Transfer Of Photons Research Articles

Cyclotron line resonant transfer through neutron star atmospheres

Monte Carlo methods are used to study in detail the resonant radiative transfer of cyclotron line photons with recoil through a purely scattering neutron star atmosphere for both the polarized and unpolarized cases. For each case, the number of scatters, the path length traveled, the escape frequency shift, the escape direction cosine, the emergent frequency spectra, and the angular distribution of escaping photons are investigated. In the polarized case, transfer is calculated using both the cold plasma e- and o-modes and the magnetic vacuum perpendicular and parallel modes.

Optical spectra of a two-level atom in a quantized biharmonic field

A two-level atom in the field of two quantized laser modes with equal frequencies is considered. It is shown that the energy spectrum of the system forms a ladder of pair bands analogous to those of one-dimensional two-atom lattice. The band states correspond to quasi-particles describing the transfer of photons between the modes. The flourescence and weak probe field as well as strong field absorption spectra are calculated.

Determination of mass-loss rates from the first order momentW 1 of unsaturated P Cygni line profiles

The escape probability method introduced by Sobolev to treat the transfer of line photons is used in order to derive the expressions of thenth order momentW n ∝∫(E(λ)/E c −1)(λ−λ12) n ·d λ of a P Cygni profile formed in rapidly expanding envelopes around a central point-like source under various physical and geometrical conditions.

Resonance radiative transfer for cyclotron line emission with recoil

view Abstract Citations (67) References (32) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Resonance radiative transfer for cyclotron line emission with recoil Wasserman, I. ; Salpeter, E. Abstract The radiative transfer of cyclotron line photons through an optically thick resonant scattering atmosphere of recoiling electrons is discussed in light of the discovery of a 58 keV emission line in the spectrum of Her X-1 attributed to cyclotron emission near the magnetic poles of the accreting neutron star. Expressions are derived for the absorption and redistribution functions, core and wing scattering and approximate scaling laws for the main frequency shift, path length and number of scatters, taking into account electron recoil and features arising from the one-dimensional dynamics of the scattering electrons. It is found that most line photons escape in the red wing, forming a single sharp feature rather than the twin-peaked absorption profile characteristic of resonance radiative transfer without electron recoil. Results are noted to be in agreement with the Her X-1 observations, and to imply a depth of the line-emitting layer of less than 10 g/sq cm for the observed line width. Publication: The Astrophysical Journal Pub Date: November 1980 DOI: 10.1086/158426 Bibcode: 1980ApJ...241.1107W Keywords: Binary Stars; Cyclotron Radiation; Neutron Stars; Radiative Transfer; Stellar Mass Accretion; Stellar Spectra; X Ray Sources; Distribution Functions; Electromagnetic Absorption; Electron Scattering; Emission Spectra; Line Spectra; Resonance; X Ray Spectra; Astrophysics full text sources ADS |

The emission lines of quasars and similar objects

Much of our information about quasars is derived from their emission-line spectra. The analysis of such spectra has become an intricate subject which differs considerably from traditional, low-density nebular astrophysics. This review is intended to explain our present understanding of the situation, including some aspects of galactic nuclei whose luminosities are more modest than quasars. Quasars' line-emitting regions are probably photoionized (even if supplementary heating processes also occur). So far, models have been constructed which include ionization and thermal equilibria, the transfer of resonance-line and related photons, and the likely effects of absorption and scattering by dust grains. From comparisons between emission-line intensities produced in these models and observed quasars' spectra, it appears that certain densities and pressures and size scales occur in or around quasars. The relative abundances of elements are not very far from solar values, although it is suspected that heavy elements---carbon, nitrogen, and oxygen in particular---are moderately "overabundant" in quasars. The emission-line intensities also provide indirect information about quasars' ultraviolet and soft-x-ray continua; there are hints that photons with energies between 20 and 300 eV---which are not directly observable---may even represent the peak of the luminous output of a typical quasar. Finally, some gas-dynamical questions, while extremely important, are very difficult to answer, because of a lack of observables.

