The Sun as an X-ray star: Active region evolution, rotational modulation, and implications for stellar X-ray variability

AbstractOn the base of the 17 GHz radio maps of the Sun taken with the Nobeyama Radio Heliograph we estimate plasma parameters in the specific region of the sunspot atmosphere in the active region AR 11312. This region of the sunspot atmosphere is characterized by the depletion in coronal emission (soft X-ray and EUV lines) and the reduced absorption in the a chromospheric line (He I 1.083 μm). In the ordinary normal mode of 17 GHz emission the corresponding dark patch has the largest visibility near the central solar meridian. We infer that the reduced coronal plasma density of about ~ 5 × 10

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Magnetic Loop Models: from Sun to Stars

Symposium - International Astronomical Union ◽

10.1017/s0074180900182555 ◽

2004 ◽

Vol 219 ◽

pp. 529-540 ◽

Cited By ~ 1

Author(s):

M. Jardine ◽

A. Collier Cameron ◽

K. Wood ◽

J.-F. Donati

Keyword(s):

Recent Observation ◽

Magnetic Loop ◽

Doppler Imaging ◽

Magnetic Flux Density ◽

The Sun ◽

X Rays ◽

X Ray ◽

Magnetic Structures ◽

Rotation Rates ◽

Rotational Modulation

I review recent progress in determining the nature of the loop structures that form the coronae of solar-like stars. This progress has been driven by observational advances, in particular the new results from X-ray satellites (Chandra and XMM-Newton) and the availability of surface magnetograms from Zeeman-Doppler imaging. It is now clear that stars that are similar to the Sun in mass, but which rotate more rapidly, have a very different magnetic field structure. Their surfaces are more heavily spotted, with spots appearing at all latitudes, extending all the way up to the rotation pole. Their coronae are correspondingly much brighter in X-rays, containing plasma that is hotter and denser than on the Sun. In addition, stellar coronae can support massive co-rotating prominences out to many stellar radii. Recent efforts in modelling these magnetic structures are now bringing together both the surface magnetograms and also the coronal X-ray emission. The resulting coronal loop models show complex loop structures on all scales, with much of the X-ray emission coming from high latitudes where is does not suffer rotational self-eclipse. The observed high densities and X-ray emission measures are a natural consequence of the high magnetic flux density at the surface. The stripping of the corona due to centrifugal effects at high rotation rates can also explain the saturation and supersaturation of X-ray emission with increasing rotation rates, and the recent observation of a high rotational modulation in a supersaturated star.

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Slowly-Moving Disturbances in the X-Ray Corona

International Astronomical Union Colloquium ◽

10.1017/s0252921100065659 ◽

1979 ◽

Vol 44 ◽

pp. 276-277 ◽

Cited By ~ 2

Author(s):

D.M. Rust ◽

Z. Švestka

Keyword(s):

Active Region ◽

Solar Radius ◽

Central Point ◽

The Sun ◽

X Ray ◽

Quiescent Filament ◽

Coronal Structures

From 28 May through 27 November 1973, the S-054 X-ray telescope on Skylab took almost 1000 pictures of the Sun with exposure times (64 sec) long enough to show the faint structures of the inner corona. These pictures of the X-ray (≈ 2-54 Å) corona were made into a synoptic movie on which it is possible to see many variations in brightness and structure that escape notice in studies of individual images. In particular, the movie has led to the discovery of disturbances propagating with velocities under 100 km/sec and extending over distances of the order of one solar radius. The disturbances reveal themselves as brightened coronal structures at progressively greater distances from a central point, usually an active region with an activated or disappearing filament. In a number of cases these coronal brightenings were accompanied by quiescent filament disappearances.

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Recent High Resolution X-Ray Spectra of the Sun

International Astronomical Union Colloquium ◽

10.1017/s0252921100089922 ◽

1972 ◽

Vol 14 ◽

pp. 740-741

Author(s):

J. H. Parkinson ◽

K. Evans ◽

K. A. Pounds

Keyword(s):

High Resolution ◽

Active Region ◽

Wavelength Range ◽

South Australia ◽

Active Regions ◽

Effective Area ◽

Field Of View ◽

The Sun ◽

X Ray

New results are presented from high resolution Bragg crystal spectrometers flown in late 1970 on two Skylark rockets. The first instrument, launched on 24 November 1970 at 22 13 UT from Woomera, South Australia, contained two crystal spectrometers, each with an effective area of 50 cm2 and field collimation to 3’ FWHM. This instrument obtained the X-ray spectrum of the quiet corona in the wavelength range 5–14 Å. The second instrument was launched on 6 December 1970 at 11 13 UT from Sardinia, Italy, and contained four crystals of 6 cm2, each collimated to 4’ FWHM. This instrument was pointed at a non-flaring active region near N20 W40(McMath region 11060), and obtained an X-ray spectrum between 5 and 23 Å. This first use of a collimator to limit the field of view has considerably increased the spectral clarity compared with earlier observations by excluding the contributions of other active regions.

