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1
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.º 3 (29 de maio de 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.º 23 (7 de dezembro de 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.º 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.º 4 (26 de novembro de 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.º 6 (25 de junho de 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.º 2 (10 de fevereiro de 2014): 1275–304. http://dx.doi.org/10.5194/amtd-7-1275-2014.
Texto completo da fonteResumo:
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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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.º 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.º 4 (13 de julho de 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.º 11 (14 de novembro de 2012): 2713–22. http://dx.doi.org/10.5194/amt-5-2713-2012.
Texto completo da fonteResumo:
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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Longair, Malcolm S. "Antony Hewish. 11 May 1924—13 September 2021". Biographical Memoirs of Fellows of the Royal Society 72 (16 de março de 2022): 173–96. http://dx.doi.org/10.1098/rsbm.2021.0045.
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Antony (Tony) Hewish was a pioneer radio astronomer who will always be remembered as the leader of the team in 1967 that discovered the pulsars, which proved to be rapidly rotating, magnetized neutron stars. The discovery resulted from Tony's programme of systematic all-sky surveys to detect the scintillation, or flickering, of small angular diameter radio sources due to electron density fluctuations in the solar wind flowing out from the Sun. The large low-frequency 4.5-acre array was designed by Tony to find radio quasars, which often display radio scintillations, to estimate the angular sizes of the sources and to study the physics of the interplanetary medium. In the course of commissioning the telescope, his research student, Jocelyn Bell (Jocelyn Bell Burnell, FRS 2003), noted a strange 100% scintillating source unlike anything seen before. Tony and the team soon established that this source was a pulsating radio source, Jocelyn first observing the pulsations with period 1.33 s in November 1967. The discovery paved the way for the rapid development of high energy astrophysics and an appreciation that general relativity plays a key role in the stability of neutron stars. Tony's contributions spanned a very wide range of pioneering studies in the new discipline of radio astronomy, including telescope and electronic design, cosmological studies of distant radio sources and the physics of the ionospheric, interplanetary and interstellar plasmas. He was awarded the 1974 Nobel Prize in physics for ‘his decisive role in the discovery of pulsars’.
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Moniez, M., R. Ansari, F. Habibi e S. Rahvar. "Search for Turbulent Gas through Interstellar Scintillation". Proceedings of the International Astronomical Union 7, S285 (setembro de 2011): 376–78. http://dx.doi.org/10.1017/s1743921312001123.
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AbstractStars twinkle because their light propagates through the atmosphere. The same phenomenon is expected when the light of remote stars crosses a Galactic—disk or halo—refractive medium such as a molecular cloud. We present the promising results of a test performed with the ESO–NTT, and consider its potential.
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Lim, J., G. J. Nelson e A. E. Vaughan. "A Multi-Purpose, Multi-Channel Radiospectrograph for the Parkes Telescope". Publications of the Astronomical Society of Australia 7, n.º 2 (1987): 197–204. http://dx.doi.org/10.1017/s1323358000022207.
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AbstractThe design and scientific applications of a 96-channel filter spectrograph of 1 MHz resolution are presented. The spectrograph is currently under construction and will be installed on the Parkes telescope in 1987-1988. Its main scientific objective is dynamic spectral studies of decimetre- and metre-wavelength bursts from flare stars. However, it will also be used for performing large-scale pulsar surveys, and dynamic spectral observations of interplanetary scintillation of compact sources, interstellar scintillation of compact extragalactic sources, and interesting radio sources in general.We show that plasma emission generated in the coronae of flare stars should be detectable at metre- and decimetre-wavelengths. We plan to search for fundamental and second-harmonic plasma radiation by observing in two harmonically related bands, 200 to 250 MHz and 400 to 500 MHz. With noise-adding to stabilize receiver gain, the sensitivity (3σ) of each channel of the spectrograph is ∼ 1.5 Jy for a 1-s integration. Previous studies have reported peak flux densities of up to ∼ 35 Jy and ∼ 12 Jy at 240 MHz and 410 MHz respectively for radio bursts from flare stars.
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Cordes, J. M. "Interstellar Scintillations and Neutron Star Kinematics". Symposium - International Astronomical Union 125 (1987): 35–46. http://dx.doi.org/10.1017/s0074180900160322.
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The interstellar scintillation technique for measuring neutron star speeds is described and results are given for 71 radio pulsars. The mean transverse neutron star speed is 100 km s−1 and the distribution extends to 300 km s−1. The transverse speed correlates with the z velocity derived independently using distance from the galactic plane, consistent with most neutron stars having been born near the galactic plane. A correlation of transverse speed with the quantity PP ∝ (magnetic moment)2 is a general property of the neutron star population. Monte Carlo simulations of the progenitors of neutron stars show that the velocity distribution is inconsistent with the disruption of binary systems solely by symmetric supernova explosions. Either explosions are asymmetric or there are additional accelerations of neutron stars after their formation.
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Dravins, D., L. Lindegren, E. Mezey e A. T. Young. "Atmospheric Intensity Scintillation of Stars. II. Dependence on Optical Wavelength". Publications of the Astronomical Society of the Pacific 109 (junho de 1997): 725. http://dx.doi.org/10.1086/133937.
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Dravins, Dainis, Lennart Lindegren, Eva Mezey e Andrew T. Young. "Atmospheric Intensity Scintillation of Stars. III. Effects for Different Telescope Apertures". Publications of the Astronomical Society of the Pacific 110, n.º 747 (maio de 1998): 610–33. http://dx.doi.org/10.1086/316161.
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Dravins, Dainis, Lennart Lindegren, Eva Mezey e Andrew T. Young. "Atmospheric Intensity Scintillation of Stars, I. Statistical Distributions and Temporal Properties". Publications of the Astronomical Society of the Pacific 109 (fevereiro de 1997): 173. http://dx.doi.org/10.1086/133872.
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Inoue, H. "ASCA Observations of White Dwarfs, Neutron Stars and Black Holes". Symposium - International Astronomical Union 165 (1996): 321–31. http://dx.doi.org/10.1017/s0074180900055789.
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ASCA, the fourth Japanese X-ray astronomy satellite, was launched by the Institute of Space and Astronautical Science (ISAS) on 1993 February 20. ASCA is designed to be a high-capability X-ray observatory (Tanaka et al. 1994). It is equipped with nested thin-foil mirrors which provide a large effective area over a wide energy range from 0.5 to 10 keV. Two different types of detectors, CCD cameras (SIS) and imaging gas scintillation proportional counters (GIS) are employed as the focal plane instruments.
