Bright Regions Research Articles

The magnetic field and accretion regime of CI Tau

ABSTRACT This paper exploits spectropolarimetric data of the classical T Tauri star CI Tau collected with ESPaDOnS at the Canada–France–Hawaii Telescope, with the aims of detecting and characterizing the large-scale magnetic field that the star hosts, and of investigating how the star interacts with the inner regions of its accretion disc through this field. Our data unambiguously show that CI Tau has a rotation period of 9.0 d, and that it hosts a strong, mainly poloidal large-scale field. Accretion at the surface of the star concentrates within a bright high-latitude chromospheric region that spatially overlaps with a large dark photospheric spot, in which the radial magnetic field reaches −3.7 kG. With a polar strength of −1.7 kG, the dipole component of the large-scale field is able to evacuate the central regions of the disc up to about 50 per cent of the co-rotation radius (at which the Keplerian orbital period equals the stellar rotation period) throughout our observations, during which the average accretion rate was found to be unusually high. We speculate that the magnetic field of CI Tau is strong enough to sustain most of the time a magnetospheric gap extending to at least 70 per cent of the co-rotation radius, which would explain why the rotation period of CI Tau is as long as 9 d. Our results also imply that the 9 d radial velocity (RV) modulation that CI Tau exhibits is attributable to stellar activity, and thus that the existence of the candidate close-in massive planet CI Tau b to which these RV fluctuations were first attributed needs to be reassessed with new evidence.

Imaging relative stasis of the blood column in human retinal capillaries.

Capillary flow largely consists of alternating red cells and plasma whose speed oscillates predictably with the cardiac cycle. Superimposed on this regular background are sporadic events potentially disruptive to capillary exchange: the passage of white cells, aggregates of red cells, epochs of sparse haematocrit, or unusually slow flow. Such events are not readily differentiated with velocimetry or perfusion mapping. Here we propose a method to identify these phenomena in retinal capillaries imaged with high frame-rate adaptive optics, by calculating and representing pictorially the autocorrelation of intensity through time at each pixel during short epochs. The phenomena described above manifest as bright regions which transiently appear and propagate across an otherwise dark image. Drawing data from normal subjects and those with Type I diabetes, we demonstrate proof of concept and high sensitivity and specificity of this metric to variations in capillary contents and rate of flow in health and disease. The proposed metric offers a useful adjunct to velocimetry and perfusion mapping in the study of normal and abnormal capillary blood flow.

Radio emission from interstellar shocks: Young type Ia supernova remnants and the case of N 103B in the Large Magellanic Cloud

Here we present a radio continuum study based on new and archival data from the Australia Telescope Compact Array towards N 103B, a young (<=1000 yrs) spectroscopically confirmed type Ia SNR in the Large Magellanic Cloud (LMC) and proposed to have originated from a single degenerate progenitor. The radio morphology of this SNR is asymmetrical with two bright regions towards the north-west and south-west of the central location as defined by radio emission. N 103B identified features include: a radio spectral index of -0.75+-0.01 (consistent with other young type Ia SNRs in the Galaxy); a bulk SNR expansion rate as in X-rays; morphology and polarised electrical field vector measurements where we note radial polarisation peak towards the north-west of the remnant at both 5500 and 9000 MHz. The spectrum is concave-up and the most likely reason is the non-linear diffusive shock acceleration effects or presence of two different populations of ultra-relativistic electrons. We also note unpolarized clumps near the south-west region which is in agreement with this above scenario. We derive a typical magnetic field strength for N 103B, of 16.4 microG for an average rotation measurement of 200 rad m^-2. However, we estimate the equipartition field to be of the order of ~235 microG with an estimated minimum energy of Emin=6.3*10^48 erg. The close (~0.5 degree) proximity of N 103B to the LMC mid-plane indicates that an early encounter with dense interstellar medium may have set an important constrain on SNR evolution. Finally, we compare features of N 103B, to six other young type Ia SNRs in the LMC and Galaxy, with a range of proposed degeneracy scenarios to highlight potential differences due to a different models. We suggest that the single degenerate scenario might point to morphologically asymmetric type Ia supernova explosions.

