Control valve: Hot gas fast response

The design of a warm gas control valve is reviewed outlining the problems posed by the requirement for extremely fast response combined with a severe environment and a hot, dirty, and corrosive operating fluid

Lateral Shock of the R Aquarii Jet

The R Aqr jet was observed with the VLA B-configuration at two epochs separated by ~13.2 yr. Comparison of the resulting 6 cm continuum images show that the radio jet has undergone a lateral counterclockwise rotation of ~6-12 on the plane of the sky. The model of jet parcels on independent trajectories is difficult to reconcile with these observations and leads us to consider a path-oriented jet (i.e., younger parcels follow the same path as older parcels). Comparison of the most recent radio image with a nearly contemporaneous HST /FOC ultraviolet image at ~2330 A suggests that the ultraviolet emission lies along the leading side of the rotating radio jet. In conjunction with a proper motion analysis of the jet material that yields empirical space-velocity and resulting acceleration-magnitude relationships as a function of distance from the central source, we evaluate the observational results in terms of a schematic model in which the jet emission consists of plane-parallel isothermal shocks along the leading edge of rotation. In such a radiating shock, the ultraviolet-emitting region is consistent with the adiabatic region in the form of a high-temperature, low-density sheath that surrounds the cooled postshock radio-emitting region. Within the context of the schematic model, we obtain the temperatures, densities, and pressures within the preshock, adiabatic, and postshock regions as a function of distance from the central source; the physical parameters so derived compare favorably to previously published estimates. We obtain a total jet mass of 3.1x10^-5 M and an age of ~115 yr. We evaluate the model in the context of its density-boundary condition, its applicability to an episodic or quasi-continuous jet, and angular momentum considerations

Lateral Shock of the R Aquarii Jet

The R Aqr jet was observed with the VLA B-configuration at two epochs separated by approximately 13.2 yr. Comparison of the resulting 6 cm continuum images show that the radio jet has undergone a lateral counterclockwise rotation of approximately 6 deg-12 deg on the plane of the sky. The model of jet parcels on independent trajectories is difficult to reconcile with these observations and leads us to consider a path-oriented jet (i.e., younger parcels follow the same path as older parcels). Comparison of the most recent radio image with a nearly contemporaneous HST/FOC ultraviolet image at approximately 2330 Angstroms suggests that the ultraviolet emission lies along the leading side of the rotating radio jet. In conjunction with a proper motion analysis of the jet material that yields empirical space-velocity and resulting acceleration-magnitude relationships as a function of distance from the central source, we evaluate the observational results in terms of a schematic model in which the jet emission consists of plane-parallel isothermal shocks along the leading edge of rotation. In such a radiating shock, the ultraviolet-emitting region is consistent with the adiabatic region in the form of a high-temperature, low-density sheath that surrounds the cooled postshock radio-emitting region. Within the context of the schematic model, we obtain the temperatures, densities, and pressures within the preshock, adiabatic, and postshock regions as a function of distance from the central source; the physical parameters so derived compare favorably to previously published estimates. We obtain a total jet mass of 3.1 x 10(exp -5) solar mass and an age of approximately 115 yr. We evaluate the model in the context of its density-boundary condition, its applicability to an episodic or quasi-continuous jet, and angular momentum considerations

High Spatial Resolution VLA Observations of the R Aquarii Jet

High spatial resolution observations (~1 ) of the jet feature associated with the symbiotic variable R Aquarii were obtained with the Very Large Array (VLA). The peak radio intensity of the jet lies at a 29~3 P.A. with respect to the radio emission from R Aquarii itself. If the line defined by the jet and star is extended ~196 , it intercepts a previously reported and heretofore unresolved radio source. In our high spatial resolution 6 cm map, this feature is resolved into a compact double radio source, whose peak intensity lies on an axis defined by the jet and star. The possible association of this feature with R Aquarii or with the extended filamentary nebula that surrounds the system cannot be determined from these radio morphology studies alone. If this feature is associated with R Aquarii, it may represent ejecta from the system which occurred previously. Moreover, a new unresolved radio feature has been detected - 2\u27\u27:7 from the central star at - 45° P.A. It may represent material recently ejected from the system, perhaps as the object precesses. Weak evidence for a counter-jet is suggested from radio contours centered on R Aquarii

