Engineering topics
Publications and source records attributed to Keller, H. U..
Cometary hydrogen observations are reviewed with emphasis on observations of comet Bennett. The results are theoretically interpreted and a brief summary of ultraviolet observations other than Lyman alpha is given.
Cometary Lyman alpha observations are interpreted, with focus on the hydrogen halo. It is concluded that H2O is the dominant parent molecule of the observed hydrogen. Hydrogen (H) and OH are produced in a ratio of approximately 2 to 1.
The hydrogen Lyman-alpha emission line of comet Kohoutek (1973f) was observed and resolved by the high-dispersion Skylab/ATM S082B spectrograph shortly after the comet's perihelion passage (29-31 December 1973). The Lyman-alpha line width was determined from three different exposures of the comet nuclear region. A simplified analysis of the optical thickness effects showed that this line width is consistent with the established hydrogen outflow velocity of 8 to 10 km/sec.
A model is constructed for the hydrogen cloud of Comet Bennett (1970 II) based on highly sensitive observations of its Lyman alpha emission by a photometer on board OGO-5 and taking into account the cometary motion, field gradients, solar L-alpha profile, and finite lifetime of the H atoms along their trajectories. The solar L-alpha flux is determined independently of instrumental calibration using the strong curvature of the hydrogen cloud in the orbital plane of the comet, and the cometary production rate of hydrogen atoms is calculated. The combination of two equally weighted Maxwellian velocity distributions with mean velocities of 7 and 21 km/sec is found to match the photometer scans across the comet better than any single Maxwellian distribution. A complete L-alpha isophote map is presented for the model hydrogen cloud on Mar. 20, 1970.
Analysis of the OAO-2 photometry of the OH-lambda-3090 and H-lambda-1216 emission features of comet Bennett (1970 II). The results are consistent with the assumption that water is the most abundant parent molecule in comets and that water vaporization controls the production rate of gas in comets at small heliocentric distances.
Explore the source record for details and available documents.