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Letteratura scientifica selezionata sul tema "Stars Scintillation"

Autore: Grafiati

Pubblicato: 4 giugno 2021

Ultima modifica: 29 gennaio 2023

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Articoli di riviste sul tema "Stars Scintillation"

Sofieva, V. F., V. Kan, F. Dalaudier, E. Kyrölä, J. Tamminen, J. L. Bertaux, A. Hauchecorne, D. Fussen e F. Vanhellemont. "Influence of scintillation on GOMOS ozone retrievals". Atmospheric Chemistry and Physics Discussions 9, n. 3 (29 maggio 2009): 12615–43. http://dx.doi.org/10.5194/acpd-9-12615-2009.

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Abstract. The stellar light passed through the Earth atmosphere is affected by refractive effects, which should be taken into account in retrievals from stellar occultation measurements. Scintillation caused by air density irregularities is a nuisance for retrievals of atmospheric composition. In this paper, we consider the influence of scintillation on stellar occultation measurements and on quality of ozone retrievals from these measurements, based on experience of the GOMOS (Global Ozone Monitoring by Occultation of Stars) instrument on board the Envisat satellite. In the GOMOS retrievals, the scintillation effect is corrected using scintillation measurements by the fast photometer. We present quantitative estimates of the current scintillation correction quality and of the impact of scintillation on ozone retrievals by GOMOS. The analysis has shown that the present scintillation correction efficiently removes the distortion of transmission spectra caused by anisotropic scintillations. The impact of errors of dilution and anisotropic scintillation correction on quality of ozone retrievals is negligible. However, the current scintillation correction is not able to remove the wavelength-dependent distortion of transmission spectra caused by isotropic scintillations, which can be present in off-orbital-plane occultations. This distortion may result in error of ozone retrievals of 0.5–1.5% at altitudes 20–40 km. This contribution to the error budget is significant for bright stars. The advanced inversion methods that can minimize the influence of scintillation correction error are also discussed.

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Sofieva, V. F., V. Kan, F. Dalaudier, E. Kyrölä, J. Tamminen, J. L. Bertaux, A. Hauchecorne, D. Fussen e F. Vanhellemont. "Influence of scintillation on quality of ozone monitoring by GOMOS". Atmospheric Chemistry and Physics 9, n. 23 (7 dicembre 2009): 9197–207. http://dx.doi.org/10.5194/acp-9-9197-2009.

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Abstract. Stellar light passing through the Earth atmosphere is affected by refractive effects, which should be taken into account in retrievals from stellar occultation measurements. Scintillation caused by air density irregularities is a nuisance for retrievals of atmospheric composition. In this paper, we consider the influence of scintillation on stellar occultation measurements and on the quality of ozone retrievals from these measurements, based on experience of the GOMOS (Global Ozone Monitoring by Occultation of Stars) instrument on board the Envisat satellite. In GOMOS retrievals, the scintillation effect is corrected using scintillation measurements by the fast photometer. We present quantitative estimates of the current scintillation correction quality and of the impact of scintillation on ozone retrievals by GOMOS. The analysis has shown that the present scintillation correction efficiently removes the distortion of transmission spectra caused by scintillations, which are generated by anisotropic irregularities of air density. The impact of errors of dilution and anisotropic scintillation correction on the quality of ozone retrievals is negligible. However, the current scintillation correction is not able to remove the wavelength-dependent distortion of transmission spectra caused by isotropic scintillations, which can be present in off-orbital-plane occultations. This distortion may result in ozone retrieval errors of 0.5–1.5% at altitudes 20–40 km. This contribution constitutes a significant percentage of the total error for bright stars. The advanced inversion methods that can minimize the influence of scintillation correction error are also discussed.

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Melrose, D. B. "Twinkle, Twinkle Little Pulsar/Quasar". Australian Journal of Physics 52, n. 1 (1999): 1. http://dx.doi.org/10.1071/p98076.

