Photospheric Radiation Research Articles

A systematic method for the analysis of high-resolution fraunhofer line profiles

A fraunhofer line profile depends on various parameters, partly related to the photospheric structure (T, Pg, Pe, vconv, vturb), partly to the atom or ion involved (such as oscillator strength, energy levels), partly also resulting from the interaction of the relevant kind of particles with the photosphere, and the photospheric radiation field. In this paper we shall mainly pay attention to the determination of: the macroturbulent (convective) velocities, vconv (τ); the damping constant γ (τ); the abundance, Ael; the distribution function ϕ(vconv, τ) of the convective velocities at each depth τ; the source function, S (τ); the microturbulent velocities, vturb (τ).

Radiation transfer problems in the rocket ultra-violet lines

WE PRESENT here a summary of a current investigation of the radiative transfer problem in the solar corona, in its effect upon the excitation state of coronal ions. [Complete details of the investigation will be published elsewhere; C. PECKER and THOMAS”).] The investigation is one phase of a systematic treatment of the influence of ionic configuration and physical environment upon the excitation state of an ion. We have called this treatment the New Spectroscopy, to contrast it with the Local Thermodynamic Equilibrium treatment of a gas, where the excitation state of an ion depends only upon the local electron temperature, and is independent of ionic configuration or the physical environment. The situation usually assumed for the solar corona falls, conceptually, intermediate to the LTE situation and that of the chromososphere and photosphere. The coronal optical thickness is taken to be so small that any radiation field produced by the corona itself has negligible effect upon excitation of the ions. Consequently, the excitation state depends upon ionic configuration, but only locally upon physical environment. That is, the excitation state at a point depends only upon the values of electron density, electron temperature, and photospheric radiation field at the point. It does not depend upon the atmosphere as a whole-upon values of electron density and temperature at other points in the atmosphere-as it would were the optical thickness of the atmosphere large enough to produce significant self-emission. In the present work we have asked whether the assumption of negligible optical thickness for the corona is valid and, if not, what is the influence of coronal self-emission as a function of coronal optical thickness. We show that an upper limit on the effect of coronal self-emission in any transition comes from isolating the transition to solve the radiative transfer problem in it. That is, the actual atomic configuration is replaced by that of the 2-level-atom. Thus this upper limit does not depend upon ionic configuration, but only upon physical environment. An estimate of the largest optical depths likely to be encountered in resonance transitions of the most abundant ions falls below 104. At coronal densities, the ratio of collisional to radiative de-excitation, c, does not exceed 10-r. In this situation, the excitation effect due to coronal self-emission in some transition can be expressed as a function only of the coronal optical thickness in this transition, for an isothermal, constant-ns corona. Numerical results are given in the complete investigation cited. Here, we note only that a detection of the presence of a significant, optical depth in some line, by observing a self-reversed emission profile, appears to demand an optical thickness exceeding a value which lies between 10 and 100.

Excitation of Chromospheric Emission

The presence of the Lyman-alpha line in emission across the whole disk of the Sun suggests that the chromosphere is excited by a mechanism additional to that given by the absorption of photospheric radiation. To find some of the properties of this additional excitation the observed intensity of a chromospheric line, as observed at the limb of the Sun outside an eclipse, is derived as an integral containing the source function. A numerical method of solving this integral equation is outlined, and from the solution the excitatio temperature and the density can be found as functions of radial height in the chromosphere. Other applications of the integral equation are briefly discussed.

The Helium Equilibrium in Prominences and the Chromosphere.

view Abstract Citations (20) References (7) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Helium Equilibrium in Prominences and the Chromosphere. Zirin, Harold Abstract The equilibrium of helium in a gas suspended above the photosphere is analyzed by computing in detail the various atomic processes involved and writing down the equilibrium equations. These equations are solved for the occupation numbers of He iii, He ii, and the various important He I levels, in order to predict the relative intensity of helium lines. The triplet levels are in equilibrium (referred to the state) with the photospheric radiation with the proper dilution factor. This gives good agreement with the 5876/10830 ratio measured by Severny. Particular attention is paid to the ratio of the lines 6678/5876. This is found to vary with temperature only, and the observed ratio should be a good measure of the temperature of helium. Publication: The Astrophysical Journal Pub Date: May 1956 DOI: 10.1086/146191 Bibcode: 1956ApJ...123..536Z full text sources ADS |

