Some Experiments on the Scintillation of Stars and Planets

Ellison, M. A.; Seddon, H. R.

doi:10.1093/mnras/112.1.73

Cited by 39 publications

(15 citation statements)

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“…That the intensity variance decreases with increasing telescope collecting area had been realized already in early measurements (see, e.g., Mikesell et al 1951;Ellison & Seddon 1952;Siedentopf & Elsässer 1954;Bufton & Genatt 1971;Iyer & Bufton 1977;Stecklum 1985).…”

Section: Observed Aperture-size Dependencesmentioning

confidence: 68%

Atmospheric Intensity Scintillation of Stars. III. Effects for Different Telescope Apertures

Dravins¹,

Lindegren²,

Mezey³

et al. 1998

PUBL ASTRON SOC PAC

125

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ABSTRACT. Stellar intensity scintillation in the optical was extensively studied at the astronomical observatory on La Palma (Canary Islands). Atmospheric turbulence causes "flying shadows" on the ground, and intensity fluctuations occur both because this pattern is carried by winds and is intrinsically changing. Temporal statistics and time changes were treated in Paper I, and the dependence on optical wavelength in Paper II. This paper discusses the structure of these flying shadows and analyzes the scintillation signals recorded in telescopes of different size and with different (secondary-mirror) obscurations. Using scintillation theory, a sequence of power spectra measured for smaller apertures is extrapolated up to very large (8 m) telescopes. Apodized apertures (with a gradual transmission falloff near the edges) are experimentally tested and modeled for suppressing the most rapid scintillation components. Double apertures determine the speed and direction of the flying shadows. Challenging photometry tasks (e.g., stellar microvariability) require methods for decreasing the scintillation "noise." The true source intensity I(l) may be segregated from the scintillation component in DI(t,l,x,y) postdetection computation, using physical modeling of the temporal, chromatic, and spatial properties of scintillation, rather than treating it as mere "noise." Such a scheme ideally requires multicolor high-speed (Շ10 ms) photometry on the flying shadows over the spatially resolved (Շ10 cm) telescope entrance pupil. Adaptive correction in real time of the two-dimensional intensity excursions across the telescope pupil also appears feasible, but would probably not offer photometric precision. However, such "second-order" adaptive optics, correcting not only the wavefront phase but also scintillation effects, is required for other critical tasks such as the direct imaging of extrasolar planets with large ground-based telescopes.

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Section: Observed Aperture-size Dependencesmentioning

confidence: 68%

Atmospheric Intensity Scintillation of Stars. III. Effects for Different Telescope Apertures

Dravins¹,

Lindegren²,

Mezey³

et al. 1998

PUBL ASTRON SOC PAC

125

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“…Like earlier observers, Zwicky noted that the color-intensity patterns are most regular at the zenith and become more irregular closer to the horizon. Related experiments were also made by Ellison and Seddon (1952).…”

Section: Early Studiesmentioning

confidence: 99%

Atmospheric Intensity Scintillation of Stars. II. Dependence on Optical Wavelength

Dravins¹,

Lindegren²,

Mezey³

et al. 1997

PASP

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ABSTRACT. Atmospheric intensity scintillation of stars on milli-and microsecond time scales was extensively measured at the astronomical observatory on La Palma (Canary Islands). Scintillation statistics and temporal changes were discussed in Paper I, while this paper shows how scintillation depends on optical wavelength. Such effects originate from the changing refractive index of air, and from wavelength-dependent diffraction in atmospheric inhomogeneities. The intensity variance aj increases for shorter wavelengths, at small zenith distances approximately consistent with a theoretical X -7/6 slope, but with a tendency for a somewhat weaker dependence. Scintillation in the blue is more rapid than in the red. The increase with wavelength of autocorrelation time scales (roughly proportional to >/\) is most pronounced in very small apertures, but was measured up to 0 20 cm. Scintillation at different wavelengths is not simultaneous: atmospheric chromatic dispersion stretches the atmospherically induced "flying shadows" into "flying spectra" on the ground. As the "shadows" fly past the telescope aperture, a time delay appears between fluctuations at different wavelengths whenever the turbulence-carrying winds have components parallel to the direction of dispersion. These effects increase with zenith distance (reaching -100 ms cross-correlation delay between blue and red at Z = 60° ), and also with increased wavelength difference. This time delay between scintillation in different colors is a property of the atmospheric flying shadows, and thus a property that remains unchanged even in very large telescopes. However, the wavelength dependence of scintillation amplitude and time scale is "fully" developed only in small telescope apertures ( ^ 5 cm), the scales where the "flying shadows" on the Earth's surface become resolved. Although these dependences rapidly vanish after averaging in larger apertures, an understanding of chromatic effects may still be needed for the most accurate photometric measurements. These will probably require a sampling of the (stellar) signal with full spatial, temporal, and chromatic resolution to segregate the scintillation signatures from those of astrophysical variability.

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“…In the atmosphere, condition (2.3) is met for light waves, since the inner dimensions of the turbulent fluctuations range from a few millimeters up to the order of many tens of centimeters [Goedeke, 1936;Chandrasekhar, 1952;Ellison and Seddon, 1952;Villars and Weisskopf, 1954;Megaw, 1954;Furth, 1956;Tatarsky, 1961). Condition (2.4) limits the value of the path in the turbulent medium to lengths of the order of 100 m, for r0 of the order of centimeters, and becomes less stringent for larger values of r0•…”

Section: (22)mentioning

confidence: 99%

Deterioration of the Coherence Properties of a Laser Beam by Atmospheric Turbulence and Molecular Scattering

Consortini¹,

Ronchi²,

Scheggi³

et al. 1966

Radio Science

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Turbulence and scattering can be considered as chiefly responsible for the deterioration of coherence properties of laser radiation when propagating through the atmosphere.The effect of atmospheric turbulence as well as the effect of molecular scattering (in a quiet atmosphere) on the space and time coherence, respectively, have been theoretically investigated within the limits of ray theory.As a result we found that there is a limiting diameter for the beam cross section beyond which the advantages of the space coherence are largely offset by the intervention of turbulence. On the other hand, the thermal movements of molecules may affect the time coherence (that is, the monochromaticity) of a highly monochromatic beam.

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Some Experiments on the Scintillation of Stars and Planets

Cited by 39 publications

References 0 publications

Atmospheric Intensity Scintillation of Stars. III. Effects for Different Telescope Apertures

Atmospheric Intensity Scintillation of Stars. III. Effects for Different Telescope Apertures

Atmospheric Intensity Scintillation of Stars. II. Dependence on Optical Wavelength

Deterioration of the Coherence Properties of a Laser Beam by Atmospheric Turbulence and Molecular Scattering

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