1,123 research outputs found
The FERRUM Project: experimental and theoretical transition rates of forbidden [Sc II] lines and radiative lifetimes of metastable Sc II levels
Context. In many plasmas, long-lived metastable atomic levels are depopulated
by collisions (quenched) before they decay radiatively. In low-density regions,
however, the low collision rate may allow depopulation by electric dipole (E1)
forbidden radiative transitions, so-called forbidden lines (mainly M1 and E2
transitions). If the atomic transition data are known, these lines are
indicators of physical plasma conditions and used for abundance determination.
Aims. Transition rates can be derived by combining relative intensities between
the decay channels, so-called branching fractions (BFs), and the radiative
lifetime of the common upper level. We use this approach for forbidden [Sc ii]
lines, along with new calculations. Methods. Neither BFs for forbidden lines,
nor lifetimes of metastable levels, are easily measured in a laboratory.
Therefore, astrophysical BFs measured in Space Telescope Imaging Spectrograph
(STIS) spectra of the strontium filament of Eta Carinae are combined with
lifetime measurements using a laser probing technique on a stored ion-beam
(CRYRING facility,MSL, Stockholm). These quantities are used to derive the
absolute transition rates (A-values). New theoretical transition rates and
lifetimes are calulated using the CIV3 code. Results. We report experimental
lifetimes of the Sc ii levels 3d2 a3P0,1,2 with lifetimes 1.28, 1.42, and 1.24
s, respectively, and transition rates for lines from these levels down to 3d4s
a3D in the region 8270-8390 A. These are the most important forbidden [Sc ii]
transitions. New calculations for lines and metastable lifetimes are also
presented, and are in good agreement with the experimental data.Comment: 5 pages. Accepted for A&
An innovative method of extraction of coffee oil using an advanced microwave system: in comparison with conventional Soxhlet extraction method
The production of energy and chemicals from waste biomass is an attractive alternative by comparison with first generation biofuels and fossil feedstocks. This paper investigates oil extraction from spent coffee grounds (SCG) by means of an advanced microwave process and compares this with a conventional Soxhlet extraction (SE) method. Microwave assisted oil extraction (MAE) from SCG was performed over different durations, varying solvent volumes and extraction temperatures. It was found that each of these parameters had an effect on the process, with the largest yield being over 11.54 wt %, oil extracted in 10 minutes using 160 ml of hexane at 95 oC. In 10 minutes, MAE was successful in extracting more oil than SE. MAE achieved a 24 fold decrease in duration for the extraction compared with SE and used less solvent per gram of oil produced. It is proposed that a certain moisture content in the SCG would be beneficial to the extraction process and might it also play a role in the heating process. The extracted oil can be converted into biodiesel and biochemicals leaving the remaining solids suitable for processing into bioethanol, fertiliser, adsorptive material and fuel pellets
The FERRUM project: Transition probabilities for forbidden lines in [FeII] and experimental metastable lifetimes
Accurate transition probabilities for forbidden lines are important
diagnostic parameters for low-density astrophysical plasmas. In this paper we
present experimental atomic data for forbidden [FeII] transitions that are
observed as strong features in astrophysical spectra.
Aims: To measure lifetimes for the 3d^6(^3G)4s a ^4G_{11/2} and 3d^6(^3D)4s b
^4D_{1/2} metastable levels in FeII and experimental transition probabilities
for the forbidden transitions 3d^7 a ^4F_{7/2,9/2}- 3d^6(^3G)4s a ^4G_{11/2}.
Methods: The lifetimes were measured at the ion storage ring facility CRYRING
using a laser probing technique. Astrophysical branching fractions were
obtained from spectra of Eta Carinae, obtained with the Space Telescope Imaging
Spectrograph onboard the Hubble Space Telescope. The lifetimes and branching
fractions were combined to yield absolute transition probabilities.
Results: The lifetimes of the a ^4G_{11/2} and the b ^4D_{1/2} levels have
been measured and have the following values, 0.75(10) s and 0.54(3) s
respectively. Furthermore, we have determined the transition probabilities for
two forbidden transitions of a ^4F_{7/2,9/2}- a ^4G_{11/2} at 4243.97 and
4346.85 A. Both the lifetimes and the transition probabilities are compared to
calculated values in the literature.Comment: 5 pages, accepted for publication in A&
The deuterium-to-oxygen ratio in the interstellar medium
Because the ionization balances for HI, OI, and DI are locked together by
charge exchange, D/O is an important tracer for the value of the D/H ratio and
for potential spatial variations in the ratio. As the DI and OI column
densities are of similar orders of magnitude for a given sight line,
comparisons of the two values will generally be less subject to systematic
errors than comparisons of DI and HI, which differ by about five orders of
magnitude. Moreover, D/O is additionally sensitive to astration, because as
stars destroy deuterium, they should produce oxygen. We report here the results
of a survey of D/O in the interstellar medium performed with FUSE. We also
compare these results with those for D/N. Together with a few results from
previous missions, the sample totals 24 lines of sight. The distances range
from a few pc to ~2000 pc and log N(DI) from ~13 to ~16 (cm-2). The D/O ratio
is constant in the local interstellar medium out to distances of ~150 pc and
N(DI) ~ 1x10^15 cm-2, i.e. within the Local Bubble. In this region of the
interstellar space, we find D/O = (3.84+/-0.16)x10^-2 (1 sigma in the mean).
The homogeneity of the local D/O measurements shows that the spatial variations
in the local D/H and O/H must be extremely small, if any. A comparison of the
Local Bubble mean value with the few D/O measurements available for low
metallicity quasar sight lines shows that the D/O ratio decreases with cosmic
evolution, as expected. Beyond the Local Bubble we detected significant spatial
variations in the value of D/O. This likely implies a variation in D/H, as O/H
is known to not vary significantly over the distances covered in this study.
Our dataset suggests a present-epoch deuterium abundance below 1x10^-5, i.e.
lower than the value usually assumed, around 1.5x10^-5.Comment: 17 pages, 9 figures, 4 tables, accepted for publication in the
Astrophysical Journa
Mixed configuration-interaction and many-body perturbation theory calculations of energies and oscillator strengths of J=1 odd states of neon
Ab-initio theory is developed for energies of J=1 particle-hole states of
neutral neon and for oscillator strengths of transitions from such states to
the J=0 ground state. Hole energies of low-Z neonlike ions are evaluated.Comment: 5 pages, 1 figure, 4 table
V453 Oph: a s-process enriched, but carbon-deficient RV Tauri star of low intrinsic metallicity
This paper reports the detection of a heavy element enriched RV Tauri
variable with an abundance pattern that differs significantly from a standard
s-process enriched object: V453 Oph. Based on optical high-resolution spectra,
we determined that this object of low intrinsic metallicity ([Fe/H] = -2.2) has
a mild, but significant, enrichment ([s/Fe] ~ +0.5) of heavy elements for which
the distribution points to slow neutron capture nucleosynthesis. This result is
strengthened by a comparative analysis to the non-enriched RV Tauri star DS Aqr
([s/Fe] = 0.0). Although V453 Oph is the first RV Tauri star showing a strong
s-process signature, it is NOT accompanied by C enhancement, challenging our
current nucleosynthetic models of post-AGB stars that predict a simultaneous
enrichment in C and s-process elements. The low N abundance excludes CN cycling
as being responsible for the low C abundance. We explore three different
scenarios to explain the heavy element distribution in this evolved object: an
enrichment of the parental cloud, an accretion scenario in which the chemical
patterns were acquired by mass transfer in a binary system and an intrinsic
enrichment by dredge-up.Comment: Accepted for publication in A&
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