Intensities Of Recombination Lines Research Articles

Maser Effects in Recombination Lines: the case of Eta Carinae

AbstractPopulation of high quantum number states can differ from their LTE values at high densities (Ne ~106− 108cm−3) and temperatures of the order of 104K. In this case, the intensity of recombination lines can be strongly amplified. The amount of amplification depends on density and temperature, and it is different for different quantum numbers, allowing the determination of the physical and kinematic conditions of the emitting region through the observation of recombination lines of different quantum numbers. This was the case of the massive binary system η Carinae. This system was observed with ALMA in the recombination lines H21α, H28α, H30α, H40α and H42α and the continuum at the frequencies of the corresponding lines. The continuum spectrum was characteristic of a compact HII region, becoming optically thin at around 300 GHz. From the intensity and width of the recombination lines we concluded that the not-resolved emission region, assumed spherically symmetric, is a shell of 40 AU radius and 4 AU width, expanding at velocities between 20 and 60 km s−1, with density of 107cm−3and temperature of 17000 K.

Negative trion emission spectrum in stacked quantum dots: External electric field and valence band mixing

We study the negatively charged exciton trion in stacked quantum dots by the configuration interaction method. We discuss the trion recombination spectrum in an external electric field ($F$) and look for the effects of the valence band mixing leading to the antibonding-hole ground-state formation in the quantum dot molecule. We find that the antibonding-hole ground state produces a distinct modification of the trion emission for strongly coupled dots inverting the intensities of recombination lines in the principal avoided crossing appearing in the spectrum within the range of low $F$. This avoided crossing is very similar to the one observed for the neutral exciton only with a shift of the anticrossing centra on the scale of $F$. The exciton and trion emission spectra are distinctly different for weak interdot tunnel coupling, for which the effects of the antibonding-hole ground state are less evident for both the exciton and the trion. In particular for both the bonding and the antibonding-hole ground states the dissociation of the negative trion ground state appears as a two-stage process with a characteristic shape of the recombination line as observed experimentally.

전리수소 영역의 물리량 측정을 위한 방출선 모형연구

A diagnostic tool has been proposed to convert the observed surface distribution of hydrogen recombination line intensities into the radial distributions of the electron temperature and the density in HII regions. The observed line intensity is given by an integral of the volume emission coefficient along the line of sight, which comprises the Abel type integral equation for the volume emission coefficient. As the emission coefficient at a position is determined by the temperature and density of electrons at the position, the local emission coefficient resulted from the solution of the Abel equation gives the radial distribution of the temperature and the density. A test has been done on the feasibility of our diagnostic approach to probing of HII regions. From model calculations of an HII region of pure hydrogen, we have theoretically generated the observed surface brightness of hydrogen recombination line intensities and analyzed them by our diagnostic tool. The resulting temperatures and densities are then compared with the model values. For this case of uniform density, errors in the derived density are not large at all the positions. For the electron temperature, however, the largest errors appear at the central part of the HII region. The errors in the derived temperature decrease with the radial distance, and become negligible in the outer part of the model HII region.

Semiclassical theory of the radiative-collisional cascade in a Rydberg atom

We have developed a two-dimensional semiclassical model of the radiative-collisional cascade for hydrogen-like systems. We describe the collisions with electrons and ions by classical diffusion in the space of principal and orbital quantum numbers and use an iterative procedure that consistently takes into account the quantum nature of the radiative cascade for radiative transitions. The model establishes the correspondence between the quantum and classical approaches and indicates that the latter cannot be directly used to calculate the population kinetics of highly excited atomic states. Our calculations of the two-dimensional populations of highly excited atomic hydrogen states for selective, three-body, and photorecombination sources of population allow the data of one-dimensional kinetic models to be refined. The calculated intensities of recombination lines demonstrate the degree of nonequilibrium of the Rydberg state populations under typical astrophysical plasma conditions.

The highly excited hydrogen b n -factors calculated

Radio recombination line intensities are functions of highly excited atom nonequilibrium populations. These populations are determined by the spontaneous, collision and induced radiation transition rates that arise from the balance equations. The population balance equations are solved in a diffusion approximation which is proved for the departure factors from LTE. Diffusion equation departure coefficients are far from LTE due to the spontaneous transition flow, found as a second-order differential equation general solution. This solution is chosen in an explicit form from a physical situation with the temperature and density determined. The background radiation induced transition rates strongly influence the population flow to the equilibrium distribution. Radio recombination line amplification coefficients are calculated for the different medium temperatures and electron densities; these coefficients permit interpretation of the line intensities in the actual experiments.

