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11 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2012

Reducing the Read Noise of HAWAII-2RG Detector Systems with Improved Reference Sampling and Subtraction (IRS2)

IRS2 is a Wiener-optimal approach to using all of the reference information that Teledyne's HAWAII-2RG detector arrays provide. Using a new readout pattern, IRS2 regularly interleaves reference pixels with the normal pixels during readout. This differs from conventional clocking, in which the reference pixels are read out infrequently, and only in a few rows and columns around the outside edges of the detector array. During calibration, the data are processed in Fourier space, which is <;:lose to the noise's eigenspace. Using IRS2, we have reduced the read noise of the James Webb Space Telescope Near Infrared Spectrograph by 15% compared to conventional readout. We are attempting to achieve further gains by calibrating out recently recognized non-stationary noise that appears at the frame rate.

Rauscher, Bernard J.↗
DOE OSTI2020

Materials Data on IrS2 by Materials Project

IrS2 is Marcasite-like structured and crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. there are two inequivalent Ir4+ sites. In the first Ir4+ site, Ir4+ is bonded to six S2- atoms to form IrS6 octahedra that share corners with eight IrS6 octahedra, a cornercorner with one SIr3S tetrahedra, and edges with two equivalent IrS6 octahedra. The corner-sharing octahedra tilt angles range from 57–62°. There are a spread of Ir–S bond distances ranging from 2.31–2.41 Å. In the second Ir4+ site, Ir4+ is bonded to six S2- atoms to form IrS6 octahedra that share corners with four equivalent IrS6 octahedra, corners with two equivalent SIr3S tetrahedra, and edges with four equivalent IrS6 octahedra. The corner-sharing octahedra tilt angles range from 57–62°. There are a spread of Ir–S bond distances ranging from 2.34–2.42 Å. There are four inequivalent S2- sites. In the first S2- site, S2- is bonded in a 3-coordinate geometry to three equivalent Ir4+ atoms. In the second S2- site, S2- is bonded to three equivalent Ir4+ and one S2- atom to form distorted SIr3S tetrahedra that share corners with three IrS6 octahedra and corners with six equivalent SIr3S tetrahedra. The corner-sharing octahedra tilt angles range from 76–82°. The S–S bond length is 2.38 Å. In the third S2- site, S2- is bonded in a 4-coordinate geometry to three Ir4+ and one S2- atom. In the fourth S2- site, S2- is bonded in a distorted trigonal non-coplanar geometry to three Ir4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on IrS2 by Materials Project

IrS2 is pyrite-like structured and crystallizes in the cubic Pa-3 space group. The structure is three-dimensional. Ir4+ is bonded to six equivalent S2- atoms to form corner-sharing IrS6 octahedra. The corner-sharing octahedral tilt angles are 62°. All Ir–S bond lengths are 2.37 Å. S2- is bonded in a distorted trigonal planar geometry to three equivalent Ir4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Cu(IrS2)2 by Materials Project

CuIr2S4 is Spinel structured and crystallizes in the tetragonal I4_1/amd space group. The structure is three-dimensional. Ir+3.50+ is bonded to six equivalent S2- atoms to form IrS6 octahedra that share corners with six equivalent CuS4 tetrahedra and edges with six equivalent IrS6 octahedra. All Ir–S bond lengths are 2.38 Å. Cu1+ is bonded to four equivalent S2- atoms to form CuS4 tetrahedra that share corners with twelve equivalent IrS6 octahedra. The corner-sharing octahedra tilt angles range from 57–59°. All Cu–S bond lengths are 2.33 Å. S2- is bonded to three equivalent Ir+3.50+ and one Cu1+ atom to form a mixture of distorted edge and corner-sharing SCuIr3 trigonal pyramids.

36 MATERIALS SCIENCE↗
NASA NTRS1981

Infrared and radio observations of W51: Another Orion-KL at a distance of 7kpc

The bright infrared sources W51-IRS2 has at least three components with different physical and evolutionary properties. The spatial distribution and the near infrared spectra of the components in IRS2 are remarkably similar to, but more luminous than those found in Orion, where an H2 region of comparable linear size is also located close to a cluster of compact infrared sources. The characteristics of the nearby W51-NORTH H2O maser source, and the detection of 2 micro m H2 quadrupole emission in IRS2 indicate that the mass loss phenomena found in Orion-KL also exist in W51.