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A long-duration active region: Evolution and quadrature observations of ejective events

Proceedings of the International Astronomical Union ◽

10.1017/s174392131700028x ◽

2016 ◽

Vol 12 (S327) ◽

pp. 60-66

Author(s):

H. Cremades ◽

C. H. Mandrini ◽

M. C. López Fuentes ◽

L. Merenda ◽

I. Cabello ◽

...

Keyword(s):

Magnetic Field ◽

Remote Sensing ◽

Active Region ◽

Remote Sensing Data ◽

Time Interval ◽

The Sun ◽

Weather Forecasts ◽

Long Duration ◽

Triggering Mechanisms ◽

Region Evolution

AbstractUnknown aspects of the initiation, evolution, and associated phenomena of coronal mass ejections (CMEs), together with their capability of perturbing the fragile technological equilibrium on which nowadays society depends, turn them a compelling subject of study. While space weather forecasts are thus far not able to predict when and where in the Sun will the next CME take place, various CME triggering mechanisms have been proposed, without reaching consensus on which is the predominant one. To improve our knowledge in these respects, we investigate a long-duration active region throughout its life, from birth until decay along five solar rotations, in connection with its production of ejective events. We benefit from the wealth of solar remote-sensing data with improved temporal, spatial, and spectral resolution provided by the ground-breaking space missions STEREO, SDO, and SOHO. During the investigated time interval, which covers the months July – November 2010, the STEREO spacecraft were nearly 180 degrees apart, allowing for the uninterrupted tracking of the active region and its ensuing CMEs. The ejective aspect is examined from multi-viewpoint coronagraphic images, while the dynamics of the active region photospheric magnetic field are inspected by means of SDO/HMI data for specific subintervals of interest. The ultimate goal of this work in progress is to identify common patterns in the ejective aspect that can be connected with the active region characteristics.

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High Energy Exoplanet Transits

Proceedings of the International Astronomical Union ◽

10.1017/s1743921317004379 ◽

2016 ◽

Vol 12 (S328) ◽

pp. 356-362

Author(s):

Joe Llama ◽

Evgenya L. Shkolnik

Keyword(s):

Active Region ◽

Wavelength Range ◽

Solar Disk ◽

High Energy ◽

Activity Levels ◽

The Sun ◽

X Rays ◽

X Ray ◽

High Energies ◽

Wide Wavelength Range

AbstractX-ray and ultraviolet transits of exoplanets allow us to probe the atmospheres of these worlds. High energy transits have been shown to be deeper but also more variable than in the optical. By simulating exoplanet transits using high-energy observations of the Sun, we can test the limits of our ability to accurately measure the properties of these planets in the presence of stellar activity. We use both disk-resolved images of the Solar disk spanning soft X-rays, the ultraviolet, and the optical and also disk-integrated Sun-as-a-star observations of the Lyα irradiance to simulate transits over a wide wavelength range. We find that for stars with activity levels similar to the Sun, the planet-to-star radius ratio can be overestimated by up to 50% if the planet occults an active region at high energies. We also compare our simulations to high energy transits of WASP-12b, HD 189733, 55 Cnc b, and GJ 436b.

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Characteristics of Soft X-Ray Radiation of the Solar Active Region NOAA 1024 Registered by the PINGVIN-M Device in July 2009

Geomagnetism and Aeronomy ◽

10.1134/s001679322007021x ◽

2020 ◽

Vol 60 (7) ◽

pp. 936-941

Author(s):

M. I. Savchenko ◽

P. V. Vatagin ◽

P. B. Dmitriev ◽

M. G. Ogurtsov ◽

E. M. Kruglov ◽

...

