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J. W. Cook - One of the best experts on this subject based on the ideXlab platform.
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Magnetic Fields, Oscillations, and Heating in the Quiet Sun Temperature Minimum Region from Ultraviolet Observations at 1600 Å
Symposium - International Astronomical Union, 1994Co-Authors: J. W. CookAbstract:The High Resolution Telescope and Spectrograph (HRTS) instrument has obtained broadband spectroheliograph images at 1600 Å of the Solar Temperature minimum region. I discuss HRTS observations of quiet areas and their relation with magnetic fields, five minute oscillations, and heating. The brightness Temperature of Solar fine structure elements composing the supergranular network is found to be linearly proportional to the local absolute value of magnetic field strength. There is evidence for a 250-s period oscillation occurring in 10-arcsec scale patches, which however is energetically unimportant to the local heating budget. A general nonmagnetic background heating and five minute oscillations occur globally, while the network bright points occur in magnetic regions, heated perhaps from partial dissipation of Alfvén waves (whose energy flux is linearly proportional to B) in individual elemental 1500-G (at the photosphere) flux tubes which expand to form the Temperature minimum fine structure bright points.
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Magnetic Fields, Oscillations, and Heating in the Quiet Sun Temperature Minimum Region From Ultraviolet Observations At 1600 Å
Infrared Solar Physics, 1994Co-Authors: J. W. CookAbstract:The High Resolution Telescope and Spectrograph (HRTS) instrument has obtained broadband spectroheliograph images at 1600 A of the Solar Temperature minimum region. I discuss HRTS observations of quiet areas and their relation with magnetic fields, five minute oscillations, and heating. The brightness Temperature of Solar fine structure elements composing the super-granular network is found to be linearly proportional to the local absolute value of magnetic field strength. There is evidence for a 250-s period oscillation occurring in 10-arcsec scale patches, which however is energetically unimportant to the local heating budget. A general nonmagnetic background heating and five minute oscillations occur globally, while the network bright points occur in magnetic regions, heated perhaps from partial dissipation of Alfven waves (whose energy flux is linearly proportional to B) in individual elemental 1500-G (at the photosphere) flux tubes which expand to form the Temperature minimum fine structure bright points.
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Evidence for a 250 second brightness oscillation at 1600 A in the Solar Temperature minimum region
The Astrophysical Journal, 1991Co-Authors: J. W. Cook, J. A. EwingAbstract:A 330 s sequence of Solar images at 1600 A, where the Solar flux arises predominantly from the Temperature minimum continuum, obtained from a sounding rocket flight, has been studied. The statistical distributions of the periods and amplitudes which result from fitting a sine wave to each individual 5 arcsec square box within a 350 x 350 arcsec quiet-sun field were obtained. Evidence is found for 250 s oscillations in the quiet-sun brightness Temperature in about 10 arcsec coherent patches, with an average amplitude of 50 K. The amplitude corresponds to an energy flux of 180,000 ergs/sq cm/s for undamped, adiabatic, propagating sound waves, which is small compared to the heating requirement in the Temperature minimum region. 16 refs.
Shizhao Shen - One of the best experts on this subject based on the ideXlab platform.
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Evaluation of Solar Temperature field under different wind speeds for Shanghai 65 m radio telescope
International Journal of Steel Structures, 2016Co-Authors: Hongliang Qian, Feng Fan, Deshen Chen, Ye Liu, Shizhao ShenAbstract:The Shanghai 65 m radio telescope is currently the largest full range rotatable radio telescope in Asia. Gravity, wind and Temperature are the three main factors which may have a bad effect on the reflector’s surface precision. To study the effect of the thermal deformation caused by daily non-uniform Temperature fields on the surface precision of the main reflector, both the Temperature field and its effect were studied in detail for two typical days (January 15th and July 15th). The method to simulate Temperature fields was studied initially, considering heat conduction, Solar radiation, shadowing, air convection, sky radiation and ground radiation. Then, an integral parametric thermal finite element model (FEM) of the telescope was established using the ANSYS thermal analysis module. Finally, the effect of non-uniform Temperature fields on the surface precision of the main reflector was estimated in terms of the Root Mean Square (RMS) deformation based on Temperature transient analysis. The proposed methods and conclusions drawn can provide valuable information for thermal design, thermal monitoring and thermal control of the Shanghai 65 m radio telescope and other similar giant antenna structures.
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Solar cooker effect test and Temperature field simulation of radio telescope subreflector
Applied Thermal Engineering, 2016Co-Authors: Deshen Chen, Huajie Wang, Hongliang Qian, Gang Zhang, Shizhao ShenAbstract:Abstract The Solar cooker effect can cause a local high Temperature of the subreflector and can directly affect the working performance of the radio telescope. To study the daily Temperature field and Solar cooker effect of a subreflector, experimental studies are carried out with a 3-m-diameter radio telescope model for the first time. Initially, the Solar Temperature distribution rules, especially the Solar cooker effect, are summarized according to the field test results under the most unfavorable conditions. Then, a numerical simulation for the Solar Temperature field of the subreflector is studied by light beam segmentation and tracking methods. Finally, the validity of the simulation methods is evaluated using the test results. The experimental studies prove that the Solar cooker effect really exists and should not be overlooked. In addition, simulation methods for the subreflector Temperature field proposed in this paper are effective. The research methods and conclusions can provide valuable references for thermal design, monitoring and control of similar high-precision radio telescopes.
