638 research outputs found
Boron Abundances in Diffuse Interstellar Clouds
We present a comprehensive survey of B abundances in diffuse interstellar
clouds from HST/STIS observations along 56 Galactic sight lines. Our sample is
the result of a complete search of archival STIS data for the B II resonance
line at 1362 angstroms, with each detection confirmed by the presence of
absorption from other dominant ions at the same velocity. The data probe a
range of astrophysical environments including both high-density regions of
massive star formation as well as low-density paths through the Galactic halo,
allowing us to clearly define the trend of B depletion onto interstellar grains
as a function of gas density. Many extended sight lines exhibit complex
absorption profiles that trace both local gas and gas associated with either
the Sagittarius-Carina or Perseus spiral arm. Our analysis indicates a higher
B/O ratio in the inner Sagittarius-Carina spiral arm than in the vicinity of
the Sun, which may suggest that B production in the current epoch is dominated
by a secondary process. The average gas-phase B abundance in the warm diffuse
ISM is consistent with the abundances determined for a variety of Galactic disk
stars, but is depleted by 60 percent relative to the solar system value. Our
survey also reveals sight lines with enhanced B abundances that potentially
trace recent production of B-11 either by cosmic-ray or neutrino-induced
spallation. Such sight lines will be key to discerning the relative importance
of the two production routes for B-11 synthesis.Comment: To be published in the proceedings of the IAU Symposium 268, Light
Elements in the Universe, C. Charbonnel, M. Tosi, F. Primas & C. Chiappini,
ed
The Interstellar Rubidium Isotope Ratio toward Rho Ophiuchi A
The isotope ratio, 85Rb/87Rb, places constraints on models of the
nucleosynthesis of heavy elements, but there is no precise determination of the
ratio for material beyond the Solar System. We report the first measurement of
the interstellar Rb isotope ratio. Our measurement of the Rb I line at 7800 A
for the diffuse gas toward rho Oph A yields a value of 1.21 +/- 0.30 (1-sigma)
that differs significantly from the meteoritic value of 2.59. The Rb/K
elemental abundance ratio for the cloud also is lower than that seen in
meteorites. Comparison of the 85Rb/K and 87Rb/K ratios with meteoritic values
indicates that the interstellar 85Rb abundance in this direction is lower than
the Solar System abundance. We attribute the lower abundance to a reduced
contribution from the r-process. Interstellar abundances for Kr, Cd, and Sn are
consistent with much less r-process synthesis for the solar neighborhood
compared to the amount inferred for the Solar System.Comment: 12 pages with 2 figures and 1 table; will appear in ApJ Letter
Oscillator Strengths for B-X, C-X, and E-X Transitions in Carbon Monoxide
Band oscillator strengths for electronic transitions in CO were obtained at
the Synchrotron Radiation Center of the University of Wisconsin-Madison. Our
focus was on transitions that are observed in interstellar spectra with the Far
Ultraviolet Spectroscopic Explorer; these transitions are also important in
studies of selective isotope photodissociation where fractionation among
isotopomers can occur. Absorption from the ground state (X ^1Sigma^+ v'' = 0)
to A ^1Pi (v'= 5), B ^1Sigma^+ (v' = 0, 1), C ^1Sigma^+ (v' = 0, 1), and E ^1Pi
(v' = 0) was measured. Fits to the A - X (5, 0) band, whose oscillator strength
is well known, yielded the necessary column density and excitation temperature.
These parameters were used in a least-squares fit of the observed profiles for
the transitions of interest to extract their band oscillator strengths. Our
oscillator strengths are in excellent agreement with results from recent
experiments using a variety of techniques. This agreement provides the basis
for a self-consistent set of f-values at far ultraviolet wavelengths for
studies of interstellar (and stellar) CO.Comment: 22 pages, 3 figures, ApJS (in press
What is the Total Deuterium Abundance in the Local Galactic Disk?
