scholarly journals Thomson Scattering in the Lower Corona in the Presence of Sunspots

2021 ◽  
Vol 923 (2) ◽  
pp. 276
Author(s):  
Pascal Saint-Hilaire ◽  
Juan Carlos Martínez Oliveros ◽  
Hugh S. Hudson
Keyword(s):  
Scattered Light ◽  
Solar Limb ◽  
Thomson Scattering ◽  
Full Description ◽  
Solar Dynamics Observatory ◽  
Magnetic Image ◽  
Lower Corona ◽  
Polarization Component ◽  
Solar Dynamics ◽  
Limb Darkening

Abstract Polarized scattered light from low (few tens of megameter altitudes) coronal transients has been recently reported in Solar Dynamics Observatory/Helioseismic and Magnetic Image (HMI) observations. In a classic paper, Minnaert (1930) provided an analytic theory of polarization via electron scattering in the corona. His work assumed axisymmetric input from the photosphere with a single-parameter limb-darkening function. This diagnostic has recently been used to estimate the free-electron number and mass of HMI transients near the solar limb, but it applies equally well to any coronal material, at any height. Here we extend his work numerically to incorporate sunspots, which can strongly effect the polarization properties of the scattered light in the low corona. Sunspot effects are explored first for axisymmetric model cases, and then applied to the full description of two sunspot groups as observed by HMI. We find that (1) as previously reported by Minnaert, limb darkening has a strong influence, usually increasing the level of linear polarization tangential to the limb; (2) unsurprisingly, the effects of the sunspot generally increase at the lower scatterer altitudes, and increase the larger the sunspot is and the closer to their center the scatterer subpoint is; (3) assuming the Stokes Q > 0 basis to be tangential to the limb, sunspots typically decrease the Stokes Q/I polarization and the perceived electron densities below the spotless case, sometimes dramatically; and (4) typically, a sizeable non-zero Stokes U/I polarization component will appear when a sunspot’s influence becomes non-negligible. However, that is not true in rare cases of extreme symmetry (e.g., scattering mass at the center of an axisymmetric sunspot). The tools developed here are generally applicable to an arbitrary image input.

scholarly journals The stellar variability noise floor for transiting exoplanet photometry with PLATO

2020 ◽  
Vol 493 (4) ◽  
pp. 5489-5498 ◽  
Author(s):  
Brett M Morris ◽  
Monica G Bobra ◽  
Eric Agol ◽  
Yu Jin Lee ◽  
Suzanne L Hawley
Keyword(s):  
Impact Parameter ◽  
Solar Dynamics Observatory ◽  
Depth Measurement ◽  
Stellar Oscillations ◽  
Mission Duration ◽  
Intensity Images ◽  
Solar Dynamics ◽  
In Transit ◽  
Limb Darkening ◽  
The Impact

ABSTRACT One of the main science motivations for the ESA PLAnetary Transit and Oscillations (PLATO) mission is to measure exoplanet transit radii with 3 per cent precision. In addition to flares and starspots, stellar oscillations and granulation will enforce fundamental noise floors for transiting exoplanet radius measurements. We simulate light curves of Earth-sized exoplanets transiting continuum intensity images of the Sun taken by the Helioseismic and Magnetic Imager (HMI) instrument aboard the Solar Dynamics Observatory (SDO) to investigate the uncertainties introduced on the exoplanet radius measurements by stellar granulation and oscillations. After modelling the solar variability with a Gaussian process, we find that the amplitude of solar oscillations and granulation is of order 100 ppm – similar to the depth of an Earth transit – and introduces a fractional uncertainty on the depth of transit of 0.73 per cent assuming four transits are observed over the mission duration. However, when we translate the depth measurement into a radius measurement of the planet, we find a much larger radius uncertainty of 3.6 per cent. This is due to a degeneracy between the transit radius ratio, the limb darkening, and the impact parameter caused by the inability to constrain the transit impact parameter in the presence of stellar variability. We find that surface brightness inhomogeneity due to photospheric granulation contributes a lower limit of only 2 ppm to the photometry in-transit. The radius uncertainty due to granulation and oscillations, combined with the degeneracy with the transit impact parameter, accounts for a significant fraction of the error budget of the PLATO mission, before detector or observational noise is introduced to the light curve. If it is possible to constrain the impact parameter or to obtain follow-up observations at longer wavelengths where limb darkening is less significant, this may enable higher precision radius measurements.

scholarly journals The effect of telescope aperture, scattered light and human vision on early measurements of sunspot and group numbers

2019 ◽  
Vol 488 (3) ◽  
pp. 3804-3809 ◽  
Author(s):  
Nina V Karachik ◽  
Alexei A Pevtsov ◽  
Yury A Nagovitsyn
Keyword(s):  
White Light ◽  
Scattered Light ◽  
Detection Threshold ◽  
Human Vision ◽  
Common Denominator ◽  
Average Intensity ◽  
Solar Dynamics Observatory ◽  
Small Aperture ◽  
Group Number ◽  
Solar Dynamics

ABSTRACT Early telescopic observations of sunspots were conducted with instruments of relatively small aperture. These instruments also suffered from a higher level of scattered light, and the human eye served as a ‘detector’. The eye’s ability to resolve small details depends on image contrast, and on average intensity variations smaller than ≈3 per cent contrast relative to background are not detected even if they are resolved by the telescope. Here we study the effect of these three parameters (telescope aperture, scattered light and detection threshold of human vision) on sunspot number, group number and area of sunspots. As an ‘ideal’ dataset, we employ white-light (pseudo-continuum) observations from the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory, and we model the appearance of sunspots by degrading the HMI images to corresponding telescope apertures with added scattered light. We discuss the effects of different parameters on sunspot counts and derive functional dependences, which could be used to normalize historical observations of sunspot counts to a common denominator.

