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This paper presents new measurements of the microwave flux of Ceres obtained at wavelengths between 3.3 mm and 20 cm using the 12 m Kitt Peak antenna and the Very Large Array. These new measurements are combined with previous measurements to confirm a substantial decrease in flux density at centimeter wavelengths compared to millimeter wavelength. Using a statistical technique adapted from terrestrial microwave remote sensing, this spectrum has been compared with that of various candidate materials and models for the subsurface structure of Ceres. It is concluded that Ceres is largely covered with a 3-cm-thick layer whose dielectric properties resemble dry terrestrial clay. This layer may have formed by micrometeorite impact on hydrothermally altered basic or ultrabasic rock or on carbonaceous chondrite material.

Results are presented from a study of the 2 cm natural radio emissions from the class U asteroid 704 Interamnia. The study was performed with the NRAO VLA using 26 antennas in a compact hybrid configuration with baselengths from 0.1-2.2 km. The IF scans were centered at 14.97 GHz and 14.92 GHz. A brightness temperature plot is provided for 2 AU distance, assuming a 338 km diam for the asteroid. The scans revealed a surface dust layer at least 3 cm thick. Comparisons with spectra of 15 Eunomia, another rapidly rotating minor planet with a similar diameter reveals that this second object also has a surface dust layer a few centimeters thick.

Emission (2 cm) from 15 Eunomia was detected on March 27, 1983, using the VLA. At this time, 15 Eunomia was 2.0 AU distant from earth. A flux density of 687 + or - 70 micro-Jy was measured at 14.96 GHz (50-MHz bandwidth). If 246 km is adopted for the diameter, a disk temperature of 184 + or - 20 K results. This is consistent with a rapidly rotating, black sphere with 15 Eunomia's diameter and distance (171 K).

Observations were obtained with the International Ultraviolet Explorer (IUE) of four symbiotic stars. The UV spectra of YY Her, SY Mus, CL Sco, and BX Mon are characterized by varying degrees of thermal excitation. These low resolution spectra have been analyzed in terms of line-blanketed model atmospheres of early A, B, and F type stars in order to identify the nature of the hot companion in these systems. The expected emission from early main sequence stars does not fully explain the observed distribution of UV continuum energy over the entire IUE spectral range (1200-3200 A). More likely the observed continuum may be originating from an accretion disk and/or hot subdwarf that photoionizes circumstellar material, and gives rise to the high excitation lines that have been detected. The Bowen fluorescent excited lines of O III in SY Mus exhibit slightly broadened profiles that suggest possible turbulent motions in an extended circumstellar cloud with characteristic velocities of approximately 300 km/s.

The NRAO-Green Bank 43-m telescope and 18-cm receiver have detected OH maser main-line emission at 1665 MHz, in the direction of the two late-type supergiants TV Gem and BI Cyg. The detection of the two new OH maser sources is noteworthy in view of the small number of late-type supergiants known to be molecular radio sources, or associated in close proximity with OH emission clouds. The IR, UV and radio properties of the two stars are discussed.

Thermal emission spectra for a variety of cometary nucleus models were evaluated by a radiative transfer technique adapted from modeling of terrestrial ice and snow fields. It appears that millimeter wave sensing from an interplanetary spacecraft is the most effective available means for distinguishing between alternate models of the nucleus and for evaluating the thermal state of the layer which is below the instantaneous surface where modern theories of the nucleus indicate that sublimation of the cometary volatiles actually occurs.

Infrared observation are important for deducing a great deal about properties of the cometary dust surrounding the cometary nucleus. All observations in the infrared are limited to long period comets. Three features of the spectrum which seem to be present in nearly all of the comets observed are discussed. First, there is a peak in the spectrum in the near infrared and visible wavelength, which can be attributed to scattered sunlight. This feature, as expected, gets fainter as a comet recedes from the sun. The second dominant feature in the spectrum is a broad peak in the infrared which is attributed to the thermal emission of the dust in the coma. This part of the spectrum also gets dimmer as the comet gets further from the sun but, at the same time the peak of the spectrum shifts to longer wavelengths, indicating that the dust from which this radiation arises is cooling as the comets recedes. The other feature in the spectrum which is noted is the emission feature at about 10 microns attributed to emission from metallic ilicates. T.M.

