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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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NASA NTRS2002

X-ray Observations of the Supernova Remnants G349.7+0.2 and CTA 1

This compact, high luminosity SNR is known to be interacting with a molecular cloud, based on the observation of OH masers. The maser lines provide velocity measurements which place the remnant at a distance of 22 kpc. The analysis of our ASCA data is now complete. We find that the X-ray emission from this remnant is dominated by material of solar abundances, consistent with the picture of a molecular cloud interaction. At the very large distance indicated by the masers, the observed flux makes G349.7+0.2 one of the most luminous SNRs in our galaxy. We show that the X-ray emitting plasma is not in ionization equilibrium, and that while the remnant has swept up large amounts of material, it is actually relatively young, holding some promise for identification of stellar ejecta in future high resolution studies. A paper detailing our analysis and results has been completed and is in the final stages of circulation amongst co-authors prior to submission to ApJ.

Slane, Patrick O.↗
NASA NTRS2004

Is there an Obscured AGN in the Normal Galaxy IRASF01063-8034

The target galactic nucleus is ostensibly "normal," but the presence of water maser emission indicates that it may be an obscured AGN. Our primary goal has been to test this hypothesis through the detection hard X-ray emission and an X-ray spectrum characteristic of heavy absorption. The data for this program became available in May 2003. Light curves show that most of the data are good and that the background was well behaved. We have constructed images and found the X-ray emission in this target is a hard and may be extended. The presence of an AGN has been confirmed through observation with XMM. This is one of many edge-on normal galaxies that may contain AGN. The orientation of the extension will be compared to the structure of molecular gas observed at high angular resolution with VLBI. These radio observations were completed in August 2003. Correlation was completed in late 2003. The data have yet to be delivered by the ATNF. Since the start of the program, we have also obtained six radio spectra, on top of the two obtained at or close to the epoch of discovery for the maser. Early indications were that the maser emission exhibited unusually broad velocity extent and that it "jumped in velocity on time scales of weeks. This behavior has been speculated to be the signature of emission excited by jet-ISM interactions. After more extensive and more sensitive radio study, we find that (1) the emission does not in fact change velocity centroid substantially and (2) it comprises narrower, more "normal" emission features. The joint interpretation of radio and XMM data will be possible once the VLBI images and position-resolved X-ray spectra have been made, probably in summer 2004. If the radio emission arises in an accretion disk, rather than a jet, then we may predict that the VLBI images will exhibit velocity-position gradients orthogonal to the extension of X-ray emission, which presumably traces an optical narrow line or outflow region.

Greenhill, Lincoln J.↗
NASA NTRS2006

Deep Space Network, Cryogenic HEMT LNAs

Exploration of the Solar System with automated spacecraft that are more than ten astronomical units (1 AU = 149,597,870.691 km) from earth requires very large antennae employing extremely sensitive receivers. A key figure of merit in the specification of the spacecraft-to-earth telecommunications link is the ratio of the antenna gain to operatio nal noise temperature (G/Top) of the system. The Deep Space Network (DSN) receivers are cryogenic, low-noise amplifiers (LNAs) which addres s the need to maintain Top as low as technology permits. Historicall y, the extra-ordinarily sensitive receive systems operated by the DSN have required ctyogenically cooled, ruby masers, operating at a physi cal temperature near the boiling point of helium, as the LNA. Althoug h masers continue to be used today, they are hand crafted at JPL and expensive to manufacture and maintain. Recent advances in the developm ent of indium phosphide (InP) based high electron mobility transistor s (HEMTs) combined with cryogenic cooling near the boiling point of h ydrogen have made this alternate technology comparable with and a fraction of the cost of maser technology. InP HEMT LNA modules are demons trating noise temperatures less than ten times the quantum noise limi t (10hf/k) from 1 to 100 GHz. To date, the lowest noise LNA modules developed for the DSN have demonstrated noise temperatures of 3.5 K and 8.5 K at 8.5 K at 32 GHz, respectively. Front-end receiver packages employing these modules have demonstrated operating system noise temperatures of 17 K at 8.4 GHz (on a 70m antenna at zenith) and 39 K at 3 2 GHz (on a 34m antenna at zenith). The development and demonstration of cryogenic, InP HEMT based front-end amplifiers for the DSN requir es accurate component and module characterization, and modeling from 1 to 100 GHz at physical temperatures down to 12 K. The characterizati on and modeling begins with the HEMT chip, proceeds to the multi-stag e HEMT LNA module, and culminates with the complete front-end cryogenic receiver package for the antenna. This presentation will provide a n overview of this development process. Examples will be shown for de vices, LNA modules, front-end receiver packages, antennae employing these packages and the improvements to the down-link capacity.

