Robert W. Hobbs

Planetary temperatures at 9.55 mm wavelength

Abstract Measurements of Mercury, Mars, Venus, Jupiter, and Saturn have been made with the 85-ft reflector of the Naval Research Laboratory at 9.55 mm wavelength. The measurements were made in the interval August 1966 to April 1969. The gain of the antenna at the zenith is calibrated using several radio sources with easily extrapolated spectra; the change of gain with antenna position is calibrated using measurement of Jupiter. Average temperatures of 260 ± 18°K, 207 ± 13°K, 441 ± 30°K, 157 ± 8°K, and 126 ± 6°K are found for Mercury, Mars, Venus, Jupiter, and Saturn, respectively.

IUE Observations of Circumstellar Emission from the Late Type Variable R Aquarii (M7 + pec)

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.

Microwave continuum radiation from comet Kohoutek 1973f: Emission from the icy-grain halo

Cometary emission was measured at 3.71 cm on 1974 January 10--11. 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 313plus-or-minus80 K. The radiation presumably originates in the icy-grain halo postulated by Delsemme. (AIP)

A short-lived chromospheric flare-point with a lifetime of 20 seconds and rise and fall times of 5 seconds

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.

Ultraviolet observations of four symbiotic stars

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.

Reversal of the /O III/lambda 4363/H sub gamma lambda 4340 ratio in the planetary nebula IC 4997

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 nebulas central star accompanied by a transient event which led to a temporarily high value for the ratio in mid-1977.

AN EMISSION-LINE OBJECT FOUND IN THE ORION NEBULA

T. R. GULL Kitt Peak National Observatoryt, Tucson L. GOAD Harvard College Observatory H-Y. CHIU Goddard Institute for Space Studies S. P. MARAN AND R. W. HOBBS NASA, Goddard Space Flight Center A small, low-temperature, high-density object has been found superimposed upon the Orion nebula. The observed spectrum suggests it is a Herbig-Haro object. Key words: interstellar medium - diffuse nebulae - Orion nebula - emission-line object

Evidence for an optically thick component in the galactic radio source Sagittarius B2

Galactic radio source Sagittarius optically thick component evidence based on flux density measurement

Electron densities for 10 planetary nebulae derived from the semiforbidden C III lambda 1907/1909 ratio. II

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.

Cygnus A at 99 GHz: Observations of the three principal components and interpretation of the central source

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.