Spectral Analysis of the Dynamic Behavior of a Welding Arc During Pulsed Gas Metal Arc Welding of AA5083 Aluminum Alloy With ER5183 Wire

The dynamic behavior of an arc plasma involves the complex heat and mass transfer process in the arc welding process, especially for pulsed gas metal arc welding (P-GMAW). The spectral diagnostics of the arc plasma is essential to both the validation of simulation results and the monitoring and control of the arc welding process. In this article, we studied the dynamic behavior and spatial spectral characteristics of the welding arc during the pulsed gas metal arc welding of the AA5083 aluminum alloy with an ER5183 wire using a high-speed camera and spectrometer. Based on the acquired spectra at different time points of the pulse, we calculated the plasma characteristics using the spectral lines emitted from the shielding gas and the metal vapor. The variation and spectral diagnosis of the arc indicated that the bright region was mainly caused by radiation from the metal vapor, which easily increased at the peak current. The measured arc temperature and electron density were elevated along with the welding current. Moreover, the ratio of metal vapor in the arc plasma also increased due to strengthened evaporation from the electrode. Along the horizontal axis, the arc temperature increased and reached a maximum in the central part of the arc. There was a potential local minimum near the electrode as the current increased. The drop of temperature near the electrode was mainly caused by the rapid evaporation and cooling effects of metal vapor.

Origin of hydrogen fluoride emission in the Orion Bar

Context. The hydrogen fluoride (HF) molecule is seen in absorption in the interstellar medium (ISM) along many lines of sight. Surprisingly, it is observed in emission toward the Orion Bar, which is an interface between the ionized region around the Orion Trapezium stars and the Orion molecular cloud. Aims. We aim to understand the origin of HF emission in the Orion Bar by comparing its spatial distribution with other tracers. We examine three mechanisms to explain the HF emission: thermal excitation, radiative dust pumping, and chemical pumping. Methods. We used a Herschel/HIFI strip map of the HF J = 1 → 0 line, covering 0.5′ by 1.5′ that is oriented perpendicular to the Orion Bar. We used the RADEX non-local thermodynamic equilibrium (non-LTE) code to construct the HF column density map. We use the Meudon PDR code to explain the morphology of HF. Results. The bulk of the HF emission at 10 km s−1 emerges from the CO-dark molecular gas that separates the ionization front from the molecular gas that is deeper in the Orion Bar. The excitation of HF is caused mainly by collisions with H2 at a density of 105 cm−3 together with a small contribution of electrons in the interclump gas of the Orion Bar. Infrared pumping and chemical pumping are not important. Conclusions. We conclude that the HF J = 1 → 0 line traces CO-dark molecular gas. Similarly, bright photodissociation regions associated with massive star formation may be responsible for the HF emission observed toward active galactic nuclei.

The Variability of Solar Coronal Abundances in Active Regions and the Quiet Sun

Abstract Measurements of elemental abundances hold important clues to how mass and energy flow through the solar atmosphere. Variations in abundances are organized by an element’s first ionization potential (FIP), and many previous studies have assumed that low FIP (less than 10 eV) elements are enriched by a factor of 3–4 in the corona. In this paper, we use spatially resolved observations from the Extreme-ultraviolet Imaging Telescope on board the Hinode spacecraft to examine the spatial variability of elemental abundance in and around active regions. We find substantial variations within some active regions. In general, however, we find that the enrichment of low FIP elements is limited to bright, active region structures. In faint active region structures and in the dark, quiet regions around active regions, the measured abundances are close to photospheric. These measurements use the ratio of low FIP Si to high FIP S. Similar conclusions concerning quiet Sun regions have been reached recently by Del Zanna using full-Sun spectra. He has found that the coronal quiet Sun (at temperatures greater than 1 MK) has photospheric abundances. Transition region abundances (at temperatures less than 1 MK in the solar atmosphere) have been found to be photospheric. These results and results from this paper suggest that a coronal composition is not a general property of million-degree plasma, but is limited to bright active region loops, and is variable.

Luminescence properties of reddish orange emitting BaLa2ZnO5:Sm3+ phosphor prepared by citric based sol-gel synthesis

A series of BaLa2ZnO5:Sm3+ phosphors were synthesized with the sol-gel technique. The crystalline structure of each sample was characterized by X-ray diffraction (XRD). Phase formation was investigated using scanning electron microscope (SEM). Photoluminescence studies revealed an efficient excitation of phosphors at near blue light (~410 nm), providing emission in the bright reddish-orange region (603 nm). Concentration quenching through multipolar interaction was observed in BaLa2ZnO5 phosphor system doped with 0.015 mol of Sm3+ concentration. The optimum phosphor showed prominent characteristics for application in white LEDs.