The Radio Recombination Line Intensities Of Atoms And Ions: Helium, Carbon And Oxygen

The radio recombination line intensities of heavy elements of helium, carbon and oxygen are calculated with accounting for dielectronic recombination. Dielectronic recombination rates are determined accurate to the second order of a perturbation theory and the rates are described as function of principal quantum number for helium-like atom or ion. Balance equations are solved for the departure coefficients from LTE bn. The collision and spontaneous transition rates are accounted for the balance equations, in which non-equilibrium distribution source is dielectronic recombination. Non-equilibrium amplification coefficients are found as functions of a medium temperature, density and ion charge z = 1–3 for radio recombination lines.

Carbon and Oxygen Galactic Gradients: Observational Values from H ii Region Recombination Lines

We present results of deep echelle spectrophotometry of eight Galactic H ii regions located at Galactocentric distances between 6.3 and 10.4 kpc. The data have been taken with the Very Large Telescope Ultraviolet Echelle Spectrograph in the 3100–10360 range. We have derived C and O abundances from recombination lines for u A all the objects as well as O abundances from this kind of line for three of the nebulae. The intensity of recombination lines is almost independent of the assumed electron temperature as well as of the possible presence of spatial temperature variations or fluctuations inside the nebulae. These data allow the determination of the gas-phase C and O abundance gradients of the Galactic disk, of paramount importance for chemical evolution models. This is the first time the C gradient is derived from such a large number of H ii regions distributed in such a wide range of Galactocentric distances. Abundance gradients are found of the form dex kpc 1 , D log (O/H) p 0.044 0.010 dex kpc 1 , and dex kpc 1 . D log (C/H) p 0.103 0.018 D log (C/O) p 0.058 0.018 Subject headings: Galaxy: abundances — H ii regions — ISM: abundances

Recombination coefficients for the 5g - 4f transitions of O$_{\mathrm{III}}$ at nebular temperatures and densities

We calculate effective recombination coefficients for the formation of the 5g - 4f lines of O III in the intermediate coupling scheme. Photoionization data for the 5g levels calculated using the R-matrix method are used to derive their recombination coefficients. Cascading from higher states is included, allowing for the effects of finite electron density in a hydrogenic approximation. We explicitly include the distribution of population between the two ground levels of O 3+ in the calculation of the line intensities. The results are presented as a simple programmeable formula allowing the calculation of recombination line intensities for electron temperatures, T e in the range K and electron densities, N e in the range cm -3 .

Recombination line intensities for hydrogenic ions: The fine-structure components of HI and HeII

Emissivities have been calculated for finestructure components of selected UV and optical recombination lines of HI and He II. Results are given for a range of electron temperatures and densities, and in Cases A and B of Baker & Menzel (1938). Relative intensities, wavelengths and velocity shifts of the fine-structure components are tabulated. Applications to the spectra of gaseous nebulae are discussed. Depending on the temperature, density and Case, the centres of unresolved lines can shift by up to 0.9 km s(-1) for H I and 3.3 km s(-1) for He II. A new calibration of the H alpha-[N II] method for determining electron temperatures is given.

Outmoving Clumps in the Wind of the Hot O Supergiant ζ Puppis

We present time series of ultra-high S/N, high-resolution spectra of the He II 4686 A emission line in the O4I(n)f supergiant ζ Puppis, the brightest early-type O star in the sky. These reveal stochastic variable substructures in the line, which tend to move away from the line center with time. Similar scaled-up features are well established in the strong winds of Wolf-Rayet stars (the presumed descendants of O stars), where they are explained by outward-moving inhomogeneities (e.g., blobs, clumps, and shocks) in the winds. If all hot star winds are clumped like that of ζ Pup, as is plausible, then mass loss rates based on recombination-line intensities will have to be revised downward. Using a standard velocity law, we deduce a value of β = 1.0-1.2 to account for the kinematics of these structures in the wind of ζ Pup. In addition to the small-scale stochastic variations, we also find a slow systematic variation of the mean central absorption reversal.

