16,883 research outputs found
Improved V II log() Values, Hyperfine Structure Constants, and Abundance Determinations in the Photospheres of the Sun and Metal-poor Star HD 84937
New experimental absolute atomic transition probabilities are reported for
203 lines of V II. Branching fractions are measured from spectra recorded using
a Fourier transform spectrometer and an echelle spectrometer. The branching
fractions are normalized with radiative lifetime measurements to determine the
new transition probabilities. Generally good agreement is found between this
work and previously reported V II transition probabilities. Use of two
spectrometers, independent radiometric calibration methods, and independent
data analysis routines enables a reduction in systematic uncertainties, in
particular those due to optical depth errors. In addition, new hyperfine
structure constants are measured for selected levels by least squares fitting
line profiles in the FTS spectra. The new V II data are applied to high
resolution visible and UV spectra of the Sun and metal-poor star HD 84937 to
determine new, more accurate V abundances. Lines covering a range of wavelength
and excitation potential are used to search for non-LTE effects. Very good
agreement is found between our new solar photospheric V abundance, log
{\epsilon}(V) = 3.95 from 15 V II lines, and the solar-system meteoritic value.
In HD 84937, we derive [V/H] = -2.08 from 68 lines, leading to a value of
[V/Fe] = 0.24.Comment: 32 pages, 7 tables (3 machine-readable), 8 figures; accepted for
publication in ApJ
A Linear Iterative Unfolding Method
A frequently faced task in experimental physics is to measure the probability
distribution of some quantity. Often this quantity to be measured is smeared by
a non-ideal detector response or by some physical process. The procedure of
removing this smearing effect from the measured distribution is called
unfolding, and is a delicate problem in signal processing, due to the
well-known numerical ill behavior of this task. Various methods were invented
which, given some assumptions on the initial probability distribution, try to
regularize the unfolding problem. Most of these methods definitely introduce
bias into the estimate of the initial probability distribution. We propose a
linear iterative method, which has the advantage that no assumptions on the
initial probability distribution is needed, and the only regularization
parameter is the stopping order of the iteration, which can be used to choose
the best compromise between the introduced bias and the propagated statistical
and systematic errors. The method is consistent: "binwise" convergence to the
initial probability distribution is proved in absence of measurement errors
under a quite general condition on the response function. This condition holds
for practical applications such as convolutions, calorimeter response
functions, momentum reconstruction response functions based on tracking in
magnetic field etc. In presence of measurement errors, explicit formulae for
the propagation of the three important error terms is provided: bias error,
statistical error, and systematic error. A trade-off between these three error
terms can be used to define an optimal iteration stopping criterion, and the
errors can be estimated there. We provide a numerical C library for the
implementation of the method, which incorporates automatic statistical error
propagation as well.Comment: Proceedings of ACAT-2011 conference (Uxbridge, United Kingdom), 9
pages, 5 figures, changes of corrigendum include
Nucleosynthesis: Stellar and Solar Abundances and Atomic Data
Abundance observations indicate the presence of often surprisingly large
amounts of neutron capture (i.e., s- and r-process) elements in old Galactic
halo and globular cluster stars. These observations provide insight into the
nature of the earliest generations of stars in the Galaxy -- the progenitors of
the halo stars -- responsible for neutron-capture synthesis. Comparisons of
abundance trends can be used to understand the chemical evolution of the Galaxy
and the nature of heavy element nucleosynthesis. In addition age
determinations, based upon long-lived radioactive nuclei abundances, can now be
obtained. These stellar abundance determinations depend critically upon atomic
data. Improved laboratory transition probabilities have been recently obtained
for a number of elements. These new gf values have been used to greatly refine
the abundances of neutron-capture elemental abundances in the solar photosphere
and in very metal-poor Galactic halo stars. The newly determined stellar
abundances are surprisingly consistent with a (relative) Solar System r-process