High contrast mechanochromic luminescence of aggregation-induced emission (AIE)-based 9,9-dimethyl-9,10-dihydroacridine-containing cruciform luminophores

Two twisted D–A type cruciform luminophores DMTCS-AC and DBTCS-AC displaying rigid cross-conjugated structures with two conjugated donor and acceptor moieties intersecting at the central benzene core have been synthesized. Due to the existence of electron donor 9,9-dimethyl-9,10-dihydroacridine and electron acceptor dicyanodistyrylbenzene, both cruciforms show unique intramolecular charge transfer (ICT) emission. Moreover, both DMTCS-AC and DBTCS-AC bear highly twisted molecular conformations, which endow them with obvious aggregation-induced emission (AIE) properties and high contrast mechanofluorochromic (MFC) behavior. Under external force stimuli, the emissions of DMTCS-AC and DBTCS-AC powders changes from initial bright orange regions (586 nm and 599 nm) to the final red region (655 nm) and far red/near-infrared (FR/NIR) region (678 nm). PXRD and spectral results suggest that the remarkable MFC phenomenon originates from extension of the planarization of molecular conformation and subsequent planar intramolecular charge transfer (PICT) during the process of destruction of the crystals in the as-prepared original samples by external force. Moreover, the more significant MFC behavior of DBTCS-AC relative to DMTCS-AC is due to its the larger distortion degree and the stronger ICT process than that of DBTCS-AC.

Infrared Interferometric Three-dimensional Diagnosis of the Atmospheric Dynamics of the AGB Star R Dor with VLTI/AMBER*

Abstract The mechanism of mass loss in late evolutionary stages of low- and intermediate-mass stars is not yet well understood. Therefore, it is crucial to study the dynamics of the region within a few R ⋆, where the wind acceleration is considered to take place. We present a three-dimensional diagnosis of the atmospheric dynamics of the closest asymptotic giant branch star R Dor from the low photospheric layers to the extended outer atmosphere, for the first time for a star other than the Sun. The images reconstructed with a spatial resolution of 6.8 mas—seven times finer than the star’s angular diameter of 51.2 mas in the continuum—using the AMBER instrument at the Very Large Telescope Interferometer show a large, bright region over the surface of the star and an extended atmosphere. The velocity-field maps over the star’s surface and atmosphere obtained from the Mg and H2O lines near 2.3 μm forming at atmospheric heights below ∼1.5 R ⋆ show little systematic motion beyond the measurement uncertainty of 1.7 km s−1. In marked contrast, the velocity-field map obtained from the CO first overtone lines reveals systematic outward motion at 7–15 km s−1 in the extended outer atmosphere at a height of ∼1.8 R ⋆. Given the detection of dust formation at ∼1.5 R ⋆, the strong acceleration of material between ∼1.5 and 1.8 R ⋆ may be caused by the radiation pressure on dust grains. However, we cannot yet exclude the possibility that the outward motion may be intermittent, caused by ballistic motion due to convection and/or pulsation.

Spectral variations of Lyman $\alpha$ emission within strongly lensed sources observed with MUSE

ABSTRACT We present an analysis of ${\rm H\,\rm{\small {I}}}$ Lyman $\alpha$ emission in deep VLT/MUSE observations of two highly magnified and extended galaxies at $z=3.5$ and 4.03, including a newly discovered, almost complete Einstein ring. While these Lyman $\alpha$ haloes are intrinsically similar to the ones typically seen in other MUSE deep fields, the benefits of gravitational lensing allow us to construct exceptionally detailed maps of Lyman $\alpha$ line properties at sub-kpc scales. By combining all multiple images, we are able to observe complex structures in the Lyman $\alpha$ emission and uncover small ($\sim120$ km s−1 in Lyman $\alpha$ peak shift), but significant at $ \gt $4 $\sigma$, systematic variations in the shape of the Lyman $\alpha$ line profile within each halo. Indeed, we observe a global trend for the line peak shift to become redder at large radii, together with a strong correlation between the peak wavelength and line width. This systematic intrahalo variation is markedly similar to the object-to-object variations obtained from the integrated properties of recent large samples. Regions of high surface brightness correspond to relatively small line shifts, which could indicate that Lyman $\alpha$ emission escapes preferentially from regions where the line profile has been less severely affected by scattering of Lyman $\alpha$ photons.

