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At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

ALMA OBSERVATIONS OF THE IRDC CLUMP G34.43+00.24 MM3: 278 GHz CLASS I METHANOL MASERS

We have observed a molecular clump (MM3) associated with the infrared dark cloud G34.43+00.24 in the CH{sub 3}OH J{sub K} = 9{sub –1}-8{sub 0} E, 5{sub 0}-4{sub 0} E, and 5{sub –1}-4{sub –1} E lines at sub-arcsecond resolution by using the Atacama Large Millimeter/submillimeter Array. By comparing the CH{sub 3}OH J{sub K} = 9{sub –1}-8{sub 0} E emission with the CH{sub 3}OH 5{sub 0}-4{sub 0} E and 5{sub –1}-4{sub –1} E emission, we have found that the CH{sub 3}OH J{sub K} = 9{sub –1}-8{sub 0} E emission is masing. We have clearly shown that the CH{sub 3}OH J{sub K} = 9{sub –1}-8{sub 0} masers arise from the post shocked gas in the interacting regions between the outflows and ambient dense gas. Toward the strongest peak of the CH{sub 3}OH maser emission, SiO J = 6-5 emission is very weak. This indicates that the CH{sub 3}OH maser emission traces relatively old shocks or weak shocks.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

On the Relation of Silicates and SiO Maser in Evolved Stars

The SiO molecule is one of the candidates for the seed of silicate dust in the circumstellar envelope of evolved stars, but this opinion is challenged. In this work we investigate the relation of the SiO maser emission power and the silicate dust emission power. With both our own observation by using the PMO/Delingha 13.7 m telescope and archive data, a sample is assembled of 21 SiO v = 1, J = 2 − 1 sources and 28 SiO v = 1, J = 1 − 0 sources that exhibit silicate emission features in the ISO /SWS spectrum as well. The analysis of their SiO maser and silicate emission power indicates a clear correlation, which is not against the hypothesis that the SiO molecules are the seed nuclei of silicate dust. On the other hand, no correlation is found between SiO maser and silicate crystallinity, which may imply that silicate crystallinity does not correlate with mass-loss rate.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

SMA Line Observations of the CH{sub 3}OH-maser Outflow in DR21(OH)

We present a (sub)millimeter line survey of the methanol maser outflow located in the massive star-forming region DR21(OH) carried out with the Submillimeter Array (SMA) at 217/227 GHz and 337/347 GHz. We find transitions from several molecules toward the maser outflow such as CH{sub 3}OH, H{sub 2}CS, C{sup 17}O, H{sup 13}CO{sup +}, and C{sup 34}S. However, with the present observations, we cannot discard the possibility that some of the observed species such as C{sup 17}O, C{sup 34}S, and H{sub 2}CS, might be instead associated with the compact and dusty continuum sources located in the MM2 region. Given that most of transitions correspond to methanol lines, we have computed a rotational diagram with CASSIS and an LTE synthetic spectra with XCLASS for the detected methanol lines in order to estimate the rotational temperature and column density in the small solid angle of the outflow where enough lines are present. We obtain a rotational temperature of 28 ± 2.5 K and a column density of 6.0 ± 0.9 × 10{sup 15} cm{sup −2}. These values are comparable to those column densities/rotational temperatures reported in outflows emanating from low-mass stars. Extreme and moderate physical conditions to excite the maser and thermal emission coexist within the CH{sub 3}OH flow. Finally, we do not detect any complex molecules associated with the flow, e.g., CH{sub 3}OCHO, (CH{sub 3}){sub 2}CO, and CH{sub 3}CH{sub 2}CN.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1965

The helium system of the maser installation at the Goonhilly satellite-communication earth station

A travelling-wave solid-state maser anlplifier is used to provide the first stage of amplification in the receiving system at the communication-satellite earth-station at Goonhilly Downs. While the maser itself was built by an industrial research laboratory, the auxiliary supplies and equipment essential for the operation of the maser were designed and built by staff of the Post Office Research Station. A major part of this auxiliary equipment consists of apparatus for handling the helium refrigerant.

GROUND STATION↗
NASA NTRS1995

A Circumstellar H2O Maser Associated With the Galactic Circumnuclear Molecular Disk?

In the course of conducting a survey of 22-GHzH2O masers in the inner galaxy, we discovered a maser source in Sgr A West. It is located ~30'N and 35'E of Sgr A*, near the edge of the Eastern arm of the radio mini-spiral, which presumably coincides with the inside edge of the circumnuclear disk. Furthermore, the radial velocity of the maser is remarkably similar to that expected for gas in the circumnuclear disk at this location. We have also found a luminous, reddened star having a bolometric magnitude and IR spectrum characteristic of an M supergiant at this location. The extinction is consistent with a location in the inner galaxy, near or possibly within the circumnuclear disk. If this star is associated with the circumnuclear disk, it will have implications for star formation in the unusual galactic center environment.