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The twinkling of stars is a familiar example of scintillations, due to turbulence in the Earth’s atmosphere causing fluctuations in the refractive index of the air along the line of sight. Scintillations lead to time variations in the apparent position of the source, and hence to an angular broadening on integration over an observation time. Scintillations also lead to fluctuations in the intensity of the source. Pointlike astronomical radio sources such as pulsars and (the compact cores of some) quasars scintillate due to fluctuations in the electron density along the line of sight through the interstellar medium. For quasars, low-frequency (100s of MHz) variability over periods of years is a scintillation effect, as are probably more rapid (as short as an hour) intensity variations at higher radio frequencies. Unlike the twinkling of stars, which is due to weak scintillations, the scintillations of radio sources are usually strong. Important qualitative effects associated with strong scattering are multipath propagation and a clear separation into diffractive and refractive scintillations. Quasars exhibit only refractive scintillations. Pulsars are extremely small and bright, and they vary temporally on a very short time scale, making them almost ideal sources on which to test our ideas on scintillations. Pulsars exhibit a variety of scintillation phenomena, due to both refractive and diffractive effects, the latter seen most clearly in dynamic spectra. These data are used to model the distribution of electrons through the Galaxy, to determine the distribution of pulsar velocities, and potentially to resolve the source region in a pulsar magnetosphere. These scintillation phenomena and their interpretation in terms of the theory of strong scintillations are reviewed briefly. The generalisation of the theory to include the birefringence of the plasma (Faraday effect), and its possible implications on the interpretation of circular polarisation, are then outlined. An attempt to generalise the theory to describe scattering by a distribution of discrete scattering objects is also discussed briefly.

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O’Brien, Sean M., Daniel Bayliss, James Osborn, Edward M. Bryant, James McCormac, Peter J. Wheatley, Jack S. Acton et al. "Scintillation-limited photometry with the 20-cm NGTS telescopes at Paranal Observatory". Monthly Notices of the Royal Astronomical Society 509, n. 4 (26 novembre 2021): 6111–18. http://dx.doi.org/10.1093/mnras/stab3399.

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ABSTRACT Ground-based photometry of bright stars is expected to be limited by atmospheric scintillation, although in practice observations are often limited by other sources of systematic noise. We analyse 122 nights of bright star (Gmag ≲ 11.5) photometry using the 20-cm telescopes of the Next-Generation Transit Survey (NGTS) at the Paranal Observatory in Chile. We compare the noise properties to theoretical noise models and we demonstrate that NGTS photometry of bright stars is indeed limited by atmospheric scintillation. We determine a median scintillation coefficient at the Paranal Observatory of $C_{\scriptscriptstyle \text{Y}}= 1.54$, which is in good agreement with previous results derived from turbulence profiling measurements at the observatory. We find that separate NGTS telescopes make consistent measurements of scintillation when simultaneously monitoring the same field. Using contemporaneous meteorological data, we find that higher wind speeds at the tropopause correlate with a decrease in long-exposure (t = 10 s) scintillation. Hence, the winter months between June and August provide the best conditions for high-precision photometry of bright stars at the Paranal Observatory. This work demonstrates that NGTS photometric data, collected for searching for exoplanets, contains within it a record of the scintillation conditions at Paranal.

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Kan, V., V. F. Sofieva e F. Dalaudier. "Variable anisotropy of small-scale stratospheric irregularities retrieved from stellar scintillation measurements by GOMOS/Envisat". Atmospheric Measurement Techniques 7, n. 6 (25 giugno 2014): 1861–72. http://dx.doi.org/10.5194/amt-7-1861-2014.

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Abstract. In this paper, we consider possibilities for studying the anisotropy of small-scale air density irregularities using satellite observations of bi-chromatic stellar scintillations during tangential occultations. Estimation of the anisotropy coefficient (the ratio of the characteristic horizontal to vertical scales) and other atmospheric parameters is based on the comparison of simulated/theoretical and experimental auto-spectra and coherency spectra of scintillation. Our analyses exploit a 3-D model of the spectrum of atmospheric inhomogeneities, which consists of anisotropic and isotropic components. For the anisotropic component, a spectral model with variable anisotropy is used. Using stellar scintillation measurements by GOMOS (Global Ozone Monitoring by Occultation of Stars) fast photometers, estimates of the anisotropy coefficient are obtained for atmospheric irregularities with vertical scales of 8–55 m at altitudes of 43–30 km. It is shown that the anisotropy increases from about 10 to 50 with increasing vertical scales.

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Kan, V., V. F. Sofieva e F. Dalaudier. "Variable anisotropy of small-scale stratospheric irregularities retrieved from stellar scintillation measurements by GOMOS/Envisat". Atmospheric Measurement Techniques Discussions 7, n. 2 (10 febbraio 2014): 1275–304. http://dx.doi.org/10.5194/amtd-7-1275-2014.

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Hamacher, Duane W., John Barsa, Segar Passi e Alo Tapim. "Indigenous use of stellar scintillation to predict weather and seasonal change". Proceedings of the Royal Society of Victoria 131, n. 1 (2019): 24. http://dx.doi.org/10.1071/rs19003.

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Indigenous peoples across the world observe the motions and positions of stars to develop seasonal calendars. Changing properties of stars, such as their brightness and colour, are also used for predicting weather. Combining archival studies with ethnographic fieldwork in Australia’s Torres Strait, we explore the various ways Indigenous peoples utilise stellar scintillation (twinkling) as an indicator for predicting weather and seasonal change, and examine the Indigenous and Western scientific underpinnings of this knowledge. By observing subtle changes in the ways the stars twinkle, Meriam people gauge changing trade winds, approaching wet weather and temperature changes. We then examine how the Northern Dene of Arctic North America utilise stellar scintillation to forecast weather.