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Rickett, Barney. "Intermittency and Anisotropy in the Ionized Interstellar Medium". Proceedings of the International Astronomical Union 13, S337 (setembro de 2017): 283–86. http://dx.doi.org/10.1017/s1743921317009206.
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AbstractThe discovery of pulsars was closely followed by the discovery of dispersion and scattering in the interstellar plasma (ionized interstellar medium - IISM). The rich phenomena of scattering and scintillation have since been successfully modelled as propagation through a statistically uniform plasma turbulence with an isotropic Kolmogorov spectrum of density. However, this enticingly simple model fails to explain the many recent observations, that show anisotropic scattering from highly localized regions of the IISM often referred to as phase screens. I summarize the recent evidence from pulsars and also from very compact AGN sources, which can exhibit rapid scintillation and occasionally ESEs. The unknown astrophysical origin of these phenomena includes thin current sheets, the diffuse remnants of old supernova shells, and plasma filaments surrounding ubiquitous molecular clumps near young hot stars.
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Ashikhmin, V. V., R. I. Enikeev, A. V. Pokropivny, O. G. Ryazhskaya e V. G. Ryasny. "Search for neutrino radiation from collapsing stars with the Artyomovsk scintillation detector". Bulletin of the Russian Academy of Sciences: Physics 77, n.º 11 (novembro de 2013): 1333–35. http://dx.doi.org/10.3103/s1062873813110051.
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Dravins, Dainis, Lennart Lindegren, Eva Mezey e Andrew T. Young. "Atmospheric Intensity Scintillation of Stars. III. Effects for Different Telescope Apertures: Erratum". Publications of the Astronomical Society of the Pacific 110, n.º 751 (setembro de 1998): 1118. http://dx.doi.org/10.1086/316232.
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Sofieva, Viktoria F., Francis Dalaudier, Alain Hauchecorne e Valery Kan. "High-resolution temperature profiles retrieved from bichromatic stellar scintillation measurements by GOMOS/Envisat". Atmospheric Measurement Techniques 12, n.º 1 (28 de janeiro de 2019): 585–98. http://dx.doi.org/10.5194/amt-12-585-2019.
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Abstract. In this paper, we describe the inversion algorithm for retrievals of high vertical resolution temperature profiles (HRTPs) using bichromatic stellar scintillation measurements in the occultation geometry. This retrieval algorithm has been improved with respect to nominal ESA processing and applied to the measurements by Global Ozone Monitoring by Occultation of Stars (GOMOS) operated on board Envisat in 2002–2012. The retrieval method exploits the chromatic refraction in the Earth's atmosphere. The bichromatic scintillations allow the determination of the refractive angle, which is proportional to the time delay between the photometer signals. The paper discusses the basic principle and detailed inversion algorithm for reconstruction of high-resolution density, pressure and temperature profiles in the stratosphere from scintillation measurements. The HRTPs are retrieved with a very good vertical resolution of ∼200 m and high precision (random uncertainty) of ∼1–3 K for altitudes of 15–32 km and with a global coverage. The best accuracy is achieved for in-orbital-plane occultations, and the precision weakly depends on star brightness. The whole GOMOS dataset has been processed with the improved HRTP inversion algorithm using the FMI's scientific processor; and the dataset (HRTP FSP v1) is in open access. The validation of small-scale fluctuations in the retrieved HRTPs is performed via comparison of vertical wavenumber spectra of temperature fluctuations in HRTPs and in collocated radiosonde data. We found that the spectral features of temperature fluctuations are very similar in HRTPs and collocated radiosonde temperature profiles. HRTPs can be assimilated into atmospheric models, used in studies of stratospheric clouds and used for the analysis of internal gravity waves' activity. As an example of geophysical applications, gravity wave potential energy has been estimated using the HRTP dataset. The obtained spatiotemporal distributions of gravity wave energy are in good agreement with the previous analyses using other measurements.
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Kreidl, T. J. "Chaos in Pulsating Variable Stars: Preliminary Analysis of Photometric Photometry and Observational Constraints of Detection". International Astronomical Union Colloquium 139 (1993): 133. http://dx.doi.org/10.1017/s0252921100117105.
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AbstractChaos theory has been applied to a variety of variable stars, but few convincing candidates for chaos have been identified. Here, well-established analysis methods have been applied to some very extensive data sets of rapidly oscillating Ap (roAp) stars and one white dwarf. It it shown that in spite of the amount of data, the signal-to-noise ratio makes positive detection of chaos extremely difficult, especially due to scintillation noise. A new form of dimension computation is presented and discussed. Simple models were constructed to show what noise levels can be tolerated before the detection of chaos is no longer possible and comparisons are drawn with data that could be obtained in the future from space. The lack of phase and amplitude stability in HD 134214 and mode switching in HD217522 and HD 137949 are pointed out as the possible results of chaos, making frequent monitoring of roAp stars desirable.
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Jauncey, David L., Lucyna Kedziora-Chudczer, J. E. J. Lovell, Jean-Pierre Macquart, George D. Nicolson, Rick A. Perley, John E. Reynolds, A. K. Tzioumis, Mark A. Wieringa e Hayley E. Bignall. "Intraday Variability and Microarcsecond Structure in Blazar Cores". Symposium - International Astronomical Union 205 (2001): 84–87. http://dx.doi.org/10.1017/s0074180900220524.
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The accumulation of evidence now strongly favours interstellar scintillation (ISS) as the principal mechanism causing intra-day variability (IDV) at cm wavelengths. While ISS reduces the implied brightness temperatures, they remain uncomfortably high. The distance to the scattering screen is an important parameter in determining the actual brightness temperature encountered. The high brightness temperatures, the presence of strong and variable circular polarization and the observed lifetimes of a decade or more for several IDV sources, pose significant problems for synchrotron theory. “The fault, dear Brutus, is not in our stars, but in ourselves, that we are underlings.” William Shakespeare, Julius Caesar
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Bacchus, P. "Amateur Astronomers’ Contribution to the HIPPARCHOS Programme". International Astronomical Union Colloquium 98 (1988): 90–92. http://dx.doi.org/10.1017/s0252921100092289.
