Stellar Occultations Achieve 2[(π*R/λ_F)^2]*phi0 Flash Peak Via Diffraction

Scientists are investigating the intriguing central flashes observed during stellar occultations , events where a foreground object passes in front of a distant star. Bruno Sicardy and Luc Dettwiller, from the Laboratoire Temps Espace and Université Jean Monnet Saint-Etienne respectively, alongside their colleagues, present a detailed analysis of these flashes, considering the complex interplay of diffraction, interference, and the finite size of the star itself. This research significantly advances our understanding of light propagation through atmospheres and shadows, revealing how factors like atmospheric density and stellar diameter dramatically alter the characteristics of these fleeting signals. By applying principles from Huygens’ and Clausius’ theorems, the team demonstrates that diffraction can amplify flash intensity and broaden its extent, with potentially observable consequences for occultation events like those involving Pluto and Triton.

Central flash diffraction during stellar occultations provides valuable

Scientists have demonstrated a detailed analysis of central flashes occurring during stellar occultations, meticulously cataloging diffraction effects with point-like stars and varying atmospheric conditions. The research team achieved a comprehensive understanding of how light behaves when a celestial body passes in front of a distant star, revealing subtle yet significant phenomena related to wave optics. This study unveils the intricate interplay between diffraction, interference, and stellar diameter in shaping the observed central flash, a surge of brightness experienced as the star’s light grazes the edge of the occulting object’s atmosphere. Experiments show that the shape of the central flash deviates from a simple point source, exhibiting a larger height and complex fringe patterns dependent on atmospheric density and scale height.
The study rigorously applies the principles of diffraction, employing the Huygens principle, the Sommerfeld lemma, and the stationary phase method to model the propagation of light waves. Finite stellar diameter effects are incorporated using Clausius’ theorem, allowing for a nuanced description of how a star’s apparent size influences the observed flash. Researchers prove that for point-like stars, the central flash resembles the classical Poisson spot, but with an amplified height, particularly in tenuous atmospheres unable to focus stellar rays. For denser atmospheres capable of focusing light, the flash peaks at a value proportional to the square of the central flash layer radius divided by the Fresnel scale, and the atmospheric flux, establishing a precise quantitative relationship between atmospheric properties and observed brightness.

Furthermore, the work establishes that for isothermal atmospheres, the height of the flash is directly related to the atmosphere’s scale height and the central flash layer radius, providing a means to remotely characterise atmospheric structure. Fringes surrounding the central flash are separated by a distance dependent on the Fresnel scale and the flash layer radius, mirroring the separation between primary and secondary stellar images. When the projected stellar diameter exceeds this fringe separation, the flash is described by complete elliptic integrals, resulting in a full width at half maximum of 1.14times the stellar diameter and a peak value inversely proportional to it. In practical application to Earth-based occultations of Pluto and Triton, the research indicates that diffraction generates flashes with substantial heights, ranging from 10,000 to 100,000 meters, concentrated within a small, meter-sized region in the shadow plane.

Although typically smoothed by the stellar diameter, these flashes still reach significant values of approximately 50 and 200 during Pluto and Triton occultations, respectively. The study conclusively demonstrates that diffraction becomes dominant at millimeter wavelengths or longer, and discusses the impact of deviations from spherical symmetry, atmospheric waves, and stellar limb darkening on the observed phenomena. This breakthrough opens avenues for more accurate atmospheric characterisation of distant celestial bodies through detailed analysis of stellar occultation events.

Diffraction modelling of stellar occultation central flashes

Scientists investigated central flashes occurring during stellar occultations by solar system objects, meticulously cataloging diffraction effects on these flashes using point-like stars and monochromatic waves. The research team employed the principles of the Huygens principle, Sommerfeld lemma, and stationary phase method to model diffraction, incorporating Clausius’ theorem to account for finite stellar diameters. This work pioneered a detailed analysis of central flash characteristics under varying atmospheric conditions, revealing how diffraction significantly alters the observed signal. Experiments focused on calculating the amplification of the flash for tenuous atmospheres unable to focus stellar rays, demonstrating a factor of (R₀/r₀)² compared to the classical Poisson spot, where R₀ represents the object radius and r₀ the shadow radius.

Conversely, for denser atmospheres capable of focusing rays, the study established that the flash peaks at 2[(πR/λ F )²]φ₀, with R being the central flash layer radius, λ F the Fresnel scale, and φ₀ the flux observed without focusing. Researchers further derived a height calculation for isothermal atmospheres, finding it to be 2(RH)(π/λ F )², where H denotes the atmospheric scale height. The study innovatively determined the separation between fringes surrounding the central flash as λ P = λ F ²/R, directly relating this to the separation between primary and secondary stellar images. When the projected stellar diameter, D, exceeds λ P, the flash profile is described using complete elliptic integrals, yielding a full width at half maximum of 1.14D* and a peak value of 8H/D*.

