2,276 research outputs found
Warm HCN, C2H2, and CO in the disk of GV Tau
We present the first high-resolution, ground-based observations of HCN and
C2H2 toward the T Tauri binary star system GV Tau. We detected strong
absorption due to HCN nu_3 and weak C2H2 (nu_3 and nu_2 + (nu_4 + nu_5)^0_+)
absorption toward the primary (GV Tau S) but not the infrared companion. We
also report CO column densities and rotational temperatures, and present
abundances relative to CO of HCN/CO ~0.6% and C2H2/CO ~1.2% and an upper limit
for CH4/CO < 0.37% toward GV Tau S. Neither HCN nor C2H2 were detected toward
the infrared companion and results suggest that abundances may differ between
the two sources.Comment: 23 pages, 6 figures, accepted by Ap
Antarctic Analog for Dilational Bands on Europa
Europa's surface shows signs of extension, which is revealed as lithospheric dilation expressed along ridges, dilational bands and ridged bands. Ridges, the most common tectonic feature on Europa, comprise a central crack flanked by two raised banks a few hundred meters high on each side. Together these three classes may represent a continuum of formation. In Tufts' Dilational Model ridge formation is dominated by daily tidal cycling of a crack, which can be superimposed with regional secular dilation. The two sources of dilation can combine to form the various band morphologies observed. New GPS data along a rift on the Ross Ice Shelf, Antarctica is a suitable Earth analog to test the framework of Tufts' Dilational Model. As predicted by Tufts' Dilational Model, tensile failures in the Ross Ice Shelf exhibit secular dilation, upon which a tidal signal can be seen. From this analog we conclude that Tufts' Dilational Model for Europan ridges and bands may be credible and that the secular dilation is most likely from a regional source and not tidally driven
Assessment of ICESat-2 Ice Sheet Surface Heights, Based on Comparisons over the Interior of the Antarctic Ice Sheet
We collected kinematic Global Navigation Satellite Systems (GNSS) surface height data, on a 750km groundbased traverse of the flat interior of the Antarctic ice sheet, for comparison with Ice, Cloud, and Land Elevation Satellite2 (ICESat2) surface heights. Vertical errors in the GNSS data are estimated to be 5.6 cm, comparable to results from a previous traverse and with yeartoyear comparisons. Comparisons of the GNSS heights and 6 months of ICESat2 ATL03 photonbased heights and ATL06 segmentbased heights indicate that the accuracy and precision of ICESat2 data are comparable to that of results from the ICESat mission: ATL03 is currently accurate to better than 5 cm with better than 13 cm of surface measurement precision, while ATL06 is currently accurate to better than 3 cm with better than 9 cm of surface measurement precision
Air pollution, deprivation and health: Understanding relationships to add value to local air quality management policy and practice in Wales, UK
© The Author 2016. Published by Oxford University Press on behalf of Faculty of Public Health. All rights reserved. Background Air pollution exposure reduces life expectancy. Air pollution, deprivation and poor-health status combinations can create increased and disproportionate disease burdens. Problems and solutions are rarely considered in a broad public health context, but doing so can add value to air quality management efforts by reducing air pollution risks, impacts and inequalities. Methods An ecological study assessed small-area associations between air pollution (nitrogen dioxide and particulate matter), deprivation status and health outcomes in Wales, UK. Results Air pollution concentrations were highest in 'most' deprived areas. When considered separately, deprivation-health associations were stronger than air pollution-health associations. Considered simultaneously, air pollution added to deprivation-health associations; interactions between air pollution and deprivation modified and strengthened associations with all-cause and respiratory disease mortality, especially in 'most' deprived areas where most-vulnerable people lived and where health needs were greatest. Conclusion There is a need to reduce air pollution-related risks for all. However, it is also the case that greater health gains can result from considering local air pollution problems and solutions in the context of wider health-determinants and acting on a better understanding of relationships. Informed and co-ordinated air pollution mitigation and public health action in high deprivation and pollution areas can reduce risks and inequalities. To achieve this, greater public health integration and collaboration in local air quality management policy and practice is needed
The Supernova Remnant CTB104A : Magnetic Field Structure and Interaction with the Environment
We present new, high resolution 1420 and 408 MHz continuum images and HI and
12CO (J=1-0) spectral line maps of the diffuse supernova remnant CTB104A
(G93.7-0.3). Analysis of the complex continuum emission reveals no significant
spectral index variations across the remnant. Three prominences around CTB104A
are found to be related to the SNR, while one extension to the east is
identified as an HII region associated with a background molecular shell. Small
scale polarization and rotation measure (RM) structures are turbulent in
nature, but we find a well-ordered RM gradient across the remnant, extending
from southeast to northwest. This gradient does not agree with the direction of
the global Galactic magnetic field, but does agree with a large-scale RM
anomaly inferred from rotation measure data by Cleg et al. (1992). We show that
the observed morphology of CTB104A is consistent with expansion in a uniform
magnetic field, and this is supported by the observed RM distribution. By
modeling the RM gradient with a simple compression model we have determined the
magnetic field strength within the remnant as Bo ~ 2.3 micro G. We have
identified signatures of the interaction of CTB104A with the surrounding