low-noise amplifiers (LNAs)↗
NASA NTRS2011

The EVN Galactic Plane Survey - EGaPS

I present a catalogue of the positions and correlated flux densities of 109 compact extragalactic radio sources in the Galactic plane determined from an analysis of a 48-h Very Long Baseline Interferometry (VLBI) experiment at 22 GHz with the European VLBI Network. The median position uncertainty is 9 mas. The correlated flux densities of the detected sources are in the range of 2-300 mJy. In addition to the target sources, nine water masers have been detected, of which two are new. I derived the positions of the masers with an accuracy of 30-200 mas and determined the velocities of the maser components and their correlated flux densities. The catalogue and the supporting material are available at http://astrogeo.org/egaps.

Petrov, Leonid↗
NASA NTRS2010

Simulating Future GPS Clock Scenarios with Two Composite Clock Algorithms

Using the GPS Toolkit, the GPS constellation is simulated using 31 satellites (SV) and a ground network of 17 monitor stations (MS). At every 15-minutes measurement epoch, the monitor stations measure the time signals of all satellites above a parameterized elevation angle. Once a day, the satellite clock estimates the station and satellite clocks. The first composite clock (B) is based on the Brown algorithm, and is now used by GPS. The second one (G) is based on the Greenhall algorithm. The composite clock of G and B performance are investigated using three ground-clock models. Model C simulates the current GPS configuration, in which all stations are equipped with cesium clocks, except for masers at USNO and Alternate Master Clock (AMC) sites. Model M is an improved situation in which every station is equipped with active hydrogen masers. Finally, Models F and O are future scenarios in which the USNO and AMC stations are equipped with fountain clocks instead of masers. Model F is a rubidium fountain, while Model O is more precise but futuristic Optical Fountain. Each model is evaluated using three performance metrics. The timing-related user range error having all satellites available is the first performance index (PI1). The second performance index (PI2) relates to the stability of the broadcast GPS system time itself. The third performance index (PI3) evaluates the stability of the time scales computed by the two composite clocks. A distinction is made between the "Signal-in-Space" accuracy and that available through a GNSS receiver.

global positioning system↗
NASA NTRS2004

Local oscillator distribution using a geostationary satellite

A satellite communication system suitable for distribution of local oscillator reference signals for a widely spaced microwave array has been developed and tested experimentally. The system uses a round-trip correction method of the satellite This experiment was carried out using Telstar-5, a commercial Ku-band geostationary satellite. For this initial experiment, both earth stations were located at the same site to facilitate direct comparison of the received signals. The local oscillator reference frequency was chosen to be 300MHz and was sent as the difference between two Ku-band tones. The residual error after applying the round trip correction has been measured to be better than 3psec for integration times ranging from 1 to 2000 seconds. For integration times greater then 500 seconds, the system outperforms a pair of hydrogen masers with the limitation believed to be ground-based equipment phase stability. The idea of distributing local oscillators using a geostationary satellite is not new; several researchers experimented with this technique in the eighties, but the achieved accuracy was 3 to 100 times worse than the present results. Since substantially and the performance of various components has improved. An important factor is the leasing of small amounts of satellite communication bandwidth. We lease three 100kHz bands at approximately one hundredth the cost of a full 36 MHz transponder. Further tests of the system using terminal separated by large distances and comparison tests with two hydrogen masers and radio interferometry is needed.

hydrogen maser↗
NASA NTRS1972

Classical laser.

