Waves and Quasi-Periodic-Pulsations in Weak Active Solar Emissions

Author(s):  
Divya Oberoi ◽  
Atul Mohan ◽  
Surajit Mondal

<p>The presence of Quasi-periodic pulsations (QPPs) is found to be a common feature of flaring energy release processes on the Sun. They are observed all across the EM range from hard X-rays to radio and provide insights into the physical conditions in the coronal plasma and the processes involved in the generation of these waves and oscillations. There have been numerous observations of spatially resolved QPPs at higher energies, though there are fewer examples at radio frequencies. Spatially resolved observations of these phenomena are particularly rare at low radio frequencies and there are none which are associated with the weaker episodes of active emissions which are much more numerous and frequent. The key reason limiting such studies has been the lack of availability of spectroscopic snapshot images of sufficient quality to detect and characterise the low level changes in the morphology of the sources of active emissions. Together, the data from the Murchison Widefield Array (MWA), a SKA precursor, and an imaging pipeline developed to meet the specific needs of solar imaging, now meet this challenge and enable us to explore this rich and interesting science area. Our work has led to the discovery of several previously unknown phenomena - second-scale QPPs in the size and orientation of a type III source, with simultaneous QPPs in intensity; 30 s QPPs in the radio light curve of a type I emission source associated with active region loop hosting a transient brightening; and intermittent presence of an anti-correlation in the size and intensity of a type I noise storm source along with QPPs. In this presentation we will briefly summarise these recent results and discuss their implications.</p>

2011 ◽  
Vol 728 (2) ◽  
pp. L27 ◽  
Author(s):  
Divya Oberoi ◽  
Lynn D. Matthews ◽  
Iver H. Cairns ◽  
David Emrich ◽  
Vasili Lobzin ◽  
...  

1993 ◽  
Vol 137 ◽  
pp. 801-803
Author(s):  
V.V. Zharkova ◽  
V.A. Kobylinsky

Flares are very frequent phenomena on the sun and on other stars and are actively investigated with precise observational techniques. These studies are particularly stimulated by recent X-ray and UV observations on spacecraft (Skylab, SMM). From all these observations the flares on the sun and stars seem to be of the same physical nature but of different energetic power. A number of investigations devoted to comparison between the solar and stellar flares led to the conclusion that they have the similar mechanisms for the energy release and transport and for their manifestations in different ranges of electromagnetic radiation.The hydrogen emission is easy to observe in these events, and thus it is convenient for diagnostic analysis of physical conditions in the flares. However, the impulsive events were considered to be observed in X-rays so only. Zharkova & Kobylinsky (1992, 1993) have recently shown that the hydrogen continuous radiation of the solar flares is sensitive to the electron beam parameters. We also develop an approach to detection of the flares of non-thermal or thermal origin by observing the hydrogen Balmer and Pashen continuum emissions with high temporal resolution.


Author(s):  
S. S. Panini ◽  
S. Narendranath ◽  
P. Sreekumar ◽  
K. Sankarasubramanian

Soft X-ray spectroscopy of the Sun is an important tool to understand the coronal dynamics and composition. The solar coronal X-ray spectrum below 1 keV is the least explored with high-resolution spectroscopy. Recent observations with Hinode XRT using coarse spectroscopy along with high-resolution imaging have shown that abundances in the coronae have variability associated with structures on the Sun. Disk averaged abundances with better spectral resolution spectrometers show time variability associated with flares. Both spatial and temporal variabilities seem to be related to changes in the magnetic field topology. Understanding such short term variabilities is necessary to model the underlying dynamics and mixing of material between different layers of the Sun. A Sensitive high-resolution spectrometer that covers the range in plasma temperatures and emission line complexes would uniquely reveal the entire evolution of flares. We are investigating a design of a multi-layer mirror-based X-ray spectrograph in the spectral range from 0.5 to 7 keV. The instrument operates in four asynchronous spectral channels operating one at a time. The multi-layer mirror placed at the focus of a Wolter type I telescope reflects a narrow band X-rays to the CCD which is placed at Nasmyth defocus. Converging X-rays from the front end optics helps to increase the spectral range of each channel while preserving the spectral resolution. This design is estimated to achieve a spectral resolution of 20 eV in the spectral range of 0.5–7 keV. With such high spectral resolution, we can resolve individual spectral features e.g., 6.7 keV Fe complex which can be used to diagnose high-temperature transient plasma during flares. The instrument design estimated performance and the science capabilities of this instrument will be discussed in detail in the paper.