Influence of Mg on Micro-Mechanical Behaviour of as Cast Al–Mg System

In the present work, a study was carried out for various possible Mg concentrations in order to optimize Mg amount in Al–Mg system as far as metallurgical and mechanical properties are concerned. In molten Al, variations of amount of Mg were made from 0.05–7 wt % Mg using a resistance heating furnace. Intermetallics like Al–Mg, Mg–Si, Al–Si, etc.,—were formed at processing temperature. During solidification, these intermetallics were pushed towards the grain boundaries and formed clusters, which was studied using SEM–EDS analysis. Heavier phases revealed as dark regions whereas lighter phases as less dark or bright regions. Due to such pushing effects of intermetallics during solidifications of bath in metallic die, development of grain boundaries started in the form of remarkable thickening of it into the Al matrix. This phenomenon was found to be more pronounced, as the Mg concentration was increased. Hence, in case of 7 wt % Mg, it was found that maximum amount of intermetallics gathered at grain boundaries. Segregation tendencies of various intermetallics and excess free Mg were found non uniform for a higher range of Mg. Ultimate tensile strength, specific strength, and hardness properties were studied and they were found to be highest in Al–3 wt % Mg system along with low density and ductility values. Therefore, in the present study, 3 wt % Mg is considered to be an optimum level of Mg concentration based on its micro-mechanical behaviour.

Building Detection in SAR Images Based on Bi-Dimensional Empirical Mode Decomposition Algorithm

This letter proposes a new synthetic aperture radar (SAR) image building detection method based on the bi-dimensional empirical mode decomposition (BEMD) algorithm, well adapted to nonlinear and nonstationary signals. First, the SAR image is decomposed by the BEMD algorithm to generate intrinsic mode functions (IMFs), and the IMFs are combined to extract bright regions and dark regions from the SAR image. Next, the Markov random field (MRF) model is used to cluster the SAR image, and according to the centroid of the dark region, the dark category with a complete edge is located. Finally, the building is detected by combining the bright region, the dark region, and the given shadow direction. Analytical and experimental evidence show that the proposed method has high detection accuracy and has wide applicability for medium, large, and irregular shaped buildings with shadows.

Identification and Separation of Turbulence Echo From the Multipeaked VHF Radar Spectra During Precipitation

This paper describes an automated data processing algorithm to identify the turbulence echo in the multipeaked very high-frequency radar spectra, generally observed during the precipitation. Although a few multipeak-picking algorithms exist, they identify the turbulence echo from the clutter and noise, but they do not distinguish turbulence and precipitation echoes. The present algorithm identifies the turbulence echo from multiple peaks based on several criteria, such as the significance of the echoes, separation between the echoes within a sliding window, and a reference turbulence echo. A new method [symmetric method (SM)] is introduced to estimate the moments after proper identification of the turbulence echo, in fact, half portion of the echo. Comparison of the moments estimated by the SM and dual-frequency method (another popular method for the extraction of moments from multipeaked spectra) with those obtained by the routine single-peak detection algorithm reveals large discrepancies, particularly in convective cores and in and above the radar bright band region. In these regions, the error in moments by the traditional single-peak-picking algorithm is found to be substantial. Performance evaluation of these two methods has also been carried out against simulated spectra. The analysis reveals that the error in obtaining moments by the SM and dual-frequency method is less than 15%, except for a few cases. Also, the error in moments by the SM is, in general, smaller than by the dual-frequency method.

Revisiting the Fanaroff–Riley dichotomy and radio-galaxy morphology with the LOFAR Two-Metre Sky Survey (LoTSS)

Abstract The relative positions of the high and low surface brightness regions of radio-loud active galaxies in the 3CR sample were found by Fanaroff and Riley to be correlated with their luminosity. We revisit this canonical relationship with a sample of 5805 extended radio-loud active galactic nuclei (AGN) from the LOFAR Two-Metre Sky Survey (LoTSS), compiling the most complete data set of radio-galaxy morphological information obtained to date. We demonstrate that, for this sample, radio luminosity does not reliably predict whether a source is edge-brightened (FRII) or centre-brightened (FRI). We highlight a large population of low-luminosity FRIIs, extending three orders of magnitude below the traditional FR break, and demonstrate that their host galaxies are on average systematically fainter than those of high-luminosity FRIIs and of FRIs matched in luminosity. This result supports the jet power/environment paradigm for the FR break: low-power jets may remain undisrupted and form hotspots in lower mass hosts. We also find substantial populations that appear physically distinct from the traditional FR classes, including candidate restarting sources and ‘hybrids’. We identify 459 bent-tailed sources, which we find to have a significantly higher SDSS cluster association fraction (at z &amp;lt; 0.4) than the general radio-galaxy population, similar to the results of previous work. The complexity of the LoTSS faint, extended radio sources not only demonstrates the need for caution in the automated classification and interpretation of extended sources in modern radio surveys, but also reveals the wealth of morphological information such surveys will provide and its value for advancing our physical understanding of radio-loud AGN.

