Engineering topics

Rieke, G. H.

Publications and source records attributed to Rieke, G. H..

At least 37 records · Page 2

NASA NTRS1989

Laboratory and telescope use of the NICMOS2 128 x 128 HgCdTe array

The second generation of Hubble Space Telescope (HST) instruments will include a near-infrared instrument. This choice has driven the development of near-infrared arrays to larger sizes and lower read noises. Rockwell International has delivered an array for use in the Near Infrared Camera and Multi-Object Spectrometer (NICMOS) instrument; this array has been dubbed NICMOS2. NICMOS2 is a 128x128 array of HgCdTe diodes In-bonded to a switched MOSFET readout. The readout was specifically designed for astronomical use with the HST requirement of low read noise a prime goal. These arrays use detector material which is similar to that used by Rockwell in previous arrays (e.g., HgCdTe produced on a sapphire substrate), but the NICMOS2 devices differ substantially from other 128x128 arrays produced by Rockwell in having a read noise of only 30 electrons when read out using appropriate correlated sampling. NICMOS2 has now been characterized in the laboratory, and it has been used on groundbased telescopes.

Rieke, Marcia J.↗

NASA NTRS1989

An infrared color gradient in the inner coma of Comet Halley

A well-defined gradient is noted in the J-H and H-K colors of near-IR images obtained for Comet Halley in November, 1985, within about 8000 km of the nucleus; the bluest colors are at the photocenter, in conjunction with surface brightness profiles that are steeper than those expected. The color gradient and the brightness profiles are both explainable by the present analysis in terms of the presence of volatile, dirty-ice grains in the inner coma. An outburst of Rayleigh-scattering dust particles (unsupported by spacecraft measurements obtained to date) may also account for the observational data.

Campins, H.↗

NASA NTRS1988

Deep 2 micron imaging of the sky - Evidence for a new extragalactic population

Deep near-infrared imaging was obtained to study extragalactic populations, and a color-magnitude diagram was used to identify both normal galaxies with z = 0.3-1 and what appears to be a new distinct population. The latter has properties roughly similar to what would be expected for large galaxies at z greater than six undergoing a rapid luminous phase of star formation. It is suggested that these galaxies are good candidates for primeval galaxies. The normal galaxies identified are also important for studies of galaxy evolution, since they are found in the near-infrared, which is only weakly affected by evolution of the stellar populations.

Elston, R.↗

NASA NTRS1988

Hard X-ray observations of ultraluminous infrared galaxies

X-ray flux upper limits of 2-10 keV for ultraluminous infrared galaxies were drawn from the HEAO A-1 data base. The hard X-ray luminosities of these sources are much weaker relative to their total luminosities than would be expected for Seyfert 1 galaxies or quasi-stellar objects. Because of the low level of interstellar extinction for hard X-rays, this result suggests that the ultraluminous galaxies are not powered by embedded QSOs that are otherwise similar to other QSOs. Three other possibilities are: (1) the infrared galaxies may contain a form of X-ray-quiet active nucleus; (2) the X-ray sources in active nuclei may not turn on until after the circumnuclear gas has cleared; or (3) the bulk of the infrared luminosity in these galaxies may be generated by intense circumnuclear star formation.

Rieke, G. H.↗

NASA NTRS1988

Overview of measurements from the infrared telescope on Spacelab 2

A small helium cooled IR telescope flown on Spacelab-2 in July/August 1985 was used to make infrared measurements between 2 microns and 120 microns. New data were obtained on the structure of the Galaxy at 2 microns and 7 microns showing it to be much broader at these wavelengths than at longer wavelengths. The IR emission due to contamination from the Shuttle was found to be greater than anticipated, indicating the induced environment to be much higher than the planned limits. Aspects of superfluid helium management in zero-G and of a cryogenically cooled telescope design were also tested.

Koch, D. G.↗

NASA NTRS1987

Broad-band properties of the CfA Seyfert Galaxies. II - Infrared to millimeter properties

IR and mm observations of the 48 Seyfert 1 and 2 galaxies (SG1s and SG2s) of the CfA sample (Huchra and Berg, 1987) are reported. Data obtained (1) in the NIR using the 1.55-m reflector at Stewart Observatory and the 3-m IRTF during 1984-1986, (2) in the FIR with IRAS, and (3) at 1.3 mm using the 12-m NRAO telescope at KPNO in June 1984 are presented in extensive tables and graphs and characterized in detail. None of the objects was detected at 1.3 mm, and the IR spectra of the SG2s are found to be significantly steeper (indicating thermal emission) than those of SG1s and QSOs (nonthermal emission). Turnover in the IR emission below 100 microns (in half of the objects detected at three or more IRAS wavelengths) is shown to be consistent with an accretion disk in dust-free SG1s and with unusually warm (35-65 K) dust in SG2s. It is inferred that a 60-100-micron cool excess is masking turnover in the other SGs, so that a general association of SG nuclei with strong star formation can be confirmed.