Keyword(s):

Active Region ◽

Solar Active Region ◽

Active Region Noaa ◽

X Ray ◽

Region Noaa

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Energetics of magnetic transients in a solar active region plage

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834548 ◽

2019 ◽

Vol 623 ◽

pp. A176 ◽

Cited By ~ 3

Author(s):

L. P. Chitta ◽

A. R. C. Sukarmadji ◽

L. Rouppe van der Voort ◽

H. Peter

Keyword(s):

Magnetic Field ◽

Active Region ◽

Magnetic Flux ◽

Numerical Simulations ◽

Extreme Ultraviolet ◽

Spatial Scales ◽

Coronal Loops ◽

The Sun ◽

Flux Emergence ◽

Transient Events

Context. Densely packed coronal loops are rooted in photospheric plages in the vicinity of active regions on the Sun. The photospheric magnetic features underlying these plage areas are patches of mostly unidirectional magnetic field extending several arcsec on the solar surface. Aims. We aim to explore the transient nature of the magnetic field, its mixed-polarity characteristics, and the associated energetics in the active region plage using high spatial resolution observations and numerical simulations. Methods. We used photospheric Fe I 6173 Å spectropolarimetric observations of a decaying active region obtained from the Swedish 1-m Solar Telescope (SST). These data were inverted to retrieve the photospheric magnetic field underlying the plage as identified in the extreme-ultraviolet emission maps obtained from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). To obtain better insight into the evolution of extended unidirectional magnetic field patches on the Sun, we performed 3D radiation magnetohydrodynamic simulations of magnetoconvection using the MURaM code. Results. The observations show transient magnetic flux emergence and cancellation events within the extended predominantly unipolar patch on timescales of a few 100 s and on spatial scales comparable to granules. These transient events occur at the footpoints of active region plage loops. In one case the coronal response at the footpoints of these loops is clearly associated with the underlying transient. The numerical simulations also reveal similar magnetic flux emergence and cancellation events that extend to even smaller spatial and temporal scales. Individual simulated transient events transfer an energy flux in excess of 1 MW m−2 through the photosphere. Conclusions. We suggest that the magnetic transients could play an important role in the energetics of active region plage. Both in observations and simulations, the opposite-polarity magnetic field brought up by transient flux emergence cancels with the surrounding plage field. Magnetic reconnection associated with such transient events likely conduits magnetic energy to power the overlying chromosphere and coronal loops.

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Correlations of solar-flare electron events with radio and X-ray emission from the sun

Canadian Journal of Physics ◽

10.1139/p68-345 ◽

1968 ◽

Vol 46 (10) ◽

pp. S757-S760 ◽

Cited By ~ 7

Author(s):

R. P. Lin

Keyword(s):

Solar Flare ◽

Solar Radio ◽

Interplanetary Space ◽

The Sun ◽

Radio Bursts ◽

Radio Observations ◽

X Ray ◽

Type Iii ◽

Electron Event ◽

Burst Emission

The > 40-keV solar-flare electrons observed by the IMP III and Mariner IV satellites are shown to be closely correlated with solar radio and X-ray burst emission. In particular, intense type III radio bursts are observed to accompany solar electron-event flares. The energies of the electrons, the total number of electrons, and the size of the electron source at the sun can be inferred from radio observations. The characteristics of the electrons observed in interplanetary space are consistent with these radio observations. Therefore these electrons are identified as the exciting agents of the type III emission. It has been noted that the radio and X-ray bursts are part of the flash phase of flares. The observations indicate that a striking feature of the flash phase is the production of electrons of 10–100 keV energies.

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Hydrodynamic Models of Solar and Stellar Flares

International Astronomical Union Colloquium ◽

10.1017/s0252921100031948 ◽

1989 ◽

Vol 104 (1) ◽

pp. 289-298

Author(s):

Giovanni Peres

Keyword(s):

High Resolution ◽

Light Curve ◽

Solar Flares ◽

Impulsive Phase ◽

Light Curves ◽

Physical Parameters ◽

The Sun ◽

Hydrodynamic Models ◽

X Ray ◽

Stellar Flares

AbstractThis paper discusses the hydrodynamic modeling of flaring plasma confined in magnetic loops and its objectives within the broader scope of flare physics. In particular, the Palermo-Harvard model is discussed along with its applications to the detailed fitting of X-ray light curves of solar flares and to the simulation of high-resolution Caxix spectra in the impulsive phase. These two approaches provide complementary constraints on the relevant features of solar flares. The extension to the stellar case, with the fitting of the light curve of an X-ray flare which occurred on Proxima Centauri, demonstrates the feasibility of using this kind of model for stars too. Although the stellar observations do not provide the wealth of details available for the Sun, and, therefore, constrain the model more loosely, there are strong motivations to pursue this line of research: the wider range of physical parameters in stellar flares and the possibility of studying further the solar-stellar connection.

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