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NASA NTRS1981

Behavior of Titan's atmosphere during a total eclipse

During its emergence from the Saturnian shadow on June 28, 1980, Titan was observed simultaneously in the visible and IR ranges (6000-9000 A, and 11.8 and 20 microns). The eclipse observation indicates that thin-atmosphere models with a modest greenhouse effect are likely to be incorrect. A thin atmosphere of pure methane in equilibrium with an ice surface of methane is in marginal agreement with the present data, but improved VLA temperature measurements would be a crucial test of this model. Both the eclipse observation and VLA measurements agree with a nitrogen-dominant atmospheric model, as indicated by preliminary Voyager results.

Combes, M.↗
NASA NTRS1983

International Ultraviolet Explorer observations of the peculiar variable spectrum of the eclipsing binary R Arae

The eclipsing binary system R Arae = HD 149730 is a relatively bright southern system with an orbital period of about 4.4 days. It is a single-lined spectroscopic binary. The spectral class of the primary component is B9 Vp. The system was included in a study of mass flow and evolution in close binary systems using the International Ultraviolet Explorer satellite (IUE). Four spectra in the wavelength range from 1150 to 1900 A were obtained with the far-ultraviolet SWP camera, and six spectra in the range from 1900 to 3200 range were obtained with the mid-ultraviolet LWR camera. The close binary R Arae exhibits very unusual ultraviolet spectra. It appears that no other close binary system, observed with any of the orbiting satellites, shows outside-eclipse ultraviolet continuum flux variations of this nature.

Mccluskey, G. E.↗
NASA NTRS1983

SS Bootis - A totally eclipsing binary of the RS CVn type

Photoelectric photometry gathered for SS Bootis over the 1976-1981 period shows a distortion wave amplitude variation from 0.05 to 0.20 mag, with no apparent pattern. From the rectified light curve, a new time of midprimary eclipse was found to be 2444332.0335 + or - 0.0005 days. Solutions of the primary eclipse data, rectified for star spots as well as for ellipticity and reflection, are presented.

Vaucher, C. A.↗
NASA NTRS1983

Electron density and energetic particle precipitation observed during the eclipse of 26 February 1979

Electron density profiles and energetic particle fluxes are obtained based on data collected by two rockets launched from Red Lake, Ontario, respectively, at the beginning and end of totality during the solar eclipse of February 26, 1979. Data obtained by a rocket launched on February 24, 1979 showed that the electron density was normal (at 10,000 cu cm) above 110 km, to rocket apogee (130.5 km). Below 110 km, the electron density was found to be enhanced compared with data from Wallops Island at the same solar zenith angle (63 deg). It is proposed that this enhancement was due to the large flux of field-aligned energetic particles observed on the same rocket. The electron density above 110 km to rocket apogee (132.6 and 132. 3 km) was found to be reduced during totality by a factor of about three. However, below 110 km, the electron density was found to be much greater than observed during previous eclipses, probably due to the additional ionization resulting from energetic particles. The particle flux measured on February 26 was found to be an order of magnitude less than on February 24 but showed greater variability, particularly at the higher energies (100 keV).

Smith, L. G.↗
NASA NTRS1983

A collection of Galilean satellite eclipses 1652-1982

Data from visual observations of the eclipses of the Jovian Galilean satellites recorded in two 17th and 18th century manuscripts are analyzed. It is shown that a 'lost' group of more than 6800 eclipse observations known as the Delambre collection is actually contained in two smaller manuscripts, the Pingre book and the Delisle manuscript. The data in the collections are expected to be useful in determining the ephemerides, masses and libration parameters of the Jovian satellites, for the study of questions related to Delta T (Ephemeris Time-Universal Time) as it was recorded in the 17th century, and for the study of the Laplace commensurability.

Lieske, J. H.↗
NASA NTRS1984

Discovery of a 7.1 hour period and eclipses from MXB 1659-29

A 7.1 hr period has been discovered in the X-ray emission from the 'transient' X-ray burst source MXB 1659-29. Erratic variations in X-ray flux are seen during approximately 25 percent of the 7.1 hr cycle; at the end of this period, a stable dip in the flux occurs. Further analysis indicates that this dip is, in all probability, an eclipse by the companion star in the low-mass binary system. The short (about 15 minute) eclipse duration is used to refine the period determination (7.114104 + or - 0.000168 hr) and to constrain the companion star mass and binary system parameters. The companion star is found to be in the range 0.25-0.9 solar mass; probabilistic arguments and observations of cataclysmic variables with comparable periods indicate that the companion star is most likely less massive than the standard theories would indicate.