2000 ◽  
Vol 179 ◽  
pp. 263-264
Author(s):  
K. Sundara Raman ◽  
K. B. Ramesh ◽  
R. Selvendran ◽  
P. S. M. Aleem ◽  
K. M. Hiremath

Extended AbstractWe have examined the morphological properties of a sigmoid associated with an SXR (soft X-ray) flare. The sigmoid is cospatial with the EUV (extreme ultra violet) images and in the optical part lies along an S-shaped Hαfilament. The photoheliogram shows flux emergence within an existingδtype sunspot which has caused the rotation of the umbrae giving rise to the sigmoidal brightening.It is now widely accepted that flares derive their energy from the magnetic fields of the active regions and coronal levels are considered to be the flare sites. But still a satisfactory understanding of the flare processes has not been achieved because of the difficulties encountered to predict and estimate the probability of flare eruptions. The convection flows and vortices below the photosphere transport and concentrate magnetic field, which subsequently appear as active regions in the photosphere (Rust & Kumar 1994 and the references therein). Successive emergence of magnetic flux, twist the field, creating flare productive magnetic shear and has been studied by many authors (Sundara Ramanet al.1998 and the references therein). Hence, it is considered that the flare is powered by the energy stored in the twisted magnetic flux tubes (Kurokawa 1996 and the references therein). Rust & Kumar (1996) named the S-shaped bright coronal loops that appear in soft X-rays as ‘Sigmoids’ and concluded that this S-shaped distortion is due to the twist developed in the magnetic field lines. These transient sigmoidal features tell a great deal about unstable coronal magnetic fields, as these regions are more likely to be eruptive (Canfieldet al.1999). As the magnetic fields of the active regions are deep rooted in the Sun, the twist developed in the subphotospheric flux tube penetrates the photosphere and extends in to the corona. Thus, it is essentially favourable for the subphotospheric twist to unwind the twist and transmit it through the photosphere to the corona. Therefore, it becomes essential to make complete observational descriptions of a flare from the magnetic field changes that are taking place in different atmospheric levels of the Sun, to pin down the energy storage and conversion process that trigger the flare phenomena.


2013 ◽  
Vol 9 (S304) ◽  
pp. 180-186
Author(s):  
Luigi Spinoglio

AbstractVarious observational techniques have been used to survey galaxies and AGN, from X-rays to radio frequencies, both photometric and spectroscopic. I will review these techniques aimed at the study of galaxy evolution and of the role of AGNs and star formation as the two main energy production mechanisms. I will then present as a new observational approach the far-IR spectroscopic surveys that could be done with planned astronomical facilities of the next future, such as SPICA from the space and CCAT from the ground.


2012 ◽  
Vol 749 (2) ◽  
pp. 116 ◽  
Author(s):  
L. Colina ◽  
M. Pereira-Santaella ◽  
A. Alonso-Herrero ◽  
A. G. Bedregal ◽  
S. Arribas

2021 ◽  
pp. 2150015
Author(s):  
Emilio Enrietti ◽  
Marco Bechis ◽  
Giulia Nicolaci ◽  
Domenico Messina ◽  
Michele Reboli ◽  
...  

Introduction: Classification systems for femoral neck fractures are very helpful for surgeons in order to choose the correct treatment. The purpose of this study was to verify the reliability and reproducibility in the most used classifications for proximal medial femoral fracture: Garden and Pauwels classifications. Materials and methods: Five surgeons independently classified 82 intra-capsular femur fractures treated with 3 cannulated screws using Pauwels and Garden classifications measured on pre- and post-operatively X-Rays. Inter-observer agreement was calculated for both classifications using the multi-rater Fleiss’ kappa; intra-observer agreement from pre-operative to post-operative XRs for Pauwels classification was also calculated with the same method. Results: Only six cases of AVN were registered. The inter-observers agreement based on pre-operative X-rays was moderate for Pauwels classification ([Formula: see text] 0.528) and slightly lower for Garden classification ([Formula: see text] 0.448); but in the simplified Garden classification (type I and II not displaced vs type III and IV displaced) the agreement measured was almost perfect ([Formula: see text] 0.908). The intra-observer agreement for Pauwels classification was moderate ([Formula: see text] 0.456). All the results were statistically significant. Conclusions: This is the first study evaluating the Pauwels angle on both preoperative and postoperative X-rays to assess their reproducibility. Garden classification has a really high reliability and reproducibility in evaluating displaced and not displaced fractures and consequently can be helpful in choosing the correct treatment. Pauwels classification has a lower inter and intra-observer agreement.


