The finite Fourier transform definition of an edge on the solar disk

Hill, H. A.; Stebbins, R. T.; Oleson, James R.

doi:10.1086/153814

Cited by 78 publications

(23 citation statements)

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“…Deubner (1975) confirmed experimentally the existence of eigenmodes, finding a relationship between the period and horizontal wavelength consistent with the predictions done by (Ulrich 1970). While previous observations showed evidences of spatially-localized oscillations in the solar atmosphere, Hill et al (1975) announced the detection of oscillations in the solar diameter, suggesting the existence of global oscillations and, consequently, the possibility to use these pulsations to probe the solar interior (e.g. Scuflaire et al 1975;Christensen-Dalsgaard & Gough 1976).…”

Section: Acoustic Modessupporting

confidence: 80%

Observational techniques to measure solar and stellar oscillations

García

2015

EAS Publications Series

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Abstract.As said by Sir A. Eddington in 1925: "Our telescopes may probe farther and farther into the depths of space. At first sight it would seem that the deep interior of the sun and stars is less accessible to scientific investigation than any other region of the universe. What appliance can pierce through the outer layers of a star and test the conditions within?" Eddington (1926). Nowadays, asteroseismology has proven its ability to pierce below stellar photospheres and allow us to "see" inside the interior of thousands of stars down to the stellar cores, answering the question asked by Eddington ninety years ago. In this chapter we review the general properties of the spectral analysis which is the base of any asteroseismic investigation. After describing the stellar power spectrum, we will describe in details the characterization of the modal spectrum. This chapter will end by a brief description of the instrumentation in both helio and asteroseismology.

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Section: Acoustic Modessupporting

confidence: 80%

Observational techniques to measure solar and stellar oscillations

García

2015

EAS Publications Series

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“…A special numerical technique (Finite Fourier Transform Definition = FFTD) defines the position of the limb by integration of the recorded signal with a weighting function, chosen to minimize the effects of seeing. For diameters of the seeing disk a ranging from less than one arc sec to about 3 arcsec the position determined in such a way is nearly independent of a (Hill et al, 1975).…”

Section: Measurements At the Limbmentioning

confidence: 88%

Global Oscillations of the Sun

Deubner

1980

Highlights astron.

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The topic of this Joint Discussion has received enormously increased interest in the last couple of years, owing to its potential for the investigation of the structure of the interior of the sun, including related topics like the structure of the convection zone, solar metal abundance, and the still unsettled neutrino problem.The first stimuli came from the startling observations of Hill et al. (1976) in Arizona, Severny et al. (1976) on Crimea, and Brookes et al. (1976) in Birmingham, accompanied by a large volume of theoretical papers, the details of analysis of which soon went beyond the actual status of the observational facts.We then witnessed, however, the success of considerable refinements of the techniques of observation, together with an obvious widespread temptation to push the interpretation of many of the new results to the limits of optimism. Yet, despite of the still increasing body of data suggesting the reality of the solar origin of the observed phenomena, much scepticism was prompted by the complicated statistics and the intricate numerical procedures involved in the data analysis, as well as by the great uncertainty about the significance and the amounts of “noise” contributed to the signal by electronics, changes of the conditions of the ray path within the telescope, terrestrial atmospheric inhomogeneities and solar quasi-stationary motions.

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“…first with the zero-crossing of the second derivative of the intensity profile, and second with the FFTD technique used by Hill, Stebbins, and Oleson (1975). Then five parameters of the He I 1083 nm line were measured: the spectrally integrated intensity, the line-center peak intensity, the line-center wavelength, the spectral full-width at half-maximum (FWHM), and finally the ratio of emission in the main component (1.083.0 nm) to the blue component (1082.9 nm).…”

Section: Discussionmentioning

confidence: 99%

“…First, the second derivative of the continuum intensity was computed, and the zero-crossing point of the derivative was found using linear interpolation. The second techique employed the FFTD method (Hill, Stebbins, and Oleson, 1975); here the limb is measured with the zero-crossing point of the weighted integral of the continuum intensity F(I; r, a), defined by F(I;r.a), = a-l/2rl/2 I(r + asin(Trs)) cos(27r.s) ds, where r is the radial distance from disk center, I is the measured continuum intensity, a is the averaging size, and s is a dummy variable of integration. The averaging size a was optimally set to a = 4or, where cr is the Gaussian width of the atmospheric and telescopic transfer function, computed for each slit position from the e-folding width of the continuum limb profile.…”

Section: Line Intensitymentioning

confidence: 99%

Limb observations of He I 1083 nm

Penn¹,

Jones

1996

Sol Phys

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Imaging spectroscopic data of the He i 1083 nm limb emission were taken on several dates in October and November 1995 with the NASA/NSO spectromagnetograph at the NSO/Kitt Peak vacuum telescope and on 9 December, 1993 with the Michigan infrared camera at the NSO/Sacramento Peak vacuum tower telescope. Emission line profiles were observed in quiet-Sun and coronal hole locations on the northern and southern solar poles and on the east solar limb. The height of the He I 1083 nm shell above the continuum limb at 1083 nm was measured to be 2.11 -4-0.12 Mm with the Kitt Peak data, and 1.74 -4-0.05 Mm with the Sacramento Peak data. The Kitt Peak data show (1) within the measurement error there is no significant difference in the height or thickness of the emission shell in coronal holes compared with the quiet Sun, (2) the 1083 nm emission intensity drops by 50% in coronal holes, (3) the line width decreases by about 2 km s -~ in coronal holes (suggesting less inclined spicules), (4) the line width of the He l 1083 nm line jumps significantly as the line of sight crosses the solar limb (consistent with a higher temperature upper shell), (5) a quiescent prominence shows a smaller spectral line width (consistent with a cooler temperature or less velocity broadening), and (6) the entire emission shell and the prominence show a He I spectral component ratio of about 8 (suggesting optically thin emission).

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The finite Fourier transform definition of an edge on the solar disk

Cited by 78 publications

References 0 publications

Observational techniques to measure solar and stellar oscillations

Observational techniques to measure solar and stellar oscillations

Global Oscillations of the Sun

Limb observations of He I 1083 nm

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