Observations for the Role of Flux rope Eruption in a Geoeffective Solar Flare

2014 ◽  
Vol 4 (2) ◽  
pp. 555-564
Author(s):  
A.M Aslam
Keyword(s):  
Solar Flare ◽  
Flux Rope ◽  
Magnetic Configuration ◽  
Solar Dynamics Observatory ◽  
Multi Wavelength ◽  
Solar Dynamics ◽  
Halo Coronal Mass Ejection ◽  
Mass Ejection ◽  
The Waves

On September 24, 2011 a solar flare of M 7.1 class was released from the Sun. The flare was observed by most of the space and ground based observatories in various wavebands. We have carried out a study of this flare to understand its causes on Sun and impact on earth. The flare was released from NOAA active region AR 11302 at 12:33 UT. Although the region had already produced many M class flares and one X- class flare before this flare, the magnetic configuration was not relaxed and still continued to evolve as seen from HMI observations. From the Solar Dynamics Observatory (SDO) multi-wavelength (131 Ã…, 171 Ã…, 304 Ã… and 1600Ã…) observations we identified that a rapidly rising flux rope triggered the flare although HMI observations revealed that magnetic configuration did not undergo a much pronounced change. The flare was associated with a halo Coronal Mass Ejection (CME) as recorded by LASCO/SOHO Observations. The flare associated CME was effective in causing an intense geomagnetic storm with minimum Dst index -103 nT. A radio burst of type II was also recorded by the WAVES/WIND. In the present study attempt is made to study the nature of coupling between solar transients and geospace.

scholarly journals The Solar and Heliospheric Observatory

1984 ◽  
Vol 86 ◽  
pp. 155-158 ◽  
Author(s):  
Giancarlo Noci
Keyword(s):  
Solar Physics ◽  
Grazing Incidence ◽  
Spectral Irradiance ◽  
The Sun ◽  
Solar Dynamics Observatory ◽  
Solar Constant ◽  
Heliospheric Observatory ◽  
Explorer Mission ◽  
Solar Dynamics ◽  
Euv Spectrum

In the past years several space missions have been proposed for the study of the Sun and of the Heliosphere. These missions were intended to clarify various different aspects of solar physics. For example, the GRIST (Grazing Incidence Solar Telescope) mission was intended as a means to improve our knowledge of the upper transition region and low corona through the detection of the solar EUV spectrum with a spatial resolution larger than in previous missions; the DISCO (Dual Spectral Irradiance and Solar Constant Orbiter) and SDO (Solar Dynamics Observatory) missions were proposed to gat observational data about the solar oscillations better than those obtained from ground based instruments; the SOHO (Solar and Heliospheric Observatory) mission was initially proposed to combine the properties of GRIST with the study of the extended corona (up to several radii of heliocentric distance) by observing the scattered Ly-alpha and OVI radiation, which was also the basis of the SCE (Solar Corona Explorer) mission proposal; the development of the interest about the variability of the Sun, both in itself and for its consequences in the history of the Earth, led to propose observations of the solar constant (included in DISCO).

scholarly journals Multi-Stranded Coronal Loops: Quantifying Strand Number and Heating Frequency from Simulated Solar Dynamics Observatory (SDO) Atmospheric Imaging Assembly (AIA) Observations

Solar Physics ◽  
2021 ◽  
Vol 296 (6) ◽  
Author(s):  
Thomas Williams ◽  
Robert W. Walsh ◽  
Stephane Regnier ◽  
Craig D. Johnston
Keyword(s):  
Energy Content ◽  
Time Lag ◽  
Low Frequency ◽  
Building Blocks ◽  
Coronal Loops ◽  
Loop Model ◽  
Solar Dynamics Observatory ◽  
Heat Deposition ◽  
Total Energy Content ◽  
Solar Dynamics

AbstractCoronal loops form the basic building blocks of the magnetically closed solar corona yet much is still to be determined concerning their possible fine-scale structuring and the rate of heat deposition within them. Using an improved multi-stranded loop model to better approximate the numerically challenging transition region, this article examines synthetic NASA Solar Dynamics Observatory’s (SDO) Atmospheric Imaging Assembly (AIA) emission simulated in response to a series of prescribed spatially and temporally random, impulsive and localised heating events across numerous sub-loop elements with a strong weighting towards the base of the structure: the nanoflare heating scenario. The total number of strands and nanoflare repetition times is varied systematically in such a way that the total energy content remains approximately constant across all the cases analysed. Repeated time-lag detection during an emission time series provides a good approximation for the nanoflare repetition time for low-frequency heating. Furthermore, using a combination of AIA 171/193 and 193/211 channel ratios in combination with spectroscopic determination of the standard deviation of the loop-apex temperature over several hours alongside simulations from the outlined multi-stranded loop model, it is demonstrated that both the imposed heating rate and number of strands can be realised.

