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  • Other Sources  (11)
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  • 1
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    Policy opportunities (1991)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Recommendations are given regarding National Science Foundation (NSF) astronomy programs and the NASA Space Astrophysics program. The role of ground based astronomy is reviewed. The role of National Optical Astronomy Observatories (NOAO) in ground-based night-time astronomical research is discussed. An enhanced Explored Program, costs and management of small and moderate space programs, the role of astrophysics within NASA's space exploration initiative, suborbital and airborne astronomical research, the problems of the Hubble Space Telescope, and astronomy education are discussed. Also covered are policy issues related to the role of science advisory committees, international cooperation and competition, archiving and distribution of astronomical data, and multi-wavelength observations of variable sources.
    Keywords: ASTRONOMY
    Type: National Academy of Sciences(National Research Council, Working Papers: Astronomy and Astrophysics Panel Reports; 18 p
    Format: application/pdf
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  • 2
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    Differential rotation in the solar corona (1994)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The soft X-ray telescope (SXT) instrument on board the Yohkoh satellite was designed to observe the solar corona for over three years. It was shown in previous works that different tracers of solar rotation, each sensitive to a different part of the solar atmosphere, yield varying results for the latitude dependence of the rotation rate; the differential rotation measured using photospheric structures is markedly different from that obtained using coronal tracers. The long term observations of the solar corona by the SXT make it ideal for the investigation of coronal differential rotation. The soft X-ray emission of the solar corona is used to trace out the rotation rate at different latitudes. This is done by dividing the solar disk into a number of latitude strips and carrying out a power-spectrum analysis of the total soft X-ray intensity in each strip over a twelve week period of the Yohkoh observations. The results are compared with the differential rotation rates obtained from other coronal tracers.
    Keywords: SOLAR PHYSICS
    Type: ESA, Proceedings of 3rd SOHO Workshop on Solar Dynamic Phenomena and Solar Wind Consequences; p 405-407
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  • 3
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    XSST/TRC rocket observations of July 13, 1982 flare (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The present analysis of UV filtergrams of the July 13, 1982 solar flare obtained by the XSST/TRC rocket experiments has used calibrated intensities of the flare components to directly estimate the Lyman-alpha line flux, C IV line flux, and excess 160-nm continuum temperature brighness over the underlying plage. The values obtained are small by comparison with other observed or calculated equivalent quantities from the Machado (1980) model of flare F1. The corresponding power required to heat up to the temperature minimum over the 1200 sq Mm area is found to be 3.6 x 10 to the 25th erg/sec for this small X-ray C6 flare, 7 min after the ground-based observed flare maximum.
    Keywords: SOLAR PHYSICS
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  • 4
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    The point spread function of the soft X-ray telescope aboard Yohkoh (1995)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The point spread function of the SXT telescope aboard Yohkoh has been measured in flight configuration in three different X-ray lines at White Sands Missile Range. We have fitted these data with an elliptical generalization of the Moffat function. Our fitting method consists of chi squared minimization in Fourier space, especially designed for matching of sharply peaked functions. We find excellent fits with a reduced chi squared of order unity or less for single exposure point spread functions over most of the CCD. Near the edges of the CCD the fits are less accurate due to vignetting. From fitting results with summation of multiple exposures we find a systematic error in the fitting function of the order of 3% near the peak of the point spread function, which is close to the photon noise for typical SXT images in orbit. We find that the full width to half maximum and fitting parameters vary significantly with CCD location. However, we also find that point spread functions measured at the same location are consistent to one another within the limit determined by photon noise. A 'best' analytical fit to the PSF as function of position on the CCD is derived for use in SXT image enhancemnent routines. As an aside result we have found that SXT can determine the location of point sources to about a quarter of a 2.54 arc sec pixel.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Solar Physics (ISSN 0038-0938); 157; 2-Jan; p. 141-168
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  • 5
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    Multispectral observations of chromospheric evaporation in the 1991 November 15 X-class solar flare (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-08-27
    Description: We analyze simultaneous H(alpha) images and spectra (from Mees Solar Observatory), and soft and hard X-ray images and spectra (from YOHKOH) during the early phase of an X1.5/3B flare. We investigate the morphological relationship between chromospheric downflows, coronal upflows, and particle precipitation sites, and the energetic relationship between conductive heating, nonthermal particle heating, and the chromospheric response. We find that the observations consistently fit the chromospheric evaporation model. In particular, we demonstrate that the observed upflowing coronal and downflowing chromospheric plasma components originate in the same locations, and we show that our unique set of optical and X-ray observations can clearly distinguish between conductively driven and electron beam driven evaporation.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 424; 1; p. 459-465
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  • 6
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    The structure of the coronal soft X-ray source associated with the dark filament disappearance of 1991 September 28 using the Yohkoh Soft X-ray Telescope (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The structure of the coronal soft X-ray source associated with the dark filament disappearance on September 28, 1991, observed with the Soft X-ray Telescope, is examined as a possible example of the 'eruption-reconnection' model of filament disappearance. The results suggest, however, that this model may not fit. There is a strong possibility that much of the dark filament mass remains in the heated unwinding axial field.
