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Discussion of the limits on surface temperature (under 190 K) and reflectivity (under 0.5) corresponding to an upper limit set on the 4.9-micron flux from Titan. Special attention is given to the possibility of the presence of an opaque cloud layer or some gaseous absorber on Titan and to the subsequent implications.
It is pointed out that the measurement of the deceleration parameter by Sandage (1972) implies an upper limit of a few tens of electron volts on the sum of the masses of all the possible light, stable particles that interact only weakly. In the discussion of the problem, it is assumed that the universe is expanding from an initially hot and condensed state as envisaged in the 'big-bang' theories.
Elektron-2 measurements of upper limits of ion temperatures between 7000 and 30,000 km
It is shown that application of standard MHD arguments to hydromagnetic waves observed in the Crab Nebula dramatically improves the upper bound on photon rest mass. The standard argument that massive photons are governed by the Phoca field equations is outlined and applied to wisp features (identified as hydromagnetic waves) observed in the Crab. The results imply an upper limit for the photon rest mass of between 3 by 10 to the -54th power and 3 by 10 to the -53rd power gram, which is smaller than the best previous limits by a factor of 10,000 to 100,000. It is noted that although the present limit is probably valid in order of magnitude, some doubt remains since there are inconsistencies in the standard arguments.
Data from the ultraviolet spectrometer on the Mariner 9 Mars orbiter have been used to set upper limits on the redshifted Lyman-alpha flux from the Perseus and Pegasus I (NGC 7619) clusters of galaxies. The limit for the Perseus cluster implies that the temperature of the intergalactic gas required for gravitational binding must be greater than 100,000 K, if it exists. A less severe limit is set for the Pegasus I cluster.
A measurement of Sco X-1 with the graphite-crystal polarimeters on the OSO 8 satellite yields upper limits (3 sigmas) to the linear polarization of 2.7% and 4.9% at 2.6 keV and 5.2 keV, respectively. The results are discussed in terms of an accretion-disk model.
The May 14, 1971, occultation of beta Scorpii C by Io was successfully observed in ultraviolet light near Kingston, Jamaica. Within the limits established by time resolution and the signal-to-noise ratio, both the disappearance and reappearance were found to be instantaneous. Upper limits for the surface pressure for N2, CH4, and H2 atmospheres are 0.09, 0.13, and 44. microbar, respectively. The corresponding number densities are 6.2 x 10 to the 12th power, 9.4 x 10 to the 12th power, and 3.2 x 10 to the 15th power per cu cm. An isothermal atmosphere at a temperature of 100 K was assumed.
An unsuccessful search is described for the J = 7-6 transition of HCN ... HCN in several interstellar clouds known to be rich in HCN. An upper limit to the abundance of the dimer relative to the monomer is typically 1 percent. It is suggested that this implies a low abundance for similar weakly bound species.
Interstellar ethyl-cyanide has been sought via its 2(02)-1(01) transition towards two cold, dark clouds, and upper limits of the total column densities of 3 x 10 to the 12th/sq cm and 2 x 10 to the 12th/sq cm for TMC-1 and L134N, respectively. The 2(02)-1(01) transition of vynil cyanide, previously identified in TMC-1 by Matthews and Sears (1983b), was also observed. The detection of vinyl cyanide and the nondetection of ethyl cyanide in TMC-1 are consistent with gas phase ion-molecule chemical models, and there is thus no necessity of invoking grain surface synthesis for vinyl cyanide in cold clouds.
We examine the electrodynamic power output from a thin accretion disk surrounding a Kerr black hole. We derive an upper limit for the total power. We find that this limit is only moderately sensitive to most of the relativistic correction factors. In fact, this limit is less sensitive to the change in the black hole spin than one would expect from the change in the inner radius of the accretion disk. The disk around a rapidly rotating black hole will produce more nonthermal radiation than a similar disk around a slowly rotating black hole of identical mass, but the difference is only a factor of approximately 1.7.
