41,426 research outputs found
Synthesising, using, and correcting for telluric features in high-resolution astronomical spectra
We present a technique to synthesise telluric absorption and emission
features both for in-situ wavelength calibration and for their removal from
astronomical spectra. While the presented technique is applicable for a wide
variety of optical and infrared spectra, we concentrate in this paper on
selected high-resolution near-infrared spectra obtained with the CRIRES
spectrograph to demonstrate its performance and limitation. We find that
synthetic spectra reproduce telluric absorption features to about 2%, even
close to saturated line cores. Thus, synthetic telluric spectra could be used
to replace the observation of telluric standard stars, saving valuable
observing time. This technique also provides a precise in-situ wavelength
calibration, especially useful for high-resolution near-infrared spectra in the
absence of other calibration sources.Comment: 11 pages, 11 figures, accepted for publication in A&A (updated
version
Wet scavenging of soluble gases in DC3 deep convective storms using WRF-Chem simulations and aircraft observations
We examine wet scavenging of soluble trace gases in storms observed during the Deep Convective Clouds and Chemistry (DC3) field campaign. We conduct high-resolution simulations with the Weather Research and Forecasting model with Chemistry (WRF-Chem) of a severe storm in Oklahoma. The model represents well the storm location, size, and structure as compared with Next Generation Weather Radar reflectivity, and simulated CO transport is consistent with aircraft observations. Scavenging efficiencies (SEs) between inflow and outflow of soluble species are calculated from aircraft measurements and model simulations. Using a simple wet scavenging scheme, we simulate the SE of each soluble species within the error bars of the observations. The simulated SEs of all species except nitric acid (HNO_3) are highly sensitive to the values specified for the fractions retained in ice when cloud water freezes. To reproduce the observations, we must assume zero ice retention for formaldehyde (CH_2O) and hydrogen peroxide (H_2O_2) and complete retention for methyl hydrogen peroxide (CH_3OOH) and sulfur dioxide (SO_2), likely to compensate for the lack of aqueous chemistry in the model. We then compare scavenging efficiencies among storms that formed in Alabama and northeast Colorado and the Oklahoma storm. Significant differences in SEs are seen among storms and species. More scavenging of HNO_3 and less removal of CH_3OOH are seen in storms with higher maximum flash rates, an indication of more graupel mass. Graupel is associated with mixed-phase scavenging and lightning production of nitrogen oxides (NO_x), processes that may explain the observed differences in HNO_3 and CH_3OOH scavenging
Photostatistics Reconstruction via Loop Detector Signatures
Photon-number resolving detectors are a fundamental building-block of optical
quantum information processing protocols. A loop detector, combined with
appropriate statistical processing, can be used to convert a binary on/off
photon counter into a photon-number-resolving detector. Here we describe the
idea of a signature of photon-counts, which may be used to more robustly
reconstruct the photon number distribution of a quantum state. The methodology
is applied experimentally in a 9-port loop detector operating at a
telecommunications wavelength and compared directly to the approach whereby
only the number of photon-counts is used to reconstruct the input distribution.
The signature approach is shown to be more robust against calibration errors,
exhibit reduced statistical uncertainty, and reduced reliance on a-priori
assumptions about the input state.Comment: 13 pages, 12 figure
New attempts to understand nanodiamond stardust
We report on a concerted effort aimed at understanding the origin and history
of the pre-solar nanodiamonds in meteorites including the astrophysical sources
of the observed isotopic abundance signatures. This includes measurement of
light elements by secondary ion mass spectrometry (SIMS), analysis of
additional heavy trace elements by accelerator mass spectrometry (AMS) and
dynamic calculations of r-process nucleosynthesis with updated nuclear
properties. Results obtained indicate: a) there is no evidence for the former
presence of now extinct 26Al and 44Ti in our diamond samples other than what
can be attributed to silicon carbide and other "impurities"; this does not
offer support for a supernova (SN) origin but neither does it negate it; b)
analysis by AMS of platinum in "bulk diamond" yields an overabundance of r-only
198Pt that at face value seems more consistent with the neutron burst than with
the separation model for the origin of heavy trace elements in the diamonds,
although this conclusion is not firm given analytical uncertainties; c) if the
Xe-H pattern was established by an unadulterated r-process, it must have been a
strong variant of the main r-process, which possibly could also account for the
new observations in platinum.Comment: Workshop on Astronomy with Radioactvities VII; Publications of the
Astronomical Society of Australia, accepte
Resolving the chemical substructure of Orion-KL
The Kleinmann-Low nebula in Orion (Orion-KL) is the nearest example of a
high-mass star-forming environment. For the first time, we complemented 1.3 mm
Submillimeter Array (SMA) interferometric line survey with IRAM 30 m
single-dish observations of the Orion-KL region. Covering a 4 GHz bandwidth in
total, this survey contains over 160 emission lines from 20 species (25
isotopologues), including 11 complex organic molecules (COMs).