1999 ◽  
Vol 170 ◽  
pp. 268-277 ◽  
Author(s):  
Dainis Dravins

AbstractWavelength positions of photospheric absorption lines may be affected by surface convection (stellar granulation). Asymmetries and wavelength shifts originate from correlated velocity and brightness patterns: rising (blueshifted) elements are hot (bright), and convective blueshifts result from a larger contribution of such blueshifted photons than of redshifted ones from the sinking and cooler (darker) gas. For the Sun, the effect is around 300 m s−1, expected to increase in F-type stars, and in giants. Magnetic fields affect convection and induce lineshift variations over stellar activity cycles. A sufficient measuring precision reveals also the temporal variability of line wavelengths (due to the evolution of granules on the stellar surface). A major future development to come from adaptive optics and optical interferometry will be the study of wavelength variations across spatially resolved stars, together with their spatially resolved time variability. Thus, precise radial velocities should soon open up new vistas in stellar atmospheric physics.


Author(s):  
Miriam Peña ◽  
Liliana Hernández-Martínez ◽  
Francisco Ruiz-Escobedo

Abstract The analysis of 20 years of spectrophotometric data of the double shell planetary nebula PM 1-188 is presented, aiming to determine the time evolution of the emission lines and the physical conditions of the nebula, as a consequence of the systematic fading of its [WC 10] central star whose brightness has declined by about 10 mag in the past 40 years. Our main results include that the [O iii], [O ii], [N ii] line intensities are increasing with time in the inner nebula as a consequence of an increase in electron temperature from 11 000 K in 2005 to more than 14 000 K in 2018, due to shocks. The intensity of the same lines are decreasing in the outer nebula, due to a decrease in temperature, from 13 000 K to 7000 K, in the same period. The chemical composition of the inner and outer shells was derived and they are similar. Both nebulae present subsolar O, S and Ar abundances, while they are He, N and Ne rich. For the outer nebula the values are 12+log He/H = 11.13 ± 0.05, 12+log O/H = 8.04 ± 0.04, 12+log N/H = 7.87 ± 0.06, 12+log S/H = 7.18 ± 0.10 and 12+log Ar = 5.33 ± 0.16. The O, S and Ar abundances are several times lower than the average values found in disc non-Type I PNe, and are reminiscent of some halo PNe. From high resolution spectra, an outflow in the N-S direction was found in the inner zone. Position-velocity diagrams show that the outflow expands at velocities in the −150 to 100 km s−1 range, and both shells have expansion velocities of about 40 km s−1.


2009 ◽  
Vol 5 (S264) ◽  
pp. 3-18 ◽  
Author(s):  
Ignasi Ribas

AbstractProper characterization of the host star to a planet is a key element to the understanding of its overall properties. The star has a direct impact through the modification of the structure and evolution of the planet atmosphere by being the overwhelmingly larger source of energy. The star plays a central role in shaping the structure, evolution, and even determining the mere existence of planetary atmospheres. The vast majority of the stellar flux is well understood thanks to the impressive progress made in the modeling of stellar atmospheres. At short wavelengths (X-rays to UV), however, the information is scarcer since the stellar emission does not originate in the photosphere but in the chromospheric and coronal regions, which are much less understood. The same can be said about particle emissions, with a strong impact on planetary atmospheres, because a detailed description of the time-evolution of stellar wind is still lacking. Here we review our current understanding of the flux and particle emissions of the Sun and low-mass stars and briefly address their impact in the context of planetary atmospheres.


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