In this paper a completely classical model for laser action is discussed. An active medium consisting of classical anharmonic oscillators interacts with a classical electromagnetic field in a resonant cavity. Comparison with the case of a medium consisting of harmonic oscillators shows the significance of nonlinearities for producing self-sustained oscillations in the radiation field. The results for the classical model are found to be similar to those for a semiclassical model of the ammonia-beam maser. The conclusion is that laser action is not intrinsically a quantum-mechanical effect. The classical-laser theory as given in this paper can also be applied to the case of the electron-cyclotron maser.

Borenstein, M.↗
NASA NTRS1974

Expected far infrared polarization of H2 regions and the nuclei of galaxies

The expected polarization of far infrared sources is discussed, and it is shown that the observed degree of polarization generally depends on two factors: (1) the availability of a mechanism that can produce polarization, and (2) the gain in polarization which absorption or stimulated emission can produce within a source. It is pointed out that stimulated emission could produce sizeable gain changes in compact dust clouds such as those associated with H2 regions and possibly also in dense regions exhibiting OH and H2O masers. Whether such a gain can actually become positive (maser-like behavior) is not clear, but this would in any case depend on the chemical structure of the grain material and the spectral range of interest.

Harwit, M. O.↗
NASA NTRS1974

A comparison of the cesium and hydrogen hyperfine frequencies by means of Loran-C and portable clocks

A comparison of the hydrogen and cesium hyperfine frequencies is made using a hydrogen maser calibrated directly against the Flexible Bulb Large Storage Box Hydrogen Maser and a Hewlett-Packard portable high performance cesium clock calibrated indirectly against the USNO Master Clock via a Loran-C link. The portable cesium clock is transported from the USNO to Harvard University in operating condition. This allows the evaluation of the portable clock's performance under transport. Data are presented on the epoch and frequency stability of the portable clock under transport as well as the usefulness of a closure measurement in determining clock drift.

Reinhardt, V. S.↗
NASA NTRS1975

Very long baseline interferometric observations of OH/IR stars

Results are reported for spectral-line very long baseline interferometric observations of the following II OH/IR objects, which emit strong 1612-MHz OH maser radiation concentrated at two velocities: NML Cyg, R Aql, IRC+10011, IRC-10529, and OH 1837-05. The apparent angular sizes were obtained for NML Cyg and R Aql, and lower limits upon the apparent sizes were obtained for the other objects. The data for NML Cyg agree with previous size determinations and indicate that the low- and high-velocity components are separated by about 20 times their apparent size. The maser component of R Aql is calculated within a factor of two to be about 5 by 10 to the 14th power cm, although the emitting region can be significantly larger. A qualitative description is given for II OH/IR objects with late M-type Mira variable center stars and circumstellar dust shells of similar dimensions.

Reid, M. J.↗
NASA NTRS1977

On the relationship between the infrared source CRL 2591 /UOA-27/ and its radio and H2O counterparts

Recent radio, infrared, and H2O maser observations show that there is a 7-arcsec angular separation between the protostarlike infrared source CRL 2591 and the compact H II region which has until now been identified with it, while the H2O maser coincides with the infrared source. This result, together with an extension of photometric measurements to 20 microns and a much improved upper limit to its angular size, reinforces the apparent similarity of CRL 2591 to the BN object in Orion and to W3/IRS 5.

