297 research outputs found
Panchromatic Hubble Andromeda Treasury IX: A Photometric Survey of Planetary Nebulae in M31
We search Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) and
Wide Field Camera 3 (WFC3) broadband imaging data from the Panchromatic Hubble
Andromeda Treasury (PHAT) survey to identify detections of cataloged planetary
nebulae (PNe). Of the 711 PNe currently in the literature within the PHAT
footprint, we find 467 detected in the broadband. For these 467 we are able to
refine their astrometric accuracy from ~0."3 to 0."05. Using the resolution of
HST, we are able to show that 152 objects currently in the catalogs are
definitively not PNe, and we show that 32 objects thought to be extended in
ground-based images are actually point-like and therefore good PN candidates.
We also find one PN candidate that is marginally resolved. If this is a PN, it
is up to 0.7 pc in diameter. With our new photometric data, we develop a method
of measuring the level of excitation in individual PNe by comparing broadband
and narrowband imaging and describe the effects of excitation on a PN's
photometric signature. Using the photometric properties of the known PNe in the
PHAT catalogs, we search for more PN, but do not find any new candidates,
suggesting that ground-based emission-line surveys are complete in the PHAT
footprint to F475W 24.Comment: 41 pages, 20 figures, 4 tables, accepted for publication in Ap
Contact inhibition of locomotion and mechanical cross-talk between cell-cell and cell-substrate adhesion determines the pattern of junctional tension in epithelial cell aggregates
We generated a computational approach to analyze the biomechanics of
epithelial cell aggregates, either island or stripes or entire monolayers, that
combines both vertex and contact-inhibition-of-locomotion models to include
both cell-cell and cell-substrate adhesion. Examination of the distribution of
cell protrusions (adhesion to the substrate) in the model predicted high order
profiles of cell organization that agree with those previously seen
experimentally. Cells acquired an asymmetric distribution of basal protrusions,
traction forces and apical aspect ratios that decreased when moving from the
edge to the island center. Our in silico analysis also showed that tension on
cell-cell junctions and apical stress is not homogeneous across the island.
Instead, these parameters are higher at the island center and scales up with
island size, which we confirmed experimentally using laser ablation assays and
immunofluorescence. Without formally being a 3-dimensional model, our approach
has the minimal elements necessary to reproduce the distribution of cellular
forces and mechanical crosstalk as well as distribution of principal stress in
cells within epithelial cell aggregates. By making experimental testable
predictions, our approach would benefit the mechanical analysis of epithelial
tissues, especially when local changes in cell-cell and/or cell-substrate
adhesion drive collective cell behavior.Comment: 39 pages, 8 Figures. Supplementary Information is include
A FEROS spectroscopic study of the extreme O supergiant He 3-759
We present a study of the extreme O-type supergiant He 3-759 using new
high-resolution FEROS data, revealing that it is a near spectroscopic twin of
HD 151804 (O8 Iaf). We investigate the extinction towards He 3-759 using a
variety of methods, revealing A_V ~ 4.7 mag. If we assume He 3-759 has an
identical absolute K-band magnitude to HD 151804 we find that it lies in the
Sagittarius-Carina spiral arm at a distance of ~6.5 kpc. We derive the physical
and wind properties for He 3-759, revealing T* = 30.5 kK, log L/L(sun) = 5.9
and dM/dt = 10^-5.17 M(sun)/yr for a clumped wind whose terminal velocity is
estimated at 1000 km/s. The atmosphere of He 3-759 is enriched in helium (X_He
= 49%) and nitrogen (X_N = 0.3%). A reanalysis of HD 151804 and HD 152408
(WN9ha) reveals similar parameters except that the WN9ha star possesses a
stronger wind and reduced surface hydrogen content. HD 151804 and HD 152408 lie
within the Sco OB1 association, with initial masses of ~60 M(sun) and ages ~2.7
Myr, consistent with NGC 6231 cluster members using standard Geneva isochrones.
Improved agreement with observed surface abundances are obtained for similar
initial masses with more recent Geneva group predictions from which higher ages
of ~3.75 Myr are obtained. No young, massive star cluster is known to be
associated with He 3-759.Comment: 6 pages, 4 figures, accepted for A&
Woodland Expansion\u27s Influence on Belowground Carbon and Nitrogen in the Great Basin U.S.
