Observations of Comet Kohoutek (1973f) in the spectral region between 1200 and 3200 angstroms were made from an Aerobee rocket on 5.1 January 1974 universal time. The strongest features observed were the Lyman alpha line of neutral atomic hydrogen at 1216 angstroms and the hydroxyl (OH) bands at 3090 and 3142 angstroms. Atomic oxygen and atomic carbon were also detected, and their luminosity implies a production rate (of carbon monoxide or carbon dioxide) commensurate with that of water vapor.

Rocket ultraviolet spectrophotometry of comet Kohoutek (1973f).

Line ratios from the helium-like ions O vii and Ne ix are useful as plasma diagnostics for both flaring and nonflaring solar coronal active regions. The photon flux ratio, R, of the forbidden 1s/sup 2/ /sup 1/S/sub 0/-1s2s /sup 3/S/sub 1/ line to the intercombination 1s/sup 2/ /sup 1/S/sub 0/-1s2p /sup 3/P/sub 1/ line in O vii is useful as a density diagnostic at coronal temperatures of approx.2 x 10/sup 6/ K. If the electron density n/sub e/ is less than n/sub e/*roughly-equal3 x 10/sup 9/ cm/sup -3/, Rroughly-equalR/sub 0/ (where R/sub 0/ is the low-density limit), and R decreases with increasing density. Uncertainties in R and R/sub 0/ both contribute to uncertainties in n/sub e/. R/sub 0/ uncertainties are especially important for nonflaring plasmas having n/sub e/roughly-equaln/sub e/*. We analyzed 29 nonflare X-ray spectra, each a sum of approx.10 scans by the SOLEX B spectrometer on the USAF P78-1 satellite, to conclude that R/sub 0/ is in the range 3.7--4.1 G, the photon flux ratio of the forbidden plus intercombination line to the resonance 1s/sup 2/ /sup 1/S/sub 0/-1s2p /sup 1/P/sub 1/ line, can be used as an indicator of whether or not the emitting plasma is in amore » state of ionization equilibrium. For both O vii and Ne ix, G is modified by resonance scattering in the solar atmosphere, which lowers the resonance line flux. This scattering allows us to estimate the column densities of O vii and Ne ix in the corona above the active region source. We also estimate the value of G in the absence of resonance scattering.« less

X-Ray Lines of Helium-Like Oxygen and Neon in the Solar Corona.

Oscillator-strength determinations for EUV branching emissions of atomic oxygen, nitrogen and sulfur are reported. The transitions studied were excited using a beam-foil source and both branching ratios and radiative lifetimes were determined. Calculated transition-probability data for multiply-ionized neon and oxygen emissions were used to obtain an in situ relative sensitivity curve for the EUV detection system used. New oscillator strengths for NII, OII, SII, and SIII EUV branching emissions that terminate on metastable states of the respective ions are reported, together with new lifetime data for ionized sulfur emissions.

Measurements of oscillator strengths for EUV emissions of ionized oxygen, nitrogen and sulfur

A laboratory simulation of the inter-stellar 220 nanometer feature

UV-photons are detected by a low-pressure photosensitive multistep gaseous detector. Photoelectrons are multiplied in two charge amplification stages. A third, light amplification stage operating in a scintillation mode, provides light yields > 5×10 7 visible photons per single photoelectron avalanche, in ArC 2 H 6 -TMAE gas mixtures. We present results on absolute photon yields in various TMAE gas mixtures, at low gas pressures and at low charge gains. We describe the operation mechanism and some basic properties of the gated 3-stage detectors, such as stability of operation at high background rates and localization resolution, particularly at large TMAE concentration and high temperature operation conditions. Further applications are discussed.

A 3-stage gated UV-photon gaseous detector with optical imaging

A general presentation of astrophysical observations in the ultraviolet is given. First the particular nature of ultraviolet studies is emphasises. This is followed by a brief historical presentation of some of the typical instrumentation used. Then, in the framework of galactic observations, some of the most important results obtained concerning the physics of planetary, solar, stellar and interstellar media are presented. Future instrumentation and, in particular the Hubble Space Telescope, are briefly presented. In this framework extragalactic ultraviolet studies, not covered in this review, will certainly occupy an important place. Finally, the outlook for other projects is mentioned showing that ultraviolet astrophysics is a lively branch of observational space science.

https://iopscience.iop.org/article/10.1088/0034-4885/50/1/002/pdf

J C Henoux

Papers

Galactic ultraviolet astronomy