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Effect of Non-Uniform Solar Temperature Field on Cable-Net Structure of Reflector of Large Radio Telescope-FAST
Advances in Structural Engineering, 2009Co-Authors: Feng Fan, Xiao-fei Jin, Shizhao ShenAbstract:The effect of a non-uniform Solar Temperature field on the cable-net structure of the reflector of a five-hundred-meter aperture spherical radio telescope-FAST was analyzed using the thermal analysis module of ANSYS. The integral parametric finite element model of the reflector structure with its measured landform was built, and the boundary conditions of periodic air Temperature, Solar radiation, long-wave radiation and shadows of surrounding environment, etc, were computed at intervals of half an hour under a cloudless sky on a summer day, as one of the worst-case climate conditions. The transient structural Temperatures were then analyzed under sunshine which lasted for several days with a rational initial structural Temperature distribution until the whole set of structural Temperatures converged to the results obtained the day before. The corresponding structural analysis was then carried out. The results indicate that the highest local Temperature difference goes up to 11° and the maximum r.m.s. err...
David F. Gray - One of the best experts on this subject based on the ideXlab platform.
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Non-Radial Oscillation in the Solar-Temperature Star 51 Pegasi
The Astrophysical Journal, 1997Co-Authors: David F. Gray, Artie P. HatzesAbstract:We present results of high-resolution spectroscopic observations of the Solar-Temperature star 51 Peg taken between 1989 and 1996. Variations in the shape of the Fe I λ6252.53 Fe I spectral line are investigated in detail to establish their reality, nature, and likely cause. Because our spectroscopic data were gathered for purposes other than the present one, they are thinly distributed over the 7 years. This makes it difficult for us to prove beyond doubt that the variations in the shapes of the profiles are one and the same as the 4.23 day period of radial velocity variations found by Mayor & Queloz and Marcy et al. Nevertheless, we show that the probability of our data matching the periodicity of the radial velocity data the way it does by pure chance is only one in several hundred. Since the probability strongly favors the reality of the 4.23 day profile shape variations, we proceed to model them with nonradial oscillations having low order and low degree. The shifts and distortions of spectral lines induced by oscillations having l = -m = 4 fully account for both the radial velocity observations and the changes in line profiles delineated by our high-resolution spectroscopy. The planet hypothesis, proposed in the above mentioned papers, cannot account for implicit variations of the spectral line profiles. Assuming these variations are real, the planet hypothesis is no longer viable, and the need to explain the unseen and puzzling planet in an unusual orbit no longer exists. Instead, the door may have been opened to the important new area of research: low-order nonradial pulsation in Solar-Temperature stars. In the Appendix we refute various suggestions by which the originally proposed planet might induce the line-profile variations.
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Monitoring the Solar Temperature: Spectroscopic Temperature Variations of the Sun
The Astrophysical Journal, 1997Co-Authors: David F. Gray, William C. LivingstonAbstract:The C I λ5380 line in the Solar flux spectrum was measured over the 1978-1992 interval. Analysis of the data shows seasonal and instrumental effects, but after allowance for these, the ratios of spectral line depths, C I λ5380 to Fe I λ5379 and to Ti II λ5381, are shown to be robust indicators of effective Temperature. These data show the Solar Temperature to have varied systematically during the activity cycle and nearly in phase with other indicators of the cycle. The amplitude of the variation is 1.5 K ± 0.2 K, similar to but slightly less than the range implied by the variations of the sunspot-corrected irradiance. There is also evidence for a secular trend amounting to ≈ +0.014 K per year.
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Monitoring the Solar Temperature: Empirical Calibration of the Temperature Sensitivity of C I λ5380
The Astrophysical Journal, 1997Co-Authors: David F. Gray, William LivingstonAbstract:We observed a set of six dwarf stars spanning a range in Temperatures around the Solar value, and from them we have determined empirically the Temperature sensitivity of C I λ5380.32, a line that has been monitored in the Solar flux spectrum for nearly two decades at Kitt Peak. When the C I line is compared to the adjacent Fe I λ5379.58 line, it should be possible to detect apparent Temperature differences of a fraction of 1 K.
J. A. Ewing - One of the best experts on this subject based on the ideXlab platform.
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Evidence for a 250 second brightness oscillation at 1600 A in the Solar Temperature minimum region
The Astrophysical Journal, 1991Co-Authors: J. W. Cook, J. A. EwingAbstract:A 330 s sequence of Solar images at 1600 A, where the Solar flux arises predominantly from the Temperature minimum continuum, obtained from a sounding rocket flight, has been studied. The statistical distributions of the periods and amplitudes which result from fitting a sine wave to each individual 5 arcsec square box within a 350 x 350 arcsec quiet-sun field were obtained. Evidence is found for 250 s oscillations in the quiet-sun brightness Temperature in about 10 arcsec coherent patches, with an average amplitude of 50 K. The amplitude corresponds to an energy flux of 180,000 ergs/sq cm/s for undamped, adiabatic, propagating sound waves, which is small compared to the heating requirement in the Temperature minimum region. 16 refs.
William C. Livingston - One of the best experts on this subject based on the ideXlab platform.
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Monitoring the Solar Temperature: Spectroscopic Temperature Variations of the Sun
The Astrophysical Journal, 1997Co-Authors: David F. Gray, William C. LivingstonAbstract:The C I λ5380 line in the Solar flux spectrum was measured over the 1978-1992 interval. Analysis of the data shows seasonal and instrumental effects, but after allowance for these, the ratios of spectral line depths, C I λ5380 to Fe I λ5379 and to Ti II λ5381, are shown to be robust indicators of effective Temperature. These data show the Solar Temperature to have varied systematically during the activity cycle and nearly in phase with other indicators of the cycle. The amplitude of the variation is 1.5 K ± 0.2 K, similar to but slightly less than the range implied by the variations of the sunspot-corrected irradiance. There is also evidence for a secular trend amounting to ≈ +0.014 K per year.