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The HIPPARCHOS satellite (High Precision Parallax Collecting Satellite) is designed to determine position, proper motion and parallax for a large number of stars. The precision expected (0.002 arcsec), and the absence of systematic errors with position in the sky arise from the following characteristics of the system: –Measurements of angular distances between stars a long way apart (58°), are by comparison with a very stable angular reference. This reference is formed by an optical block consisting of two plane mirrors, rigidly mounted, forming an angle of 29° between them, and sending two separate stellar fields into the same telescope;–the absence of flexure (thanks to weightlessness) and of thermal deformation (non-expansion material and thermal control) ensure that the angular reference is very stable;–operation outside the atmosphere allows the theoretical resolution to be reached; refraction, dispersion and atmospheric scintillation are avoided; diurnal and seasonal effects that interfere with ground-based measurements are non-existent.
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Dalaudier, Francis, Valery Kan e Alexandre S. Gurvich. "Chromatic refraction with global ozone monitoring by occultation of stars I Description and scintillation correction". Applied Optics 40, n.º 6 (20 de fevereiro de 2001): 866. http://dx.doi.org/10.1364/ao.40.000866.
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Belmonte, J. A., T. Roca Cortés, I. Vidal, F. X. Schmider, E. Michel, A. Baglin, M. Chevreton et al. "Stephi: A New Approach to δ Scuti Asteroseismology". International Astronomical Union Colloquium 137 (1993): 739–42. http://dx.doi.org/10.1017/s0252921100018765.
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The STEPHI network (STEllar PHotometry International) is a multinational cooperation stablished in order to get as perfect data as possible on several δ Scuti stars, within a reasonable period of time. STEPHI is currently integrated by nearly 15 people, belonging to the first four institutions cited above. However, astronomers of other institutions have eventually contributed to the network. The idea was born in 1986 and the network has been working to full operation since August 1989. A campaign, observing one or two δ Scuties is normally undertaken every 15 months. They are usually order of three weeks long, avoiding full-moon periods. Up to now, four campaigns have been performed, the last ending February 1992.Very good outcomes on five δScuties [63 Herculis in June 1987 (Belmonte et al, 1991), GX Pegasi in September 1989 (Michel et al, 1992a), v650 Tauri in November 1990 (Belmonte and Michel, 1991; Michel et al, 1992b) and, finally, BN Cancri and BU Cancri in February 1992] have been obtained. Indeed, some very useful aditional information on comparison stars (see e.g. Belmonte et al, 1990) and sky conditions (transparency, brightness, scintillation, etc..) has been obtained as well. Aditionally, some key information about mostly all multiperiodic (four or more periods) δ Scuti stars studied up to March 1992, with good quality data, is presented in this report.
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Dietz, M., C. Lederer-Woods, O. Aberle, J. Andrzejewski, L. Audouin, M. Bacak, J. Balibrea et al. "First Measurement of 72Ge(n, γ) at n_TOF". EPJ Web of Conferences 184 (2018): 02005. http://dx.doi.org/10.1051/epjconf/201718402005.
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The slow neutron capture process (s-process) is responsible for producing about half of the elemental abundances heavier than iron in the universe. Neutron capture cross sections on stable isotopes are a key nuclear physics input for s-process studies. The 72Ge(n, γ) cross section has an important influence on production of isotopes between Ge and Zr during s-process in massive stars and therefore experimental data are urgently required. 72Ge(n, γ) was measured at the neutron time-of-flight facility n_TOF (CERN) for the first time at stellar energies. The measurement was performed using an enriched 72GeO2 sample at a flight path of 185m with a set of liquid scintillation detectors (C6D6). The motivation, experiment and current status of the data analysis are reported.
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Tamminen, J., E. Kyrölä, V. F. Sofieva, M. Laine, J. L. Bertaux, A. Hauchecorne, F. Dalaudier et al. "GOMOS data characterization and error estimation". Atmospheric Chemistry and Physics Discussions 10, n.º 3 (11 de março de 2010): 6755–96. http://dx.doi.org/10.5194/acpd-10-6755-2010.
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Abstract. The Global Ozone Monitoring by Occultation of Stars (GOMOS) instrument uses stellar occultation technique for monitoring ozone and other trace gases in the stratosphere and mesosphere. The self-calibrating measurement principle of GOMOS together with a relatively simple data retrieval where only minimal use of a priori data is required, provides excellent possibilities for long term monitoring of atmospheric composition. GOMOS uses about 180 brightest stars as the light source. Depending on the individual spectral characteristics of the stars, the signal-to-noise ratio of GOMOS is changing from star to star, resulting also varying accuracy to the retrieved profiles. We present the overview of the GOMOS data characterization and error estimation, including modeling errors, for ozone, NO2, NO3 and aerosol profiles. The retrieval error (precision) of the night time measurements in the stratosphere is typically 0.5–4% for ozone, about 10–20% for NO2, 20–40% for NO3 and 2–50% for aerosols. Mesospheric O3, up to 100 km, can be measured with 2–10% precision. The main sources of the modeling error are the incompletely corrected atmospheric turbulence causing scintillation, inaccurate aerosol modeling, uncertainties in cross sections of the trace gases and in the atmospheric temperature. The sampling resolution of GOMOS varies depending on the measurement geometry. In the data inversion a Tikhonov-type regularization with pre-defined target resolution requirement is applied leading to 2–3 km resolution for ozone and 4 km resolution for other trace gases.
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Tamminen, J., E. Kyrölä, V. F. Sofieva, M. Laine, J. L. Bertaux, A. Hauchecorne, F. Dalaudier et al. "GOMOS data characterisation and error estimation". Atmospheric Chemistry and Physics 10, n.º 19 (8 de outubro de 2010): 9505–19. http://dx.doi.org/10.5194/acp-10-9505-2010.