Edelson, R. A.↗

NASA NTRS1987

The relation between star formation and active nuclei

Three questions relevant to the relation between an active nucleus and surrounding star formation are discussed. The infrared stellar CO absorption bands can be used to identify galaxies with large populations of young, massive stars and thus can identify strong starburst unambiguously, such as in NGC 6240, and can help identify composite active/starburst systems such as Arp 220. An active nucleus is probably not required for LINER spectral characteristics; dusty starburst galaxies, particularly if they are nearly edge-on, can produce LINER spectra through the shock heating of their interstellar media by supernovae combined with the obscuration of their nuclei in the optical. The Galactic Center would be an ideal laboratory for studying the interaction of starbursts and active nuclei, if both could be demonstrated to occur there. Failure to detect a cusp in the stellar distribution raises questions about the presence of an active nucleus, which should be answered by additional observations in the near future.

Rieke, G. H.↗

NASA NTRS1986

Molecular hydrogen in the young starburst in NGC 253

Shocked molecular hydrogen has been observed around the nucleus of the nearby galaxy, NGC 253. This galaxy has a relatively modest luminosity (approx. 3 x 10 to the 10th power solar luminosities) and appears to have no distortions or companions that would indicate a possible interaction. The energy of the galaxy appears to be derived primarily from a starburst. Thus, our observations have caused us to examine the starburst process in some detail to identify how the molecular hydrogen is excited. It is proposed that the molecular hydrogen emission is produced by collisions of dense molecular clouds accelerated by supernovae explosions. Within the nucleus, this process occurs early in the life of the starbust. This suggest a sequence of nuclear starburst development; examples along this sequence from young to old would include NGC 253, M82, NGC 1097, and M31.

Rieke, G. H.↗

NASA NTRS1986

Infrared observations of planets

A positive correlation was found between the strength of the 3-micron water feature and the strength of the absorption feature shortward of 0.4 microns. This is similar to what is seen in laboratory spectra of carbonaceous chondrites whose silicate compositions range from hydrated phyllosilicates to anhydrous olivine. Features were found in the IRAS images that appear to be related to solar system objects. Analysis of the data has yielded narrow trails of dust coincident with the orbits of comets Temple 2, Encke, and Gunn. Dust is found both ahead and behind comet orbital positions due to low-velocity ejection of large particles during perihelion passage. The occultation diameters of Ceres and Pallas were used to improve the standard thermal model used in the reduction of thermal IR observations of asteroids.

Lebofsky, L. A.↗

NASA NTRS1986

Infrared astronomy after IRAS

The development of infrared astronomy in the wake of IRAS is discussed. Attention is given to an overview of next generation infrared telescope technology, with emphasis on the Space Infrared Telescope Facility (SIRTF) which has been built to replace IRAS in the 1990s. Among the instruments to be included on SIRTF are: a wide-field high-resolution camera covering the infrared range 3-30 microns with large arrays of detectors; an imaging photometer operating in the range 3-700 microns; and a spectrograph covering the range 2.5-200 microns with resolutions of 2 and 0.1 percent. Observational missions for the SIRTF are proposed in connection with: planetary formation; star formation; cosmic energy sources; active galactic nuclei; and quasars.

Rieke, G. H.↗

NASA NTRS1986

MIPS - The Multiband Imaging Photometer for SIRTF

The Multiband Imaging Photometer for SIRTF (MIPS) is to be designed to reach as closely as possible the fundamental sensitivity and angular resolution limits for SIRTF over the 3 to 700 micron spectral region. It will use high performance photoconductive detectors from 3 to 200 micron with integrating JFET amplifiers. From 200 to 700 microns, the MIPS will use a bolometer cooled by an adiabatic demagnetization refrigerator. Over much of its operating range, the MIPS will make possible observations at and beyond the conventional Rayleigh diffraction limit of angular resolution.

Rieke, G. H.↗

NASA NTRS1986

MIPS - The Multiband Imaging Photometer for SIRTF

The Multiband Imaging Photometer System (MIPS) for SIRTF is to be designed to reach as closely as possible the fundamental sensitivity and angular resolution limits for SIRTF over the 3 to 700 microns spectral region. It will use high performance photoconductive detectors from 3 to 200 microns with integrating JFET amplifiers. From 200 to 700 microns, the MIPS will use a bolometer cooled by an adiabatic demagnetization refrigerator. Over much of its operating range, the MIPS will make possible observations at and beyond the conventional Rayleigh diffraction limit of angular resolution.