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Dravins, D., L. Lindegren e E. Mezey. "Atmospheric Intensity Scintillation of Stars on Milli- and Microsecond Time Scales". International Astronomical Union Colloquium 136 (1993): 113–19. http://dx.doi.org/10.1017/s0252921100007454.

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AbstractStellar intensity scintillation on short and very short time scales (≃ 100 ms - 100 ns) was studied using an optical telescope on La Palma (Canary Islands). Photon counting detectors and real-time signal processing equipment were used to study atmospheric scintillation as function of telescope aperture size, degree of apodization, for single and double apertures, in different optical colors, at different zenith distances, times of night, and seasons of year. The statistics of temporal intensity variations can be adequately described by log-normal distributions, varying with time. The scintillation timescale (≃10 ms) decreases for smaller telescope apertures until ≃5 cm, where the atmospheric ‘shadow bands’ apparently are resolved. Some astrophysical sources may undergo very rapid intrinsic fluctuations. To detect such phenomena through the turbulent atmosphere requires optimized observing strategies.

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Kan, V., V. F. Sofieva e F. Dalaudier. "Anisotropy of small-scale stratospheric irregularities retrieved from scintillations of a double star α-Cru observed by GOMOS/ENVISAT". Atmospheric Measurement Techniques Discussions 5, n. 4 (13 luglio 2012): 4881–904. http://dx.doi.org/10.5194/amtd-5-4881-2012.

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Abstract. In this paper, we discuss estimating anisotropy of air density irregularities (ratio of characteristic horizontal and vertical scales) from satellite observations of bi-chromatic scintillations of a double star whose components are not resolved by the detector. The analysis is based on fitting experimental auto- and cross-spectra of scintillations by those computed using the 3-D spectral model of atmospheric irregularities consisting of anisotropic and isotropic components. Application of the developed method to the scintillation measurements of the double star α-Cru by GOMOS (Global Ozone Monitoring by Occultation of Stars) fast photometers results in estimates of anisotropy coefficient of ~15–20 at altitudes 30–38 km, as well as other parameters of atmospheric irregularities. The obtained estimates of the anisotropy coefficient correspond to small-scale irregularities, close to the buoyancy scale.

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Kan, V., V. F. Sofieva e F. Dalaudier. "Anisotropy of small-scale stratospheric irregularities retrieved from scintillations of a double star α-Cru observed by GOMOS/ENVISAT". Atmospheric Measurement Techniques 5, n. 11 (14 novembre 2012): 2713–22. http://dx.doi.org/10.5194/amt-5-2713-2012.

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Più fonti

Tesi sul tema "Stars Scintillation"

Campbell, Laurence. "Stellar scintillation and its use in atmospheric measurements /". Title page, contents and summary only, 1991. http://web4.library.adelaide.edu.au/theses/09PH/09phc1885.pdf.

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Bignall, Hayley Emma. "Radio variability and interstellar scintillation of blazars". [Adelaide : H.E. Bignall, 2003. http://web4.library.adelaide.edu.au/theses/09PH/09phb5931.pdf.

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Bibliography: leaves 191-202. 1. Introduction -- 2. Instrumentation and calibration -- 3. A radio monitoring program for southern blazars -- 4. Analysis of long-term blazar radio variability -- 5. Probing microarcsecond-scale structure using interstellar scintillation -- 6. The rapid scintillator, PKS 1257-326 -- 7. Conclusions and scope for further work.

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Pooser, Eric J. "The GlueX Start Counter & Beam Asymmetry $\Sigma$ in Single $\pi^{0}$ Photoproduction". FIU Digital Commons, 2016. http://digitalcommons.fiu.edu/etd/2450.