Solid-state phase transformation of TC11 titanium during unstable thermal cycling in laser melting deposition process

Thermal cycling procedure during laser additive manufacturing (LAM) process causes the appearance of bright and dark patterns on the etched surface of TC11 alloy components. The formation mechanisms of these patterns and the solid-state transformation related to LAM process are systematically investigated with the predication of temperature fields using the finite element software ABAQUS. The results indicate that by increasing subsequent thermal cycles, the peak temperatures for every cycle decrease. When peak temperatures are above Tβ (phase transition temperature of β phase), which is 1010 °C in TC11 alloy, no pattern is observed. Meanwhile, a decrease in peak temperature leads to appearance of an ultra-fine basket-weave α + β microstructure (dark contrast) with gradually increased amount of α colonies in the alloy. A special bimodal microstructure with ‘fork-like’ α lamella appears in the layer when the peak temperatures of thermal cycles firstly fall into α + β dual-phase region. And this special bimodal microstructure gives a bright contrast and only appears at the region where the peak temperatures are below 970 °C, leaving the rest region with a dark contrast. With the continuous increase in thermal cycles in α + β dual-phase region, α lamella gradually coarsens. After five thermal cycles in α + β two-phase region, no further changes in microstructure are observed, and the morphologies of α lamella in dark and bright regions are almost the same but with different amounts of α phase.

The Fornax3D project: Tracing the assembly history of the cluster from the kinematic and line-strength maps

The 31 brightest galaxies (mB ≤ 15 mag) inside the virial radius of the Fornax cluster were observed from the centres to the outskirts with the Multi Unit Spectroscopic Explorer on the Very Large Telescope. These observations provide detailed high-resolution maps of the line-of-sight kinematics, line strengths of the stars, ionised gas reaching 2–3 Re for 21 early-type galaxies, and 1–2 Re for 10 late-type galaxies. The majority of the galaxies are regular rotators, with eight hosting a kinematically distinct core. Only two galaxies are slow rotators. The mean age, total metallicity, and [Mg/Fe] abundance ratio in the bright central region inside 0.5 Re and in the galaxy outskirts are presented. Extended emission-line gas is detected in 13 galaxies, most of them are late-type objects with wide-spread star formation. The measured structural properties are analysed in relation to the galaxies’ position in the projected phase space of the cluster. This shows that the Fornax cluster appears to consist of three main groups of galaxies inside the virial radius: the old core; a clump of galaxies, which is aligned with the local large-scale structure and was accreted soon after the formation of the core; and a group of galaxies that fell in more recently.

An in vivo study of ultrasonic monitoring imaging of microwave ablation based on Nakagami statistic parameter

This paper explored the feasibility of using ultrasonic Nakagami statistic parameter imaging to evaluate the thermal lesion induced by microwave ablation (MWA) in porcine models. In this paper, thermal lesions were induced in livers and kidneys in 5 swines using a clinical MWA system. During this treatment progress, ultrasonic radiofrequency (RF) data were collected. The dynamic changes of Nakagami parameter in the thermal lesion were calculated, and the ultrasonic B-mode images and Nakagami images were reconstructed simultaneously. The contrast-to-noise ratio (CNR) between the thermal lesion and the surrounding normal tissue was calculated over the MWA procedure. After MWA, a bright hyperechoic region appeared in the ultrasonic Nakagami image as an indicator of the thermal lesion and this bright spot enlarged with lesion development during MWA exposure. The mean value of Nakagami parameter in the liver and kidney increased from 0.78 and 0.79 before treatment to 0.91 and 0.92 after treatment, respectively. During MWA exposure, the mean values of CNR calculated from the Nakagami parameter increased from 0.49 to 1.13 in the porcine liver and increased from 0.51 to 0.85 in the kidney, which were both higher than those calculated from the B-mode images. This in vivo study on porcine models suggested that the ultrasonic Nakagami imaging may provide an alternative modality for monitoring MWA treatment.