Texto completo da fonteResumo:
Abstract. The Global Ozone Monitoring by Occultation of Stars (GOMOS) instrument uses stellar occultation technique for monitoring ozone, other trace gases and aerosols in the stratosphere and mesosphere. The self-calibrating measurement principle of GOMOS together with a relatively simple data retrieval where only minimal use of a priori data is required provides excellent possibilities for long-term monitoring of atmospheric composition. GOMOS uses about 180 of the brightest stars as its light source. Depending on the individual spectral characteristics of the stars, the signal-to-noise ratio of GOMOS varies from star to star, resulting also in varying accuracy of retrieved profiles. We present here an overview of the GOMOS data characterisation and error estimation, including modeling errors, for O3, NO2, NO3, and aerosol profiles. The retrieval error (precision) of night-time measurements in the stratosphere is typically 0.5–4% for ozone, about 10–20% for NO2, 20–40% for NO3 and 2–50% for aerosols. Mesospheric O3, up to 100 km, can be measured with 2–10% precision. The main sources of the modeling error are incompletely corrected scintillation, inaccurate aerosol modeling, uncertainties in cross sections of trace gases and in atmospheric temperature. The sampling resolution of GOMOS varies depending on the measurement geometry. In the data inversion a Tikhonov-type regularization with pre-defined target resolution requirement is applied leading to 2–3 km vertical resolution for ozone and 4 km resolution for other trace gases and aerosols.
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Bradt, H. V., A. M. Levine, E. H. Morgan, R. A. Remillard, J. H. Swank, B. L. Dingus, S. S. Holt et al. "The X-Ray Timing Explorer". International Astronomical Union Colloquium 123 (1990): 89–110. http://dx.doi.org/10.1017/s0252921100076946.
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AbstractThe capabilities of the X-ray Timing Explorer (XTE) are described with particular attention paid to current scientific problems it will address from galactic neutron star systems to active galactic nuclei. It features a low-background continuous 2-200 keV response with large apertures (a 0.63-m2 proportional counter array and a 0.16-m2 dual rocking NaI/CsI scintillation array). Rapid response (in hours) to temporal phenomena, e.g. transients, is obtained by virtue of a scanning all-sky monitor and rapid maneuverability. XTE will carry out detailed energy-resolved studies of phenomena close to neutron stars (e.g. QPO’s) because of its sub-millisecond timing (to 10 μs), its high telemetry rates (to 256 kb/s), and the high throughput of its data system (to ≳ 2 × 105 c s−1).
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Wlodarczyk-Sroka, B. S., M. A. Garrett e A. P. V. Siemion. "Extending the Breakthrough Listen nearby star survey to other stellar objects in the field". Monthly Notices of the Royal Astronomical Society 498, n.º 4 (8 de setembro de 2020): 5720–29. http://dx.doi.org/10.1093/mnras/staa2672.
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ABSTRACT We extend the source sample recently observed by the Breakthrough Listen (BL) Initiative by including additional stars (with parallaxes measured by Gaia) that also reside within the full width at half-maximum of the Green Bank 100-m Telescope and Parkes radio telescope target fields. These stars have estimated distances as listed in the extensions of the Gaia DR2 catalogue. Enlarging the sample from 1327 to 288 315 stellar objects permits us to achieve substantially better Continuous Waveform Transmitter Rate Figures of Merit (CWTFM) than any previous analysis, and allows us to place the tightest limits yet on the prevalence of nearby high-duty-cycle extraterrestrial transmitters. The results suggest ≲0.0660$^{+0.0004}_{-0.0003}$ per cent of stellar systems within 50 pc host such transmitters (assuming an EIRP ≳ 1013 W) and ≲0.039$^{+0.004}_{-0.008}$ per cent within 200 pc (assuming an EIRP ≳ 2.5 × 1014 W). We further extend our analysis to much greater distances, though we caution that the detection of narrow-band signals beyond a few hundred pc may be affected by interstellar scintillation. The extended sample also permits us to place new constraints on the prevalence of extraterrestrial transmitters by stellar type and spectral class. Our results suggest targeted analyses of Search for Extraterrestrial Intelligence radio data can benefit from taking into account the fact that in addition to the target at the field centre, many other cosmic objects reside within the primary beam response of a parabolic radio telescope. These include foreground and background Galactic stars, but also extragalactic systems. With distances measured by Gaia, these additional sources can be used to place improved limits on the prevalence of extraterrestrial transmitters, and extend the analysis to a wide range of cosmic objects.
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Bryant, Edward M., Daniel Bayliss, James McCormac, Peter J. Wheatley, Jack S. Acton, David R. Anderson, David J. Armstrong et al. "Simultaneous TESS and NGTS transit observations of WASP-166 b". Monthly Notices of the Royal Astronomical Society 494, n.º 4 (24 de abril de 2020): 5872–81. http://dx.doi.org/10.1093/mnras/staa1075.
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ABSTRACT We observed a transit of WASP-166 b using nine Next Generation Transit Survey (NGTS) telescopes simultaneously with the Transiting Exoplanet Survey Satellite (TESS) observations of the same transit. We achieved a photometric precision of 152 ppm per 30 min with the nine NGTS telescopes combined, matching the precision reached by TESS for the transit event around this bright (T = 8.87) star. The individual NGTS light-curve noise is found to be dominated by scintillation noise and appears free from any time-correlated noise or any correlation between telescope systems. We fit the NGTS data for TC and Rp/R*. We find TC to be consistent to within 0.25σ of the result from the TESS data, and the difference between the TESS and NGTS measured Rp/R* values is 0.9σ. This experiment shows that multitelescope NGTS photometry can match the precision of TESS for bright stars, and will be a valuable tool in refining the radii and ephemerides for bright TESS candidates and planets. The transit timing achieved will also enable NGTS to measure significant transit timing variations in multiplanet systems.
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Querci, François R. "Network of Oriental Robotic Telescopes". Highlights of Astronomy 10 (1995): 677–79. http://dx.doi.org/10.1017/s1539299600012557.
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We should like to report on the Network of Oriental Robotic Telescopes, otherwise the ORT network. Our objective is non-stop observations of variable stars by collaboration with other networks of automated photometric telescopes, complementary to the ORT network in longitude and latitude intervals, such as the GNAT in the U.S.A., the Chilean cordillera stations, the South African stations, etc. As a first step we will deal with photometric telescopes, then we will extend them to spectroscopy.From 12-year archives of meteorological satellites, it appeared that sites located around the north latitude from 15° to 35° and from 10° west to 110° east in longitude have high-quality astronomical conditions with a significant annual number of clear nights. Such sites involve Islamic countries from Morocco to the western deserts of China. In addition to their astronomical history, the Islamic countries are suitable because they have high mountains in semi-desert areas, i.e. a clear sky with low telluric absorption. The final site selection will be based upon local astronomical tests, such as seeing and scintillation measurements.