Predicted brightness temperatures, computed by means of radiative transfer techniques adapted from the modeling of terrestrial ice and snow fields, are given for cometary nucleus models consisting of homogeneous layers of water ice and refractory grain mixtures presented as functions of wavelength. The computed millimeter-wave spectra are sensitive to the values of such physically significant nucleus parameters as (1) crust thickness, (2) subsurface temperature gradient, and (3) sublimating surface boundary temperature. Although antenna beam dilution is a major obstacle for ground-based molecular spectral line radio observations of comets, a millimeter-wave radiometer in the vicinity of the comet would be immune to this effect and able to make observations of several candidate parent molecules in the gas phase.

Electron densities for IC 351, IC 2165, J900, IC 3568, NGC 6644, NGC 6891, IC 4997, NGC 7009, Hu 1-2, and IC 5217 are derived from high-dispersion semiforbidden C III spectrograms. For seven of these nebulae, the derived electron density is larger than the values derived from either surface brightness measurements or forbidden line ratios. Only one object, Hu 1-2, shows pronounced splitting of the semiforbidden C III emission lines due to a large expansion velocity.

Several IUE spectra of planetary nebulae show an absorption feature shortward of 1500 A which is believed to be due to H2(+). The nebulae are excited by stars of spectral type O3-O7 or continuum, and all but one have double-shell structure.

The IUE observations of R Aqr (M7 + pec) obtained in low dispersion are discussed with particular reference to circumstellar emission. Strong permitted, semiforbidden, and forbidden emission lines are seen, superimposed on a bright ultraviolet continuum. It is deduced that the strong emission line spectrum that involves C III, C IV, Si III, (0 II) and (0 III) probably arises from a dense compact nebula the size of which is comparable to the orbital radius of the binary system of which R Aqr is the primary star. The low excitation emission lines of Fe II, Mg II, 0 I, and Si II probably a white dwarf, comparable to or somewhat brighter than the Sun, since such a star can produce enough ionizing photons to excite the continuum and emission line spectrum and yet be sufficiently faint as to escape detection by direct observation. The UV continuum is attributed to Balmer recombination from the dense nebula and not to blackbody emission from the hot companion.

The IUE observations of two late type stars BX Mon and TV Gem that reveal the emission properties in the ultraviolet of subluminous companions are discussed. Analysis of the continuum emission observed from BX Mon suggests the companion, is a middle A III star. High excitation emission lines observed between 1200 A and 2000 A that generally do not typify emission observed in either late M type variables or A type stars are also detected. It is suggested that these strong high excitation lines arise in a large volume of gas heated by nonradiation processes that could be the result of tidal interaction and mass exchange in the binary system. In contrast to stars such as BX Mon, the luminous M1 supergiant TV Gem shows unexpected intense UV continuum throughout the sensitivity range of IUE. The UV spectrum of TV Gem is characterized by intense continuum with broad absorption features detected in the short wavelength range. The analysis shows that the companion could be a B9 or A1 III-IV star. Alternate suggestions are presented for explaining the UV continuum in terms of an accretion disk in association with TV Gem.

IUE data of this late giant reveal strong Mg II resonance doublet emission that in high dispersion exhibits reversed symmetric h and k line profile emission, suggesting that material ejected from the surface forms a low excitation expanding circumstellar shell. The weak continuum is identified as being a combination of possibly stellar continuum and blended Fe II features of multiplets. The UV spectra does not suggest the presence of a hot companion as believed to exist in symbiotic stars, because a number of high excitation lines such as C IV and He II are not observed in the short wavelength range. The UV and Mg II line emission is most likely the result of the M giant having undergone an eruptive event in which a moderate excitation shell heated by hydromagnetic shocks dominates the UV emission. The general properties of the circumstellar shell are obtained from the Mg II line profiles.