neutral material, and determined its distance, from the kinematics of the HI
structure encompassing the radio emission, as 1.5 kpc. We also observed clear
breaks in the HI shell that correspond well to the positions of two of the
prominences, indicating regions where hot gas is escaping from the interior of
the SNR.Comment: 7 pages, Latex with aastex and emulateapj5, 12 figures, ApJ accepte
ICESat-2 Simulated Data from Airborne Altimetery
Ice, Cloud, and land Elevation Satellite-2 (ICESat-2) is scheduled to launch in 2015 and will carry onboard the Advanced Topographic Laser Altimeter System (ATLAS), which represents a new approach to spaceborne determination of surface elevations. Specifically, the current ATLAS design is for a micropulse, multibeam, photon-counting laser altimeter with lower energy, a shorter pulse width, and a higher repetition rate relative to the Geoscience Laser Altimeter (GLAS), the instrument that was onboard ICESat. Given the new and untested technology associated with ATLAS, airborne altimetry data is necessary (1) to test the proposed ATLAS instrument geometry, (2) to validate instrument models, and (3) to assess the atmospheric effects on multibeam altimeters. We present an overview of the airborne instruments and datasets intended to address the ATLAS instrument concept, including data collected over Greenland (July 2009) using an airborne SBIR prototype 100 channel, photon-counting, terrain mapping altimeter, which addresses the first of these 3 scientific concerns. Additionally, we present the plan for further simulator data collection over vegetated and ice covered regions using Multiple Altimeter Beam Experimental Lidar (MABEL), intended to address the latter two scientific concerns. As the ICESAT-2 project is in the design phase, the particular configuration of the ATLAS instrument may change. However, we expect this work to be relevant as long as ATLAS pursues a photon-counting approach
Assessment of altimetry using ground-based GPS data from the 88S Traverse, Antarctica, in support of ICESat-2
We conducted a 750 km kinematic GPS survey, referred to
as the 88S Traverse, based out of South Pole Station, Antarctica, between
December 2017 and January 2018. This ground-based survey was designed to
validate spaceborne altimetry and airborne altimetry developed at NASA. The
88S Traverse intersects 20 % of the ICESat-2 satellite orbits on a route
that has been flown by two different Operation IceBridge airborne laser
altimeters: the Airborne Topographic Mapper (ATM; 26 October 2014) and the
University of Alaska Fairbanks (UAF) Lidar (30 November and 3 December 2017). Here we present an overview of the ground-based GPS data quality and
a quantitative assessment of the airborne laser altimetry over a flat
section of the ice sheet interior. Results indicate that the GPS data are
internally consistent (1.1±4.1 cm). Relative to the ground-based 88S
Traverse data, the elevation biases for ATM and the UAF lidar range from
−9.5 to 3.6 cm, while surface measurement precisions are equal to or better
than 14.1 cm. These results suggest that the ground-based GPS data and
airborne altimetry data are appropriate for the validation of ICESat-2
surface elevation data.</p
The Molecular Environment of the Gamma-ray Source TeV J2032+4130
The mysterious very high energy gamma-ray source, TeV J2032+4130, is
coincident with the powerful Cygnus OB2 stellar association, though a physical
association between the two remains uncertain. It is possible that the detected
very high energy photons are produced via an overdensity of locally accelerated
cosmic rays impinging on molecular clouds in the source region. In order to
test this hypothesis, we used the Kitt Peak 12m, the Heinrich-Hertz
Submillimeter Telescope (HH-SMT), and the Five College Radio Astronomy
Observatory (FCRAO), to obtain observations in the J=1-->0 and J=2-->1 lines of
both 12CO and 13CO. We report here on the detection of significant molecular
material toward the TeV source region which could be acting as the target of
locally accelerated CRs. We also find evidence of compact molecular clumps,
showing large line widths in the CO spectra, possibly indicative of energetic
processes in this region of Cygnus OB2.Comment: Accepted for publication in ApJ
Probing the evolution of molecular cloud structure II: From chaos to confinement
We present an analysis of the large-scale molecular cloud structure and of
the stability of clumpy structures in nearby molecular clouds. In our recent
work, we identified a structural transition in molecular clouds by studying the
probability distributions of gas column densities in them. In this paper, we
further examine the nature of this transition. The transition takes place at
the visual extinction of A_V^tail = 2-4 mag, or equivalently, at \Sigma^tail =
40-80 Ms pc^{-2}. The clumps identified above this limit have wide ranges of
masses and sizes, but a remarkably constant mean volume density of n = 10^3
cm^{-3}. This is 5-10 times larger than the density of the medium surrounding
the clumps. By examining the stability of the clumps, we show that they are
gravitationally unbound entities, and that the external pressure from the
parental molecular cloud is a significant source of confining pressure for
them. Then, the structural transition at A_V^tail may be linked to a transition
between this population and the surrounding medium. The star formation rates in
the clouds correlate strongly with the total mass in the clumps, i.e, with the
mass above A_V^tail, dropping abruptly below that threshold. These results
imply that the formation of pressure confined clumps introduces a prerequisite
for star formation. Furthermore, they give a physically motivated explanation
for the recently reported relation between the star formation rates and the
amount of dense material in molecular clouds. Likewise, they give rise to a
natural threshold for star formation at A_V^tail.Comment: 11 pages, 12 figures, accepted for publication in Astronomy and
Astrophysic
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