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Koay, J. Y., D. L. Jauncey, T. Hovatta, S. Kiehlmann, H. E. Bignall, W. Max-Moerbeck, T. J. Pearson et al. "The presence of interstellar scintillation in the 15 GHz interday variability of 1158 OVRO-monitored blazars". Monthly Notices of the Royal Astronomical Society 489, n.º 4 (7 de setembro de 2019): 5365–80. http://dx.doi.org/10.1093/mnras/stz2488.
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ABSTRACT We have conducted the first systematic search for interday variability in a large sample of extragalactic radio sources at 15 GHz. From the sample of 1158 radio-selected blazars monitored over an ∼10 yr span by the Owens Valley Radio Observatory 40-m telescope, we identified 20 sources exhibiting significant flux density variations on 4-d time-scales. The sky distribution of the variable sources is strongly dependent on the line-of-sight Galactic H α intensities from the Wisconsin H α Mapper Survey, demonstrating the contribution of interstellar scintillation (ISS) to their interday variability. 21 per cent of sources observed through sightlines with H α intensities larger than 10 rayleighs exhibit significant ISS persistent over the ∼10 yr period. The fraction of scintillators is potentially larger when considering less significant variables missed by our selection criteria, due to ISS intermittency. This study demonstrates that ISS is still important at 15 GHz, particularly through strongly scattered sightlines of the Galaxy. Of the 20 most significant variables, 11 are observed through the Orion–Eridanus superbubble, photoionized by hot stars of the Orion OB1 association. The high-energy neutrino source TXS 0506+056 is observed through this region, so ISS must be considered in any interpretation of its short-term radio variability. J0616−1041 appears to exhibit large ∼20 per cent interday flux density variations, comparable in magnitude to that of the very rare class of extreme, intrahour scintillators that includes PKS0405−385, J1819+3845, and PKS1257−326; this needs to be confirmed by higher cadence follow-up observations.
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Cesarsky, C. J., R. A. Sunyaev, G. W. Clark, R. Giacconi, Vin-Yue Qu, E. E. Salpeter, P. A. Scheuer et al. "Commission N°48: High Energy Astrophysics (Astrophysique Des Hautes Energies)". Transactions of the International Astronomical Union 20, n.º 1 (1988): 671–75. http://dx.doi.org/10.1017/s0251107x00007549.
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The european X-ray observatory (EXOSAT), which was launched in 1983 and which finished operations in April 1986, has brought a rich harvest of results in the period 1984-1987, surveyed here. The EXOSAT payload consisted of three sets of instruments: two low energy imaging telescopes (LE:E<2 KeV), a medium-energy experiment (ME:E=l-50KeV) and a gas scintillation proportional counter (GSPC:E=2-20KeV). Over most of the energy range covered, EXOSAT was not more sensitive than its predecessor, the american EINSTEIN satellite. But the EINSTEIN satellite is far from having exhausted the treasures of the X-ray sky. And EXOSAT, thanks to its elliptical 90-hour orbit, had the extra advantage of being able to make long, continuous observations of interesting objects, lasting up to 72 hours. Thus, EXOSAT was very well suited for variability studies, and many of its most important findings are in this area. EXOSAT observations sample a vide range of astrophysical sources: X-ray binaries, cataclysmic variables and active stars; supernova remnants and the interstellar medium; active galactic nuclei, and clusters of galaxies. Among the highlights, let us mention:
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Djuric, N., e L. Field. "On the detectability of intelligent civilizations in the galaxy". Serbian Astronomical Journal, n.º 167 (2003): 1–10. http://dx.doi.org/10.2298/saj0367001d.
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In this paper we argue for the possibility that even in the event of a Galaxy teeming with extraterrestrial intelligence (ETI) the probability of receiving recognizable signals from the ETIs may be very low. There are two majors factors that may limit our ability to detect other civilizations. (i) Evolutionary mismatches may cause difficulties analogous to humans attempting to communicate with lower primates. (ii) Independent evolutionary paths resulting from differing planetary/stellar environments may result in life whose cognitive processes and consequent perceptions of the universe are very different from ours. Interpreting signals from such civilizations may prove a very difficult or even futile task. Even on Earth, an example of a cognitive mismatch is that between humans and dolphins, where evolution in very different environments has led to difficulty in establishing communication between these two species. The main effect of the second factor is to limit communication while the effect of the first is to constrain what communication is possible to a "window of opportunity", a finite period of time, ??, when communication may be possible before diverging evolution makes it impossible. For example, if the number of ETIs in the Galaxy is one million and if ?? < 10 6 years, the average separation of "contactable" civilizations, (r) > 5 ? 10 3 light years so that one star in 10 10 harbors such a civilization. If the above arguments are correct we reach the following conclusions. The absence of detected signals does not translate into an absence of ETI?s. Targeting individual stars in the search for ETI has a low probability of success. The use of radio signals is of limited value because with such large separations between "contactable" civilizations interstellar scintillation strongly limits the propagation of radio signals. Similarly, optical communication would be hindered by interstellar extinction. Possible alternatives to current searches for narrow band signals include listening for modulated broadband signals searching for narrow-band signals in the microwave/FIR spectrum and searching for evidence of artificially processed environments. All such searches would need to be "all sky" to have a reasonable chance of success.
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Kan, Valery, Francis Dalaudier e Alexandre S. Gurvich. "Chromatic refraction with global ozone monitoring by occultation of stars II Statistical properties of scintillations". Applied Optics 40, n.º 6 (20 de fevereiro de 2001): 878. http://dx.doi.org/10.1364/ao.40.000878.
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Kyrölä, E., J. Tamminen, V. Sofieva, J. L. Bertaux, A. Hauchecorne, F. Dalaudier, D. Fussen et al. "Retrieval of atmospheric parameters from GOMOS data". Atmospheric Chemistry and Physics Discussions 10, n.º 4 (19 de abril de 2010): 10145–217. http://dx.doi.org/10.5194/acpd-10-10145-2010.
