strengthens the possibility that the 10 micron emission observed from grains in the nucleus is powered by a nonthermal source. In the context of earlier visible and radio studies, these results considerably strengthen the case for jet induced star formation in NGC 1068.

8.3 and 12.4 micron imaging of the Galactic Center source complex with the Goddard infrared array camera

A 30 x 30 arcsec field at the Galactic Center (1.5 x 1.5 parsec) was mapped at 8.3 microns and 12.41 microns with high spatial resolution and accurate relative astrometry, using the 16 x 16 Si:Bi accumulation mode charge injection device Goddard infrared array camera. The design and performance of the array camera detector electronics system and image data processing techniques are discussed. Color temperature and dust opacity distributions derived from the spatially accurate images indicate that the compact infrared sources and the large scale ridge structure are bounded by warmer, more diffuse material. None of the objects appear to be heated appreciably by internal luminosity sources. These results are consistent with the model proposing that the complex is heated externally by a strong luminosity source at the Galactic Center, which dominates the energetics of the inner few parsecs of the galaxy.

High spatial resolution observations of NGC 7027 with a 10 micron array camera

First observations of a planetary nebula with an infrared charge injection device (CID) array camera are reported. The 10 micron images of NGC 7027 have spatial resolution comparable to that of the highest resolution (less than 2 arcsec) radio aperture-synthesis maps of this source. A much closer correspondence between the mid-infrared and radio appearance of NGC 7027 was found than was known previously, confirming that warm dust is coextensive and well mixed with the gas in the ionized zone. Using maps at three wavelengths, the spatial dependence of the shape of the 8-13 micron spectrum within the nebula is examined. The dip at 9.60 microns is shallowest in regions of enhanced optical extinction (as determined from new images near 4000 and 9000 A obtained with an optical charge coupled device). The 9.60 micron emission is strongest in these same positions. It is shown that the results may be explained not by silicate absorption, but by a combination of emission from two distinct grain populations, one of which is also partly responsible for the variation in extinction across the nebula.

Infrared Camera For Ten Micrometer Astronomy

We describe an infrared imaging photometer employing a monolithic 32 X 32 pixel bismuth doped silicon charge injection device array. The device is primarily useful in the 8 to 13 karl atmospheric window. The detector is sufficiently sensitive to provide good performance on ground-based telescopes and promises to be very good for low background space flight operation.

Astronomical Applications Of The New Goddard Si:Bi 16X16 Array Camera System

An improved 4 - 18 micron array camera system has been developed at NASA Goddard Space Flight Center for astronomical photometry, using an Aerojet ElectroSystems Co. 16 x 16 Si:Bi (Bismuth doped Silicon) accumulation mode charge injection device (AMCID) with 256 active pixels, obtained from NASA/Ames Research Center as part of a new scientific collaboration between the Ames and Goddard infrared array research groups. An astronomical observing program using this device has been carried out as a collaboration between NASA Goddard Space Flight Center (Infrared and Radio Astronomy Branch and Micro Electronics Branch) , the Harvard-Smithsonian Center for Astrophysics, and Steward Observatory of the University of Arizona, and NASA Ames Research Center. The 16 x 16 device had sufficiently good sensitivity, uniformity and noise characteristics to be used for successful observations at the Steward Observatory Mt. Lemmon 60 and 61-inch telescopes in May 1983, and at the NASA Infrared Telescope Facility (IRTF) at Mauna Kea in August 1983. Initial results indicate that this detector has sensitivity and noise characteristics comparable to other devices from the same generation of Aerojet arrays. Si:Bi AMCID detector array characteristics and performance have been discussed in general by Parry (1980) , McCreight and Goebel (1981) , and by Parry (1983). For a discussion of earlier array camera work at Goddard see Arens et al. (1981), Lamb et al. (1983) , and references therein.

Infrared Camera For 10 μm Astronomy

We describe an infrared imaging photometer employing a monolithic 32x32 pixel bismuth doped silicon charge injection device array. The device is primarily useful in the 8-13 pm atmospheric window. The detector is sufficiently sensitive to provide good performance on ground-based telescopes and promises to be very good for low background space flight operation.

Images of the 10-micron source in the Cygnus 'Egg'

Mid-IR images of AFGL 2688, the Egg nebula, obtained with a 16 x 16 pixel array camera (field of view 12.5 x 12.5 arcsec) resolve the central source. It appears as a centrally peaked ellipsoid with major axis of symmetry parallel to the axis of the visible nebulosity. This is contrary to the expected extension perpendicular to this axis implied by proposed dust-toroid models of the IR source. Maps of the spatial distribution of 8-13 micron color temperature and warm dust opacity derived from the multiwavelength images further characterize the IR emission. The remarkable flatness of the color temperature conflicts with the radial temperature gradient expected across a thick shell of material with a single heat source at its center. The new data suggest instead that the source consists of a central star surrounded by a dust shell that is too thin to provide a detectable temperature gradient and too small to permit the resolution of limb brightening. 29 references.

Wide Field And Diffraction Limited Array Camera For Sirtf

The Infrared Array Camera for the Space Infrared Telescope Facility (SIRTF/IRAC) is capable of two-dimensional photometry in either a wide field or diffraction-limited mode over the wavelength interval from 2 to 30 microns. Three different two-dimensional direct readout (DRO) array detectors are being considered: Band 1 - InSb or Si:In (2 - 5 microns) 128 x 128 pixels, Band 2 - Si:Ga (5 - 18 microns) 64 x 64 pixels, and Band 3 - Si:Sb (18 -30 microns) 64 x 64 pixels. The hybrid DRO readout architecture has the advantages of low read noise, random pixel access with individual readout rates, and non-destructive readout. The scientific goals of IRAC are discussed, which are the basis for several important requirements and capabilities of the array camera: 1) diffraction-limited resolution from 2 - 30 microns, 2) use of the maximum unvignetted field of view of SIRTF, 3) simultaneous observations within the three infrared spectral bands, 4) the capability for broad and narrow bandwith spectral resolution. A strategy has been developed to minimize the total electronic and environmental noise sources to satisfy the scientific requirements.