High Rydberg state carbon recombination lines toward Cassiopeia A: Physical conditions and a new class of models

view Abstract Citations (47) References (52) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS High Rydberg State Carbon Recombination Lines toward Cassiopeia A: Physical Conditions and a New Class of Models Payne, H. E. ; Anantharamaiah, K. R. ; Erickson, W. C. Abstract We present models of physical conditions in Perseus arm clouds observed in the direction of Cas A. Theoretical predictions of carbon radio recombination line intensities are compared with observations spanning the frequency range 14 to 775 MHz. Best-fitting model parameters are then combined with the results of lambda 21 cm H I absorption line observations, and low-frequency hydrogen recombination line observations, to evaluate the thermal and pressure balance in these clouds. A critical reexamination of the available recombination line data shows that the lowest frequency carbon line observations have underestimated the integrated optical depths in the line by up to a factor of 3. This is due to the removal of large Lorentzian wings from the pressure broadened line profiles during baseline subtraction. Models where some or all of the recombination line optical depth originates in molecular clouds do not give satisfactory results. Models based on standard calculations of recombination line intensites (Salem & Brocklehurst 1979; Walmsley & Watson 1982) have high pressures and are out of thermal balance. We modified the theoretical calculation of line intensities, described by Salem & Brocklehurst (1979) and Walmsley & Watson (1982), by imposing a different boundary condition at large principal quantum number n. Instead of assuming an infinite number of levels populated according to thermodynamic equilibrium, we impose a cutoff in level populations above a critical principal quantum number ncr, as suggestd b y Gulyaev & Nefedov (1989). We followed the occupation probability formalism presented by Hummer & Mihalas (1988) to calculate ncr. Using these new line intensity calculations, we find that, with the exception of the recombination line width, all of the Cas A recombination line and lambda 21 cm H I absorption line data can be attributed to a region where the physical conditions are typical of the cold neutral medium of the interstellar medium. We show a model in which this region is in thermal balance at a temperature near 36 K and has a reasonable interstellar pressure. In this model, the photoionization of polycyclic aromatic hydrogen molecules is the dominant mechanism for heating the region. Publication: The Astrophysical Journal Pub Date: August 1994 DOI: 10.1086/174441 Bibcode: 1994ApJ...430..690P Keywords: Abundance; Carbon; Cassiopeia A; Interstellar Matter; Radio Emission; Recombination Reactions; Rydberg Series; Absorption Spectra; Astronomical Models; Cosmology; Molecular Clouds; Spectrum Analysis; Star Formation; Astrophysics; ISM: ABUNDANCES; ATOMIC PROCESSES; LINE: FORMATION; RADIO LINES: ISM full text sources ADS | data products SIMBAD (4)

Recombination line intensities for hydrogenic ions – III. Effects of finite optical depth and dust

We explore systematically the effect on the recombination spectrum of hydrogen arising from: (i) finite optical thickness in the Lyman lines; (ii) the overlapping of Lyman lines near the series limit; (iii) the absorption of Lyman lines by dust or photoionization, and (iv) the long-wave radiation emitted by dust. Full account is taken of electron and heavy particle collisions in redistributing energy and angular momentum. We find that each of these deviations from the classical Case B leads to observable effects, and that dust influences the recombination spectrum in characteristic ways that may make possible new observational constraints on dust properties in nebulosities. On the basis of these calculations we believe the uncertainty in the determination of the helium-to-hydrogen abundance ratio in the Universe may be larger than currently claimed.

Recombination line intensities for hydrogenic ions - II. Case B calculations for C VI, N VII and O VIII

The intensities of recombination lines of C VI, N VII and O VIII are calculated, accounting for both electron and heavy particle collisions and assuming Case B of Baker & Menzel. The intensities of lines formed by transitions |$n_\text u\rightarrow n_l$|⁠, are tabulated for nu≼50, nl≼29, at log Ne=4(l)13 and at 10 values of electron temperature in the interval 10 000 K≼Te≼500 000 K.

Recombination-line intensities for hydrogenic ions - I. Case B calculations for H I and He II

Assuming Case B of Baker and Menzel (1938), the relative intensities of H I and He II recombination lines are determined for a larger range of temperature and density than previously considered and with the upper principle quantum number up to 50 and the lower number up to 29. Full collisional effects are included, and new collision strengths for the n = 1, 2, and 3 states of He(+) are presented. Case B theory is found to be invalidated for collisional excitation of the n = 3 levels from both n = 1 and n = 2 states under certain conditions which depend upon electron density and the Lyman-alpha escape probability, and the regimes of temperature and density for which Case B is valid are also considered.

A non-isothermal calculation of radio recombination-line intensities of NGC 2024, Orion A and W3

Etude detaillee des intensites des raies de C et d'autres raies de recombinaison anormales de NGC 2024, Orion A et W3. On a calcule les densites electroniques et les temperatures a partir des equilibres thermique, chimique et d'ionisation a l'aide d'une methode auto-compatible. La meilleure valeur des intensites observees des raies de recombinaison dans le spectre 0,6-15 GHz est utilisee pour calculer les parametres physiques de chaque nuage dans les hypotheses d'abondances solaires et d'abondances deficientes

Some Atomic Parameters Pertinent to Studies of Nebular Ionized Plasmas

In order to predict emission line and continuum intensities and assess plasma diagnostics for gaseous nebulae, it is necessary to have accurate atomic parameters. In some Instances the requirements for accuracy are very severe. A variety of data is required:1)Coefficients of continuous absorption;2)Direct and dielectronic recombination coefficients;3)Transition probabilities for permitted lines, so we can accurately predict both recombination line intensities and fluorescent phenomena (e.g., OI λ8446);4)Transition probabilities for forbidden and intercombination lines;5)Collision cross sections for levels which give rise to: a)resonance transitions,b)intercombination lines,c)forbidden lines;6)Charge-exchange cross sections.

Extinction of NGC 7027

Emission intensities of recombination lines in hydrogenic spectra are known accurately relative to intensities in the free–free radio continuum. For NGC 7027 intensities have been measured for the radio continuum and for H I and He II lines in the wavelength range from λ = 2.17 µm to λ = 1640 Å: comparison with the calculated emission intensities gives the extinction Aλ. Determinations of the standard interstellar extinction function, |${A}_{\lambda}/{E}_{B-V} $|⁠, are critically discussed. The extinction deduced for the total radiation from NGC 7027 has a dependence on wavelength for 6563 Å |$\geqslant\,\lambda \geqslant$| 1640 Å which is in excellent agreement with the adopted standard results, but there are some anomalies for longer wavelengths and for the ratio of total to selective extinction. These can be explained using a model which allows for a local contribution to the extinction which is variable over the surface of the nebula.

High-Frequency Observations and Theoretical Interpretation of Recombination-Line Emission in the Direction of the Supernova Remnant 3c 391

view Abstract Citations (27) References (25) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS High-Frequency Observations and Theoretical Interpretation of Recombination-Line Emission in the Direction of the Supernova Remnant 3c 391 Cesarsky, Diego A. ; Cesarsky, Catherine J. Abstract The comparison of radio recombination-line intensities and the amount of low-frequency absorption along the same line of sight provides a unique method of obtaining information on the electron temperature of the regions involved. This method, when applied to high-frequency line observations in the direction of the remnant 3C 391, suggests that the line emission originates in regions having an electron temperature Te < 400 K, and a most probable value of Te = 20 K. Subject headings: interstellar matter - radio lines - supernova remnants Publication: The Astrophysical Journal Pub Date: August 1973 DOI: 10.1086/152307 Bibcode: 1973ApJ...184...83C full text sources ADS |

Infrared Line Emission from H II Regions

view Abstract Citations (92) References (32) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Infrared Line Emission from H II Regions Petrosian, Vahé Abstract Formulae are given relating the infrared line intensities to radio and optical fluxes of H ii regions. The line intensities expected from the Orion Nebula are calculated. With present techniques a number of fine-structure lines and only a few infrared recombination lines of hydrogen could be detected. The observations of the infrared fine-structure lines and the forbidden-line intensities of pi and p4 ions can he used for simultaneous determination of electron temperature and density. The fine-structure lines from p and p5 ions are the best means of measuring the abundances of these ions. The ratios of infrared to optical recombination-line intensities could be used to determine the interstellar absorption. Publication: The Astrophysical Journal Pub Date: March 1970 DOI: 10.1086/150361 Bibcode: 1970ApJ...159..833P full text sources ADS | data products SIMBAD (1)

Infrared-Line Emission from Planetary Nebulae

view Abstract Citations (52) References (49) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Infrared-Line Emission from Planetary Nebulae Delmer, Thomas N. ; Gould, Robert J. ; Ramsay, William Abstract The general physical processes are considered which determine the intensities of infrared emission lines resulting from magnetic dipole transitions between fine-structure levels in certain abundant ions. Ionization equilibrium and fine-structure level population are discussed. Radiative recombination is treated in some detail in an appendix where general results are given for averaged recombination Gaunt factors and for approximate intensities of helium recombination line intensities. By means of the quantum defect method, some important collision strengths for fine structure transitions are calculated. On the basis of optical data, estimates are given of the expected infrared-line intensities from nine bright planetary nebulae. There are a number of lines from these planetaries which should have intensities in the range of 10- -16 W/cm2 and which should be observable from below the atmosphere through the 8-14- and 17-24- windows. Improved estimates are given of the expected thermal bremsstrahlung radio emission from these nebulae, with the assumption that they are optically thin to radio radiation; comparison with radio observations indicates generally satisfactory agreement with these calculations of radio emission. Publication: The Astrophysical Journal Pub Date: September 1967 DOI: 10.1086/149281 Bibcode: 1967ApJ...149..495D full text sources ADS | data products SIMBAD (9)