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Abstract. The Global Ozone Monitoring by Occultation of Stars (GOMOS) instrument on board the European Space Agency's ENVISAT satellite measures attenuation of stellar light in occultation geometry. Daytime measurements also record scattered solar light from the atmosphere. The wavelength regions are the ultraviolet-visible band 248–690 nm and two infrared bands at 755–774 nm and at 926–954 nm. From UV-Visible and IR spectra the vertical profiles of O3, NO2, NO3, H2O, O2 and aerosols can be retrieved. In addition there are two 1 kHz photometers at blue 473–527 nm and red 646–698 nm. Photometer data are used to correct spectrometer measurements for scintillations and to retrieve high resolution temperature profiles as well as gravity wave and turbulence parameters. Measurements cover altitude region 5–150 km. Atmospherically valid data are obtained in 15–100 km. In this paper we present an overview of the GOMOS retrieval algorithms for stellar occultation measurements. The low signal-to-noise ratio and the refractive effects due to the point source nature of stars have been important drivers in the development of GOMOS retrieval algorithms. We present first the Level 1b algorithms that are used to correct instrument related disturbances in the spectrometer and photometer measurements The Level 2 algorithms deal with the retrieval of vertical profiles of atmospheric gaseous constituents, aerosols and high resolution temperature. We divide the presentation into correction for refractive effects, high resolution temperature retrieval and spectral/vertical inversion. The paper also includes discussion about the GOMOS algorithm development, expected improvements, access to GOMOS data and alternative retrieval approaches.
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Kyrölä, E., J. Tamminen, V. Sofieva, J. L. Bertaux, A. Hauchecorne, F. Dalaudier, D. Fussen et al. "Retrieval of atmospheric parameters from GOMOS data". Atmospheric Chemistry and Physics 10, n.º 23 (14 de dezembro de 2010): 11881–903. http://dx.doi.org/10.5194/acp-10-11881-2010.
Texto completo da fonteResumo:
Abstract. The Global Ozone Monitoring by Occultation of Stars (GOMOS) instrument on board the European Space Agency's ENVISAT satellite measures attenuation of stellar light in occultation geometry. Daytime measurements also record scattered solar light from the atmosphere. The wavelength regions are the ultraviolet-visible band 248–690 nm and two infrared bands at 755–774 nm and at 926–954 nm. From UV-Visible and IR spectra the vertical profiles of O3, NO2, NO3, H2O, O2 and aerosols can be retrieved. In addition there are two 1 kHz photometers at blue 473–527 nm and red 646–698 nm. Photometer data are used to correct spectrometer measurements for scintillations and to retrieve high resolution temperature profiles as well as gravity wave and turbulence parameters. Measurements cover altitude region 5–150 km. Atmospherically valid data are obtained in 15–100 km. In this paper we present an overview of the GOMOS retrieval algorithms for stellar occultation measurements. The low signal-to-noise ratio and the refractive effects due to the point source nature of stars have been important drivers in the development of GOMOS retrieval algorithms. We present first the Level 1b algorithms that are used to correct instrument related disturbances in the spectrometer and photometer measurements The Level 2 algorithms deal with the retrieval of vertical profiles of atmospheric gaseous constituents, aerosols and high resolution temperature. We divide the presentation into correction for refractive effects, high resolution temperature retrieval and spectral/vertical inversion. The paper also includes discussion about the GOMOS algorithm development, expected improvements, access to GOMOS data and alternative retrieval approaches.
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Amaducci, Simone, Nicola Colonna, Luigi Cosentino, Sergio Cristallo, Paolo Finocchiaro, Milan Krtička, Cristian Massimi et al. "First Results of the 140Ce(n,γ)141Ce Cross-Section Measurement at n_TOF". Universe 7, n.º 6 (17 de junho de 2021): 200. http://dx.doi.org/10.3390/universe7060200.
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An accurate measurement of the 140Ce(n,γ) energy-dependent cross-section was performed at the n_TOF facility at CERN. This cross-section is of great importance because it represents a bottleneck for the s-process nucleosynthesis and determines to a large extent the cerium abundance in stars. The measurement was motivated by the significant difference between the cerium abundance measured in globular clusters and the value predicted by theoretical stellar models. This discrepancy can be ascribed to an overestimation of the 140Ce capture cross-section due to a lack of accurate nuclear data. For this measurement, we used a sample of cerium oxide enriched in 140Ce to 99.4%. The experimental apparatus consisted of four deuterated benzene liquid scintillator detectors, which allowed us to overcome the difficulties present in the previous measurements, thanks to their very low neutron sensitivity. The accurate analysis of the p-wave resonances and the calculation of their average parameters are fundamental to improve the evaluation of the 140Ce Maxwellian-averaged cross-section.
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Bertaux, J. L., E. Kyrölä, D. Fussen, A. Hauchecorne, F. Dalaudier, V. Sofieva, J. Tamminen et al. "Global ozone monitoring by occultation of stars: an overview of GOMOS measurements on ENVISAT". Atmospheric Chemistry and Physics Discussions 10, n.º 4 (16 de abril de 2010): 9917–10076. http://dx.doi.org/10.5194/acpd-10-9917-2010.
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Abstract. GOMOS on ENVISAT (launched in February, 2002) is the first space instrument dedicated to the study of the atmosphere of the Earth by the technique of stellar occultations (Global Ozone Monitoring by Occultation of Stars). From a polar orbit, it allows to have a good latitude coverage. Because it is self-calibrated, it is particularly well adapted to the long time trend monitoring of stratospheric species. With 4 spectrometers the wavelength coverage of 248 nm to 942 nm allows to monitor ozone, H2O, NO2, NO3, air, aerosols, and O2. Two additional fast photometers (1 kHz sampling rate) allow for the correction of scintillations, as well as the study of the structure of air density irregularities, resulting from gravity waves and turbulence. A high vertical resolution profile of the temperature may also be obtained from the time delay between the red and the blue photometer. Noctilucent clouds (Polar Mesospheric Clouds, PMC), are routinely observed in both polar summers, and global observations of OCLO and sodium are achieved. The instrument configuration, dictated by the scientific objectives rationale and technical constraints, are described, together with the typical operations along one orbit, and statistics over 5 years of operation. Typical atmospheric transmission spectra are presented, and some retrieval difficulties are discussed, in particular for O2 and H2O. An overview of a number of scientific results is presented, already published or found in more details as companion papers in the same ACP GOMOS special issue. This paper is particularly intended to provide the incentive for GOMOS data exploitation, available to the whole scientific community in the ESA data archive, and to help the GOMOS data users to better understand the instrument, its capabilities and the quality of its measurements, for an optimized scientific return.
