Engineering topics
Publications and source records attributed to Hall, D. S..
Three years of photometry in V and B of the UBV system are presented to confirm the suspicion of Herbst (1973) that HR 7275 is a variable star. The photometry is used to derive the photometric period, which proves to be about 3% shorter than the spectroscopically determined optical period of 28.59 d. Total variation observed during the three years was 0.22 m in the V, and the light curve was always asymmetrical.
Differential photometry of the RS CVn-type binary 54 Cam is presented, which shows that the light was variable with a period of 10.163 + or - 0.009 d, and with an amplitude increase from 0.03 to 0.06 m between 1979 and 1980. The photometric period of 10.163 d is 9% shorter than the orbital period of 11.0764 d, and is suggested as an explanation for the radio emission from 54 Cam due to a process of connection, disruption, and reconnection of magnetic field lines.
The K-dwarf SB2 system HD 45088, predicted to be a BY Dra variable on the basis of its orbital period and emission-line characteristics, is found to be photometrically variable. The amplitude is significantly variable, having ranged between 0.02m during February-April 1980 to 0.045m during September-October 1980. The photometric period, shown to be 7.36 days, differs appreciably from the 6.99-day orbital period. Possible explanations for this difference are (1) nonsynchronization in a young binary, (2) spot development at high latitudes on a differentially rotating star, and (3) imperfect synchronization in a binary with an eccentric orbit.
The Emergency Local Transmitter (ELT) is a radio transmitter with a self-contained power source designed to provide notification of and homing to aircraft accident sites. The Crash Research Institute has monitored general aviation fixed-wing accidents in the United States and in Canada and has found that: (1) the ELT was destroyed in approximately 25% of all fatal accidents; (2) the ELT activated in about 62% of the fatal accidents, 69% of the fatal with survivors accidents, almost 80% of the serious accidents and about 57% of the minor accidents; (3) in fatal accidents the aircraft sections least likely to be destroyed are the vertical and horizontal tail surfaces; (4) antenna cable disconnection and antenna breakage caused failure to transmit usable signals; and (5) initial alerting control occurred in nearly half of the situations where the ELT aided in search.
This review presents a brief up-to-date summary of observational properties of RS CVn binaries, with emphasis on the photometric. A table of the 69 systems known at this time give the orbital period, mean apparent V magnitude, spectral classification, range of amplitude determinations for the photometric wave, and an indication of known period variations and eclipses. Points considered are (1) the underlying cause of the extreme surface activity, (2) the evolutionary status, (3) the geometric configuration, (4) the temperature, size, shape, location, and lifetimes of the dark spot regions, (5) synchronization of rotational and orbital motion, (6) spectroscopic features in the optical and far ultraviolet, (7) the wave migration, (8) the search for spot cycles, and (9) the orbital period variations produced by the enhanced stellar wind.
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A development program was developed to design and improve the Emergency Locator Transmitter (ELT) transmitter and to improve the installation in the aircraft and its activation subsystem. There were 1135 general aviation fixed wing aircraft accident files reviewed. A detailed description of the damage to the aircraft was produced. The search aspects of these accidents were studied. As much information as possible about the ELT units in these cases was collected. The data should assist in establishing installation and mounting criteria, better design standards for activation subsystems, and requirements for the new ELT system design in the area of crashworthiness.
A starspot model is proposed to interpret the light curves of three RS CVn type binary systems. Two of the systems are RS CVn and SZ Psc, which are detached, while the third system, RT Lac, is semidetached. Solar activity and the surface activity of the RS CVn type stars are compared. It is found that the spot model permits the detailed fitting of both the out-of-eclipse complications and the distorted shapes of the secondary eclipses in the light curves of these stars.
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Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.