Detection limits in the far infrared

The advent of far infrared arrays will change fundamentally the means of analyzing observations in this spectral region. Sources much fainter than traditional confusion limits will be extracted from images by using computer algorithms similar to CLEAN or DAOPHOT. We have conducted numerical experiments to evaluate these techniques and show that they will permit long integrations (10,000 sec at 60 m, 200 sec at 100 m) to achieve nearly photon-background-limited performance and hence very deep detection limits. The dominant noise sources—photon noise, confusion by distant galaxies, and confusion by IR cirrus — scale with nearly the same power of the telescope aperture. As a result, the integration times required to reach confusion limits are nearly aperture-independent.     

The role of calcium in the regulation of hormone transport in gravistimulated roots.

Prior research has shown that gravistimulation induces preferential movement of calcium toward the lower side of the tips of maize roots and that roots depleted of calcium show impaired gravitropism. To further investigate the role of calcium in root gravitropism, we examined the effects of calcium on auxin movement in both vertical and gravistimulated roots of maize. Longitudinal movement of auxin was basipetally polar in intact roots but acropetally polar in decapped roots. Treatment of the root tip with calcium increased basipetal auxin movement in both intact and decapped roots. Gravistimulation induced asymmetric auxin movement toward the lower side of the root tip. Both asymmetric auxin movement and gravicurvature were inhibited by treatment of the root tip with auxin transport inhibitors or with EGTA. The results indicate that there is a close correlation between curvature and gravity-induced asymmetric auxin movement across the root cap. Since gravistimulation causes calcium movement toward the lower side of the root tip, our observation that calcium promotes basipetal auxin movement supports the idea that gravity-induced calcium asymmetry is a key step linking gravistimulation to the establishment of auxin asymmetry during root gravitropism.     

The Two Wide-angle Imaging Neutral-atom Spectrometers (TWINS) NASA Mission-of-Opportunity

Two Wide-angle Imaging Neutral-atom Spectrometers (TWINS) is a NASA Explorer Mission-of-Opportunity to stereoscopically image the Earth’s magnetosphere for the first time. TWINS extends our understanding of magnetospheric structure and processes by providing simultaneous Energetic Neutral Atom (ENA) imaging from two widely separated locations. TWINS observes ENAs from 1–100 keV with high angular (～4°×4°) and time (～1-minute) resolution. The TWINS Ly-α monitor measures the geocoronal hydrogen density to aid in ENA analysis while environmental sensors provide contemporaneous measurements of the local charged particle environments. By imaging ENAs with identical instruments from two widely spaced, high-altitude, high-inclination spacecraft, TWINS enables three-dimensional visualization of the large-scale structures and dynamics within the magnetosphere for the first time. This “instrument paper” documents the TWINS design, construction, calibration, and initial results. Finally, the appendix of this paper describes and documents the Southwest Research Institute (SwRI) instrument calibration facility; this facility was used for all TWINS instrument-level calibrations.     

Multi-experiment determination of plasma density and temperature

An attempt has been made to combine data from five instruments on GEOS-1 in order to determine the characteristics of the ambient cold plasma, assess the effects of spacecraft sheaths on the different techniques and establish cross calibration criteria. In addition to measuring plasma density and temperature it is necessary to consider the influence of satellite potential and motion, ionic composition, ion drifts (electric fields), electrons emitted from spacecraft surfaces and any consequent departures from isotropy or Maxwellian distribution.9 October 1977 was selected for the study, the orbit covers a range of L-values between 3.5 and 7.5 giving outbound and inbound plasmapause crossings with plasma densities spanning more than two orders of magnitude. Eclipse data from 7 February 1978 is used to determine the influence of photoelectron emission.Three techniques — active sounding of the plasma frequency resonance (S-301), a mutual impedance measurement (S-304) and DC electric field probe determination of floating potential (S-300) — utilize the long boom sensors in either AC or DC modes. Electrons and ions are measured directly by electrostatic analysers (S-302), mounted on one short radial boom. On the day chosen for study here ions are predominantly protons as determined by the body mounted ion composition experiment (S-303).The techniques using the 20 m long booms agree well in determining density whereas the short boom and body mounted ion detectors are seriously compromised when satellite potential becomes several volts positive. Measurements of satellite potential and plasma temperature agree within 20% among the several instruments making these measurements. Data obtained during the transition from eclipse to sunlight conditions show no discontinuity in the long boom instruments caused by the sudden appearance of photoelectrons.     

Fast time-resolution spectroscopy of BW Vulpeculae

An experimental Fairchild CCD-211 was placed in the 2. 1-m coudé spectrograph at the Kitt Peak National Observatory and used to record an 87 Å spectral band centered on Ha. On the night of 1979 July 11 UT date, this system was used to observe continuously the extreme Cephei variable BW Vulpeculae throughout one of its 4^h 49^m cycles with an average exposure of 13 minutes per observation. A total of 18 observations was secured. The results show dramatic profile variations of H, including features not previously reported, and extreme variations of the C II 6578, 6582 lines, including variations of equivalent width. The fast time-resolution capability and the photometric linearity of the CCD have permitted the detection of subtle effects that have been missed by photographic observations and has led directly to important new interpretations of the complex atmospheric pulsations in this star, including effects of altered opacity on the formation of spectral lines and the suggestion of a helium-ionization heat engine as a mechanism for driving atmospheric pulsations.Operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation.     

Global pictures of the ozone field,from high altitudes,from DE-I

Using the imaging instrumentation aboard the Dynamics Explorer spacecraft (DE-I), total column ozone densities are obtained in the sunlit hemisphere by measuring the intensities of backscattered solar ultraviolet radiation with multiple filters and multiple photometers. The high apogee altitude (23,000 km) of the eccentric polar orbit allows high resolution global-scale images of the terrestrial ozone field to be obtained within 12 minutes. Previous ozone-monitoring spacecraft have required much longer time periods for comparable spatial coverage because of their lower altitudes (<1200 km). The much higher altitude of DE-I also provides hours of continuous imaging of features compared to minutes or seconds with previous spacecraft. Near perigee, high resolution images can be gained with pixel size as small as 3 km to view mesoscale atmospheric variations. Utilizing these data, the effects of planetary-scale, synoptic-scale, and mesoscale dynamical processes, which control the distribution of ozone near the tropopause, can be studied. Preliminary results show short-term (less than one day) variations in the synoptic ozone field and these variations appear to be in accord with meteorological data. Spatial variations in the ozone field are found to be highly negatively correlated with tropopause altitude.