Genzel, R.↗
NASA NTRS1984

Absorption features in the 5-8 micron spectra of protostars

High signal-to-noise ratio spectra in the range of 5-8 microns of four sources embedded in molecular clouds are examined using low-temperature laboratory measurements of the 5-8-micron spectra of simple molecules and their mixtures. The absorption, apparent in all four sources, is characterized by highly distinct features ranging from two relatively narrow bands at 6.0 and 6.8 microns in W33A to a broad, shallow, and partially structured feature extending from 5.2 to 7.8 microns in Mon R2-IRS2, BN, and NGC2264. The first feature (W33A) is explained by the OH bending mode in H2O and the CH deformation modes in saturated hydrocarbons; while the second feature (Mon R2-IRS2-type) is explained by the presence of a mixture of saturated and unsaturated hydrocarbons possibly containing strongly electronegative groups.

Tielens, A. G. G. M.↗
NASA NTRS1989

Near-IR imaging and imaging polarimetry of OMC 2

NIR and 2.2-micron imaging polarimetry of the molecular cloud region OMC 2, reveals a cluster of low- to intermediate-mass premain-sequence stars embedded in circumstellar disks. The 2.2-micron imaging polarimetry indicates that the compact NIR sources OMC 2 IRS1, IRS2, IRS3 and IRS4 N, are illumination centers for the surrounding extended emission. By application of Hubble's relation to the nebulae illuminated by IRS1, IRS2 and IRS4 N, the illuminating geometry is explained and the intrinsic NIR colors of these objects are estimated.

Rayner, John↗
NASA NTRS1978

Detection of star formation regions near supernova remnant W44

Observations of two infrared objects embedded in molecular clouds near the supernova remnant W44 are presented. W44-IRS1 offers compelling evidence that it is a star whose formation was recently induced by expansion of the supernova remnant. W44-IRS2 lies beyond the remnant, possibly apart from the region of its influence.

Wootten, A.↗
NASA NTRS1980

Small-scale structure of the CO emission in S255 from lunar occultation observations

Two lunar occultations of the S255 H II region/molecular cloud complex were observed in the 2.6 mm CO line during 1978 and 1979. The resolution obtained (between 4 arcsec and 7 arcsec) enables us to resolve bright sources that are much smaller than the 44 arcsec telescope beam. In addition to the large-scale structure (approximately 10 arcmin in size) seen in previous CO maps, the observations reveal two high-temperature emission regions in the cloud core associated with two compact infrared sources about 20 arcsec apart. The first CO hot spot is larger in size with a Gaussian width of 41 arcsec + or - 7 arcsec and a peak temperature of 65 K. Its center falls between the two small infrared sources S255 IRS1 and IRS2. The linear size and peak temperature of this source are remarkably similar to those in the Orion Kleinmann-Low nebula. The second source is revealed from a discontinuous change in the CO line flux as the lunar limb crossed S255 IRS1. The size of this component is less than 7 arcsec; its temperature must exceed 200 K. No evidence is found for exceptionally high temperatures at the boundary of the two H II regions crossed during the occultations.

Schloerb, F. P.↗
NASA NTRS1986

The 4 micron spectra of compact infrared sources

High resolution 5 arcsec spectra in the 4 micron region are presented of the central 5 arcsec of the compact near infrared sources K3-50, W51-IRS2 East, and G333.6-0.2. From measured Br-alpha/Pf-beta line ratios and previously published infrared and radio maps, it is concluded that standard recombination theory fails to explain our observations in at least two cases. It is demonstrated that the data are consistent with thermal excitation of the hydrogen lines in strong stellar winds. The Pf-beta Hu-epsilon line ratio, which is completely insensitive to differential extinction, confirms the need for the stellar wind model for the core of G333.6-0.2. From the (K III) line it is estimated that the potassium abundance in G333.6-0.2 is at least equal to the solar value, and possibly enhanced by a factor up to 10.

Hofmann, R.↗
NASA NTRS1990

Interstellar absorption lines toward NGC 2264 and AFGL 2591 - Abundances of H2, H3(+), and CO

Interstellar absorption-line spectroscopy of NGC 2264 is reported which shows that the CO molecule has a column density of 5 x 10 to the 18th/sq cm and a rotational excitation temperature of 28 K. A direct upper limit on the H2 column density implies that at least 6 percent of a solar carbon abundance is in the form of CO. The upper limit on the H3(+) abundance implies that the cosmic-ray ionization rate is of the order of 10 to the -16th/s or less. The H3(+) upper limit, together with a previous radio detection of H2D(+) emission, implies either an enormous overabundance of the deuterated molecule or else that most of the radio emission comes from clouds not located directly between use and the infrared source. Observations of the sources AFGL 2591 and NGC 2024 IRS2 indicate that upper limits on H3(+) imply cosmic ray ionization rates of less than 3 and 60 x 10 to the -17th/s, respectively.

Black, John H.↗