Vegetation changes associated with climate shifts and anthropogenic disturbance can have major impacts on biogeochemical cycling and soils. Much of the Great Basin, U.S. is currently dominated by sagebrush (Artemisia tridentate (Rydb.) Boivin) ecosystems. Sagebrush ecosystems are increasingly influenced by pinyon (Pinus monophylla Torr. & Frém and Pinus edulis Engelm.) and juniper (Juniperus osteosperma Torr. and Juniperus occidentalis Hook.) expansion. Some scientists and policy makers believe that increasing woodland cover in the intermountain western U.S. offers the possibility of increased organic carbon (OC) storage on the landscape; however, little is currently known about the distribution of OC on these landscapes, or the role that nitrogen (N) plays in OC retention. We quantified the relationship between tree cover, belowground OC, and total below ground N in expansion woodlands at 13 sites in Utah, Oregon, Idaho, California, and Nevada, USA. One hundred and twenty nine soil cores were taken using a mechanically driven diamond tipped core drill to a depth of 90 cm. Soil, coarse fragments, and coarse roots were analyzed for OC and total N. Woodland expansion influenced the vertical distribution of root OC by increasing 15–30 cm root OC by 2.6 Mg ha−1 and root N by 0.04 Mg ha−1. Root OC and N increased through the entire profile by 3.8 and 0.06 Mg ha−1 respectively. Woodland expansion influenced the vertical distribution of soil OC by increasing surface soil (0–15 cm) OC by 2.2 Mg ha−1. Woodland expansion also caused a 1.3 Mg ha−1 decrease in coarse fragment associated OC from 75–90 cm. Our data suggests that woodland expansion into sagebrush ecosystems has limited potential to store additional belowground OC, and must be weighed against the risk of increased wildfire and exotic grass invasion
The Kepler Smear Campaign: Light curves for 102 Very Bright Stars
We present the first data release of the Kepler Smear Campaign, using
collateral 'smear' data obtained in the Kepler four-year mission to reconstruct
light curves of 102 stars too bright to have been otherwise targeted. We
describe the pipeline developed to extract and calibrate these light curves,
and show that we attain photometric precision comparable to stars analyzed by
the standard pipeline in the nominal Kepler mission. In this paper, aside from
publishing the light curves of these stars, we focus on 66 red giants for which
we detect solar-like oscillations, characterizing 33 of these in detail with
spectroscopic chemical abundances and asteroseismic masses as benchmark stars.
We also classify the whole sample, finding nearly all to be variable, with
classical pulsations and binary effects. All source code, light curves, TRES
spectra, and asteroseismic and stellar parameters are publicly available as a
Kepler legacy sample.Comment: 35 pages, accepted ApJ
Urinary Perchlorate and Thyroid Hormone Levels in Adolescent and Adult Men and Women Living in the United States
BACKGROUND: Perchlorate is commonly found in the environment and known to inhibit thyroid function at high doses. Assessing the potential effect of low-level exposure to perchlorate on thyroid function is an area of ongoing research. OBJECTIVES: We evaluated the potential relationship between urinary levels of perchlorate and serum levels of thyroid stimulating hormone (TSH) and total thyroxine (T(4)) in 2,299 men and women, ≥ 12 years of age, participating in the National Health and Nutrition Examination Survey (NHANES) during 2001–2002. METHODS: We used multiple regression models of T(4) and TSH that included perchlorate and covariates known to be or likely to be associated with T(4) or TSH levels: age, race/ethnicity, body mass index, estrogen use, menopausal status, pregnancy status, premenarche status, serum C-reactive protein, serum albumin, serum cotinine, hours of fasting, urinary thiocyanate, urinary nitrate, and selected medication groups. RESULTS: Perchlorate was not a significant predictor of T(4) or TSH levels in men. For women overall, perchlorate was a significant predictor of both T(4) and TSH. For women with urinary iodine < 100 μg/L, perchlorate was a significant negative predictor of T(4) (p < 0.0001) and a positive predictor of TSH (p = 0.001). For women with urinary iodine ≥ 100 μg/L, perchlorate was a significant positive predictor of TSH (p = 0.025) but not T(4) (p = 0.550). CONCLUSIONS: These associations of perchlorate with T(4) and TSH are coherent in direction and independent of other variables known to affect thyroid function, but are present at perchlorate exposure levels that were unanticipated based on previous studies
Financial phantasmagoria: corporate image-work in times of crisis
Our purpose in this article is to relate the real movements in the economy during 2008 to the ?image-work? of financial institutions. Over the period January?December 2008 we collected 241 separate advertisements from 61 financial institutions published in the Financial Times. Reading across the ensemble of advertisements for themes and evocative images provides an impression of the financial imaginaries created by these organizations as the global financial crisis unfolded. In using the term ?phantasmagoria? we move beyond its colloquial sense of a set of strange images designed to dazzle towards the more technical connotation used by Ranci�re (2004) who suggested that words and images can offer a trace of an overall determining set-up if they are torn from their obviousness so they become phantasmagoric figures. The key phantasmagoric figure we identify here is that of the financial institution as timeless, immortal and unchanging; a coherent and autonomous entity amongst other actors. This notion of uniqueness belies the commonality of thinking which precipitated the global financial crisis as well as the limited capacity for control of financial institutions in relation to market events. It also functions as a powerful naturalizing force, making it hard to question certain aspects of the recent period of ?capitalism in crisis?