Spatially Resolved Stellar Populations and Kinematics with KCWI: Probing the Assembly History of the Massive Early-type Galaxy NGC 1407

Abstract Using the newly commissioned Keck Cosmic Web Imager (KCWI) instrument on the Keck II telescope, we analyze the stellar kinematics and stellar populations of the well-studied massive early-type galaxy (ETG) NGC 1407. We obtained high signal-to-noise integral field spectra for a central and an outer (around one effective radius toward the southeast direction) pointing with integration times of just 600 s and 2400 s, respectively. We confirm the presence of a kinematically distinct core also revealed by VLT/MUSE data of the central regions. While NGC 1407 was previously found to have stellar populations characteristic of massive ETGs (with radially constant old ages and high alpha-enhancements), it was claimed to show peculiar supersolar metallicity peaks at a large radius that deviated from an otherwise strong negative metallicity gradient, which is hard to reconcile within a “two-phase” formation scenario. Our outer pointing confirms the near-uniform old ages and the presence of a steep metallicity gradient, but with no evidence for anomalously high metallicity values at large galactocentric radii. We find a rising outer velocity dispersion profile and high values of the fourth-order kinematic moment—an indicator of possible anisotropy. This coincides with the reported transition from a bottom-heavy to a Salpeter initial mass function, which may indicate that we are probing the transition region from the “in situ” to the accreted phase. With short exposures, we have been able to derive robust stellar kinematics and stellar populations in NGC 1407 to ∼1 effective radius. This experiment shows that future work with KCWI will enable 2D kinematics and stellar populations to be probed within the low surface brightness regions of galaxy halos in an effective way.

Structured planar laser-induced fluorescence (S-PLIF) for the accurate identification of interfaces in multiphase flows

Annular flows are employed in numerous engineering and industrial processes relating to the chemical, oil and gas, solar and nuclear energy industries. Yet, the reliable and detailed (i.e., time- and space-resolved) measurement of film thickness in these flows continues to elude us, as the moving and wavy interface renders the application of optical diagnostics, such as planar laser-induced fluorescence (PLIF), particularly challenging. In this research article, we present a novel adaptation of PLIF, which we refer to as structured PLIF (S-PLIF), which can suppress the errors in PLIF-derived film thickness measurements that arise due to total internal reflection (TIR) of the emitted fluorescence at the phase boundary. The proposed measurement approach relies on the periodic modulation of the laser-light intensity and angled illumination of the examined region of the flow, in order to generate fluorescence images with alternating bright and dark regions at an angle to the channel wall and film interface. An image-processing methodology capable of recovering the location of the true gas-liquid interface from such images is presented, and the application of S-PLIF is demonstrated in liquid films in a vertical pipe over the Reynolds number range ReL≈150−1500. The results from this technique are compared to simultaneously recovered, “conventional” (uncorrected) PLIF data, as well as data from other techniques over the same range of conditions, demonstrating the efficacy of S-PLIF. A comparison amongst S-PLIF data obtained with the observation angle between the laser-sheet plane and the camera’s observation axis set to β=70∘ and 90 ∘ is also performed, showing that the employment of β=70∘ is highly advantageous in avoiding distortions caused by optical interactions of the emitted fluorescence at the free surface of circumferentially non-uniform films. The instantaneous and average film-thickness uncertainties of S-PLIF are estimated to be below 10% and 5%, respectively, when measuring smooth films; an improvement over the other optical measurement techniques considered in this work. Finally, the application of S-PLIF is demonstrated in the presence of a gas-shear flow with gas entrainment in the liquid, and simultaneously with particle image velocimetry (PIV).

Examining the optical intensity and magnetic field expansion factor in the open magnetic field regions associated with coronal holes

AbstractCoronal holes can be identified as the darkest regions in EUV or soft X-ray images with predominantly unipolar magnetic fields (LIRs) or as the regions with open magnetic fields (OMF). Our study reveals that only 12% of OMF regions are coincident with LIRs. The aim of this study is to investigate the conditions that affect the EUV intensity of OMF regions. Our results indicate that the EUV intensity and the magnetic field expansion factor of the OMF regions are weakly positively correlated when plotted in logarithmic scale, and that the bright OMF regions are likely to locate inside or next to the regions with closed field lines. We empirically determined a linear relationship between the expansion factor and the EUV intensity. The relationship is demonstrated to improve the consistency from 12% to 23%. The results have been published in Astrophysical Journal (Huang et al. 2019).