Related papers: Backscattering and Line Broadening in Orion
Most of the ionized mass in the Milky Way is in the Warm Ionized Medium (WIM) and not in the bright H~II regions. The WIM is traced by dispersion measure and has been extensively studied in recombination lines (primarily, H$\alpha$) and…
Ultra-compact X-ray binaries consist of a neutron star or black hole that accretes material from a white dwarf-donor star. The ultra-compact nature is expressed in very short orbital periods of less than 1 hour. In the case of 4U 0614+091…
Optical spectropolarimetry and broadband polarimetry in other wavebands has been a key to understanding many diverse aspects of AGN. In some cases polarization is due to synchrotron radiation, and in other cases it's due to scattering.…
We detail tentative detections of low-frequency carbon radio recombination lines from within the Orion molecular cloud complex observed at 99-129 MHz. These tentative detections include one alpha transition and one beta transition over…
Sensitive spectral observations made in two frequency bands near 6.0 and 17.6 GHz are described for Orion and W51. Using frequency switching we were able to achieve a dynamic range in excess of 10,000 without fitting sinusoidal or…
We analyze the physical conditions, chemical composition and other properties of the photoionized Herbig-Haro object HH~204 through Very Large Telescope (VLT) echelle spectroscopy and Hubble Space Telescope (\textit{HST}) imaging. We…
We have constructed a 3D photoionisation model of a planetary nebula (PN) similar in structure to NGC 7009 with its outer pair of knots (also known as FLIERs --fast, low-ionization emission regions). The work is motivated by the fact that…
The ionization structure of the Orion nebula can be described as a skin-like ionization structure on the surface of a dense cloud. We propose that a steep density stratification, increasing as a powerlaw ($n \propto x^{-2}$) function of…
A number of studies have shown that the visibility of scattered broad emission lines in Seyfert 2 galaxies is strongly dependent on the IRAS f_60/f_25 flux ratio, where those Seyfert 2s with `warm' IRAS colours show polarised broad line…
It is widely assumed that dust opacities in molecular clouds follow a power-law profile with an index, $\beta$. Recent studies of the Orion Molecular Cloud (OMC) 2/3 complex, however, show a flattening in the spectral energy distribution…
The Orion Nebula is the closest high-mass star-forming region, making it an ideal laboratory to investigate physical processes in complex star-forming environments. At radio frequencies, the dominant emission mechanisms are thermal…
We present results of long-slit spectroscopy in several positions of the Orion nebula. Our goal is to study the spatial distribution of a large number of nebular quantities, including line fluxes, physical conditions and ionic abundances at…
An XMM-Newton observation of the luminous Seyfert galaxy PG1211+143 in 2001 revealed the first clear evidence for a highly ionised high speed wind (in a non-BAL AGN), with a velocity of v~0.09c based on the identification of blue-shifted…
This work presents integrated flux and velocity channel maps of the planetary nebula Abell 30 (A30) inner knot system. The observations were taken with the INTEGRAL spectrograph at the William Herschel Telescope (WHT). Our IFU data cube…
The clumpy density structure of photon-dominated regions is well established, but the physical properties of the clumps and of the surrounding interclump medium are only approximately known. The aim of this paper is to constrain the…
We carried out high-sensitivity spectropolarimetric observations of the central star of the Red Rectangle proto-planetary nebula with the aim of constraining the mechanism that gives its biconical shape. The stellar light of the central…
Extensive photoionization model grids for single star HII regions using a variety of recent state-of-the-art stellar atmosphere models have been computed with the main aim of constraining/testing their predicted ionizing spectra against…
We employed observational spectroscopic data of star-forming regions compiled from the literature and photoionization models to analyse the neon ionic abundances obtained using both optical and mid-infrared emission-lines. Comparing Ne++/H+…
We measure nonlinear optical scattering from individual Au nanorods excited by ultrafast laser pulses on resonance with their longitudinal plasmon mode. Isolating single rods removes inhomogeneous broadening and allows the measurement of a…
Based on three years of deep observations of the Galactic center with the Chandra X-ray Observatory, we report the discovery of changes in the intensities and morphologies of two hard X-ray nebulosities. The nebulosities are dominated by…