It is pointed out the despite years of investigation, the solid, quasi-permanent component of comets, the nucleus, remains largely a mystery. The composition and thermal properties of the nucleus determine the evolution of the more familiar and often spectacular cometary features, the coma and tail. Under certain circumstances, the nucleus may be obscured by a dust cloud of much higher temperature. The most appropriate technology for the investigation of the surface and subsurface layers of the nucleus is considered to be millimeter-wave sensing from an interplanetary spacecraft. Simple radiative transfer models, adapted from methods employed for the interpretation of remote-sensing data on terrestrial ice and snow fields, are used to predict the millimeter-wave spectra of representative model nuclei. The spectra determine the choice of the minimum set of observing frequencies that is required. An instrument configuration driven by these requirements and guided by available technology and the restraints of a proposed NASA spacecraft is then derived.

The IUE observations of the high excitation symbiotic star RW Hya (gM2 + pec) are discussed. Analysis of the intense UV continuum observed between 1100 A to 2000 A suggests this star is a binary system in which the secondary is identified as a hot subdwarf with T sub eff being approximately 100,000 K. A distance to the system of 1000 pc is deduced. The UV spectrum consists of mainly semiforbidden and allowed transition lines of which the CIV (1548 A, 1550 A) emission lines are particularly strong, and UV continuum at both shorter and longer wavelengths. Strong forbidden lines seem to be absent suggesting the presence of a nebula of high densities. Tidal interaction between the red giant primary and the hot subdwarf is suggested as a likely means to form the observed nebula. RW Hya is suggested as a possible source of soft X-ray emission from material accreting onto the surface of the hot subdwarf. Detection of such emission with HEAO-B would give information if this accretion is taking place via Roche lobe overlow or via capture from a stellar wind emitted by the primary. A general discussion of elemental and ionic abundances in the nebula is also presented.

IUE observations of the late-type M supergiant star TV Gem which reveal an intense continuum in the far ultraviolet are discussed. TV Gem was observed in low dispersion in November 1979 and in high and low dispersion in January 1980 by the short and long wavelength cameras of the IUE spectrometer. An essentially featureless UV continuum was obtained, with the exception of a number of broad absorption features in the short wavelength region. A comparison with ground-based observations indicates that at wavelengths greater than 3200 A the continuum emission is essentially due to the M1 supergiant, while at shorter wavelengths the continuum is dominated by a hot companion. The UV continuum can be explained by a B9 or A1 III-IV early companion approximately 2 to 3 magnitudes fainter than the M1 supergiant, or by an accretion disk formed by mass transfer from the extended envelope of the M1 primary onto the surface of a highly condensed secondary. Soft X-ray observations from HEAO 2 are suggested as a means to investigate these interpretations.

A selection of infrared variable stars was studied at wavelength 2.7 microns during 1971-1975 with data from U.S. Air Force satellites. Stars observed in this program are classified as long-period variable stars, semiregular variables, and irregular variables and are among the strongest stellar sources at this wavelength. In addition, a few new, as yet unclassified variable stars were identified during the course of the investigation. Time scales of reproducible variations range from a few weeks to a few years, and amplitudes of variation are as large as a factor of three for stars with periods of order one year. The minimum infrared flux density of a long-period star repeats accurately from one cycle to the next, whereas the maximum flux density was found to be unstable. The correlation of 2.7 micron and radio emission line data from one, well-studied long-period variable is consistent with the hypothesis that the H2O and OH circumstellar masers are saturated, if pumped by the stellar infrared flux near 2.7 microns.

