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It is common to suggest the uncertainties in the atomic data for explaining difficulties that arise in interpreting astrophysical x-ray spectra. The atomic data for the Fe L-shell ions have, over the years, been considered particularly…
We obtain contemporaneous observations of the surface and corona of AB Dor using ground-based circularly polarised spectra from the Anglo-Australian Telescope and X-ray data from the Chandra satellite. The ground-based data are used to…
Hot atmospheres of massive galaxies are enriched with metals. Elemental abundances measured in the X-ray band have been used to study the chemical enrichment of supernova remnants, elliptical galaxies, groups and clusters of galaxies. Here…
We show that stellar coronae can be composed of X-ray emitting structures like those in the solar corona, using a large set of ROSAT/PSPC observations of late-type-stars, and a large set of solar X-ray data collected with Yohkoh/SXT. We…
Global coronal models seek to produce an accurate physical representation of the Sun's atmosphere which can be used, for example, to drive space weather models. Assessing their accuracy is a complex task and there are multiple observational…
A set of theoretical mass-radius relations for rigidly rotating neutron stars with exotic cores, obtained in various theories of dense matter, is reviewed. Two basic observational constraints are used: the largest measured rotation…
We present three spectra of Cygnus X-1 in the low/hard state from 3-1000 keV produced with RXTE and OSSE. We demonstrate that a pure thermal Comptonization model, with Compton reflection fits the data well, with coronal temperatures of…
We used ultraviolet spectra from HST/STIS (R=30,000), together with optical spectra from Keck/HIRES (R=45,000), to study the three MgII-selected absorption systems at z=0.9254, 0.9276, and 0.9342 toward the quasar PG 1206+459. A multi-phase…
Main sequence stars of spectral types F, G, and K with low to moderate activity levels exhibit a recognizable pattern known as the first ionization potential effect (FIP effect), where elements with lower first ionization potentials are…
The corona, a hot cloud of electrons close to the centre of the accretion disc, produces the hard X-ray power-law continuum commonly seen in luminous Active Galactic Nuclei (AGN). The continuum has a high-energy turnover, typically in the…
The hard X-ray emission of active galactic nuclei (AGN) is believed to originate from the hot coronae above the cold accretion discs. The hard X-ray spectral index is found to be correlated with the Eddington ratio, and the hard X-ray…
We studied the broadband X-ray spectra of {\it Swift}/BAT selected low-accreting AGNs using the observations from {\it XMM-Newton}, {\it Swift}, and {\it NuSTAR} in the energy range of $0.5-150$~keV. Our sample consists of 30 AGNs with…
We discuss models for coronal abundance anomalies observed in the coronae of the sun and other late-type stars following a scenario first introduced by Schwadron, Fisk & Zurbuchen of the interaction of waves at loop footpoints with the…
The different electron distributions in the hard and soft spectral states (HS and SS) of BH binaries could be caused by kinetic processes and changing because of varying physical conditions in the corona. In presence of a magnetic field in…
The results of spectral observations in the $\sim 84-92$ GHz frequency range of six objects in the southern sky containing dense cores and associated with regions of massive stars and star clusters formation are presented. The observations…
Faraday rotation measurements of the solar corona made with the Very Large Array (VLA) at frequencies of 1465 and 1665 MHz are reported. The measurements were made along 20 lines of sight to 19 extragalactic radio sources in March and…
We present new observations of the prominence system on the K3 dwarf Speedy Mic (BO Mic, HD 197890). Using an improved technique to track the absorption features in H_alpha we find a very active prominence system with approximately ten…
The planetary nebula (PN) IC 4997 is one of a few rapidly evolving objects with variable brightness and nebular emission around a hydrogen-deficient star. In this study, we have determined the physical conditions and chemical abundances of…
We present the result of a near-infrared (J H Ks) survey along the Galactic plane, -10.5deg < l < +10.5deg and b=+1.0deg, with the IRSF 1.4m telescope and the SIRIUS camera. Ks vs. H-Ks color-magnitude diagrams reveal a well-defined…
Spectroscopic observations of prominence eruptions associated with coronal mass ejections (CMEs), although relatively rare, can provide valuable plasma and 3D geometry diagnostics. We report the first observations by the Interface Region…