At a spatial resolution of 1200 AU, the continuum substructures are resolved.
Extracting the spectra from individual substructures and providing the
intensity-integrated distribution map for each species, we studied the
small-scale chemical variations in this region. Our main results are: (1) We
identify lines from the low-abundance COMs CH3COCH3 and CH3CH2OH, as well as
tentatively detect CH3CHO and long carbon-chains C6H and HC7N. (2) We find that
while most COMs are segregated by type, peaking either towards the hot core
(e.g., N-bearing species) or the compact ridge (e.g., O-bearing species like
HCOOCH3 and CH3OCH3), while the distributions of others do not follow this
segregated structure (e.g., CH3CH2OH, CH3OH, CH3COCH3). (3) We find a second
velocity component of HNCO, SO2, 34SO2, and SO lines, which may be associated
with a strong shock event in the low-velocity outflow. (4) Temperatures and
molecular abundances show large gradients between central condensations and the
outflow regions, illustrating a transition between hot molecular core and
shock-chemistry dominated regimes.
Our observations of spatially resolved chemical variations in Orion-KL
provide the nearest reference source for hot molecular core and outflow
chemistry, which will be an important example for interpreting the chemistry of
more distant HMSFRs.Comment: 51 pages, 17 figures, accepted on 12 March 2015 Dashed lines in
Figure 10 of the published paper was missin
Toward precision mass measurements of neutron-rich nuclei relevant to -process nucleosynthesis
The open question of where, when, and how the heavy elements beyond iron
enrich our Universe has triggered a new era in nuclear physics studies.\ Of all
the relevant nuclear physics inputs, the mass of very neutron-rich nuclides is
a key quantity for revealing the origin of heavy elements beyond iron.\
Although the precise determination of this property is a great challenge,
enormous progress has been made in recent decades, and it has contributed
significantly to both nuclear structure and astrophysical nucleosynthesis
studies.\ In this review, we first survey our present knowledge of the nuclear
mass surface, emphasizing the importance of nuclear mass precision in
-process calculations.\ We then discuss recent progress in various methods
of nuclear mass measurement with a few selected examples.\ For each method, we
focus on recent breakthroughs and discuss possible ways of improving the
weighing of -process nuclides.Comment: 10 figures, review articles in Frontiers of Physic
Detections of Diffuse Interstellar Bands in the SDSS Low-resolution Spectra
Diffuse interstellar bands (DIBs) have been discovered for almost a century,
but their nature remains one of the most challenging problems in astronomical
spectroscopy. Most recent work to identify and investigate the properties and
carriers of DIBs concentrates on high-resolution spectroscopy of selected
sight-lines. In this paper, we report detections of DIBs in the Sloan Digital
Sky Survey (SDSS) low-resolution spectra of a large sample of Galactic stars.
Using a template subtraction method, we have successfully identified the DIBs
5780, 6283 in the SDSS spectra of a sample of about 2,000
stars and measured their strengths and radial velocities. The sample is by far
the largest ever assembled. The targets span a large range of reddening, E(B-V)
~ 0.2 -- 1.0, and are distributed over a large sky area and involve a wide
range of stellar parameters (effective temperature, surface gravity and
metallicity), confirming that the carriers of DIBs are ubiquitous in the
diffuse interstellar medium (ISM). The sample is used to investigate relations
between strengths of DIBs and magnitudes of line-of-sight extinction, yielding
results (i.e., EW(5780)= 0.61 x E(B-V) and EW(6283) = 1.26 x E(B-V)) consistent
with previous studies. DIB features have also been detected in the
commissioning spectra of the Guoshoujing Telescope (LAMOST) of resolving power
similar to that of SDSS. Detections of DIBs towards hundreds of thousands of
stars are expected from the on-going and up-coming large scale spectroscopic
surveys such as RAVE, SDSS III and LAMOST, particularly from the LAMOST Digital
Sky Survey of the Galactic Anti-center (DSS-GAC). Such a huge database will
provide an unprecedented opportunity to study the demographical distribution
and nature of DIBs as well as using DIBs to probe the distribution and
properties of the ISM and the dust extinction.Comment: 10 pages, 5 figures, accepted for publication in MNRA
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