Cometary emission was measured at 3.71 cm on January 10-11, 1974. A possible detection at 2.8 cm and an upper limit at 11.1 cm are also reported. Interferometer measurements at 3.71 cm show that the angular diameter is less than 1.4 arc sec or less than 850 km at the comet. The corresponding disk brightness temperature is greater than 313 + or - 80 K. The radiation presumably originates in the icy-grain halo postulated by Delsemme.

Using NASA facilities in space (OSO-7) and on the ground (Goddard multi-channel spectrophotometer at Sacramento Peak, New Mexico) an active region has been mapped. By combining these ultraviolet, X-ray, and visible data, a physical picture of this structured region was constructed from the photosphere to the corona, corresponding to temperature regimes from 4500 K to 4,000,000 K. The morphology of the active region was studied by comparing grey-shaded images in which fine details stand out more clearly than in the contour plots. One result of the study is that gross similarities persist from the low photosphere up to high in the transition region, while some changes occur in the corona.

We have observed a chromospheric brightening in the H alpha and Ca II K lines with a diameter of about 1 arc second. The time structure of this event, obtained with a relative resolution of 1 second, shows the rise time to be 4 seconds, the lifetime (FWHM) to be 20 seconds, and the decay time to be 5 seconds. This imposes new constraints on flare-point models. These restrictions can be accommodated easily by either an infall-impact flare model or a model invoking the precipitation of high-energy particles from the corona.

Analysis of the intense UV continuum observed between 1100 and 2000 A suggested that observations of the late type star RW Hya is a binary system in which the secondary is the central star of a planetary nebula. The UV spectrum is characterized by semiforbidden and allowed transition lines, of which the C IV doublet is particularly strong. Tidal interaction from the M giant is proposed as a method of forming a nebula with the characteristic densities inferred from the UV line analysis. RW Hya is suggested as a possible source of soft X-ray emission if material is accreting onto the surface of the secondary.

Observations of the late type M supergiant TV Gem (M1Iab) reveal strong UV continuum between 1200 A and 3200 A. The continuum is essentially featureless with the exception of a number of broad absorption features in the short wavelength spectra range. An absorption feature centered around 1400 A could be due to Si IV absorption found typically in spectra of middle B type stars. UV emission from this star is unexpected because earlier ground-based observations give no indication of a possible association with an early companion or circumstellar ionized nebulosity. A B9 or A1 III - IV type star approximately 2to 3 magnitudes fainter than the M star could explain the level of UV continuum observed, but a fully self consistent explanation that includes the B-V color index of TV Gem is not as yet possible. The continuum flux dependence with wavelength in the UV spectral range could be attributed to a high energy source such as an accretion disc. It is suggested TV Gem is a good candidate for HEAO-2 (Einstein) satellite observations because a high energy object in close proximity to the M star would likely be a source of soft X-ray emission.

IUE observations of R Aquarii (M7 + pec) have been obtained in low dispersion in order to study its circumstellar emission. Strong permitted, semiforbidden, and forbidden emission lines are identified that are superposed on a bright ultraviolet continuum. From the analysis it is deduced that the strong emission-line spectrum that involves semiforbidden C III, C IV, semiforbidden Si III, forbidden O II, and forbidden O III probably arises from a dense compact nebula the size of which is comparable to the binary system of which R Aqr is the primary star. Low-excitation emission lines of Fe II, Mg II, O I, and Si II suggest the presence of a warm chromosphere (T less than about 10,000 K) in the primary M7 late type giant. The secondary is identified as a white dwarf, comparable to or somewhat brighter than the sun, since such a star can produce enough ionizing photons to excite the continuum and emission-line spectrum and yet be sufficiently faint to escape detection by direct observation. The UV continuum observed is attributed to Balmer recombination and not to blackbody emission from the hot companion. The general spectral properties of R Aqr between 1200 A and 3200 A are discussed in the context of the model for the circumstellar nebula, the companion, and the mass-loss rate of the primary star.