Rieke, G. H.↗

NASA NTRS1985

A search for nitrogen on Triton

Improved spectrophotometry of Triton at 2.16 microns was obtained with the MMT infrared photometer at a resolution of 1.0 percent. The observations do not reveal an absorption feature due to liquid nitrogen. Three explanations are consistent with this finding: (1) there is liquid nitrogen on the surface but it is not distributed uniformly; (2) the feature varies with time, e.g., it is sometimes obscured by cloud cover; and (3) the feature might be relatively broad.

Rieke, G. H.↗

NASA NTRS1985

Absolute calibration of photometry at 1 through 5 microns

The solar-analog method is used to determine the absolute calibration of photometry in the J, H, K, L, and M bands to an accuracy of 3 percent, (5 percent at M). This calibration agrees well with the direct calibration obtained by Blackwell et al. (1983); this agreement gives confidence that the calibration is known to an accuracy of 2 percent to 3 percent. The agreement also implies that the behavior of solar type stars is well understood in the infrared and that such stars make reliable standards for calibration of nonstandard photometric bands and for planetary reflectance studies. Both methods indicate that Vega is slightly brighter than indicated by atmospheric models.

Campins, H.↗

NASA NTRS1985

An absolute photometric system at 10 and 20 microns

Two new direct calibrations at 10 and 20 microns are presented in which terrestrial flux standards are referred to infrared standard stars. These measurements give both good agreement and higher accuracy when compared with previous direct calibrations. As a result, the absolute calibrations at 10 and 20 microns have now been determined with accuracies of 3 and 8 percent, respectively. A variety of absolute calibrations based on extrapolation of stellar spectra from the visible to 10 microns are reviewed. Current atmospheric models of A-type stars underestimate their fluxes by about 10 percent at 10 microns, whereas models of solar-type stars agree well with the direct calibrations. The calibration at 20 microns can probably be determined to about 5 percent by extrapolation from the more accurate result at 10 microns. The photometric system at 10 and 20 microns is updated to reflect the new absolute calibration, to base its zero point directly on the colors of A0 stars, and to improve the accuracy in the comparison of the standard stars.

Rieke, G. H.↗

NASA NTRS1984

2060 Chiron - Visual and thermal infrared observations

Five-color (wavelength = 0.36-0.85 microns) and thermal infrared (wavelength = 22.5 microns) photometric observations of the unusual asteroid 2060 Chiron were made. Between 0.36 and 0.85 microns, Chiron's reflectance spectrum is similar to those of C-class asteroids as well as Saturn's satellite Phoebe. However, the thermal IR measurements imply an albedo greater than 0.05 (i.e., a diameter of less than 250 km at the 2-sigma level) that is probably higher than those of C-class asteroids or Phoebe.

Lebofsky, L. A.↗

NASA NTRS1984

The spatial extent of the 3.3 micron emission feature in the Seyfert galaxy NGC 7469

Observations have been made of the 3.3-micron feature and the infrared continuum in the type 1 Seyfert galaxy NGC 7469 using multiaperture techniques. While as much as 10 to the 7th solar luminosities in 3.3-micron line emission may arise from within the nucleus, the data indicate that the 3.3-micron emission-line region is extended, with a significant fraction of the luminosity of the line originating at distances greater than 240 pc from the nucleus. Possible mechanisms for the heating of the dust associated with the extended emission are discussed together with observational tests which can be used to verify the more promising of these mechanisms.

Cutri, R. M.↗

NASA NTRS1984

Multifrequency observations of the BL Lacertae object 0735+178

In each of the present four simultaneous spectra covering the radio-through-X-ray regimes, the IR-UV synchrotron continuum dominates the total observed power and presumably becomes opague between 10 to the 11th and 10 to the 13th Hz. Nonsimultaneous observations were also conducted, over a longer time period, in order to study long- and short-term variability at X-ray, optical, and radio frequencies. These data indicate that the rapid and dramatic variations evident at IR and optical wavelengths are absent at radio and X-ray frequencies, supporting a view of IR-UV flux emanation from a small region, while the X-rays are produced by the inverse Compton process in the radio-emitting region. Particles, photons and magnetic field may not be far from equipartition in this region. Theoretical suggestions are developed regarding the radial behavior of the electron density and magnetic field.

Bregman, J. N.↗