pattern, and are also consistent with abundance predictions expected from such
neutron-capture nucleosynthesis.Comment: 8 pages, 2 figures, 1 table. To appear in the Proceedings of the NASA
Laboratory Astrophysics Workshop in Las Vegas, NV (February 2006
Recommended from our members
Improved Log(gf) Values for Lines of Ti I and Abundance Determinations in the Photospheres of the Sun and Metal-Poor Star HD 84937 (Accurate Transition Probabilities for Ti I)
New atomic transition probability measurements for 948 lines of Ti I are reported. Branching fractions from Fourier transform spectra and from spectra recorded using a 3 m echelle spectrometer are combined with published radiative lifetimes from laser-induced fluorescence measurements to determine these transition probabilities. Generally good agreement is found in comparisons to the NIST Atomic Spectra Database. The new Ti I data are applied to re-determine the Ti abundance in the photospheres of the Sun and metal-poor star HD 84937 using many lines covering a range of wavelength and excitation potential to explore possible non-local thermal equilibrium effects. The variation of relative Ti/Fe abundance with metallicity in metal-poor stars observed in earlier studies is supported in this study.NSF AST-1211055, AST-0908978, AST-1211585NSF REU grant AST-1004881ESO Science Archive Facility 073.D-0024, 266.D-5655NASA NAS 5-26555Astronom
A Study of Compact Radio Sources in Nearby Face-on Spiral Galaxies. II. Multiwavelength Analyses of Sources in M51
We report the analysis of deep radio observations of the interacting galaxy
system M51 from the Very Large Array, with the goal of understanding the nature
of the population of compact radio sources in nearby spiral galaxies. We detect
107 compact radio sources, 64% of which have optical counterparts in a deep
H Hubble Space Telescope image. Thirteen of the radio sources have
X-ray counterparts from a {\em Chandra} observation of M51. We find that six of
the associated H sources are young supernova remnants with resolved
shells. Most of the SNRs exhibit steep radio continuum spectral indices
onsistent with synchrotron emission. We detect emission from the Type Ic SN
1994I nearly a decade after explosion: the emission (Jy
beam at 20 cm, Jy beam at 6cm,
) is consistent with light curve models for Type Ib/Ic
supernovae. We detect X-ray emission from the supernova, however no optical
counterpart is present. We report on the analysis of the Seyfert 2 nucleus in
this galaxy, including the evidence for bipolar outflows from the central black
hole.Comment: 22 pages, 8 figures (5 color) in separate files, AASTeX. Full
resolution figures and preprint may be obtained by contacting
[email protected]. AJ accepte
Relativistic many-body calculations of the Stark-induced amplitude of the 6P1/2 -7P1/2 transition in thallium
Stark-induced amplitudes for the 6P1/2 - 7P1/2 transition in Tl I are
calculated using the relativistic SD approximation in which single and double
excitations of Dirac-Hartree-Fock levels are summed to all orders in
perturbation theory. Our SD values alpha S = 368 a0 3 and beta S= 298 a 0 3 are
in good agreement with the measurements alpha S=377(8) a 0 3$ and beta S =
313(8) a 0 3 by D. DeMille, D. Budker, and E. D. Commins [Phys. Rev. A 50, 4657
(1994)]. Calculations of the Stark shifts in the 6P1/2 - 7P1/2 and 6P1/2 -
7S1/2 transitions are also carried out. The Stark shifts predicted by our
calculations agree with the most accurate measured values within the
experimental uncertainties for both transitions
Recommended from our members
Improved V I Log(gf) Values and Abundance Determinations in the Photospheres of the Sun and Metal-Poor Star HD 84937
New emission branching fraction measurements for 836 lines of the first spectrum of vanadium (V I) are determined from hollow cathode lamp spectra recorded with the National Solar Observatory 1 m Fourier transform spectrometer (FTS) and a high-resolution echelle spectrometer. The branching fractions are combined with recently published radiative lifetimes from laser-induced fluorescence measurements to determine accurate absolute atomic transition probabilities for the 836 lines. The FTS data are also used to extract new hyperfine structure A coefficients for 26 levels of neutral vanadium. These new laboratory data are applied to determine the V abundance in the Sun and metal-poor star HD 84937, yielding log epsilon(V) = 3.956 +/- 0.004 (sigma = 0.037) based on 93 V I lines and log epsilon(V) = 1.89 +/- 0.03 (sigma = 0.07) based on nine Vi lines, respectively, using the Holweger-Muller 1D model. These new V I abundance values for the Sun and HD 84937 agree well with our earlier determinations based upon V II.NASA NNX10AN93GNSF AST-1211055, AST-1211585Astronom
- …