Ultraviolet Variability and Mass Expulsion from R Aquarii

Ultraviolet spectra obtained in the 1200-3200 A range over the course of 4 yr with the International Ultraviolet Explorer (IUE) indicate that the extended nebular features which resemble a jet in the peculiar variable R Aquarii (M7e+pec) have increased in excitation in 1985. This is indicated by the appearance of He II Al640 and N v AA1238, 1240 in the jet features and is consistent with the detection of soft X-rays, as found with EXOSAT in 1985. We have analyzed the emission properties of the compact H II region that surrounds the unresolved binary, and those of the extended nebular jet, from the low-resolution IUE spectra which we obtained of these regions. In particular, the UV line intensities observed in the jet appear variable on a time scale of ~1.5 yr. A new accretion disk model is proposed that explains the kinematic and ionization properties of discrete components which comprise the jet emission nebulosity, the appearance of the jet in the 1980s, and morphology that uniquely characterizes the R Aquarii system at radio, optical, UV, and X-ray wavelengths

Interstellar Carbodiimide (HNCNH) - A New Astronomical Detection from the GBT PRIMOS Survey via Maser Emission Features

In this work, we identify carbodiimide (HNCNH), which is an isomer of the well-known interstellar species cyanamide (NH2CN), in weak maser emission, using data from the GBT PRIMOS survey toward Sgr B2(N). All spectral lines observed are in emission and have energy levels in excess of 170 K, indicating that the molecule likely resides in relatively hot gas that characterizes the denser regions of this star forming region. The anticipated abundance of this molecule from ice mantle experiments is ~10% of the abundance of NH2CN, which in Sgr B2(N) corresponds to ~2 x 10^13 cm-2. Such an abundance results in transition intensities well below the detection limit of any current astronomical facility and, as such, HNCNH could only be detected by those transitions which are amplified by masing.Comment: Accepted in The Astrophysical Journal Letters, 13 pages, 2 figures, generated using AAS LaTeX Macros v 5.

The R Aquarii System at Optical and Radio Wavelengths

Observations of the symbiotic binary R Aquarii environment were obtained with the Very Large Array (VLA) at 2, 6, and 20 em at the same epoch. The observed spectral index and strong linear polarization reveal that emission from the compact double radio source discovered in previous observations is nonthermal; thus, this source is not associated with R Aquarii but is an extragalactic background object. The spectral index of the compact nebula surrounding R Aquarii indicates that the emission is thermal and the nebula is ionized by an unseen, hot companion to the Mira-like variable R Aquarii. As expected, this region shows no indication of linear polarization, and we have determined a steady state mass loss of ~ 2. 7 x 10- 7 M 0 yr- 1 from the system. However, the spectral index and polarization observations of the extended jet ~6 away from R Aquarii indicate that this amorphous source is definitely thermal and optically thin in nature. These new observations place severe constraints on possible models which have been proposed from previous investigations. We suggest that our new observations of the jet can be best explained by enhanced mass exchange occurring periodically in the symbiotic system. Comparison of 6 em data taken with the same VLA configuration but separated by 495 days does not indicate any appreciable morphological change or statistically significant integrated flux difference and thus suggests that on these time scales the jet is now quite stable. High-resolution white light images of R Aquarii and environs obtained with the 4 m telescope at Kitt Peak just prior to the VLA observations show a high degree of correlation with the 6 em radio data and place a limit on the apparent visual magnitude of the compact double radio source; optical speckle interferometry failed to resolve any components in the R Aquarii system

Evidence for Extended Radio Emission Surrounding RX Puppis

We report evidence for ~1 extended structure in 6 cm continuum emission emanating from the symbiotic star system RX Puppis. We did not detect hourly continuum flux changes as suggested in previous radio experiments by others. Our observations indicate that the predominant nature of the radio emission is thermal and consistent with an optically thick stellar wind emanating from the symbiotic star system. Our results are discussed with regard to other similar stellar binary systems