Exploratory observations at 20 microns and 350 microns have determined detection thresholds for solar flares in these wavelengths. In the 20-micron range, solar atmospheric fluctuations (the 'temperature field') set the basic limits on flare detectability at about 5 K; at 350 microns, extinction in the earth's atmosphere provides the basic limitation of about 30 K. These thresholds are low enough for the successful detection of several infrared-emitting components of large flares. The upper limits obtained for subflares indicate that the thickness of the H-alpha flare region does not exceed approximately 10 km. This result confirms the conclusion of Suemoto and Hiei (1959) regarding the small effective thickness of the H-alpha-emitting regions in solar flares.
The reaction HCl + ClONO2 yields Cl2 + HNO3 has been studied by Fourier transform infrared spectroscopy and by a static wall-less UV absorption technique. An upper limit to the homogeneous bimolecular rate constant of 10 to the -19th cu cm/molecule per sec was established, making the reaction unimportant in the stratosphere.
Thermal OH emission from IRC + 10216 in the 1665- and 1667-MHz lines has been searched for. No emission was detected, yielding an upper limit for the OH abundance in the envelope. Within the photodissociation region where OH is expected to occur, OH/CO is less than 2.7 x 10 exp -3.
The nightside ionosphere of Mars could be produced by electron precipitation or by plasma transport from the dayside, by analogy to the Venus, but few measurements are available. We report here model calculations of upper limits to the nightside ion densities on Mars that would be produced by both mechanisms. For the auroral model, we have adopted the downward traveling portions of the electron spectra measured by the HARP instrument on the Soviet Phobos spacecraft in the Martian plasma sheet and in the magnetotail lobes. For the plasma transport case, we have imposed on a model of the nightside thermosphere, downward fluxes of O(+), C(+), N(+), NO(+) and O2(+) that are near the maximum upward fluxes that can be sustained by the dayside ionosphere. The computed electron density peaks are in the range (1.3 - 1.9) x 10 exp 4/cu cm at altitudes of 159 to 179 kin. The major ion for all the models is O2(+), but significant differences in the composition of the minor ions are found for the ionospheres produced by auroral precipitation and by plasma transport. The calculations reported here provide a guide to the data that should be acquired during a future aeronomy mission to Mars, in order to determine the sources of the nightside ionosphere.
A discharge-flow system with resonance fluorescence detection of OH is used to study the reactions of CFCl3, CF2Cl2, and N2O with OH at temperatures up to 480 K. Little, if any reaction was found, with upper limits of 5, 6, and 4 x 10 to the -16th cu cm/s reported at 480 K for the three rate constants. A very simple model is used to calculate removal times exceeding 10,000 years for reaction with tropospheric OH.
Observations of Her X-1 were obtained during its ON-state in September, 1977, with the high-energy X-ray detector on board OSO-8. Upper limits on the line fluxes at 60 and 135 keV based on these observations are above, and hence consistent with, the positive results reported by Trumper, et al from a balloon flight during the same time interval. A detailed analysis of the time-variable et al background spectrum suggests that the line emission, especially in the time-averaged spectrum of Her X-1 previously reported by other workers at 25, 60, and 135 keV, is due to instrumental effects. The spectrum obtained with OSO-8 in September, 1977, is considerably steeper than that observed in pre-1976 balloon flights. These results are consistent with the results obtained by Trumper showing a decrease in the effective temperature of Her X-1 between May, 1976, and September, 1977.
Results are presented on a ground-based search for fluorescent emission from CH4 at 3.3 microns in a newly discovered long-period comet, Comet Levy (1990c). It was found that the upper limit to the CH4 abundance in Comet Levy is similar to the Comet Halley CH4 abundance estimated from lower resolution IR spectra by Kawara et al. (1988). The Comet Levy CH4 abundance is significantly lower than the abundance derived by Larson et al. (1989) from a possible detection of CH4 in Comet Wilson.
Spectra of Triton with a CCD spectrometer yielded a relative spectral reflectivity curve from 0.56 to 1.05 micron at a resolution of 25 A. Using low-temperature band model parameters from Fink et al. (1980), an upper limit for the one-way path gaseous CH4 abundance of 1 m-am was derived.