The Panchromatic Hubble Andromeda Treasury I: Bright UV Stars in the Bulge of M31
As part of the Panchromatic Hubble Andromeda Treasury (PHAT) multi-cycle
program, we observed a 12' \times 6.5' area of the bulge of M31 with the
WFC3/UVIS filters F275W and F336W. From these data we have assembled a sample
of \sim4000 UV-bright, old stars, vastly larger than previously available. We
use updated Padova stellar evolutionary tracks to classify these hot stars into
three classes: Post-AGB stars (P-AGB), Post-Early AGB (PE-AGB) stars and
AGB-manqu\'e stars. P-AGB stars are the end result of the asymptotic giant
branch (AGB) phase and are expected in a wide range of stellar populations,
whereas PE-AGB and AGB-manqu\'e (together referred to as the hot
post-horizontal branch; HP-HB) stars are the result of insufficient envelope
masses to allow a full AGB phase, and are expected to be particularly prominent
at high helium or {\alpha} abundances when the mass loss on the RGB is high.
Our data support previous claims that most UV-bright sources in the bulge are
likely hot (extreme) horizontal branch stars (EHB) and their progeny. We
construct the first radial profiles of these stellar populations, and show that
they are highly centrally concentrated, even more so than the integrated UV or
optical light. However, we find that this UV-bright population does not
dominate the total UV luminosity at any radius, as we are detecting only the
progeny of the EHB stars that are the likely source of the UVX. We calculate
that only a few percent of MS stars in the central bulge can have gone through
the HP-HB phase and that this percentage decreases strongly with distance from
the center. We also find that the surface density of hot UV-bright stars has
the same radial variation as that of low-mass X-ray binaries. We discuss age,
metallicity, and abundance variations as possible explanations for the observed
radial variation in the UV-bright population.Comment: Accepted for publication in Ap
PHAT Stellar Cluster Survey I. Year 1 Catalog and Integrated Photometry
The Panchromatic Hubble Andromeda Treasury (PHAT) survey is an on-going
Hubble Space Telescope (HST) multi-cycle program to obtain high spatial
resolution imaging of one-third of the M31 disk at ultraviolet through
near-infrared wavelengths. In this paper, we present the first installment of
the PHAT stellar cluster catalog. When completed, the PHAT cluster catalog will
be among the largest and most comprehensive surveys of resolved star clusters
in any galaxy. The exquisite spatial resolution achieved with HST has allowed
us to identify hundreds of new clusters that were previously inaccessible with
existing ground-based surveys. We identify 601 clusters in the Year 1 sample,
representing more than a factor of four increase over previous catalogs within
the current survey area (390 arcmin^2). This work presents results derived from
the first \sim25% of the survey data; we estimate that the final sample will
include \sim2500 clusters. For the Year 1 objects, we present a catalog with
positions, radii, and six-band integrated photometry. Along with a general
characterization of the cluster luminosities and colors, we discuss the cluster
luminosity function, the cluster size distributions, and highlight a number of
individually interesting clusters found in the Year 1 search.Comment: 26 pages, 22 figures, Accepted by Ap
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