Wynn-Williams, C. G.↗
NASA NTRS1978

A new, compact far-infrared source in the W31 region

In a survey of the W31 region, a compact far-infrared source was detected at the position of the radio continuum source G 10.6-0.4. Associated with this infrared source and in close coincidence with its position is an H II region with a compact core and extended halo as well as OH and H2O masers. An extended molecular cloud, centered on these sources, has also been detected. The compact source and associated masers may be located at the H II region-molecular-cloud interface in a thin shocked layer of neutral gas driven into the molecular cloud by the expansion of the H II region. The compact H II region is depleted of dust and must be surrounded by a very dense shell of dust and gas (hydrogen number density in excess of 200,000 per cu cm). The source probably represents an early stage of stellar evolution.

Fazio, G. G.↗
NASA NTRS1979

FTS maintenance and calibration at DSS 42/43

An FTS maintenance and calibration task was conducted at DSS 42/43 during August 1978. The objectives of this effort were (1) the routine maintenance and calibration of hydrogen masers, (2) installation and calibration of cesium standards, (3) installation of test equipment for frequency measurement, (4) CRG testing, (5) cabling inspection and repair, (6) check thermal and magnetic environment of H-maser/cesium room, and (7) calibration of frequency and timing subsystem.

Dachel, P. R.↗
NASA NTRS1979

An infrared study of the NGC 7538 region

Infrared observations of the NGC 7538 region at wavelengths from 1 micron to 1 mm are presented and analyzed with the aim of understanding both the large-scale structure of this region of current star formation and the properties of the individual compact objects within it. At far-infrared wavelengths (25-130 microns), emission is seen from the visible H II region, from the vicinity of the previously known maser sources and dust-embedded compact HII regions, and from a new region called NGC 7538(E). Coincident with NGC 7538(E) are a point-like 1-25 micron infrared source, NGC 7538-IRS9, which probably provides the power for the far-infrared emission, and an extended source of 2.2 micron emission which appears to be an infrared reflection nebula. The compact H II regions, the maser sources and IRS9 are located within a dense molecular cloud at the edge of the optical H II region. This cloud, which has a mass of approximately 9000 solar masses, is detected in emission at 1 mm. The NGC 7538 region appears to contain examples of different stages in the formation of massive stars; it is suggested that the center of star formation is moving systematically to the southeast in this region.

Werner, M. W.↗
NASA NTRS1981

Fiber optics transmit clock signal more reliably

Optical automatic gain control smooths maser clock amplitude fluctuations without phase shift. Uncomplicated optical system is more reliable than electrical transmission circuits which require phase-locked loops to compensate for shift. Maser feeds reference signal to linear fiber-optic analog transmitter which emits modulated laser beam directed to splitter. Splitter consists of dichroic mirrors and associated lenses for distributing beam to output ports. Cables attached there guide signals to receiving station.

Lutes, G. F., Jr.↗
NASA NTRS1980

A report on the gravitational redshift test for non-metric theories of gravitation

The frequencies of two atomic hydrogen masers and of three superconducting cavity stabilized oscillators were compared as the ensemble of oscillators was moved in the Sun's gravitational field by the rotation and orbital motion of the Earth. Metric gravitation theories predict that the gravitational redshifts of the two types of oscillators are identical, and that there should be no relative frequency shift between the oscillators; nonmetric theories, in contrast, predict a frequency shift between masers and SCSOs that is proportional to the change in solar gravitational potential experienced by the oscillators. The results are consistent with metric theories of gravitation at a level of 2%.

Source record↗
NASA NTRS1980

A study of the processes in the RF hydrogen gas dissociator

The role of the RF gas dissociator in the hydrogen maser is examined. Based on collisional and plasma transport processes, the performance of the source is investigated. It is found that while the complexity of the collisional processes in the RF dissociator prohibits an easily obtained quantitative expression for the performance of the source, it is nevertheless possible to make general inferences concerning the qualitative performance based on collisional effects. An analytical expression for the efficiency of the source in atom production is obtained based on plasma transport processes. On the basis of this study some recommendations are made for the development of more efficient RF hydrogen gas dissociators for use in masers.

Maleki, L.↗