More on the Narrowing of Impact Broadened Radio Recombination Lines at High Principal Quantum Number

Recently Alexander and Gulyaev have suggested that the apparent decrease in impact broadening of radio recombination lines seen at high principal quantum number n may be a product of the data reduction process, possibly resulting from the presence of noise on the telescope spectra that is not present on the calculated comparison spectra. This is an interesting proposal. However, there are serious problems with their analysis that need to be pointed out. Perhaps the most important of these is the fact that for principal quantum numbers below n = 200, where the widths are not in question, their processed generated profile widths do not fit the widths of the processed lines obtained at the telescope. After processing, the halfwidths of the generated and telescope profiles must agree below n = 200 if we are to believe that the processed generated linewidths above n = 200 are meaningful. Theirs do not. Furthermore, we find that after applying the linewidth reduction factors found by Alexander and Gulyaev for their noise added profiles to our generated profiles to simulate their noise adding effect, the processed widths we obtain still do not come close to explaining the narrowing seen in the telescope lines for n values in the range 200 < n < 250. It is concluded that what is needed to solve this mystery is a completely new approach using a different observing technique instead of simply a further manipulation of the frequency-switched data.Comment: Six pages with 4 figures. Accepted for publication in Astrophysics and Space Scienc

Electron-impact broadening of the 3s-3p lines in low-Z Li-like ions

The collisional electron-impact line widths of the 3s-3p transitions in Li-like ions from B III to Ne VIII are calculated with the convergent close-coupling (CCC) method from the atomic collision theory. The elastic and inelastic contributions to the line broadening and their Z-scaling are discussed in detail, and comparisons with recent experimental and theoretical results are also presented. It is found that similar to our previous study of line broadening in Be-like ions, the difference between experimental and CCC results monotonically increases with the spectroscopic charge of an ion.Comment: 23 pages, 8 figures, 1 table. To be published in JQSR

Sensitive Observations of Radio Recombination Lines in Orion and W51: The Data and Detection of Systematic Recombination Line Blueshifts Proportional to Impact Broadening

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 polynomial baselines. This enabled us to detect lines as weak as T$_{A} ~1mK in these strong continuum sources. Hydrogen recombination lines with$\Delta n$ as high as 25 have been detected in Orion. In the Orion data, where the lines are stronger, we have also detected a systematic shift in the line center frequencies proportional to linewidth that cannot be explained by normal optical depth effects.Comment: 22 pages, 13 figures. Accepted for publication in Astrophysics and Space Scienc

Collisional and Radiative Processes in Optically Thin Plasmas

Most of our knowledge of the physical processes in distant plasmas is obtained through measurement of the radiation they produce. Here we provide an overview of the main collisional and radiative processes and examples of diagnostics relevant to the microphysical processes in the plasma. Many analyses assume a time-steady plasma with ion populations in equilibrium with the local temperature and Maxwellian distributions of particle velocities, but these assumptions are easily violated in many cases. We consider these departures from equilibrium and possible diagnostics in detail

PLASMA SHIFTS OF ION LINES

Les déplacements dûs aux interactions d'atomes ou d'ions émetteurs ou absorbants avec des particules chargées dans un plasma sont généralement supposés négligeables, par exemple dans les mesures des niveaux atomiques d'énergie ou dans les calculs de transfert radiatif. Cependant on sait que les collisions électroniques causent des déplacements qui représentent une fraction importante des largeurs correspondantes et que les interactions de l'ion émetteur donnent lieu a des déplacements et des asymétries sur le profil dûs à l'effet Stark quadratique et aux corrections quadrupolaires ajoutés aux interactions dipolaires habituelles. Les relations entre ces différents effets sont particulièrement intéressantes dans le cas d'émetteurs fortement chargés pour lesquels les effets électroniques sont accrûs par la forte interaction coulombienne entre électrons et émetteurs (déplacement par polarisation du plasma). Des calculs pour les ions hydrogénoïdes et heliumoïdes seront discutés et comparés aux mesures expérimentales.Shifts due to interactions of radiating or absorbing atoms or ions with charged particles in a plasma are generally assumed to be negligible, e.g., in ments of atomic energy levels or in calculations of radiative transfer. However, it has long been known that electron collisions can cause shifts which are a significant fraction of the corresponding widths, and that ion-radiator interactions give rise to shifts and profile asymmetries through quadratic Stark effects and quadrupole corrections to the usual dipole interactions. The interplay between these various effects is particularly interesting for highly charged radiators for which electron effects are enhanced by the strong electron-radiator Coulomb attraction (plasma polarization shift). As examples, calculations for hydrogen- and helium-like ions will be discussed and be compared with measurements