scholarly journals Some Anomalies in the Raman spectrum from laser-produced plasmas

1988 ◽  
Vol 6 (2) ◽  
pp. 287-294
Author(s):  
T. J. M. Boyd ◽  
G. A. Gardner ◽  
G. A. Coutts
Keyword(s):  
Raman Spectrum ◽  
Light Wave ◽  
Scattered Light ◽  
Thomson Scattering ◽  
Hot Electron ◽  
Conventional Theory ◽  
Suprathermal Electron ◽  
Suprathermal Electrons ◽  
Scattered Spectrum

Many experiments show features of the Raman spectrum at variance with the predictions of conventional theory. One persistent discrepancy, the cut-off in the spectrum of scattered light at about 1·5λ0, led Simon and Short to postulate that the scattered spectrum is not Raman light as such, but derives from enhanced Thomson scattering from plasmas in which a population of suprathermal electrons is present. We describe a set of simulations which model the propagation of a light wave through a plasma characterized by two electron temperatures with the hot electron fraction varying between 0 and 0·05. The results show that enhanced Thomson scattering will contribute to the spectra observed in some experiments at least and confirm the contention that the spectrum of the scattered light is not especially sensitive to the width of the suprathermal electron feature. We have also examined the effect of a finite quiver velocity on the enhanced Thomson spectrum as a function of the population of suprathermal electrons, in particular its effect on the wavelength bands.

scholarly journals Energetics of Hi-C EUV brightenings

2018 ◽  
Vol 615 ◽  
pp. A47 ◽  
Author(s):  
Srividya Subramanian ◽  
Vinay L. Kashyap ◽  
Durgesh Tripathi ◽  
Maria S. Madjarska ◽  
John G. Doyle
Keyword(s):  
High Resolution ◽  
Energy Loss ◽  
Extreme Ultraviolet ◽  
Thermal Structure ◽  
Emission Measure ◽  
Light Curves ◽  
Solar Dynamics Observatory ◽  
Differential Emission Measure ◽  
Dominant Mechanism ◽  
Solar Dynamics

We study the thermal structure and energetics of the point-like extreme ultraviolet (EUV) brightenings within a system of fan loops observed in the active region AR 11520. These brightenings were simultaneously observed on 2012 July 11 by the High-resolution Coronal (Hi-C) imager and the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). We identified 27 brightenings by automatically determining intensity enhancements in both Hi-C and AIA 193 Å light curves. The energetics of these brightenings were studied using the Differential Emission Measure (DEM) diagnostics. The DEM weighted temperatures of these transients are in the range log T(K) = 6.2−6.6 with radiative energies ≈1024−25 ergs and densities approximately equal to a few times 109 cm−3. To the best of our knowledge, these are the smallest brightenings in EUV ever detected. We used these results to determine the mechanism of energy loss in these brightenings. Our analysis reveals that the dominant mechanism of energy loss for all the identified brightenings is conduction rather than radiation.

scholarly journals Электрические токи в униполярных областях с разной скоростью затухания магнитного потока в пятне

2021 ◽  
Vol 117 (1) ◽  
pp. 29-37
Author(s):  
Юрий Фурсяк ◽  
Андрей Плотников ◽  
Валентина Абраменко
Keyword(s):  
Solar Dynamics Observatory ◽  
Solar Dynamics

Используя магнитографические данные прибора Helioseismic and Magnetic Imager (HMI) на борту космического аппарата Solar Dynamics Observatory (SDO), мы вычислили параметры магнитного поля и электрических токов для униполярных активных областей (АО) с низкой (≤ 2.1 × 1019 Мкс ч−1, всего исследовано 11 АО) и высокой (≥ 7.0 × 1019 Мкс ч−1, проанализиро-вано 5 АО) скоростью затухания магнитного потока в пятне. Получены следующие результаты: 1) чем сильнее локальные (мелкомасштабные) электрические токи в окрестности униполярного пятна, тем быстрее оно затухает; 2) распределенный (глобальный, крупномасштабный) электрический ток вокруг быстро затухающих пятен практически нулевой, и от него не приходится ожидать стабилизирующего воздействия на процесс распада пятна; 3) для четырех случаев медленно затухающих пятен выявлен ненулевой распределенный электрический ток величиной до 5.0 × 1012 А. Такой ток может оказывать стабилизирующее  действие на распад пятна. Таким образом, полученные нами результаты указывают на то, что электрические токи малых масштабов оказывают скорее деструктивное воздействие на пятно, а присутствие крупномасштабных токов может стабилизировать пятно. Однако данный механизм, по-видимому, не является единственным и доминирующим в процессах стабилизации пятен.

Sign in / Sign up

Export Citation Format

Share Document