Combination of Bovine Carbonic Anhydrase with a Fluorescent Sulfonamide

Abstract Bovine erythrocyte carbonic anhydrase forms a highly complex with 5-dimethylaminonaphthalene-1-sulfonamide (DNSA). The binding, studied either by enhancement of ligand fluorescence or by the quenching of protein ultraviolet fluorescence, shows that only 1 mole of DNSA is bound per mole of protein; the dissociation constant at pH 7.4 is 2.5 x 10-7 m. The fluorescence of free DNSA in water has peak emission at 580 mµ and a quantum yield of only 0.055, but bound DNSA has an emission maximum at 468 mµ and a yield of 0.84. Arguments are presented to explain the large emission blue shift on the basis that the binding site is extremely hydrophobic and that the —SO2NH2 group of the ligand loses a proton upon binding to the enzyme. The binding appears specifically to involve the sulfonamide site known to exist in carbonic anhydrase; several other fluorescent probe compounds showed no evidence of binding to the enzyme. Calculation of the energy transfer efficiency gave the surprising result that 85% of the photons absorbed by the 7 tryptophan residues are transferred to the single bound DNSA molecule. The transfer efficiency is much higher than hitherto observed for a protein having only one 5-dimethylaminonaphthalene-1-sulfonyl group. Although the diameter of the protein is roughly 51 A, the bound DNSA group is probably within the critical transfer distance R0 (- 21.3 A) of all the tryptophans. The effective average distance between DNSA and tryptophan was found to be 16 A. The fluorescence properties of the complex were quite different from those of a conjugate prepared by reaction of 5-dimethylaminonaphthalene-1-sulfonyl chloride with carbonic anhydrase. Various considerations lead to the conclusion that the sulfonamide-binding site and the tryptophan residues are in the interior of the protein. The tryptophan fluorescence of the protein was 73% quenched by the binding of 1 DNSA molecule. Although large, this degree of quenching was less than the over-all efficiency of energy transfer of photons absorbed by the protein. This result indicates that the fluorescence efficiencies of the 7 tryptophans are different, and that DNSA is bound in such a way that energy transfer occurs with greater probability from those tryptophan residues which are relatively less fluorescent. DNSA inhibits the esterase activity of carbonic anhydrase as tested with the substrate, p-nitrophenyl acetate. Direct measurements of fluorescence decay times permitted calculation of the rotational relaxation time of carbonic anhydrase from depolarization of fluorescence data. The value of about 30 nsec for the relaxation time is consistent with a low degree of molecular asymmetry.

The relative intensities of CI lines in the solar EUV spectrum

The relative intensity of two Ci lines at 1993.6 A and 1657.4 A, observed in the limb spectrum of the sun, is a factor 2.6 × 103 larger than that expected if both lines were optically thin. It is shown that the observed intensity ratio may be explained in terms of the transfer of photons from λ 1657.4 A to λ 1993.6 A due to a large optical depth in the line at 1657.4 A. The observed upper limit on the relative intensity of two further lines at 1992.0 A and 1657.0 A has been used to show that the line at 1993.6 A is optically thin. Hence it is shown that τ(1657.4 A) = 1300, and τ(1993.6 A) = 0.44. These values provide an independent evaluation of optical depths against which chromospheric models may be checked. Assuming a mean temperature of Te = 8000 °K, and a mean scale height of 350 km, the optical depths lead to a mean hydrogen-particle density of N (H) = 1.4 × 1012 cm−3.

Theory of Temporal Growth of Ionization between Parallel Plates in the Inert Gases

It has been suggested that, in addition to the usual secondary ionization processes due to the action on the cathode of positive ions and undelayed radiation, a number of other secondary and collisional processes must be taken into account in the rare gases. These processes include the conversion of atomic ions into molecular ions, metastable atoms into metastable molecules, and the transition of atoms from metastable and resonant states with production of undelayed photons. Moreover, it has been suggested that the transfer of resonant photons through the gas takes place in accordance with the Holstein-Biberman theory, and also that delayed radiation (that is, radiation from excited states which have a long lifetime) may be of importance. On the assumption that all these processes are acting, formulae are derived in the present paper for the current growth, between parallel plates, due to specified causes of experimental interest, such as an externally generated cathode electron current of given strength, maintained since time zero, or the liberation of a single electron at time zero. The procedure by which these formulae are derived is general, and is not confined to the particular processes enumerated above.