In the present work, we perform time-series analysis on the latitude bins of the solar full disk (SFD) images of Nobeyama Radioheliograph (NoRH) at 17 GHz. The flux modulation method traces the passage of radio features over the solar disc and the autocorrelation analysis of the time-series data of SFD images (one per day) for the period 1999-2001 gives the rotation period as a function of latitude extending from 60 degree S to 60 degree N. The results show that the solar corona rotates less differentially than the photosphere and chromosphere, i.e., it has smaller gradient in the rotation rate.
For the period of 1997-2006, coronal holes detected in the SOHO/EIT 195 $Å$ full disk calibrated images are used to compute the rotation rates of high latitude and near polar coronal holes and, their latitudinal variation is investigated. We find that, for different latitude zones between $80^{o}$ north and $75^{o}$ south, for all their area, the number of days observed on the solar disk, and their latitudes, coronal holes rotate rigidly. Estimated magnitudes of sidereal rotation rate of the coronal holes are: $13.051 \pm 0.206$ deg/day for the equator, $12.993 \pm 0.064$ deg/day in the region…
Strong coronal magnetic field, when present, manifests itself as bright microwave sources at high frequencies produced by gyroresonant (GR) emission mechanism in thermal coronal plasma. The highest frequency at which this emission is observed is proportional to the absolute value of the strongest coronal magnetic field on the line of sight. Although no coronal magnetic field larger than roughly 2,000 G was expected, recently the field at least twice larger has been reported. Here, we report a search for and statistical study of such strong coronal magnetic fields using high-frequency GR emissi…
In this article, we report an evidence of very high and statistically significant relationship between hemispheric asymmetry in solar coronal rotation rate and solar activity. Our approach is based on cross correlation of hemispheric asymmetry index (AI) in rotation rate with annual solar activity indicators. To obtain hemispheric asymmetry in solar rotation rate, we use solar full disc (SFD) images at 30.4 nm, 19.5 nm, and 28.4 nm wavelengths for 24th Solar Cycle i.e., for the period from 2008 to 2018, as recorded by the Solar Terrestrial Relations Observatory (STEREO) space mission. Our anal…
Magnetic fields and differential rotation on the pre-main sequence II: The early-G star HD 141943 - coronal magnetic field, H-alpha emission and differential rotation
Early Evolution of Earth-Directed Coronal Mass Ejections in the Vicinity of Coronal Holes
Hvar Observatory, Faculty of Geodesy, University of Zagreb（萨格勒布大学测地学院哈弗观测台）；Institute of Physics, University of Graz（格拉茨大学物理研究所）；Department of Physics, University of Helsinki（赫尔辛基大学物理系）；Max-Planck-Institut für Sonnensystemforschung（马克斯·普朗克太阳系统研究所）
In-situ measurements by several spacecraft have revealed that the solar wind is frequently perturbed by transient structures (magnetic folds, jets, waves, flux-ropes) that propagate rapidly away from the Sun over large distances. Parker Solar Probe has detected frequent rotations of the magnetic field vector at small heliocentric distances, accompanied by surprisingly large solar wind rotation rates. The physical origin of such magnetic field bends, the conditions for their survival across the interplanetary space, and their relation to solar wind rotation are yet to be clearly understood. We …
We studied the characteristic physical properties and behavior of broadband microwave sub-second pulsations observed in an expanding coronal loop during the GOES C2.4 solar flare on 2011 August 10. We found sub-second pulsations and other different burst groups in the complex radio spectrum. The broadband (bandwidth about 1 GHz) sub-second pulsations (temporal period range 0.07-1.49 s, no characteristic dominant period) lasted 70 s in the frequency range 4-7 GHz. These pulsations were not correlated at their individual frequencies, had no measurable frequency drift, and zero polarization. In t…
We analyzed the band splitting of a Type II radio burst observed on 1997 May 12 by ground- and space-based radio spectrometers. Type II radio emission is the most evident signature of coronal shock waves and the observed band splitting is generally interpreted as due to plasma emission from both upstream and downstream shock regions. From the inferred compression ratio we estimated, using the magnetohydrodynamic (MHD) Rankine-Hugoniot relations, the ambient Alfven Mach number. By means of the electron density obtained by inverting white-light polarized brightness (pB) coronagraph data and the …
The Decline and Fall of ROME. V. A Preliminary Search for Star-Disrupted Planet Interactions and Coronal Activity at 5 GHz Among White Dwarfs within 25 pc
Context: The fast rotator, pre-main sequence star AB Dor A is a strong and persistent radio emitter. The extraordinary coronal flaring activity is thought to be the origin of compact radio emission and other associated phenomena as large slingshot prominences. Aim: We aim to investigate the radio emission mechanism and the milliarcsecond radio structure around AB Dor A. Methods: We performed phase-referenced VLBI observations at 22.3 GHz, 8.4 GHz, and 1.4 GHz over more than one decade using the Australian VLBI array. Results: Our 8.4 GHz images show a double core-halo morphology, similar at al…
Searching for rotational X-ray modulation on TIC 277539431
Leibniz Institute for Astrophysics Potsdam (AIP)（波茨坦莱布尼茨天体物理研究所）；Universität Potsdam（波茨坦大学）；Netherlands Institute for Radio Astronomy, ASTRON（荷兰射电天文研究所）
Context. It is possible to detect and track coronal bright points (CBPs) in SDO/AIA images. Combination of high resolution and high cadence provides a wealth of data that can be used to determine velocity flows on the solar surface with very high accuracy. Aims. We derived a very accurate solar rotation profile and investigated meridional flows, torsional oscillations and horizontal Reynolds stress based on $\approx$6 months of SDO/AIA data. Methods. We used a segmentation algorithm to detect CBPs in SDO/AIA images. We also used invariance of the solar rotation profile with central meridian di…
Supra-arcade downflows (SADs) are infrequent, wiggly opaque structures observed to descend through the solar corona, mostly in EUV and soft X-ray frequencies. From their physical characteristics, SADs have been interpreted as voided (subdense) bubbles and are related to magnetic reconnection processes during long-term erupting flares. In this work we use numerical MHD simulations to compute flux density maps, which are convolved with telescope beams to synthesise images with the aim to assess the expected SADs emission at radio wavelengths and propose observing strategies, including the instru…
Information on the rotation rate of the corona, and its variation over latitude and solar cycle, is valuable for making global connections between the corona and the Sun, for global estimates of reconnection rates, and as a basic parameter for solar wind modelling. Here, we use a time series of tomographical maps gained from coronagraph observations between 2007 - 2020 to directly measure the longitudinal drift of high-density streamers over time. The method reveals abrupt changes in rotation rates, revealing a complex relationship between the coronal rotation and the underlying photosphere. T…