Recent IUE observations reveal striking differences in the UV spectra of two symbiotic stars, R Aqr and RW Hya. RW Hya is found to be an unexpectedly intense source of UV radiation. The measurements reported demonstrate the presence of a hot component in each star, supporting the view that each is a binary system with a luminous red primary and a hot, subluminous companion. In one case, the hot companion manifests itself by exciting a compact nebulosity; in the other case the continuous spectrum of the hot star is directly detected, while the continuum of nebulosity excited by the hot star is detected at longer wavelengths.

Radio galaxies were observed for the first time at 150 GHz. The central sources in Cyg A and 3C 111 were detected, as were the two radio lobes of Cyg A. No emission was found from the central source in 3C 236. The millimeter-wavelength emission from the central sources in Cyg A and 3C 111 is probably due in each case to a compact component that is optically thin to synchrotron radiation above about 35 GHz. These components are similar, although the compact component in 3C 111 is more luminous at both radio and X-ray wavelengths than the one in Cyg A. The 3C 111 central source was much weaker than anticipated on the basis of prior observations at 90 GHz, perhaps due to variability. Even at 150 GHz, there is no evidence of a high-frequency cutoff in the spectrum of the central source in Cyg A, and variability of this source also is expected. The flux densities of the Cyg A lobes are consistent with the power laws derived at lower frequencies, indicating that no steepening occurs in their spectra out to at least 150 GHz. There is no evidence for a compact, optically thick component in 3C 236.

Five image-tube spectrograms of the planetary nebula IC 4997 obtained during August 1977 show that the intensity forbidden ratio O III 4363 A/H-gamma 4340 A was equal to unity, but a sixth one obtained in April 1978 showed the ratio to be 0.91. These results represent a significant increase in the intensity ratio, which had been declining from 1895 to 1962 (when it was considerably less than unity), and is interpreted as resulting from a gradual increase in temperature of the nebula's central star accompanied by a transient event which led to a temporarily high value for the ratio in mid-1977.

The broad impact of a cometary mission is assessed with particular emphasis on scientific interest in a fly-by mission to Halley's comet and a rendezvous with Tempel 2. Scientific results, speculations, and future plans are discussed.

The results of the first linear polarization measurements of extrasolar radio sources at a frequency above 35 GHz are presented. For the quasars 3C 273 and 3C 345, the observed position angles are in accord with the predictions of Inoue, and the measurements are consistent with the suggestion that the compact components responsible for the high-frequency emission are affected by high degrees of internal Faraday depolarization. For the radio galaxy 3C 274 (Virgo A) the observed position angle and degree of polarization are consistent with the model of Hobbs and Waak.

The three principal emission components of Cygnus A have been observed at 99 GHz, the highest frequency at which radio measurements of this source have been accomplished. The observations show no definite indication of a high-frequency cutoff in the spectrum of the compact central component, which perhaps may be attributed to an optically thin synchrotron source that peaks at a frequency of several hundred GHz.

Centaurus A (NGC 5128) has been observed at radio frequencies of 10.7, 31.4, 85.2, and 89 GHz and at X-ray energies greater than 20 keV. These observations, together with results reported by other workers, are interpreted in terms of models of the nucleus of this radio galaxy. The radio observations cover the period from 1973 through early 1977. The X-ray observations cover two 10-day intervals, one in July and August (1975) and the other in July and August 1976. The source exhibits significant variability in all the observed radio frequencies. The observed radio and X-ray intensities show some concurrent variations but do not track one another throughout the observations. A model of the source in which X-rays are produced by inverse Compton scattering of blackbody photons by relativistic electrons is proposed to explain these observations. The observed variations in the electromagnetic spectrum are shown to be consistent with adiabatic expansion of a trapped plasma in conjunction with turbulent accelerations of the relativistic electrons. Upper limits obtained with the model indicate that there may be sufficient energy available in the nucleus to form radio lobes with the same total energy as those already present.

