Report on the celescope ultraviolet observations from the OAO-2 satellite and associated research at the Smithsonian Astrophysical Observatory.
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Avrett, E.↗
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Ultraviolet observations of Titan from OAO-2
High altitude deposition of energy in Titan's atmosphere can have a significant effect on the spectral distribution of emitted thermal radiation from the satellite. This reasoning led to the prediction of emission peaks at wavelengths corresponding to allowed bands of CH4 and trace photolysis products such as C2H6. Intermediate resolution infrared spectrophotometry has encouraged this interpretation of the infrared properties of Titan, and provided the basis for initial, detailed model.
Caldwell, J. J.↗
OAO-2 observations of the helium spectrum variable a Centauri
Ultraviolet photometry and spectrometer data are presented for a Cen, which exhibits large variations in the strength of its He I lines. The photometry indicates that the star becomes brighter at the helium-weak phase by 0.05 mag throughout the ultraviolet and visual region. A model atmosphere analysis indicates that the photometric variations are not due to flux redistribution from back-warming effects, but can be interpreted as due to the rotation of a distorted stellar disk in the shape of a prolate spheroid.
Molnar, M. R.↗
Precise positions and optical search for the 38 second X-ray pulsar near OAO 1653-40 and upper limit on X-ray emission from V861 Scorpii
The region of the binary system V861 Scorpii, whose secondary has been suggested as a black hole candidate, was observed with the HEAO 1 X-ray observatory during an 8-hour pointed observation on September 4, 1978. An upper limit of 1.0 micro Jy (within three standard deviations) is placed on X-ray emission from V861 Sco during this observation. This effectively removes the secondary from the list of black hole candidates. The presence of a 38 sec pulsar in the region is confirmed, precise (0.63 sq arcmin) positions are given, and a search for the optical counterpart is described.
Armstrong, J. T.↗
Documentation for the machine-readable version of an atlas of ultraviolet stellar spectra and a second atlas of ultraviolet stellar spectra from OAO 2 observations
The magnetic tape version of the Orbiting Astronomical Observatory 2 atlases of ultraviolet stellar spectra is described. The first file of the tape contains ultraviolet stellar fluxes for 164 bright stars in lambda the spectral region 1200 to 1300 A with resolutions of 22 A in the region from 3600 to 1850 A and 12 A in the region from 1850 to 1160 A. Files two and three contain spectra for 132 stars in the region lamba 1200 to 1850 A and 34 stars in the lambda region 1800 to 3600 A, respectively, with resolutions as stated above. The monochromatic flux is given in units of ergs cm(-2)s(-1) (-1) for all data.
Warren, W. H., Jr.↗
Picture gallery: A structured presentation of OAO-2 photometric data supported by UBV, ANS, and TD1 observations
Stellar fluxes for 531 stars in the wavelength range lambda 5500-1330A lambda are presented in the form of graphs. The stars are divided into 52 different categories on the basis of their spectral types and objects within one category are shown together. The agreement between the various ultraviolet photometric systems for early type stars is generally better than 0.10 mag. Stars with known and/or observed variability have been grouped separately. A list of stars with observed photometric properties which are indicative of stellar or interstellar anomalies is also provided.
Koornneed, J.↗
OAO-C end-of-mission power subsystem engineering evaluation
The battery performance on both Orbiting Astronomical Observatory missions was excellent. The end-of-mission power subsystem tests on the battery and the solar arrays provides a real-time degradation analysis for these two components.
Tasevoli, M.↗
Doppler line profiles measurement of the Jovian Lyman Alpha emission with OAO-C
Observation of Jupiter made with the high resolution ultraviolet spectrometer of the Orbiting Astronomical Observatory copernicus in April and May, 1980, yield a Jovian Lyman alpha emission intensity of 7 + or 2.5 RR. This indicates a decrease by about a factor of two since the Voyager ultraviolet spectrometer measurements, nearly a year earlier. An unusually high column abundance of hydrogen atoms above the methane homopause at the Voyager epoch is indicated. Since the auroral charged particle bombardment of molecular hydrogen is expected to contribute significantly to the global population of the hydrogen atoms, it is suggested that at the time of the Voyager Jupiter encounter unusually high auroral activity existed, perhaps d to the high concentration of the Io plasma torus. The temporal variation of the Saturn lyman alpha emission, when contrasted with the Jovian data, reveals that the auroral processes are not nearly as important in determining the Saturn Lyman alpha intensity in the nonauroral region.
Barker, E. S.↗
OAO-3 end of mission power subsystem evaluation
(Previously announced in STAR as N83-11583)
Tasevoli, M.↗
Multitude of iron lines including a Compton-scattered component in OAO 1657 – 415 detected with Chandra
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Pragati Pradhan↗
Observing from space with the Orbiting Astronomical Observatory.
Description of the OAO-A2 satellite and of its use in carrying out stellar measurements. The OAO-A2 is an unmanned satellite which carries two experiments, one measuring individual stars and the other measuring star fields. The OAO-A2 has the ability to point anywhere in celestial space with an accuracy of one arc minute and thus gives rise to certain operational considerations not known with other satellites. A detailed description is given of the operations control center responsible for planning and directing the overall OAO mission. The mission planning cycle and mission operations are discussed. Techniques for recovery of stellar control after loss of the stellar reference provided by the star trackers are considered. Improvements in the OAO series incorporated in the OAO-C satellite are cited.