Circumstellar Maser↗
DOE OSTI2024

Modelling of the electron cyclotron emission burst from a laboratory tokamak plasma with loss-cone maser instability

The maser instability associated with the loss-cone distribution has been widely invoked to explain the radio bursts observed in the astrophysical plasma environment, such as aurora and corona. In the laboratory plasma of a tokamak, events reminiscent of these radio bursts have also been frequently observed as an electron cyclotron emission (ECE) burst in the microwave range (~2f ce near the last closed flux surface) during transient magnetohydrodynamic events. These bursts have a short duration of ~10 μs and display a radiation spectrum corresponding to a radiation temperature T e,rad of over 30 keV while the edge thermal electron temperature T e is only in the range of 1 keV. Suprathermal electrons can be generated through magnetic reconnection, and a loss-cone distribution can be generated through open stochastic field lines in the magnetic mirror of the near-edge region of a tokamak plasma. Radiation modelling shows that a sharp distribution gradient ∂f/∂v ⊥ > 0 at the loss-cone boundary can cause a negative absorption of ECE radiation through the maser instability. The negative absorption then amplifies the radiation so that the microwave intensity is significantly stronger than the thermal value. The significant T e,rad from the simulations suggests the potential role of the loss-cone maser instability in generating the ECE burst in a tokamak.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1978

Analysis of hydrogen maser frequency drift due to possible drifts in load VSWR and phase angle of reflection coefficient

Theoretical equations are derived for calculating the effects of local VSWR and reflection coefficient phase angle drifts on hydrogen maser frequency stability. Sample calculations made for a typical JPL maser show that under special load conditions, a VSWR drift of 0.000075/h or phase angle drive of 0.01 deg/h can produce a frequency drift of (10 to the -14th power f sub 0) Hz/h where f sub 0 is the maser frequency of approximately 1.42 x 10 to the 9th power Hz.

Beatty, R. W.↗
NASA NTRS1977

New infrared objects associated with OH masers

Results of a search for IR radiation at 10 microns from a sample of OH maser sources are reported. An IR source is discovered near each of six OH masers which emit mainly at 1612 MHz in two distinct velocity ranges. It is shown that all the sources have varied with time, that two sources have exhibited significant variations in color temperature, and that the energy distributions of the six objects over the spectral range from 2 to 20 microns fall into two categories. Absorption in the 2.3-micron band of CO is detected in two sources, and four are found to display substantial silicate absorption features. The energy distributions of the sources indicate that pumping by 35-micron photons is feasible, but 2.8-micron pumping is very unlikely; the distributions are best explained as emission from very thick dust shells at temperatures of about 500 K. The data are taken as supporting the hypothesis that every double-peaked OH maser emitting principally at 1612 MHz is associated with an IR object. The nature of the objects inside the dust shells and their evolutionary state are briefly discussed.

Evans, N. J., II↗
NASA NTRS1978

New silicon monoxide masers

Seven Mira variable stars with silicon monoxide maser emission have been found. All are later than M4 and heavily reddened. Two were observed near maximum light. One, Y Cas, seems to bear out the correlation of 43-GHz SiO maser luminosity and mean spectral type at maximum light. RT Aql, however, falls about 1 mag below the expected brightness. A catalog of SiO maser stars is given.

Dickinson, D. F.↗
NASA NTRS1980

improving maser frequency stability

Hydrogen maser frequency standard is more stable by addition of parallel pyrex capillary tube array collimator. With collimator, maser line width has been made as narrow as 0.24 hertz representing fivefold improvement over maser without collimator. Fluorocarbon coating in tubes virtually eliminates energy loss in collimator.

Crampton, S. B.↗
NASA NTRS1978

Hydrogen maser frequency standard computer model for automatic cavity tuning servo simulations

A computer model of the JPL hydrogen maser frequency standard was developed. This model allows frequency stability data to be generated, as a function of various maser parameters, many orders of magnitude faster than these data can be obtained by experimental test. In particular, the maser performance as a function of the various automatic tuning servo parameters may be readily determined. Areas of discussion include noise sources, first-order autotuner loop, second-order autotuner loop, and a comparison of the loops.