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The GlueX experiment aims to study meson photoproduction while utilizing the coherent bremsstrahlung technique to produce a 9 GeV linearly polarized photon beam incident on a liquid $\mathrm{H_{2}}$ target. A Start Counter detector was fabricated to properly identify the accelerator electron beam buckets and to provide accurate timing information. The Start Counter detector was designed to operate at photon intensities of up to $\mathrm{10^{8}\gamma/s}$ in the coherent peak and provides a timing resolution $\mathrm{\sim 300\ ps}$ so as to provide successful identification of the electron beam buckets to within 99\% accuracy. Furthermore, the Start Counter detector provides excellent solid angle coverage, $\sim 90 \%\ \mathrm{of}\ 4 \pi\ \mathrm{hermeticity}$, and a high degree of segmentation for background rejection. It consists of a cylindrical array of 30 scintillators with pointed ends that bend towards the beam at the downstream end. Magnetic field insensitive silicon photomultiplier detectors were selected as the readout system. An initial measurement of the beam asymmetry $\Sigma$ in the exclusive reaction $\vec{\gamma}p \rightarrow \pi^{0}p$, where $\pi^{0} \rightarrow \gamma \gamma$ has been carried out utilizing the GlueX spectrometer during the Spring 2015 commissioning run. The tagged photon energies ranged from $2.5 \leq E_{\gamma} \leq 3.0\ \mathrm{GeV}$ in the coherent peak. These measurements were then compared to the world data set and show remarkable agreement with only two hours of physics production running.

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Taylor, Simon John. "Scintillation detector development for the solenoidal tracker at RHIC (STAR) and the CEBAF large acceptance spectrometer (CLAS)". Thesis, 1996. http://hdl.handle.net/1911/14102.

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After a brief introduction describing some of the physics and mechanics of scintillation detection, results of the development for the Central Trigger Barrel (CTB) for STAR and the Start Counter for CLAS are discussed. For the CTB development, 1 cm x 20 cm x 100 cm scintillators were studied with light guides of various geometries and materials attached to one end in order to optimize the uniformity and overall gain. The best results were obtained using a 61$\sp\circ$ OP-1 light guide attached to a BC 408 scintillator. An alternate approach using a wavelength shifter produces much lower pulse heights than the other method. The CEBAF scintillators are intended to enclose the target area in order to identify the beam bucket for a particular event with timing resolution of 350 ps or less. Single paddle and coupled-paddle approaches are discussed. The coupled-paddle approach meets the design goals.

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Capitoli di libri sul tema "Stars Scintillation"

Cordes, J. M. "Interstellar Scintillations and Neutron Star Kinematics". In The Origin and Evolution of Neutron Stars, 35–46. Dordrecht: Springer Netherlands, 1987. http://dx.doi.org/10.1007/978-94-009-3913-4_4.

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Stanimirović, S., J. M. Weisberg, A. Hedden, K. Devine, T. Green e S. B. Anderson. "The Tiny-Scale Atomic Structure: Gas Cloudlets or Scintillation Phenomenon ?" In Magnetic Fields and Star Formation, 103–9. Dordrecht: Springer Netherlands, 2004. http://dx.doi.org/10.1007/978-94-017-0491-5_10.

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Kolanoski, Hermann, e Norbert Wermes. "Photodetectors". In Particle Detectors, 405–36. Oxford University Press, 2020. http://dx.doi.org/10.1093/oso/9780198858362.003.0010.

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The chapter covers photodetectors for photons in the optical and near UV range (about 200 nm to 700 nm). Important for particle and astroparticle experiments are photodetectors which detect light generated in scintillation or Cherenkov detectors, for example. The detection of photons always starts with the generation of an electron by photoeffect at a photocathode. The photoelectron can then be either multiplied in a photomultiplier tube by secondary electron emission or the cathode could be the surface of a semiconductor detector; both techniques can also be combined in hybrid photodetectors. A relatively new semiconductor detector is the silicon photomultiplier using an avalanche operation mode to obtain sufficiently large signals. In the last section the different photodetectors are compared and are assigned to typical applications according to their properties.

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Atti di convegni sul tema "Stars Scintillation"

Novoseltsev, Yu F., M. M. Boliev, I. M. Dzaparova, S. P. Mikheyev, R. V. Novoseltseva, V. B. Petkov, P. S. Striganov, G. V. Volchenko, V. I. Volchenko e A. F. Yanin. "Search for neutrino bursts from gravitational collapse of stars at the Baksan Underground Scintillation Telescope". In Proceedings of the 11th Conference. WORLD SCIENTIFIC, 2010. http://dx.doi.org/10.1142/9789814307529_0050.

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Camera, Franco, e Agnese Giaz. "New scintillator materials for future and present facilities". In EXOTIC NUCLEI AND NUCLEAR/PARTICLE ASTROPHYSICS (V). FROM NUCLEI TO STARS: Carpathian Summer School of Physics 2014. AIP Publishing LLC, 2015. http://dx.doi.org/10.1063/1.4909582.

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De La Rue, Imelda A., Patrick T. Ryan, Dustin C. Johnston e Robert Q. Fugate. "Scintillation data comparison between a star and laser returns from a high-altitude balloon payload". In Optical Science, Engineering and Instrumentation '97, a cura di Luc R. Bissonnette e Christopher Dainty. SPIE, 1997. http://dx.doi.org/10.1117/12.283895.

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