Osler, S. J.↗
Orbiting astronomical observatory battery and power system design
The battery design of OAO-C (OAO-3) is given and consists of three-20 ampere hour 22 series connected cells in the battery. There are three batteries per spacecraft. The packaging configuration is described. The charging-discharging operations and the voltage potential of the battery system are discussed. Graphs are presented for the voltage limits (battery voltage versus temperature) and end of dark voltages (battery voltage versus ampere-hours discharged) of the battery system used on OAO-3. Data tables are also presented which give a summary of the battery performance and a comparison of OAO-3 with OAO A-2.
Ford, F. E.↗
Ultraviolet observations of comets
The first observations of a comet in the vacuum ultraviolet were obtained on January 14, 1970, when OAO-2 recorded the spectrum of the bright comet Tago-Sato-Kosaka (1969g). The observations revealed, among other things, the predicted extensive hydrogen Lyman alpha halo. OAO-2 continued to collect spectrophotometric measurements of this comet throughout January of that year; a photograph of the nucleus in Lyman alpha revealed finer scale structures. In February of 1970, the bright comet Bennet (1969i) became favorable for space observations. On the basis of the OAO discovery, OGO-V made several measurements of comet Bennet with low spatial resolution photometers. Comet Enke was detected by OGO in January of 1971 at a large heliocentric distance from its Lyman alpha emission.
Code, A. D.↗
Orbiting astronomical observatory-Copernicus
Of the three observatories planned in NASA's OAO program, one, OAO-3, is still in orbit and producing scientifically useful data. The prime experiment is the Princeton telescope spectrometer. Following a brief history of the OAO program, a description is given of the Princeton telescope with its 80-cm primary mirror, and of the spectrometer, which yields a resolution of up to 0.05 A. The spacecraft guidance system is also described. This system initially points the observatory to within a few arc minutes of the target, places the 0.3-arc sec slit on the star in less than 3 minutes, and holds on the star for up to 50 minutes with errors less than 0.05 arc sec. The main scientific results are described under the following categories: (1) the widespread presence of molecular hydrogen; (2) the search for other molecules, including detection of CO; (3) the nature of the interstellar medium as inferred from the detection of various atomic lines; (4) the study of chromospheres in late type stars; and (5) the study of mass loss in binaries and single stars.
York, D. G.↗
Ultraviolet photometry from the Orbiting Astronomical Observatory. XXII Ultraviolet light variation of Beta Lyrae
Six-color ultraviolet light curves of the complex eclipsing binary system Beta Lyr were obtained with the OAO-2 Wisconsin Experiment Package. The filters had a typical width at half maximum of 150 to 200 A and were centered at 1430, 1550, 1910, 2460, 2980, and 3320 A. The most striking characteristics of the ultraviolet light curves are that the secondary minimum deepens at shorter wavelengths. This indicates that we are not observing the eclipse effect of two stars having roughly a Planckian distribution of energy. In combination with the high-resolution far-ultraviolet spectra of Beta Lyr recently obtained with Copernicus (OAO-3) Princeton Telescope Spectrometer, it is concluded that the far-ultraviolet light curves are dominated by emission from the high-temperature gas surrounding the binary system. The ultraviolet observations of OAO-2 and Copernicus are consistent with a model in which the enigmatic secondary component involves a gravitationally collapsed object; i.e., a black hole. However, alternative models are also admissible.
Kondo, Y.↗
THE ENGINEERING DESIGN OF THE ORBITING ASTRONOMICAL OBSERVATORY
The Orbiting Astronomical Observatory (OAO) is designed to provide an accurately stabilized, unmanned platform for astronomical observations from well above the earth's atmosphere. Of primary immediate interest is the observation of stellar radiation in the ultraviolet range, which is severely limited even in balloon experiments because of absorption in the ozone layers. The OAO is a 3600-pound spacecraft that will be placed in orbit by an Atlas Agena D. It can handle optical systems up to 48 inches in diameter, 10 feet in length, weighing 1000 pounds. The key design requirements of the spacecraft are discussed. The reasons behind the configuration are then explained, followed by a discussion of the major subsystems showing how they have been designed to meet the exacting requirements astronomical observation.
SATELLITE INSTRUMENTATION↗
A study of B6 stars
A study of the spectra of zeta Draconis (B6 III), beta Sextantis (B6 V), and alpha Leonis (B7 V), was made from high dispersion spectrograms which cover the spectral region 3100 A to 6700 A and from OAO 2 spectral scans covering the spectral region 1100 A to 3600 A. Profiles, equivalent widths and central intensities of many lines in the spectrum of zeta Draconis are presented, as well as for the major lines of beta Sextantis. Alpha Leonis rotates too rapidly for these measurements to be made from high resolution spectrograms. Flux envelopes for zeta Draconis and alpha Leonis, from 1100 A to 6050 A, were derived from published spectrum scans and from new scans obtained with OAO 2. Estimates of the radii and masses of these single stars are presented.
Underhill, A. B.↗
Ultra-precise attitude test facility for flight spacecraft
A test facility was designed and built for conducting complete dynamic systems tests of the OAO spacecraft. The operating principle of the facility is illustrated for a single control axis. The test facility is described which was built and used to test the stabilization and control system of the OAO B spacecraft. Fine pointing of the spacecraft was demonstrated to better than 0.5 seconds of arc. Other spacecraft functions tested were gimbaled and boresight star tracker operations, coarse and fine slew maneuvers, inertial guidance operation, settling time of the spacecraft control system, and transfers between all modes of control.
Devine, E. J.↗