Cominsky, L. R.↗
NASA NTRS1984

Rocket observations of the ionosphere during the eclipse of 26 February 1979

Electron density profiles and energetic particle fluxes were determined from two rockets launched, respectively, at the beginning and end of totality during the solar eclipse of 26 February 1979. These, and one other rocket at the same time of day on 24 February 1979, were launched from near Red Lake, Ontario. The electron density profile from 24 February shows the electron density to be normal above 110 km, to rocket apogee. Below 110 km, the electron density is enhanced, by an order of magnitude in the D region, compared with data from Wallops Island at the same solar zenith angle (63 deg). The enhancement is qualitatively explained by the large flux of field aligned energetic particles observed on the same rocket. During totality (on 26 February) the electron density above 110 km to rocket apogee is reduced by a factor of about three. Below 110 km, the electron density is much greater than observed during previous eclipses. The particle flux measured on the 26 February was an order of magnitude less than that on the 24 February but showed greater variability, particularly at the higher energies (100 keV). A feature of the particle flux is that, for the two rockets that were separated horizontally by 38 km while above the absorbing region, the variations are uncorrelated.

Mcinerney, M. K.↗
NASA NTRS1984

Infrared observations of the eclipse of Epsilon Aurigae Direct measurement of the 500 K secondary at 5, 10, and 20 microns

Photometric data of the once-every-27 yr eclipse of the Epsilon Auriga F supergiant are reported. The data were taken on 28 nights from July 1982-May 1984 and covered the 1.25-20 microns region. The secondary object was identified at 5, 10, and 20 microns when the eclipse removed 48 percent of the F star's light. The data indicated that the secondary is a compact object surrounded by a large optically thick cloud, with a luminosity under 0.01 of the primary. The secondary's mass is, however, more than 14 solar masses.

Backman, D. E.↗
NASA NTRS1985

The apsidal motion of the eccentric eclipsing binary DI Herculis - An apparent discrepancy with general relativity

The apsidal motion of the eccentric eclipsing binary DI Herculis (HD 175227) is determined from an analysis of the available observations and eclipse timings from 1959 to 1984. Least squares solutions to the primary and secondary minima extending over an 84-yr interval yielded a small advance of periastron omega dot of 0.65 deg/100 yr + or - 0.18/100 yr. The observed advance of the periastron is about one seventh of the theoretical value of 4.27 deg/100 yr that is expected from the combined relativistic and classical effects. The discrepancy is about -3.62 deg/100 yr, or a magnitude of about 20 sigma. Classical mechanisms which explain the discrepancy are discussed, together with the possibility that there may be problems with general relativity itself.

Guinan, E. F.↗
NASA NTRS1985

Optical photometry of the 1982-1984 eclipse of Epsilon Aurigae

From slightly before the 1982-1984 eclipse of Epsilon Aurigae to the present observers from around the world have been making photoelectric photometry observations of this star system. Over 2000 UBV observations have been reported as well as observations in the R, I, J, H, K, L, M, N, and Q bandpasses plus the y, b, v, and u bandpasses. Twenty nine observers from 9 countries submitted photometry data to the campaign. The data have shown many interesting features of the star system including a Cepheid-like pulsation, flare activity, mid-eclipse brightening, post egress brightening, plus other strange activity.

Hopkins, J. L.↗
NASA NTRS1985

IUE observations of the 1982-84 eclipse of Epsilon Aurigae

The major characteristics in the ultraviolet of the 1982-84 eclipse of Eps Aur as observed with IUE by various workers are summarized. This star can be observed over the entire IUE wavelength range, from 1200 to 3200 A, in low dispersion, allowing eclipse light curves to be obtained in broadband regions, but due to its steep spectral gradient and the sensitivities of IUE cameras, high resolution exposures adequately cover only the regions from 1700-1900 and 2400-3200 A. In many ways, the UV data confirms or expands upon interpretations of the stem made from observations in other wavelength regions, but in other respects the system remains as enigmatic as before.

Ake, T. B.↗
NASA NTRS1985

UBV photometry of the 1982-4 eclipse of Epsilon Aurigae: A discussion of the observed light curves

At least 29 observers in nine countries have contributed photometric measurements of Epsilon Aurigae during the recent observational campaign. The present discussion is limited to data submitted by J. L. Hopkins of the Hopkins Phoenix Observatory and S. I. Ingvarsson of the Tjornisland Astronomical Observatory. Both sources are on the UBV system, with no significant systematic differences. Combined, these two sources cover the entire eclipse, from pre-ingress up to the present (April 1985). It should be noted that this eclipse is the first to have complete photometric coverage in all three broadband filters U, B, and V.

