Spectropolarimetry of the methane and ammonia bands of Jupiter between 6800 and 8200 Å

Spectropolarimetry of Jupiter at resolutions between 22 and 35 Å reveals a strong increase of linear polarization in the 7250-$\text{A}\text{?}$ CH₄ band. This is very probably due to the decreasing contribution toward the band center of the higher orders of scattering, which have a smaller net polarization than the first few orders. The linear polarization is also enhanced in the band at 7900 $\text{A}\text{?}$ comprising the 7920-$\text{A}\text{?}$ NH₃ and 7600- to 8200-$\text{A}\text{?}$ CH₄ bands. The normalized circular polarization shows a feature at 7250 $\text{A}\text{?}$ with a dispersion shape. This is most probably produced in a double-scattering process involving either a solid or liquid aerosol with an absorption at 7250 $\text{A}\text{?}$. Methane aerosols, the obvious candidates from a spectroscopic point of view, are, however, forbidden if current estimates of the Jovian atmospheric temperature are correct.     

A remote unmanned ELF/VLF goniometer receiver in Antarctica

In March 1977 an unmanned ELF/VLF goniometer receiving station was deployed on the Antarctic plateau 110 km south south west of the British Antarctic Survey base at Halley. A UHF Telemetry link enabled the ELF and VLF signals to be monitored and recorded at Halley, simultaneously with data from an identical ELF/VLF receiver at Halley. The remote station was designed for unattended operation with a wind driven generator to recharge its battery. Design considerations and problems encountered are discussed and some preliminary results are presented.     

Galilean satellite eclipse studies: III. Jovian methane abundance

The methane abundance in the lower Jovian stratosphere is measured using Galilean satellite eclipse light curves. Spectrally selective observations in and between absorption bands are compared. An average mixing ratio at the locations measured is [CH₄]/[H₂] ～ 1.3 × 10^?3, larger than the value 0.9 × 10^?3 expected for a solar abundance of carbon. Some zenographic variation of the mixing ratio may occur. Observationally compatible values are 1.3–2.0 × 10^?3 in the STZ, 1.3– 2.6 × 10^?3 on the GRS/STrZ edge, and 0.7–1.3 × 10^?3 in the GRS.     

Magnetic properties of x-ray bright points

Using high resolution KPNO magnetograms and sequences of simultaneous S-054 soft X-ray solar images we have compared the properties of X-ray bright points (XBP) and ephemeral active regions (ER). All XBP appear on the magnetograms as bipolar features, except for very newly emerged or old and decayed XBP. We find that the separation of the magnetic bipoles increases with the age of the XBP, with an average emergence growth rate of 2.2 ± 0.4 km s^–1. The total magnetic flux in a typical XBP living about 8 hr is found to be 2 x 10¹⁹ Mx. A proportionality is found between XBP lifetime and total magnetic flux, equivalent to 10²⁰ Mx per day of lifetime.Operated by the Association of Universities for Research in Astronomy, Inc. under contract with the National Science Foundation.     

Vector magnetic field evolution,energy storage,and associated photospheric velocity shear within a flare-productive active region

The evolution of vector photospheric magnetic fields has been studied in concert with photospheric spot motions for a flare-productive active region. Over a three-day period (5–7 April, 1980), sheared photospheric velocity fields inferred from spot motions are compared both with changes in the orientation of transverse magnetic fields and with the flare history of the region. Rapid spot motions and high inferred velocity shear coincide with increased field alignment along the B _L= 0 line and with increased flare activity; a later decrease in velocity shear precedes a more relaxed magnetic configuration and decrease in flare activity. Crude energy estimates show that magnetic reconfiguration produced by the relative velocities of the spots could cause storage of 10³² erg day^–1, while the flares occurring during this time expended 10³¹ erg day^–1.Maps of vertical current density suggest that parallel (as contrasted with antiparallel) currents flow along the stressed magnetic loops. For the active region, a constant-, force-free magnetic field (J = B) at the photosphere is ruled out by the observations.Presently located at NASA/MSFC, Huntsville, Ala. 35812, U.S.A.     

Results of TV imaging of Phobos (Experiment VSK-Fregat)

From February to March 1989 the Phobos 2 spacecraft took 37 TV images of Phobos at a distance of 190-1100 km. These images complement Mariner-9 and Viking data by providing higher-resolution coverage of a large region West of the crater Stickney (40-160 degrees W) and by providing disk-resolved measurements of surface brightness at a greater range of wavelengths and additional phase angles. These images have supported updated mapping and characterization of large craters and grooves, and have provided additional observations of craters' and grooves' bright rims. Variations in surface visible/near-infrared color ratio of almost a factor of 2 have been recognized; these variations appear to be associated with the ejecta of specific large impact craters. Updated determinations of satellite mass and volume allow calculation of a more accurate value of bulk density, 1.90 +/- 0.1 g cm-3. This is significantly lower than the density of meteoritic analogs to Phobos' surface, suggesting a porous interior perhaps containing interstitial ice.     

