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OH emission regions investigated using Millstone and Haystack antennas with interferometer, noting radio sources for base-line calibration and instrumental phase monitoring
The principal optical properties of type I supernovae are summarized. These include the light curve and the spectrum. The spectra consist of broad bands with very little continuum. According to the theory presented, the observed light is principally fluorescence, excited in the medium surrounding the supernova by ultraviolet radiation originating from the explosion. It is proposed that the spectrum that impinges on the fluorescent medium while emission is taking place must fall abruptly across the Lyman edge of He II. Such a filtering action is plausibly provided by a much denser internal region, rich in helium, immediately surrounding the exploding object. This will form a Stromgren sphere during the time the intense UV pulse is passing through it. The dense region also slows down the photons below the edge by Thomson scattering, thereby spreading out the UV pulse in time. Various proposed mechanisms for the production of ionization in the Gum nebula are discussed.
Spectrographic scans for sulfur doublet intensity in the Orion nebula show that electron density decreases from about 15,000 down to about 1500 electrons per cubic centimeter within a few minutes of arc in both directions from the maximum. There appears to be small-scale structure in the electron density, with variations by a factor of two very common. Satisfactory agreement is obtained for electron density values derived from the oxygen doublet as well as from the sulfur doublet.
The 21-micron contour map of M17 is similar to radio maps with three components. Measured flux densities give color temperatures of both 240 and 75 K for the two principal components of M17 and 44 to 63 K for Sgr B2, NGC 2024, and DR-21.
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Accurate spectrophotometric observations of the nebulae Sh 156 and Sh 162 and of their exciting stars, combined with high-resolution radio maps by Israel (1976), enable the derivation of the total visual extinction towards 15 points in these nebulae. These values are compared with other values of the total visual extinction for the entire nebulae and their exciting stars.
The paper reports on combined optical, infrared, and radio observations of the compact complex S 106. The source could be resolved into ten components, three of which are compact components of size approximately 0.2 pc and were detected at 12.6 microns and 2.7 GHz. Two of the components are point-like sources detected at 8000 A. One of the components detected at 8000 A is spatially coincident with a strong 3.5 micron source and is suggested as a possible exciting star for the complex.
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Emission of forbidden S III 18.71-micron radiation has been detected in the Orion Nebula, M17, NGC 2024, and W51, and an upper limit has been set for Sgr A. The line flux from M17 has been mapped with a resolution of 2.7 arcmin. A simple theory for predicting the forbidden S III flux from radio continuum observations is presented and compared with the data. It is found that Orion and M17 are in satisfactory agreement with the observations and that NGC 2024 is consistent with a low-excitation source behind a resonable amount of 18-micron dust extinction. In W51 the low observed flux may be explained either by low S(2+) abundance or, more likely, by dust extinction. In Sgr A attenuation by dust is the most plausible explanation.
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Three extragalactic regions of rapid star formation with redshifts great enough to separate the Lyman-alpha region from geocoronal Lyman-alpha have been observed with the IUE satellite. Only the low metal abundance object had detectable Lyman-alpha emission with Lyman-alpha/H-alpha of about 6; the other two have Lyman-alpha/H-alpha less than 0.6 (2 sigma). In the normal metallicity objects, there is some evidence for Lyman-alpha extinction in addition to that computed from the Balmer decrement. Lyman-alpha is therefore expected to be weak or absent in collapsed primeval galaxies because of their predicted moderate to high metallicity.
The submillimeter (157-micron) forbidden line emission from the M17 complex has been mapped. The forbidden line emission extends over at least 1/4 deg in the sky. The regions emitting the C II radio recombination lines contribute only in a minor way to the total 157-micron flux. The total forbidden line luminosity of M17 exceeds 2,000 solar luminosities.
The dwarf galaxies NGC 5204, NGC 5474, and NGC 5585 have been shown by Sandage and Tammann (1974) to be physically associated with M101 (distance 7.2 Mpc). The present investigation is concerned with observations of the dwarf galaxies in the M101 group conducted with the aid of the Einstein satellite. Upon detection of X-ray emission from NGC 5204, it was found possible to observe this galaxy also with the International Ultraviolet Explorer (IUE). It is now feasible to compare the predictions on the stellar population of the galaxy inferred from the X-ray data with a more direct measure concerning this population. It is found that the hypothesis regarding the responsibility of binary X-ray sources of Population I progenitors for most of the X-ray emission is strengthened by the IUE short-wavelength spectrum of NGC 5204.