A study of three shell stars.

view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A study of three shell stars. Searle, Leonard Abstract The spectra of three shell stars have been studied from high dispersion plates obtained at the ioo-inch telescope of Mount Wilson Observatory. The stars involved are I Delphini, HD33232 and HD195407. The U, B and V colors were measured photoelectrically at the 6o-inch telescope. From plates at a dispersion of 4.9 A/mm, which were available for I Delphini, line profiles of 27 Fe ii, Ti ii and Cr ii lines were measured. Equivalent widths of all unblended shell-absorption lines were measured and ionic abundances derived. In all three stars dilution effects are prominent. HD33232 and I Delphini, which have similar metallic-line spectra, show the effect of dilution in the low population of the Si ii and Mg ii non-metastable levels compared with the population of the metastable levels of Fe ii. A dilution factor W I0~' is indicated for radiation long- ward of the Lyman limit; this is in agreement with the geometrical dilution factor suggested by the line profiles. The ultraviolet radiation beyond the Lyman limit is degraded into long wave-length radiation in its passage through the shell; the absence of shell lines from the metastable helium levels indicates that for 20 volt radiation W ~ I0-~. The electron density in the shells lies between 1010 and Io1,/cm'. The total number of hydrogen atoms lying in a cm2 column of the shell above the photosphere is between 10" and i~'~. The shells are estimated to have a mass of about i~'~ gm. The shell absorption spectrum of HD195407 consists of lines originating from the 2'S and 2~S metastable levels of helium and can be completely explained as originating in a highly ionized shell immersed in the photospheric radiation field geometrically diluted by a factor of 20. The line profiles obtained for I Delphini show no differences depending on the excitation potential of the lower level. There is however a striking difference between the profiles of the Fe ii lines on the one hand and the Ti ii and Cr ii lines on the other. The Ti ii lines are approximately 20 per cent wider than the Fe ii lines and while the Fe ii lines are essentially symmetrical the Ti ii lines show a pronounced asymmetry; the red wing is considerably stronger than the violet one. The profiles of Cr ii lines are similar to those of Ti ii. The colors of all three stars are normal for the spectral types of the underlying stars. Princeton University Observatory, Princeton, N. J. Publication: The Astronomical Journal Pub Date: 1956 DOI: 10.1086/107404 Bibcode: 1956AJ.....61R..12S full text sources ADS |

An Attempt to Explain the Polarization in H and D3 for Prominences

Using Heisenberg's theory as developed by Öhman for problems of this kind, it is shown that, for the line Hα , the hydrogen atom acts as a space oscillator for 35 per cent of the incident energy, and as an isotropic scatterer for the remaining 65 per cent. For the D 3 line of neutral helium the figures are 36 and 64 per cent. For the photospheric radiation an approximate value for the coefficient of darkening β1 = 0.67 is derived for the centre of Hα from Abbot's observations and Evans' residual intensities. For the D 3 line a value β1 = β = 1.36 is adopted. The theory, given for a prominence of small total optical depth, predicts for the emission a degree of polarization of 1.6 per cent at the photosphere, and 7.5 per cent at an altitude of 50,000 km., as compared with Lyot's observed values of 0.8 to 1.2 per cent in general. For the D 3 emission the theory gives 2.6 per cent at the photosphere and 8.4 per cent at an altitude of 50,000 km., as compared with the observed 0.9 to 1.2 per cent. The excess of the theoretical above the observational effect may in part be attributed to other processes of excitation like fluorescence and ionization and re-combination. The fact that the plane of vibration is not parallel to the solar limb, but shows deviations lying between 0° and 30° for Hα and 0° and 40° for D 3 , is not explained by the simple theory.

The Recent Shell Spectrum of γ Cassiopeiae.

view Abstract Citations (4) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Recent Shell Spectrum of γ Cassiopeiae. Baldwin, Ralph B. Abstract Spectrograms of `y Cassiopeiae taken since the early part of 1939 give evidence of an extensive outer shell of gas. Strong absorption lines of H, He i, and Fe m are produced in the shell. Weaker lines of other elements are also found. The lines show that there is an appreciable dilution of the photospheric radiation. An analysis of the shell spectrum is given Publication: The Astrophysical Journal Pub Date: March 1941 DOI: 10.1086/144269 Bibcode: 1941ApJ....93..333B full text sources ADS |