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Bertaux, J. L., E. Kyrölä, D. Fussen, A. Hauchecorne, F. Dalaudier, V. Sofieva, J. Tamminen et al. "Global ozone monitoring by occultation of stars: an overview of GOMOS measurements on ENVISAT". Atmospheric Chemistry and Physics 10, n.º 24 (20 de dezembro de 2010): 12091–148. http://dx.doi.org/10.5194/acp-10-12091-2010.
Texto completo da fonteResumo:
Abstract. GOMOS on ENVISAT (launched in February, 2002) is the first space instrument dedicated to the study of the atmosphere of the Earth by the technique of stellar occultations (Global Ozone Monitoring by Occultation of Stars). Its polar orbit makes good latitude coverage possible. Because it is self-calibrating, it is particularly well adapted to long time trend monitoring of stratospheric species. With 4 spectrometers, the wavelength coverage of 248 nm to 942 nm enables monitoring ozone, H2O, NO2, NO3, air density, aerosol extinction, and O2. Two additional fast photometers (with 1 kHz sampling rate) enable the correction of the effects of scintillations, as well as the study of the structure of air density irregularities resulting from gravity waves and turbulence. A high vertical resolution profile of the temperature may also be obtained from the time delay between the red and the blue photometer. Noctilucent clouds (Polar Mesospheric Clouds, PMC) are routinely observed in both polar summers and global observations of OClO and sodium are achieved. The instrument configuration, dictated by the scientific objectives' rationale and technical constraints, is described, together with the typical operations along one orbit, along with the statistics from over 6 years of operation. Typical atmospheric transmission spectra are presented and some retrieval difficulties are discussed, in particular for O2 and H2O. An overview is presented of a number of scientific results already published or found in more detail as companion papers in the same ACP GOMOS special issue. This paper is particularly intended to provide an incentive for the exploitation of GOMOS data available to the whole scientific community in the ESA data archive, and to help GOMOS data users to better understand the instrument, its capabilities and the quality of its measurements, thus leading to an increase in the scientific return.
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Sullivan, Woodruff T., Kelvin J. Wellington, G. Seth Shostak, Peter R. Backus e James M. Cordes. "A Galactic Center Search for Extraterrestrial Intelligent Signals". International Astronomical Union Colloquium 161 (janeiro de 1997): 653–56. http://dx.doi.org/10.1017/s0252921100015190.
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AbstractIn June 1995 we used the Parkes 64-m radio telescope to search for narrowband or pulsing signals of extraterrestrial intelligent (ETI) origin from the direction of the galactic center. This strategy was chosen so as to maximize the number of possibly detectable ETI signals within the beam, assuming that they are associated with stars and that their luminosity function is such that they can be detected at a distance of at least a few kiloparsecs. A total of 190 1.2–minute integrations were taken in a region of size 5.0° × 0.6° centered on the galactic center. Many positions in this region were observed 2 or 3 times in order to allow for the possibility of strong interstellar scintillations arising in any ETI signal. The spectrum analyzer was that of Project Phoenix, configured such that it covered both circular polarizations over a 20-MHz bandwidth centered on 1425.0 MHz. This bandwidth was divided into 28.7 million channels with separations of 0.64 Hz. The signal analysis system searched both for slow pulses (periods of at least 2 sec) and narrowband signals with drifts from 0 to 1 Hz/sec. A second antenna located 200 km away was used for immediate follow-up on all candidate signals. No signals of ETI origin were found. A later search of smoothed spectra with 640 Hz resolution also revealed no new features not attributable to manmade interference.
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Нарожный, Анатолий Николаевич. "КОСМІЧНЕ МІКРОХВИЛЬОВЕ ВИПРОМІНЮВАННЯ І ТЕМНА МАТЕРІЯ". Open Information and Computer Integrated Technologies, n.º 82 (19 de dezembro de 2018): 83–101. http://dx.doi.org/10.32620/oikit.2018.82.07.
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The question of the possible origin of one of the components of dark matter filling the galaxies is considered. The analysis of the “fate” of stellar electromagnetic radiation under the conditions of the eternal Universe is taken as a starting point. Based on a comparison of the average lifetime of a star in the active phase and the lifetime of the non-absorbed part of its radiation, it is concluded that the Universe is filled with stellar electromagnetic radiation. However, based on existing concepts, as well as the red shift found in the spectra of distant galaxies, the addition of new radiation to the existing in the Universe will be accompanied by the “disappearance” of radiation in the most long-wave region, that is, there will be a violation of the law of conservation of energy. The main question arises: can radiation as well as energy disappear without a trace? The answer is negative, and it is explained by the involvement of the mechanism of dissipative losses during the radiative transfer by the expanses of the Universe. For this purpose, an assumption is introduced about the presence of an agent's medium interacting with quanta of radiation with the help of excessively weak forces. It is hypothesized that photons that fall into the low-frequency region (microwave band and ranges close to it) are able to pair up in an agent's medium, creating neutral particles of extremely small masses (about 0.0013 eV). These particles - bosons - are particles of the agent itself. Based on the nature of the agent, some observational data related to the Solar System (increased distance between the Sun and the Earth, the "floating" value of the G gravitation constant, scintillations of cosmic microwave radiation), as well as detected deviations observed during spacecraft acceleration with gravitational slingshots near the Earth (Galileo, NEAR, Rosetta, Messenger, Cassini). In addition, this hypothesis regarding the origin and properties of the agent explains some of the results of laboratory research: scintillations of the rates of chemical and biochemical reactions, floating "zero" of high-precision instruments and, possibly, relaxation processes in elastic solids (material aging). The main conclusions: cosmic microwave radiation is a remnant of stellar radiation, and the agent's medium is a component of dark matter, which is closely associated with cosmic microwave radiation. Other dark matter components are extinct stars, their various cold fragments, including gases and dust, and possibly other deeper structural levels of matter.
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Belousov, Maksim, Maksim Gorbunov, Oleg Ignat'ev, Andrey Krymov, Anton Kupchinskiy, Sergey Morozov e Aleksey Pulin. "Perspectives of CsI:Tl Crystals in g-Spectrometers". ANRI, n.º 2 (29 de junho de 2021): 24–40. http://dx.doi.org/10.37414/2075-1338-2021-105-2-24-40.
