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Future microcalorimeter X-ray observations will resolve spectral features in unmatched detail. Understanding the line formation processes in the X-rays deserves much attention. The purpose of this paper is to discuss such processes in the presence of a photoionizing source. Line formation processes in one and two-electron species are broadly categorized into four cases. Case A occurs when the Lyman line optical depths are very small and photoexcitation does not occur. Line photons escape the cloud without any scattering. Case B occurs when the Lyman-line optical depths are large enough for photons to undergo multiple scatterings. Case C occurs when a broadband continuum source strikes an optically thin cloud. The Lyman lines are enhanced by induced radiative excitation of the atoms/ions by continuum photons, also known as continuum pumping. A fourth less-studied scenario, where the Case B spectrum is enhanced by continuum pumping, is called Case D. Here, we establish the mathematical foundation of Cases A, B, C, and D in an irradiated cloud with Cloudy. We also show the total X-ray emission spectrum for all four cases within the energy range 0.1 - 10 keV at the resolving power of XRISM around 6 keV. Additionally, we show that a combined effect of electron scattering and partial blockage of continuum pumping reduces the resonance line intensities. Such reduction increases with column density and can serve as an important tool to measure the column density/optical depth of the cloud.
We update our prior work on the case B collisional-recombination spectrum of He I to incorporate textit{ab initio} photoionisation cross-sections. This large set of accurate, self-consistent cross-sections represents a significant improvement in He I
All the observations available in the Chandra and XMM-Newton archives have been used to investigate the X-ray spectral properties of 3C 33. In this paper is presented a complete X-ray analysis of the nuclear emission of this narrow line radio galaxy.
Using Chandra, XMM-Newton, and optical photometric catalogs we study the young X-ray binary (XRB) populations of the Small Magellanic Cloud. We find that the Be/X-ray binaries (Be-XRBs) are observed in regions with star formation rate bursts ~25-60 M
While it is widely accepted that planets are formed in protoplanetary disks, there is still much debate on when this process happens. In a few cases protoplanets have been directly imaged, but for the vast majority of systems, disk gaps and cavities
We present a dynamical study of the narrow-line regions in two nearby QSO2s. We construct dynamical models based on detailed photoionization models of the emission-line gas, including the effects of internal dust, to apply to observations of large-sc