    Keywords: SOLAR PHYSICS
    Type: PASJ: Publications of the Astronomical Society of Japan (ISSN 0004-6264); 44; 5; p. L205-L210.
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  • 7
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    Observations of X-ray jets with the Yohkoh Soft X-ray Telescope (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The features of the multiple X-ray jets in the solar corona, revealed by the time series of the Yohkoh Soft X-ray Telescope images are described. The typical size of a jet was from 5 x 10 exp 3 to 4 x 10 exp 5 km, the translational velocity was 30-300 km/s, and the corresponding kinetic energy was estimated to be from 10 exp 25 to 10 exp 28 erg. Many of the jets were found to be associated with flares in X-ray bright points, emerging flux regions, or active regions, and they sometimes occurred several times from the same X-ray feature. One of the jets associated with a flaring bright point was identified as being an H-alpha surge.
    Keywords: SOLAR PHYSICS
    Type: PASJ: Publications of the Astronomical Society of Japan (ISSN 0004-6264); 44; 5; p. L173-L179.
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  • 8
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    White-light flares observed by Yohkoh (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The Yohkoh observatory is producing a first sample of white-light flares observed from space. We present observations of four of them, all X-class events. The Yohkoh Soft X-ray Telescope white-light data typically have a 12-s cadence for images with 2.46 arcsec pixels over a field of view of 2.62 arcmin in one of two broad-band optical filters, and the November 15, 1991 flare produced a brightness increase of about 38 percent over the photospheric brightness in the 30 A passband filter centered at 4308 A. The white-light flare morphology in the best-observed flares displays a double 'footpoint' character, establishing a close relationship with the compact magnetic flux tubes involved with both hard and soft X-ray emissions. We describe the data in the context of the soft and hard X-ray observations simultaneously carried out on board the Yohkoh satellite, emphasizing energetics and timing.
    Keywords: SOLAR PHYSICS
    Type: PASJ: Publications of the Astronomical Society of Japan (ISSN 0004-6264); 44; 5; p. L77-L81.
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  • 9
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    Observation of a solar flare at the limb with the Yohkoh Soft X-ray Telescope (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: A long-enduring soft X-ray flare at the solar limb was well observed by the Soft X-ray Telescope aboard the Yohkoh spacecraft from the preflare stage through the postflare phase. A 'helmet streamer' arch appears several hours prior to the flare, in association with a continuous expansion and restructuring of the active-region magnetic structure. This arch then starts to flare, and increases its height and footpoint separation at v = 10-30 km/s. The arch has a complex temperature structure in the rising phase, whereas the outer arches have systematically higher temperatures in the decay phase. Magnetic reconnection in a neutral sheet at the loop top, created by preflare magnetic restructuring, would explain this type of flare.
    Keywords: SOLAR PHYSICS
    Type: PASJ: Publications of the Astronomical Society of Japan (ISSN 0004-6264); 44; 5; p. L63-L69.
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  • 10
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    The morphology of 20 x 10 exp 6 K plasma in large non-impulsive solar flares (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: We have examined images of 10 flares observed by the Soft X-ray Telescope on-board the Yohkoh spacecraft. These images show that the hottest portion of the soft X-ray flare is located in compact regions that appear to be situated at the tops of loops. These compact regions form at, or shortly after, flare onset, and persist well into the decay phase of the flares. In some cases, the compact regions are only a few thousand kilometers in size and are small compared to the lengths of flaring loops. This is inconsistent with the smoother intensity distribution along the loops expected from models of chromospheric evaporation.
    Keywords: SOLAR PHYSICS
    Type: PASJ: Publications of the Astronomical Society of Japan (ISSN 0004-6264); 44; 5; p. L71-L75.
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