UBV photometry of lapetus: Results from five apparitions     

R.L. Millis 《Icarus》1977,31(1):81-88

Measurements of the brightness and B-V color index of the leading and trailing hemispheres of Iapetus during the past five apparitions of Saturn are presented. The dependence of brightness on solar phase angle is determined for the two faces of the satellite. After correction for solar phase angle and distance effects, the brighter trailing hemisphere of Iapetus was found to be constant in brightness and color index throughout the interval covered by the observations. The brightness of the dark leading hemisphere, however, decreased by about 0.2 mag over the same period, and its B-V color index reddened by 0.05 mag. These changes are interpreted as evidence for the existence of a bright southern pole cap on Iapetus.  相似文献   

Infrared imaging of Jupiter in the 8–14-micrometer spectral region     

Richard J. Terrile  James A. Westphal 《Icarus》1977,30(4):730-735

High spatial resolution images of Jupiter were produced on the Hale 200-in. telescope in August 1974 and October 1975. A programmable wobbling secondary was used to raster scan the planet with 64 by 64 1-arsec pixels. Images were made with broadband (8–14 μm) and several 1- and 2-μm wide filters. All images reveal a belt and zone structure similar to visible pjotographs. Belts, in the broadband data, appear to be about 2°K hotter than the zones, but contrast varies markedly in different parts of the 8–14-μm spectral region. The lowest belt-zone contrast is found in the hydrogen opacity dominated region at 12.5 μm, while images at 9.5 μm exhibit the greatest contrast. Isolated areas are observed to be as much as 4°K hotter than surrounding areas at 9.5 μm. This large contrast is probably due to variations in the distribution of the ammonia clouds in the upper atmosphere.  相似文献   

Venus mesosphere and thermosphere temperature structure: II. Day-night variations     

Robert E. Dickinson  E.C. Ridley 《Icarus》1977,30(1):163-178

A two-dimensional nonlinear hydrodynamic model has been developed for studying the global scale winds, temperature, and compositional structure of the mesosphere and thermosphere of Venus. The model is driven by absorption of solar radiation. Ultraviolet radiation produces both heating and photodissociation. Infrared solar heating and thermal cooling are also included with an accurate NLTE treatment. The most crucial uncertainty in determining the solar drive is the efficiency by which $\text{λ < 1080}\text{A}\text{?}$ solar radiation is converted to heat. This question was analyzed in Part I, where it was concluded that essentially all hot atom and O(¹D) energy may be transferred to vibrational-rotational energy of CO₂ molecules. If this is so, the minimum possible euv heating occurs and is determined by the quenching of the resulting excess rotational energy. The hydrodynamic model is integrated with this minimum heating and neglecting any small-scale vertical eddy mixing. The results are compared with predictions of another model with the same physics except that it assumes that 30% of $\text{λ < 1080}\text{A}\text{?}$ radiation goes into heat and that the heating from longer-wavelength radiation includes the O(¹D) energy. For the low-efficiency model, exospheric temperatures are ?300°K on the dayside and drop to < 180°K at the antisolar point. For the higher-efficiency model, the day-to-night temperature variation is from ?600°K to ?250°K. Both versions of the model predict a wind of several hundred meters per second blowing across the terminator and abruptly weakening to small values on the nightside with the mass flow consequently going into a strong tongue of downward motion on the nightside of the terminator. The presence of this circulation could be tested observationally by seeing if its signature can be found in temperature measurements. Both versions of the model indicate that a self-consistent large-scale circulation would maintain oxygen concentrations with ?5% mixing ratios near the dayside F-1 ionospheric peak but ?40% at the antisolar point at the same pressure level.  相似文献   

Observations of the sodium emission from Jupiter,region C     

Richard Goody  Jerome Apt 《Planetary and Space Science》1977,25(6):603-604

Measurements made when testing an interferometric system for imaging the sodium emission indicate that, between 3 and 7.5 arc min (9 and 23R_J) from Jupiter, the observed emissions can probably be attributed to terrestrial airglow.  相似文献   

FLOWER COLOR AND ENVIRONMENT: THE CASE OF BUTTERFLY WEED IN OKLAHOMA     

Lawrence J. Watson  Robert Q. Hanham 《The Professional geographer》1977,29(4):374-377

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AN EFFICIENCY EVALUATION OF FOUR DRAINAGE BASIN SHAPE RATIOS*     

David S. McArthur  Robert Ehrlich 《The Professional geographer》1977,29(3):290-295

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RECENT GEOGRAPHY DISSERTATIONS AND THESES COMPLETED     

Robert H. Stoddard 《The Professional geographer》1977,29(1):76-100

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The structure of a type-II supernova remnant G 160.5+2.8 (HB-9) observed at λ=12m     

E. P. Abranin  L. L. Bazelyan 《Astrophysics and Space Science》1982,88(2):299-306

A two-dimensional brightness distribution of the old supernova remnant G 160.5+2.8 (HB-9) has been measured at a frequency of 25 MHz with the T-Shaped UTR-2 radio telescope, with the resolution 29×27. The source has a distinctly pronounced, almost spherical envelope. At the same time, individual features located near the internal boundary of the source are observable.Certain considerations are put forward to validate a suggestion that the brightest feature in the decameter range (maximum at=4^h55^m.3 and =46°.37) might be of an extragalactic origin.From structure considerations, the velocity of the pulsar PSR 0459+47 projected on HB-9 is estimated. The estimate does not contradict the hypothesis of Damasheket al. (1978) concerning a possible genetic relation between HB-9 and PSR 0459+47.  相似文献   

Observation of MKN 501 at gamma-ray energies     

L. Bassani  R. C. Butler  A. J. Dean  G. Di Cocco  A. Della Ventura  F. Perotti  G. Villa 《Astrophysics and Space Science》1982,82(2):311-316

During a balloon flight in September 1979 of the MISO low-energy -ray telescope, the BL Lac-object MkN 501 was studied in the hard X-ray range above 30 keV and in the low energy -ray range up to 19 MeV. No statistically significant X- and -ray fluxes were detected. The implications of the upper limits obtained are discussed in the light of the relativistic jet theories recently proposed.  相似文献   

Search for variability in hydrogen-poor stars     

C. Bartolini  A. Bonifazi  F. D'antona  F. Fusi Pecci  L. Oculi  A. Piccioni  R. Serra 《Astrophysics and Space Science》1982,83(1-2):287-310

The evolutionary status of hydrogen-poor stars is analyzed.Photoelectric observations of six objects are reported as a first step of a long-term project devoted to search for variability of a large sample of hydrogen-poor stars.The observed stars show phenomena of microvariability with an amplitude of the order of 0^m. 1 or less.Two extreme helium stars have been examined: a period in the range of 0^d.162-0^d.164 has been found for BD+ 10⁰2179, andP=0^d.1079962 for BD+13⁰3324.The mass-losing O subdwarf (sdO) BD+37⁰ 443 presents short-term fluctuations with a time-scale of several minutes and long-term variations on a scale of months. The standard sdO BD+75⁰325 is probably non-variable, although light variations of very small amplitude (m0.03) with a time-scale of about 1 hr might be present. The high gravity sdO BD+25⁰4655, which is very close to the white dwarf stage, also presents variability on a time-scale of about 13 minutes, and might be an analog of the recently discovered pulsating sdO, or hot white dwarf, PG 1159-035.The variability of the intermediate helium star HD 37776 is finally confirmed.  相似文献