Hydrated sulphuric acid in dense molecular clouds

We consider sulphur depletion in dense molecular clouds, and suggest hydrated sulphuric acid, H₂SO₄ ·  n H₂O, as a component of interstellar dust in icy mantles. We discuss the formation of hydrated sulphuric acid in collapsing clouds and its instability in heated regions in terms of the existing hot core models and observations. We also show that some features of the infrared spectrum of hydrated sulphuric acid have correspondence in the observed spectra of young stellar objects.     

Steady-state size distributions for collisional populations:: analytical solution with size-dependent strength

The steady-state population of bodies resulting from a collisional cascade depends on how material strength varies with size. We find a simple expression for the power-law index of the population, given a power law that describes how material strength varies with size. This result is extended to the case relevant for the asteroid belt and Kuiper belt, in which the material strength is described by 2 separate power laws—one for small bodies and one for larger bodies. We find that the power-law index of the small body population is unaffected by the strength law for the large bodies, and vice versa. Simple analytical expressions describe a wave that is superimposed on the large body population because of the transition between the two power laws describing the strength. These analytical results yield excellent agreement with a numerical simulation of collisional evolution. These results will help to interpret observations of the asteroids and KBOs, and constrain the strength properties of those objects.     

Flexure of Europa's lithosphere due to ridge-loading

Using photoclinometry, topographic profiles across europan ridges have been produced. These profiles allow the identification of bulges in the terrain adjacent to the ridges. The bulges are assumed to have been produced by flexure of the elastic lithosphere due to the load of the ridges, which lie along cracks in the crust. The distance from the crack to these “fore-bulges” depends on the thickness of the elastic plate being flexed. Based on a survey of ridges in Galileo images with resolution <300 m/pixel, the thickness of the elastic lithosphere has been determined by this method at a wide variety of sites along the leading and trailing hemispheres of Europa. The average thickness is about 200 m. The elastic lithosphere underneath smooth dilational bands tends to be thicker than plains morphology, an effect that is pronounced at Thynia Linea and Astypalaea Linea. Among the ridges investigated here, more recent loading correlates with a thicker elastic lithosphere, which may either reflect an intrinsically thicker layer, or less viscous relaxation over the shorter time period.     

Theory of quadrupolar sunspots and the active region of August, 1972

Energy is stored when the force-free magnetic field in an active region departs from a potential field, the departure showing up as a shear in the field. As soon as the field untwists, energy will be released to produce flares. Based on this idea, we derived an analytical solution of the equation of force-free field under the assumption of a constant force-free factor, and found expressions for seven important quantities for quadrupolar sunspots: the magnetic energy of the twisted field, that of potential field, the extractable free energy ΔM, the magnetic flux, the total current, the force-free factor and the field decay factor, in terms of three observables: the field intensity, the twist angle and the distance between two spots of the same polarity. The expression for ΔM can be useful in solar prediction work. For the active region of August, 1972, we found ΔM up to 6 × 10³² erg, sufficient to supply the energy of the observed flare activity. Observations of this active region are in good general agreement with our theoretical expectations: in the entire twisting of the quadrupolar sunspot group, each spot assumes the form of a complete spiral in the clockwise direction for each of the four spots.     

Fatty acids and sterols as source markers of organic matter in sediments of the North Carolina continental slope

To estimate the source and diagenetic state of organic matter reaching bottom sediments, fatty acids and sterols were measured in unconsolidated surface material (flocs) at 12 sites ranging from 600 to 2000 m across the mid-Atlantic continental slope off Cape Hatteras, North Carolina. Total free and esterefied fatty acids were similar in distribution and concentration to other coastal systems, with values ranging from 0.64 to 46.52 μg mg⁻¹ organic carbon (1.10–68.85 μg g⁻¹ dry sediment). Although shallow (600 m) stations contained significantly greater fatty acid concentrations than deep (> 1400m) stations, high variability observed at mid-depth (800 m) collections precluded a consistent relationship between total fatty acid concentration and station depth. At three sites where underlying sediments were also collected, decreases in total fatty acids, reduced amounts of polyenoic acids and significant presence of bacterial fatty acid suggest rapid reworking of labile organic material that reaches the sediment surface. The distribution of sterols was remarkably consistent among all sites even though there were large variations in concentrations (1.8–20.7 μg mg⁻¹ organic carbon). Sterol composition indicated phytoplankton, principally diatoms and dinoflagellates, as the principal source of labile organic matter to sediments, together with a significant input of cholest-5-en-3β-ol typical of zooplankton and their feeding activity. A minor but widespread terrigenous input was also evident based upon significant concentrations of sterols dominant in vascular plants.     

A study of the chemistry of iodine and bromine in marine sediments

Several recent marine sediments were treated with eleven chemical reagents in order to ascertain the iodine and bromine species present. The sediments were analyzed before and after each treatment to determine which reagents released the bound halogens. By a process of elimination it is concluded that the iodine is present primarily in its electro-positive state as N-iodoamides while bromine exists in many different chemical forms.     

Far-infrared observations of main sequence stars surrounded by dust shells

We present 50 and 100µm photometry and size information for several main sequence stars surrounded by dust shells. The observations from NASA's Kuiper Airborne Observatory include the Vega-like stars, Beta Pic, Fomalhaut, as well as four stars suggested by Walker and Wolstencroft to belong possibly to the same class. The results of our observations are best interpreted as upper limits to the far-infrared sizes of the dust clouds around all of the stars except Fomalhaut and Beta Pic. We have also fit simple, optically thin models to the Beta Pic data to explore the range of shell parameters consistent with our limits and with previous observations.     

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.     

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.