Continuum emission at wavelength 3.71 cm was observed from the nuclear region of comet West 1975n on March 5, 1976. The flux density was 0.040 Jy, which is uncertain by 25% due to calibration. Assuming that the source was a uniformly illuminated disk, the diameter was no more than about 1100 km and the brightness temperature was at least 330 + or - 85 K. On March 4, 1976, similar observations yielded only an upper limit (two standard deviations) to the flux density of 0.010 Jy. Thus it appears that the source turned on with a time scale of 1 day or less, at about the time that the short-lived cometary daughter nucleus 'C' split from the main nucleus 'A'. Similar emission was observed from comet Kohoutek 1973f. In each case, it appears that the microwave emission can be interpreted as thermal radiation from a temporarily enhanced icy-grain halo (IGH). If this interpretation is correct, then the actual temperature (which is assumed to be approximately equal to the nuclear surface temperature) must be in the range 200-250 K, roughly compatible with the observations, in order to satisfy the IGH models of Delsemme (1973).

The three principal emission components of Cygnus A were observed at 99 GHz, the highest frequency at which radio measurements of this source have been accomplished. The observations show no definite indication of a high-frequency cutoff in the spectrum of the compact central component, which perhaps may be attributed to an optically thin synchrotron source that peaks at a frequency of several hundred GHz.

A total of image tube spectrograms of HM Sagittae were obtained. More than 70 emission lines, including several broad emission features, were identified. An analysis of the spectra indicates that HM Sagittae is a planetary nebula excited by a Wolf-Rayet star. The most conspicuous Wolf-Rayet feature is that attributed to a blend of C III at 4650 A and He II at 4686 A.

Results are presented for measurements of the flux densities of 10 variable extragalactic sources at 85.2 or 90 GHz, which were made over a period of almost seven years with the NRAO 36-ft millimeter-wave antenna. The primary flux-density calibration standards used include Jupiter, Saturn, Mars, and the small-diameter Galactic source DR 21. Measured flux densities are given as a function of time (in years) for the sources 3C 84, NRAO 150, 3C 120, OJ 287, 4C 39.25, 3C 273, 3C 279, 3C 345, BL Lac, and 3C 454.3. No statistically meaningful flux-density changes during an observing interval (1 to 3 days) are detected for any source, and a high degree of correlation between flux-density variations at 85.2 or 90 GHz and those observed at lower frequencies is found in all 10 sources. Some variations observed at different frequencies in several individual sources are briefly discussed.

Centaurus A was observed at radio frequencies of 10.7, 31.4, 85.2, and 89 GHz and at X-ray energies greater than 20 keV. The source exhibits significant variability in all the observed radio frequencies. The observed radio and X-ray intensities show some concurrent variations but do not track one another throughout the observations. A model of the source in which X-rays are produced by inverse Compton scattering of blackbody photons by relativistic electrons is proposed to explain these observations. The observed variations in the electromagnetic spectrum are consistent with adiabatic expansion of a trapped plasma in conjunction with turbulent accelerations of the relativistic electrons.

High-resolution spectrophotometry of the variable Ca II K line in the K2 IIIp star Alpha Boo was performed with the McMath Solar Telescope at Kitt Peak National Observatory and an experimental SEC vidicon camera. The results are compared with Copernicus observations of the Mg II h and k lines and with earlier Ca II data. It is found that either of two states may typically occur in the Arcturus chromosphere. From comparison with the results of model calculations for expanding chromospheres, it is concluded that these correspond respectively to a 'normal' state in which the mass loss is less than one billionth of a solar mass per year and an 'abnormal' state in which the mass loss is about 8 billionths of a solar mass per year. In the latter case, the expansion velocity is around 13 km/s at optical depth unity in the K-line, which exceeds the local sound speed. It is suggested that the abnormal state represents the rise to the photosphere of a very large convective element, as hypothesized for red giants by Schwarzschild (1975).