Analyses of spectra obtained with the Far Ultraviolet Spectroscopic Explorer
(FUSE) satellite, together with spectra from the Copernicus and IMAPS
instruments, reveal an unexplained very wide range in the observed
deuterium/hydrogen (D/H) ratios for interstellar gas in the Galactic disk
beyond the Local Bubble. We argue that spatial variations in the depletion of
deuterium onto dust grains can explain these local variations in the observed
gas-phase D/H ratios. We present a variable deuterium depletion model that
naturally explains the constant measured values of D/H inside the Local Bubble,
the wide range of gas-phase D/H ratios observed in the intermediate regime (log
N(H I} = 19.2-20.7), and the low gas-phase D/H ratios observed at larger
hydrogen column densities. We consider empirical tests of the deuterium
depletion hypothesis: (i) correlations of gas-phase D/H ratios with depletions
of the refractory metals iron and silicon, and (ii) correlation with the
molecular hydrogen rotational temperature. Both of these tests are consistent
with deuterium depletion from the gas phase in cold, not recently shocked,
regions of the ISM, and high gas-phase D/H ratios in gas that has been shocked
or otherwise heated recently. We argue that the most representative value for
the total (gas plus dust) D/H ratio within 1 kpc of the Sun is >=23.1 +/- 2.4
(1 sigma) parts per million (ppm). This ratio constrains Galactic chemical
evolution models to have a very small deuterium astration factor, the ratio of
primordial to total (D/H) ratio in the local region of the Galactic disk, which
we estimate to be f_d <= 1.19 +/-0.16 (1 sigma) or <= 1.12 +/- 0.14 (1 sigma)
depending on the adopted light element nuclear reaction rates.Comment: 19 pages, 9 figure
Religion and religious education : comparing and contrasting pupilsâ and teachersâ views in an English school
This publication builds on and develops the English findings of the qualitative study of European teenagersâ perspectives on religion and religious education (Knauth et al. 2008), part of âReligion in Education: A contribution to dialogue or a factor of conflict in transforming societies of European countries?â (REDCo) project. It uses data gathered from 27 pupils, aged 15-16, from a school in a multicultural Northern town in England and compares those findings with data gathered from ten teachers in the humanities faculty of the same school, collected during research for the Warwick REDCo Community of Practice. Comparisons are drawn between the teachersâ and their pupilsâ attitudes and values using the same structure as the European study: personal views and experiences of religion, the social dimension of religion, and religious education in school. The discussion offers an analysis of the similarities and differences in worldviews and beliefs which emerged. These include religious commitment/observance differences between the mainly Muslim-heritage pupils and their mainly non-practising Christian-heritage teachers. The research should inform the ways in which the statutory duties to promote community cohesion and equalities can be implemented in schools. It should also facilitate intercultural and interreligious understanding between teachers and the pupils from different ethnic and religious backgrounds
Molecular tracers of PDR-dominated galaxies
Photon-dominated regions (PDRs) are powerful molecular line emitters in
external galaxies. They are expected in galaxies with high rates of massive
star formation due to either starburst (SB) events or starburst coupled with
active galactic nuclei (AGN) events. We have explored the PDR chemistry for a
range of physical conditions representing a variety of galaxy types. Our main
result is a demonstration of the sensitivity of the chemistry to changes in the
physical conditions. We adopt crude estimates of relevant physical parameters
for several galaxy types and use our models to predict suitable molecular
tracers of those conditions. The set of recommended molecular tracers differs
from that which we recommended for use in galaxies with embedded massive stars.
Thus, molecular observations can in principle be used to distinguish between
excitation by starburst and by SB+AGN in distant galaxies. Our recommendations
are intended to be useful in preparing Herschel and ALMA proposals to identify
sources of excitation in galaxies.Comment: 18 pages, 6 figures, Accepted in Ap
Potential Variations in the Interstellar N I Abundance
We present Far Ultraviolet Spectroscopic Explorer (FUSE) and Space Telescope
Imaging Spectrograph observations of the weak interstellar N I doublet at 1160
Angstroms toward 17 high-density sight lines [N(Htot)>=10^21 cm^-2]. When
combined with published data, our results reveal variations in the fractional N
I abundance showing a systematic deficiency at large N(Htot). At the FUSE
resolution (~20 km s^-1), the effects of unresolved saturation cannot be
conclusively ruled out, although O I at 1356 Angstroms shows little evidence of
saturation. We investigated the possibility that the N I variability is due to
the formation of N_2 in our mostly dense regions. The 0-0 band of the c'_4
^1Sigma^+_u - X ^1Sigma^+_g transition of N_2 at 958 Angstroms should be easily
detected in our FUSE data; for 10 of the denser sight lines, N_2 is not
observed at a sensitivity level of a few times 10^14 cm^-2. The observed N I
variations are suggestive of an incomplete understanding of nitrogen chemistry.
Based on observations made with the NASA-CNES-CSA Far Ultraviolet
Spectroscopic Explorer, which is operated for NASA by the Johns Hopkins
University under NASA contract NAS 5-32985, and the NASA/ESA Hubble Space
Telescope, obtained from the Multimission Archive at the Space Telescope
Science Institute, which is operated by the Association of Universities for
Research in Astronomy, Inc., under the NASA contract NAS 5-26555.Comment: 12 pages, 3 figures, accepted for publication in ApJ Letter
Observation of interstellar lithium in the low-metallicity Small Magellanic Cloud
The primordial abundances of light elements produced in the standard theory
of Big Bang nucleosynthesis (BBN) depend only on the cosmic ratio of baryons to
photons, a quantity inferred from observations of the microwave background. The
predicted primordial 7Li abundance is four times that measured in the
atmospheres of Galactic halo stars. This discrepancy could be caused by
modification of surface lithium abundances during the stars' lifetimes or by
physics beyond the Standard Model that affects early nucleosynthesis. The
lithium abundance of low-metallicity gas provides an alternative constraint on
the primordial abundance and cosmic evolution of lithium that is not
susceptible to the in situ modifications that may affect stellar atmospheres.
Here we report observations of interstellar 7Li in the low-metallicity gas of
the Small Magellanic Cloud, a nearby galaxy with a quarter the Sun's
metallicity. The present-day 7Li abundance of the Small Magellanic Cloud is
nearly equal to the BBN predictions, severely constraining the amount of
possible subsequent enrichment of the gas by stellar and cosmic-ray
nucleosynthesis. Our measurements can be reconciled with standard BBN with an
extremely fine-tuned depletion of stellar Li with metallicity. They are also
consistent with non-standard BBN.Comment: Published in Nature. Includes main text and Supplementary
Information. Replaced with final title and abstrac
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