Monazite U-Pb dating of staurolite grade metamorphism in pelitic schists

A study of the occurrence of and relations between rare-earth element (REE) minerals in pelitic schists indicates that monazite forms at or near the P and T of the staurolite isograd. Samples at staurolite grade from the Silurian Perry Mountain Formation in the Rumford quadrangle of Maine yield monazite in sufficient quantities to permit accurate dating of the metamorphic events forming the monazites. The bulk chemistry of the metapelites, as seen in the major element abundances and REE patterns, does not vary significantly across the study area. Thus the appearance and disappearance of REE phases is assumed to reflect changes in metamorphic grade. In a sample from the biotite zone, scanning electron microscope and microprobe studies show allanite and monazite intimately associated on a 10 m scale. The texture suggest that metastable detrital monazite breaks down, distributing its REE components to allanite. From samples below staurolite grade in which monazite is not present, our observations suggest that REEs are partitioned into allanite. At or near the staurolite isograd monazite forms as a metamorphic mineral, initiating its role as a geochronometer. Garnet-biotite geothermometry on samples at this grade from this and other studies places constraints on the minimum temperature necessary to form monazite: 525° C±25°C at 3.1±0.25 kbar. A total of 15 separates from nine schist samples ranging up to sillimanite grade have been dated. Each date is remarkably concordant, even though petrologic and textural studies by previous workers have shown that the rocks in the area have been affected by at least three metamorphic episodes. Calculations indicate insignificant Th disequilibrium in these monazites. The conditions associated with the metamorphic events suggest that monazite remains closed to lead loss provided that subsequent metamorphisms are at or below sillimanite grade. Two distinct metamorphic events are resolved, one at around 400 Ma and one at about 370 Ma. The latter was due to thermal effects of a nearby pluton that yields concordant monazite ages of 363 Ma. This work suggests that in addition to dating plutonism and high-grade metamorphism, monazite should be viewed as a reliable geochronometer for moderate metamorphism of pelitic schists.     

Coronal holes,solar wind streams,and geomagnetic activity during the new sunspot cycle

We have extended our previous study of coronal holes, solar wind streams, and geomagnetic disturbances from the declining phase (1973–1975) of sunspot cycle 20 through sunspot minimum (1976) into the rising phase (1977) of cycle 21. Using daily He I 10830 Å spectroheliograms and photospheric magnetograms, we found the following results:

1. As the magnetic field patterns changed, the solar atmosphere evolved from a structure having a few, large, long-lived, low-latitude coronal holes to one having numerous small, short-lived, high-latitude holes (in addition to the polar holes which persisted throughout this 5-year interval).
2. The high-latitude holes recurred with a synodic rotation period of 28–29 days instead of the 27-day period already known to be characteristic of low-latitude holes.
3. During 1976–1977 many coronal holes were intrinsically ‘weak’ in the sense that their average intensities did not differ greatly from the intensity of their surroundings. Such low-contrast holes were rare during 1973–1975.

An updated Bartels display of the occurrence of holes, wind speed, and geomagnetic activity summarizes the evolution of their characteristics and interrelations as the sunspot cycle has progressed. Long-lived, low-latitude holes have become rare but remain terrestrially effective. The more common high-latitude holes are effective only when the Earth lies at a relatively high heliographic latitude in the same solar hemisphere.     

A study of the magnetic and velocity fields in an active region

A time sequence of magnetograms and velocity-grams in the H and Fe i 6569 Å lines has been made at a rate of 12 h^–1 of McMath Region 10385 from 26 to 29 October, 1969. The 14 flares observed during this period have been studied in relation to the configuration and changes in the magnetic and velocity fields. There was little correlation between flare position and the evolutionary changes in the photospheric magnetic and velocity field, except at large central meridian distances where the velocity observations suggested shearing taking place at flare locations. At central meridian distances > 30° we found that flares are located in areas of low line-of-sight photospheric velocity surrounded by higher velocity hills. The one exception to this was the only flare which produced a surge. Blue-shifted velocity changes in the photosphere of 0.3 to 1 km s^–1 were observed in localized areas at the times of 8 of 14 flares studied.Visiting Astronomer, Kitt Peak National Observatory.Operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation.