The Measurement of f-values for Lines of Astrophysical Interest by Beam-Foil Spectroscopy

1978 ◽  
Vol 3 (4) ◽  
pp. 263-264
Author(s):  
J. E. Ross ◽  
B. J. O’Mara
Keyword(s):  
Life Time ◽  
Absolute Number ◽  
Branching Ratios ◽  
Oscillator Strengths ◽  
Separate Experiment ◽  
Number Density ◽  
Reasonable Accuracy ◽  
Initial Excitation ◽  
The One ◽  
Beam Foil

The necessity of having accurate oscillator strengths in astrophysical applications is well known. The apparent discrepancy which existed between the solar and meteoritic abundance of iron is just one example of the problems which can arise from poor f-values. An excellent critique of methods for determining both absolute and relative f-values has been given by Blackwell & Collins (1972). Their comments on life-time techniques provide a clear indication of both the advantages and difficulties associated with these techniques: “In principle, a life-time method, as exemplified by the technique of beam foil spectroscopy, described for example by Wiese (1970), has the fundamental advantage that in some restricted circumstances its application does not depend upon a temperature measurement or any assumption of themodynamic equilibrium in the source: in addition it gives an absolute result without the need of an absolute number density of atoms. The hope is sometimes expressed that the method of beam foil spectroscopy will yield oscillator strengths of the required accuracy. In practice, the technique suffers from the difficulty that although the life-time of an excited state can be measured with reasonable accuracy, it is also necessary to measure in a separate experiment the branching ratios for radiative de-excitation. As these ratios are usually measured by an arc method, the accuracy of the final oscillator strengths is limited by the deficiencies of this source. Also, some atoms in the beam may be excited to higher levels than the one being examined, and because of the nature of the initial excitation is unknown, radiative de-excitation (cascading) takes place to this lower level in a way that is wholly unpredictable. This difficulty is especially important for levels of low excitation.” In this talk techniques will be described for overcoming the cascading problem in beam foil spectroscopy and for measuring the associated branching ratios.

Absorption oscillator strengths to autoionizing states in Li, N, and F and their isoelectronic sequences

1976 ◽  
Vol 54 (6) ◽  
pp. 689-694 ◽  
Author(s):  
Donald R. Beck ◽  
Cleanthes A. Nicolaides
Keyword(s):  
Excellent Agreement ◽  
Order Theory ◽  
Oscillator Strengths ◽  
First Order ◽  
First Order Theory ◽  
Electron Transitions ◽  
The One ◽  
Beam Foil ◽  
Autoionizing States ◽  
Electron Interactions

We have calculated the photoabsorption oscillator strengths of the one and two-electron transitions Li 1s22s2S → 2s22p2P0, NI 2s22p32P0 → 2s2p42D, NI 2s22p32D0 → 2s2p42D, and FI 2s22p52P0 → 2s2p62S, whose upper states are autoionizing, according to a new first order theory of oscillator strengths (FOTOS). These oscillator strengths are often very small and are sensitive to the details of electron–electron interactions. Also computed are the f values for ions in the N and F isoelectronic sequences. Comparison of our theory with three very recent beam-foil values in OII, FIII, and NeII shows excellent agreement.

scholarly journals Extended theoretical transition data in C i–iv

2021 ◽  
Vol 502 (3) ◽  
pp. 3780-3799
Author(s):  
W Li ◽  
A M Amarsi ◽  
A Papoulia ◽  
J Ekman ◽  
P Jönsson
Keyword(s):  
Transition Probabilities ◽  
Energy Levels ◽  
Oscillator Strengths ◽  
Atomic Data ◽  
Internal Validation ◽  
Hartree Fock ◽  
Relativistic Configuration ◽  
The Difference ◽  
The One ◽  
Relative Differences

ABSTRACT Accurate atomic data are essential for opacity calculations and for abundance analyses of the Sun and other stars. The aim of this work is to provide accurate and extensive results of energy levels and transition data for C i–iv. The Multiconfiguration Dirac–Hartree–Fock and relativistic configuration interaction methods were used in this work. To improve the quality of the wavefunctions and reduce the relative differences between length and velocity forms for transition data involving high Rydberg states, alternative computational strategies were employed by imposing restrictions on the electron substitutions when constructing the orbital basis for each atom and ion. Transition data, for example, weighted oscillator strengths and transition probabilities, are given for radiative electric dipole (E1) transitions involving levels up to 1s22s22p6s for C i, up to 1s22s27f for C ii, up to 1s22s7f for C iii, and up to 1s28g for C iv. Using the difference between the transition rates in length and velocity gauges as an internal validation, the average uncertainties of all presented E1 transitions are estimated to be 8.05 per cent, 7.20 per cent, 1.77 per cent, and 0.28 per cent, respectively, for C i–iv. Extensive comparisons with available experimental and theoretical results are performed and good agreement is observed for most of the transitions. In addition, the C i data were employed in a re-analysis of the solar carbon abundance. The new transition data give a line-by-line dispersion similar to the one obtained when using transition data that are typically used in stellar spectroscopic applications today.

scholarly journals Evidence that Emission and Absorption Outflows in Quasars Are Related

2020 ◽  
Author(s):  
Xinfeng Xu ◽  
Nadia L Zakamska ◽  
Nahum Arav ◽  
Timothy Miller ◽  
Chris Benn
Keyword(s):  
Electron Number Density ◽  
Physical Parameters ◽  
Evolutionary Stage ◽  
Number Density ◽  
Ionized Gas ◽  
Measured Velocity ◽  
Broad Absorption Line ◽  
James Webb Space Telescope ◽  
The Mean ◽  
The One

Abstract We analyze VLT/X-shooter data for 7 quasars, where we study the relationships between their broad absorption line (BAL) and emission line outflows. We find: 1) the luminosity of the [O iii] λ5007 emission profile decreases with increasing electron number density ($n_\mathrm{\scriptstyle e}$) derived from the BAL outflow in the same quasar, 2) the measured velocity widths from the [O iii] emission features and C iv absorption troughs in the same object are similar, and 3) the mean-radial-velocity derived from the BAL outflow is moderately larger than the one from the [O iii] emission outflow. These findings are consistent with [O iii] and BAL outflows being different manifestations of the same wind, and the observed relationships are likely a reflection of the outflow density distribution. When we have outflows with smaller distances to the central source, their $n_\mathrm{\scriptstyle e}$ is higher. Therefore, the [O iii] emission is collisionally de-excited and the [O iii] luminosity is then suppressed. Comparisons to previous studies show that the objects in our sample exhibit broad [O iii] emission features similar to the ones in extremely-red-quasars (ERQs). This might imply that BAL quasars and ERQs have the same geometry of outflows or are at a similar evolutionary stage. We find that the physical parameters derived from the BAL outflows can explain the amount of observed [O iii] luminosity, which strengthens our claim that both BAL and [O iii] outflows are from the same wind. These estimates can be tested with upcoming James Webb Space Telescope, which will be able to spatially resolve some of the ionized gas outflows.

scholarly journals Geriatric teaching in Brazilian medical schools in 2013 and considerations regarding adjustment to demographic and epidemiological transition

2016 ◽  
Vol 62 (2) ◽  
pp. 179-183 ◽  
Author(s):  
Ana Conceição Norbim Prado Cunha ◽  
Natália Norbim Prado Cunha ◽  
Maira Tonidandel Barbosa
Keyword(s):  
Age Distribution ◽  
Epidemiological Data ◽  
The Elderly ◽  
Medical Schools ◽  
Absolute Number ◽  
Southeast Region ◽  
Medical Undergraduate ◽  
Elderly Health ◽  
Using Data ◽  
The One

Summary Objective: This study aims to describe the profile of medical schools that introduced courses on Geriatrics and Elderly Health or Aging in their curriculum, and compare such information with the age distribution and health epidemiological data of the Brazilian population, using data until the year of 2013. Methods: 180 universities offering medical undergraduate courses and registered with the Ministry of Education and Culture of Brazil (MEC) were found, as seen on the MEC website (www.emec.mec.gov.br) in February 2013. Based on the list of institutions, the authors created a database. Results: Brazil's Southeast region is the one presenting most of the courses, both offered as core or elective subjects, in the area of Geriatrics. The Midwest region had the least offer of Geriatrics and Elderly Health and Care courses. The Southeast region presents the greater absolute number of institutions with elective subjects, followed by the South and Northeast regions, each with a single institution. The Southeast region was at the same time the one that presented the biggest absolute number of institutions offering core subjects in the area of Geriatrics, being followed by the Northeast, South, North, and Midwest regions. Conclusion: By analyzing the availability of courses that emphasize aging and Geriatrics in brazilian medical schools, the present study reveals that specialized training should be encouraged with respect to the specificities of health care given to the elderly population, which has a higher frequency of chronic and degenerative diseases.

scholarly journals Rare temperature histories and cirrus ice number density in a parcel and a one-dimensional model

2014 ◽  
Vol 14 (23) ◽  
pp. 13013-13022 ◽  
Author(s):  
D. M. Murphy
Keyword(s):  
Temperature Dependence ◽  
Low Temperatures ◽  
Ice Crystals ◽  
Strong Increase ◽  
Number Density ◽  
Dimensional Model ◽  
One Dimensional ◽  
Slow Growth Rate ◽  
Wide Range ◽  
The One

Abstract. A parcel and a one-dimensional model are used to investigate the temperature dependence of ice crystal number density. The number of ice crystals initially formed in a cold cirrus cloud is very sensitive to the nucleation mechanism and the detailed history of cooling rates during nucleation. A possible small spread in the homogeneous freezing threshold due to varying particle composition is identified as a sensitive nucleation parameter. In a parcel model, the slow growth rate of ice crystals at low temperatures inherently leads to a strong increase in ice number density at low temperatures. This temperature dependence is not observed. The model temperature dependence occurs for a wide range of assumptions and for either homogeneous or, less strongly, heterogeneous freezing. However, the parcel model also shows that random temperature fluctuations result in an extremely wide range of ice number densities. A one-dimensional model is used to show that the rare temperature trajectories resulting in the lowest number densities are disproportionately important. Low number density ice crystals sediment and influence a large volume of air. When such fall streaks are included, the ice number becomes less sensitive to the details of nucleation than it is in a parcel model. The one-dimensional simulations have a more realistic temperature dependence than the parcel mode. The one-dimensional model also produces layers with vertical dimensions of meters even if the temperature forcing has a much broader vertical wavelength. Unlike warm clouds, cirrus clouds are frequently surrounded by supersaturated air. Sedimentation through supersaturated air increases the importance of any process that produces small numbers of ice crystals. This paper emphasizes the relatively rare temperature trajectories that produce the fewest crystals. Other processes are heterogeneous nucleation, sedimentation from the very bottom of clouds, annealing of disordered to hexagonal ice, and entrainment.

Fast-ion-beam laser-induced-fluorescence measurements of spontaneous-emission branching ratios and oscillator strengths in Sm II

2006 ◽  
Vol 84 (8) ◽  
pp. 723-771 ◽  
Author(s):  
S J Rehse ◽  
R Li ◽  
T J Scholl ◽  
A Sharikova ◽  
R Chatelain ◽  
...  
Keyword(s):  
Spontaneous Emission ◽  
Transition Probabilities ◽  
Ion Beam ◽  
Branching Ratios ◽  
Oscillator Strengths ◽  
Single Frequency ◽  
Beam Laser ◽  
Fluorescence Measurements ◽  
Frequency Laser ◽  
Fast Ion

We measured the spontaneous-emission branching ratios of 69 levels in Sm II selectively populated via single-frequency laser excitation of a 10 keV ion beam. The levels studied had term energies up to 29 600 cm–1, and decay branches with spontaneous emission in the range 250–850 nm were detected. The experimental accuracy was in the range of 10%. We used these branching ratios along with our previously determined radiative lifetimes to infer transition probabilities and oscillator strengths for 608 transitions in the wavelength range 363–771 nm, which are useful for stellar abundance determinations.PACS Nos.: 32.70.Cs, 95.30.Ky

Oscillator strengths and radiative branching ratios in atomic Sr

1992 ◽  
Vol 46 (3) ◽  
pp. 1248-1260 ◽  
Author(s):  
H. G. C. Werij ◽  
Chris H. Greene ◽  
C. E. Theodosiou ◽  
Alan Gallagher
Keyword(s):  
Branching Ratios ◽  
Oscillator Strengths
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