Scientists harnessed these calculations to predict flash heights of ~10⁴-10⁵ meters for Earth-based occultations of Pluto and Triton, observed in the visible spectrum. Despite stellar diameter typically smoothing the flash, the research confirmed peak values reaching ~50 and ~200 during Pluto and Triton occultations, respectivel. The team demonstrated that diffraction becomes dominant at millimeter wavelengths or longer, while also acknowledging the influence of atmospheric waves and stellar limb darkening on the observed phenomena. This detailed methodology enables a more accurate interpretation of occultation data and provides a foundation for future atmospheric studies.

Diffraction amplifies stellar occultation central flashes, revealing atmospheric

Scientists have meticulously cataloged diffraction effects occurring during stellar occultations, revealing crucial details about planetary atmospheres and stellar characteristics. The research details how central flashes, observed when a star passes behind a solar system object, are significantly impacted by diffraction phenomena, particularly for tenuous atmospheres unable to focus stellar rays at the shadow center. Experiments revealed that in these cases, the flash is amplified by a factor of (R₀/r₀)² compared to the classical Poisson spot, where R₀ represents the object radius and r₀ denotes the shadow radius. The team measured the peak intensity of the central flash for denser atmospheres capable of focusing rays, finding it reaches 2[(πR/λ F )²]φ₀, with R being the central flash layer radius, λ F the Fresnel scale, and φ₀ the flux observed at the shadow center without focusing.

For isothermal atmospheres possessing a scale height H, calculations confirm the flash height is 2(RH)(π/λ F )². Data shows that fringes surrounding the central flash are separated by λ P =λ F ²/R, directly correlating to the separation between primary and secondary stellar images. Tests prove that when a projected stellar diameter exceeds λ P, the flash profile is accurately described using complete elliptic integrals, exhibiting a full width at half maximum of 1.14D and a peak value of 8H/D. Specifically, Earth-based occultations of Pluto and Triton, observed in visible light with point-like stars, generate diffraction-induced flashes reaching heights of ~10⁴-10⁵, confined to a remarkably small, meter-sized region within the shadow plane.

Measurements confirm that while stellar diameter typically smooths the flash, peak values still attain approximately ~50 and ~200 during Pluto and Triton occultations, respectively. Researchers discovered diffraction dominates at millimeter wavelengths and beyond, enhancing the visibility of these subtle atmospheric effects. The study meticulously details how departures from spherical symmetry, atmospheric waves, and stellar limb darkening influence the observed flash characteristics. This work establishes a robust framework for interpreting occultation data, providing precise quantitative relationships between atmospheric properties, stellar parameters, and the observed central flash phenomena.

Central Flash Diffraction in Occultation Atmospheres reveals atmospheric

Scientists have meticulously catalogued diffraction effects observed during stellar occultations by solar system objects. This research details how these effects manifest as central flashes, utilising principles of optics including the Huygens principle, Sommerfeld lemma, and stationary phase method to model the phenomena. The study establishes that the shape of the central flash resembles a classical Poisson spot, but with an increased height, and is significantly amplified in tenuous atmospheres, by a factor of (R₀/r₀)² where R₀ and r₀ represent object and shadow radii, respectivel. Furthermore, the work demonstrates that denser atmospheres capable of focusing stellar rays produce a flash peaking at 2[(πR/λF)²]φ₀, with height determined by atmospheric scale height in isothermal conditions.

Fringes surrounding the flash exhibit separation related to the primary and secondary stellar images, and the flash characteristics are altered when the projected stellar diameter exceeds this fringe separation, becoming describable using complete elliptic integrals. Analysis of Earth-based occultations of Pluto and Triton reveals diffraction-induced flashes reaching heights of 10⁴-10⁵, concentrated within a small region, though often smoothed by stellar diameter, yet still attaining values of approximately 50 and 200 during these occultations. The authors acknowledge limitations stemming from departures from spherical symmetry, atmospheric waves, and stellar limb darkening, which could influence the accuracy of their models. Future research could focus on incorporating these complexities to refine predictions of central flash characteristics. This work significantly advances our understanding of light propagation during occultations, offering a refined framework for interpreting observational data and potentially improving atmospheric characterisation of occulted bodies, particularly when utilising longer wavelengths where diffraction effects are dominant.