Schmidtke, P. C.↗
NASA NTRS1985

Epsilon Aurigae during eclipse - IRAS observations of the cool secondary component

Measurements of Epsilon Aur made from 5 to 60 microns over a period of less than 1 month during full eclipse, including special Infrared Astronomy Satellite (IRAS) observations at 12, 25, and 60 microns are presented. The observed flux at 60 microns agrees well with a prediction based on ground-based infrared monitoring of the eclipse ingress in 1982. Fits to the flux in excess of simple models for the primary star's infrared photospheric continuum yield T = 475 + or - 50 K, Omega = 8.6 + or - 1.0 x 10 to the -16th sr for the secondary. The total observed luminosity from the secondary is no larger than 50 solar luminosities.

Backman, D. E.↗
NASA NTRS1986

Epsilon Aurigae in eclipse. II - Optical absorption lines from the secondary

Optical high-resolution 2.7-m McDonald Observatory observations of Epsilon Aur obtained during the 1982-1985 eclipse are discussed, with focus on the K I resonance lines, some Fe II and Ti II lines in the blue, and the near-infrared N I excitation lines. The N I lines are immune to contamination by the secondary, and their radial velocity decline over the three-year interval fits the predicted velocity curve. The 7664 A and 7699 A K I lines strengthen greatly during the eclipse due to gas in orbit around the secondary passing in front of the primary, and the velocity pattern analysis indicates a mass of the secondary to solar mass ratio of between about 3 and 6 and a primary mass of 3 solar masses. The data are consistent with the picture of a low-mass post-AGB primary having lost mass through a wind and by Roche-lobe transfer to the secondary, and which will evolve to a white dwarf in less than 10,000 years.

Lambert, D. L.↗
NASA NTRS1988

Infrared observations of eclipses of Io, its thermophysical parameters, and the thermal radiation of the Loki volcano and environs

Observations of Io during eclipses by Jupiter in 1981-1984 are reported. Data obtained at 3.45-30 microns using bolometer system No. 1 on the 3-m IRTF telescope at Mauna Kea are presented in extensive tables and graphs and analyzed by means of least-squares fitting of thermophysical models to the eclipse cooling and heating curves, thermal-radiation calculations for the Io volcanoes, and comparison with Voyager data. Best fits are obtained for a model comprising (1) a bright region with a vertically inhomogeneous surface and (2) a dark vertically homogeneous region with thermal inertia only about 0.1 times that of (1). Little evidence of volcanic-flux variability during the period is found, and the majority (but not all) of the excess thermal IR radiation in the sub-Jovian hemisphere is attributed to the Loki volcano and its lava lake.

Sinton, William M.↗
NASA NTRS1988

A study of SCATHA eclipse charging

The events of charging of the SCATHA satellite in eclipse were investigated and correlated to the spacecraft surface-averaged and angle-averaged fluxes. It is shown that the large negative vehicle potentials produced in eclipse correlated with the net current due to the high-energy plasma electrons. These potentials also depend on the ion energy, ion current, and the average ion yield. An explanation for this behavior is proposed.

Li, Wei-Wei↗
NASA NTRS1988

Changes in the earth's rate of rotation between A.D. 1672 and 1806 as deduced from solar eclipse timings

Solar eclipse timings measured between A.D. 1672 and 1806 are analyzed to study the variation of Delta T (= ET - UT) over this interval. These solar eclipse observations confirm the results of Brouwer (1952), Martin (1969), and Stephenson and Morrison (1969) which were obtained from the analysis of occultations in this period. It is believed that Goldstein's (1985) analysis inadequately represents the changes in Delta T.

Stephenson, F. R.↗
NASA NTRS1989

Time-resolved spectroscopy and photometry of the eclipsing AM Herculis binary EXO 033319 - 2554.2

Time-resolved optical observations of the eclipsing AM Herculis binary EXO 033319 - 2554.2 are presented. High-speed photometry of an eclipse is presented and used to derive a new ephemeris for the system and to estimate the size of the region responsible for the cyclotron emission. Optical spectra that span the orbital cycle are presented, the cyclotron emission in these spectra is discussed, and the flux and radial velocity variations of H-beta, H-gamma, and He II 4686 A are examined. Models of the flux and radial velocity variations of the emission lines indicate that about half the line emission comes from low-velocity material that is about 1.4 x 10 to the 10th cm from the white dwarf. The rest comes from high-velocity material that is about 10 to the 10th cm from the white dwarf and is moving toward it at about 600 km/s.

Allen, Richard G.↗