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The article describes the problems of creating a scintillation spectrometer with a CsI:Tl crystal to replace spectrometers with NaI:Tl crystals which are widely used at nuclear power plants (NPPs) to monitor the activity of air, waste water and adjacent territories. The advantages of CsI:Tl-spectrometers are in the best energy resolution; much greater resistance to mechanical and electromagnetic influences due to the use of silicon photomultipliers (SiPM) instead of vacuum photomultiplier tubes (VPMT); much greater durability due to the very low hygroscopicity of the material. The strong mismatch between the emission spectrum of the crystal and the spectral sensitivity of the VPMT photocathodes, the relatively long decay time and the complex, multicomponent form of the light flash made spectrometers with CsI:Tl crystals not competitive. The paper describes the methods of constructing a spectrometer, which made it possible to realize the useful properties inherent in a crystal and to level its disadvantages. As a result of the cycle of research and development work, the Stark-02 intellectual detector has been designed and described. Typical relative energy resolution with crystals of volume 45 cm3 at an energy of 662 keV of the 137Cs source is better than 6.5% in the ambient temperature range Q = +10 ÷ +45 °C and not worse than 7.5% in the extended range Q = –25 ÷ +55 °C.
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Penek, Ö., M. Agostini, K. Altenmüller, S. Appel, V. Atroshchenko, Z. Bagdasarian, D. Basilico et al. "Observation of CNO cycle solar neutrinos in Borexino". Journal of Physics: Conference Series 2156, n.º 1 (1 de dezembro de 2021): 012128. http://dx.doi.org/10.1088/1742-6596/2156/1/012128.
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Abstract The Borexino detector, located at the Laboratori Nazionali del Gran Sasso in Italy, is a radiopure 280 ton liquid scintillator detector with a primary goal to measure low-energy solar neutrinos created in the core of the Sun. These neutrinos are a consequence of nuclear fusion reactions in the solar core where Hydrogen is burned into Helium and provide a direct probe of the energy production processes, namely the proton-proton (pp) chain and the Carbon-Nitrogen-Oxygen (CNO) cycle. The fusion of Hydrogen in the case of the CNO cycle, which is expected to contribute in the order of less than 1% to the total solar energy, is catalyzed by Carbon, Nitrogen, and Oxygen directly depending on the abundances of these elements in the solar core. The measurement of CNO neutrinos is challenging due to the high spectral correlation with the decay electrons of the background isotope 210Bi and the pep solar neutrino signal. The experimental achievement of thermal stabilization of the Borexino detector after mid 2016, has opened the possibility to develop a method to constrain the 210Bi rate through its decay daughter and α emitter 210Po which can be identified in Borexino with an efficiency close to 100 percent on an event-by-event basis. Moreover, the flux of pep neutrinos can be constrained precisely through a global analysis of solar neutrino data which is independent of the dataset used for the CNO analysis. This conference contribution is dedicated to the first experimental evidence of neutrinos produced in the CNO fusion cycle in the Sun which is at the same time the dominant energy production mechanism in heavier stars compared to the Sun.
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Bignall, Hayley E., Artem V. Tuntsov, Jamie Stevens, Keith Bannister, Mark A. Walker e Cormac Reynolds. "The annual cycle in scintillation timescale of PMN J1726+0639". Monthly Notices of the Royal Astronomical Society, 18 de abril de 2022. http://dx.doi.org/10.1093/mnras/stac1051.
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Abstract We discovered rapid intra-day variability in radio source PMN J1726+0639 at GHz frequencies, during a survey to search for such variability with the Australia Telescope Compact Array. Follow-up observations were conducted over two years and revealed a clear, repeating annual cycle in the rate, or characteristic timescale, of variability, showing that the observed variations can be attributed to scintillations from interstellar plasma inhomogeneities. The strong annual cycle includes an apparent ‘standstill’ in April and another in September. We fit kinematic models to the data, allowing for finite anisotropy in the scintillation pattern. The cycle implies a very high degree of anisotropy, with an axial ratio of at least 13 : 1, and the fit is consistent with a purely one-dimensional scintillation pattern. The position angle of the anisotropy, and the transverse velocity component are tightly constrained. The parameters are inconsistent with expectations from a previously proposed model of scattering associated with plasma filaments radially oriented around hot stars. We note that evidence for a foreground interstellar cloud causing anomalous Ca ii absorption towards the nearby star Rasalhague (α Oph) has been previously reported, and we speculate that the interstellar scintillation of might be associated with this nearby cloud.
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"The physics of pulsar scintillation". Philosophical Transactions of the Royal Society of London. Series A: Physical and Engineering Sciences 341, n.º 1660 (15 de outubro de 1992): 151–65. http://dx.doi.org/10.1098/rsta.1992.0090.
Texto completo da fonteResumo:
Scintillation is a well-known phenomenon in astronomy, e.g. twinkling of stars due to scattering in the Earth’s atmosphere, and variability of compact radio sources due to scattering in the ionosphere and the solar wind. These examples correspond to the so-called regime of weak scattering. Radio pulsars scintillate as a result of scattering in the ionized interstellar medium, but in contrast to the previous cases, the physical régime corresponds to strong scattering. Pulsars exhibit two distinct kinds of variability, called diffractive scintillation and refractive scintillation, on timescales of minutes and weeks respectively. The physics of the various régimes of scintillation are reviewed, and some basic theoretical results are summarized. The properties of imaging in the presence of strong scattering are also discussed.
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Luo, Rui, George Hobbs, Suk Yee Yong, Andrew Zic, Lawrence Toomey, Shi Dai, Alex Dunning et al. "Simulating high-time resolution radio-telescope observations". Monthly Notices of the Royal Astronomical Society, 29 de abril de 2022. http://dx.doi.org/10.1093/mnras/stac1168.
Texto completo da fonteResumo:
Abstract We describe a new software package for simulating channelised, high-time resolution data streams from radio telescopes. The software simulates data from the telescope and observing system taking into account the observation strategy, receiver system and digitisation. The signatures of pulsars, fast radio bursts and flare stars are modelled, including frequency-dependent effects such as scattering and scintillation. We also simulate more generic signals using spline curves and images. Models of radio frequency interference include signals from satellites, terrestrial transmitters and impulsive, broadband signals. The simulated signals can also be injected into real data sets. Uses of this software include the production of machine learning training data sets, development and testing of new algorithms to search for anomalous patterns and to characterise processing pipelines.