Potter, P. D.↗
NASA NTRS1979

A small, passively operated hydrogen maser

The paper describes a compact passive hydrogen maser with unique features including a reduction in size. It uses a passive operation mode, permitting the use of a small microwave TE(011) cavity dielectrically loaded by a low loss alumina. The Teflon coated quartz bulb common in other masers has been replaced by a Teflon coating on the inside wall of the cavity producing a simpler designed and a more rugged H-maser package. The cavity and the attached endcaps comprise the vacuum envelope, allowing the use of a single vacuum system. The dimensional stability of the ceramic cavity under barometric changes is sufficiently within the range of the electronic cavity servo so that a second vacuum system is not required. For temperature control, a single oven is located in the magnetic shield nest.

Howe, D. A.↗
NASA NTRS1981

Vacuum pumping system for spaceborne passive hydrogen masers

The ultimate utility of hydrogen masers as highly accurate clocks aboard navigation satellites depends on the feasibility of making the maser lightweight, compact, and capable of a 5 to 7 year unattended operation. A vacuum pumping system for the maser that is believed to meet these criteria was designed and fabricated. The pumping system was fabricated almost completely from 6Al-4V titanium alloy and incorporates two or four sintered zirconium carbon getter pumps with integral activation heaters. The manner in which the getter pumps were mounted to insure that they will stand both the activation and the shock of launch is illustrated. Data on the total hydrogen capacity and pumping of this system is also presented.

Wolf, S. A.↗
NASA NTRS1981

Precision timekeeping using a small passive hydrogen maser

The timekeeping ability of a prototype passive hydrogen maser which is a factor of 5 smaller in size, weight, and cost than any previously designed, was compared to UTC (NBS) based on 10 cesium frequency standards including a large primary standard, NBS-4. The frequency of the prototype was monitored as a function of source pressure, cavity temperature, microwave power, modulation width, and magnetic field. Based on these measurements, a frequency stability of better than 6 x 10 to the -15 power was expected, implying a timekeeping ability of order 0.5 ns/day. Measurements vs UTC(NBS) indicate a joint timekeeping a stability of order 1.2 ns/day. Simultaneous measurements made between NBS-4, UTC(6600), and the small passive me maser show peak to peak time variations of the small maser vs UTC(6600) was 10 ns for the full 32 days if the average rate and drift are considered. Frequency stability of the small prototype vs UTC (NBS) was to 1.1 x 10 to the -14th power for tau = 1 to 8 days.

Walls, F. L.↗
NASA NTRS1981

Hydrogen maser development at Laval University

The physical construction of two hydrogen masers is described and results of measurements made on one of the masers are given. These include: cavity Q, thermal time constant, line Q, signal power output, magnetic shielding factor. Preliminary results indicate that the frequency stability will be mainly affected by the thermal of the cavity. The magnetic field and the barometric fluctuations should not affect the maser at the stability level above a few parts in 10 to the 15th power, which is the goal for averaging times of several hours.

Vanier, J.↗
NASA NTRS1981

An error budget for the JPL hydrogen maser receiver

The hydrogen maser receiver is a synthesizer that converts the maser signal, at about 1420 MHz, to a set of output signals at 100, 20, 10, 5, 1, and 0.1 MHz. The contribution of the receiver and its component modules to the frequency instability and phase noise of each of its outputs is estimated, and these results are compared to published measurements of the 100-MHz output of the frequency standard, which consists of a maser plus its receiver. One can then assess how much the receiver degrades the performance of the frequency standard.

Greenhall, C. A.↗
NASA NTRS1982

Frequency stability of maser oscillators operated with cavity Q

The short term frequency stability of masers equipped with an external feedback loop to increase the cavity quality factor was studied. The frequency stability of a hydrogen and a rubidium maser were measured and compared with theoretical evaluation. It is shown that the frequency stability passes through an optimum when the cavity Q is varied. Long term fluctuations are discussed and the optimum mid term frequency stability achievably by small size active and passive H-masers is considered.

Tetu, M.↗
NASA NTRS1982

Experimental evaluation of a ruby maser at 43 GHz

Inversion ratio measurements were conducted at several frequencies between 27 and 43 GHz for a pink ruby material (0.05% Cr/3+/ in Al2O3) at the push-pull pump angle of 54.7 degrees in order to determine the upper frequency limit where pink ruby could be expected to operate as a practical maser amplifier. Based on these measurements, a single-stage maser was developed which yielded 8 + or - 1 dB net gain and a 3 dB bandwidth of 180 MHz at a center frequency of 42.5 GHz. It is concluded that a multistage reflected wave maser could achieve bandwidths exceeding 1 GHz with 30 dB net gain at center frequencies near 40 GHz.

Moore, C. R.↗