1,517,511 research outputs found
Regular holonomic D[[h]]-modules
We describe the category of regular holonomic modules over the ring D[[h]] of
linear differential operators with a formal parameter h. In particular, we
establish the Riemann-Hilbert correspondence and discuss the additional
t-structure related to h-torsion.Comment: 39 page
The Deuterium to Hydrogen Abundance Ratio Towards a Fourth QSO: HS0105+1619
We report the measurement of the primordial D/H abundance ratio towards QSO
\object. The column density of the hydrogen in the Lyman limit
system is high, \lnhi \cmm, allowing for the deuterium to
be seen in 5 Lyman series transitions. The measured value of the D/H ratio
towards QSO \object is found to be D/H. The
metallicity of the system showing D/H is found to be solar,
indicating that the measured D/H is the primordial D/H within the measurement
errors. The gas which shows D/H is neutral, unlike previous D/H systems which
were more highly ionized. Thus, the determination of the D/H ratio becomes more
secure since we are measuring it in different astrophysical environments, but
the error is larger because we now see more dispersion between measurements.
Combined with prior measurements of D/H, the best D/H ratio is now D/H, which is 10% lower than the previous value. The new
values for the baryon to photon ratio, and baryonic matter density derived from
D/H are and \ob
respectively.Comment: Minor text and reference changes. To appear in the May 10, 2001 issue
of the Astrophysical Journa
Exploring the Origins of Deuterium Enrichments in Solar Nebular Organics
Deuterium-to-hydrogen (D/H) enrichments in molecular species provide clues
about their original formation environment. The organic materials in primitive
solar system bodies have generally higher D/H ratios and show greater D/H
variation when compared to D/H in solar system water. We propose this
difference arises at least in part due to 1) the availability of additional
chemical fractionation pathways for organics beyond that for water, and 2) the
higher volatility of key carbon reservoirs compared to oxygen. We test this
hypothesis using detailed disk models, including a sophisticated, new disk
ionization treatment with a low cosmic ray ionization rate, and find that disk
chemistry leads to higher deuterium enrichment in organics compared to water,
helped especially by fractionation via the precursors CHD/CH. We
also find that the D/H ratio in individual species varies significantly
depending on their particular formation pathways. For example, from
AU, CH can reach , while D/H in CHOH
remains locally unaltered. Finally, while the global organic D/H in our models
can reproduce intermediately elevated D/H in the bulk hydrocarbon reservoir,
our models are unable to reproduce the most deuterium-enriched organic
materials in the solar system, and thus our model requires some inheritance
from the cold interstellar medium from which the Sun formed.Comment: 11 pages, 7 figures, accepted for publication in Ap
A High Deuterium Abundance at z=0.7
Of the light elements, the primordial abundance of deuterium, (D/H)_p,
provides the most sensitive diagnostic for the cosmological mass density
parameter Omega_B. Recent high redshift (D/H) measurements are highly
discrepant, although this may reflect observational uncertainties. The larger
(D/H) values, which imply a low Omega_B and require the Universe to be
dominated by non-baryonic matter (dynamical studies indicate a higher total
density parameter), cause problems for galactic chemical evolution models since
they have difficulty in reproducing the large decline down to the lower
present-day (D/H). Conversely, low (D/H) values imply an Omega_B greater than
derived from ^7Li and ^4He abundance measurements, and may require a deuterium
abundance evolution that is too low to easily explain. Here we report the first
measurement at intermediate redshift, where the observational difficulties are
smaller, of a gas cloud with ideal characteristics for this experiment. Our
analysis of the z = 0.7010 absorber toward 1718+4807 indicates (D/H) = 2.0 +/-
0.5 x 10^{-4} which is in the high range. This and other independent
observations suggests there may be a cosmological inhomogeneity in (D/H)_p of
at least a factor of ten.Comment: 6 pages, 1 figur
The Deuterium to Hydrogen Abundance Ratio Towards the QSO SDSS1558-0031
We present a measurement of the D/H abundance ratio in a metal-poor damped
Lyman alpha (DLA) system along the sightline of QSO SDSS1558-0031. The DLA
system is at redshift z = 2.70262, has a neutral column density of
log(NHI)=20.67+/-0.05 cm^2, and a gas-phase metallicity [O/H]= -1.49 which
indicates that deuterium astration is negligible. Deuterium absorption is
observed in multiple Lyman series with a column density of
log(NDI)=16.19+/-0.04 cm^2, best constrained by the deuterium Lyman-11 line. We
measure log(D/H) = -4.48+/-0.06, which when combined with previous measurements
along QSO sightlines gives a best estimate of log(D/H) = -4.55+/-0.04, where
the 1-sigma error estimate comes from a jackknife analysis of the weighted
means. Using the framework of standard big bang nucleosynthesis, this value of
D/H translates into a baryon density of Omega_b h^2 = 0.0213 +/- 0.0013 +/-
0.0004 where the error terms represent the 1-sigma errors from D/H and the
uncertainties in the nuclear reaction rates respectively. Combining our new
measurement with previous measurements of D/H, we no longer find compelling
evidence for a trend of D/H with NHI.Comment: 13 pages, 3 figures, 1 table. Accepted to the Astrophysical Journal
Letter
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
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