1,523 research outputs found
Interstellar H-Alpha Line Profiles toward HD 93521 and the Lockman Window
We have used the Wisconsin H-Alpha Mapper (WHAM) facility to measure the
interstellar H-Alpha emission toward the high Galactic latitude O star HD 93521
(l = 183.1, b = +62.2). Three emission components were detected having radial
velocities of -10 km s^{-1}, -51 km s^{-1}, and -90 km s^{-1} with respect to
the local standard of rest (LSR) and H-Alpha intensities of 0.20 R, 0.15 R, and
0.023 R, respectively, corresponding to emission measures of 0.55 cm^{-6} pc,
0.42 cm^{-6} pc, and 0.06 cm^{-6} pc. We have also detected an H-Alpha emission
component at -1 km s^{-1} (LSR) with an intensity of 0.20 R (0.55 cm^{-6} pc)
toward the direction l = 148.5, b = +53.0, which lies in the region of
exceptionally low H I column density known as the Lockman Window. In addition,
we studied the direction l = 163.5, b = +53.5. Upper limits on the possible
intensity of Galactic emission toward this direction are 0.11 R at the LSR and
0.06 R at -50 km s^{-1}. We also detected and characterized twelve faint
(~0.03-0.15 R), unidentified atmospheric lines present in WHAM H-Alpha spectra.
Lastly, we have used WHAM to obtain [O I] 6300 spectra along the line of sight
toward HD 93521. We place an upper limit of 0.060 R on the [O I] intensity of
the -51 km s^{-1} component. If the temperature of the gas is 10,000 K within
the H-Alpha emitting region, the hydrogen ionization fraction n(H+)/n(H_total)
> 0.6.Comment: 23 pages, 4 figures. Acccepted for publication in the 1 Feb issue of
The Astronomical Journa
Early Results from the Wisconsin H-Alpha Mapper Southern Sky Survey
After a successful eleven-year campaign at Kitt Peak, we moved the Wisconsin
H-Alpha Mapper (WHAM) to Cerro Tololo in early 2009. Here we present some of
the early data after a few months under southern skies. These maps begin to
complete the first all-sky, kinematic survey of the diffuse H-alpha emission
from the Milky Way. Much of this emission arises from the Warm Ionized Medium
(WIM), a significant component of the ISM that extends a few kiloparsecs above
the Galactic disk. While this first look at the data focuses on the H-alpha
survey, WHAM is also capable of observing many other optical emission lines,
revealing fascinating trends in the temperature and ionization state of the
WIM. Our ongoing studies of the physical conditions of diffuse ionized gas will
continue from the southern hemisphere following the H-alpha survey. In
addition, future observations will cover the full velocity range of the
Magellanic Stream, Bridge, and Clouds to trace the ionized gas associated with
these neighboring systems.Comment: 4 pages, 2 figures. To appear in "The Dynamic ISM: A celebration of
the Canadian Galactic Plane Survey," ASP Conference Serie
Determination of the Far-Infrared Cosmic Background Using COBE/DIRBE and WHAM Data
Determination of the cosmic infrared background (CIB) at far infrared
wavelengths using COBE/DIRBE data is limited by the accuracy to which
foreground interplanetary and Galactic dust emission can be modeled and
subtracted. Previous determinations of the far infrared CIB (e.g., Hauser et
al. 1998) were based on the detection of residual isotropic emission in skymaps
from which the emission from interplanetary dust and the neutral interstellar
medium were removed. In this paper we use the Wisconsin H-alpha Mapper (WHAM)
Northern Sky Survey as a tracer of the ionized medium to examine the effect of
this foreground component on determination of the CIB. We decompose the DIRBE
far infrared data for five high Galactic latitude regions into H I and H-alpha
correlated components and a residual component. We find the H-alpha correlated
component to be consistent with zero for each region, and we find that addition
of an H-alpha correlated component in modeling the foreground emission has
negligible effect on derived CIB results. Our CIB detections and 2 sigma upper
limits are essentially the same as those derived by Hauser et al. and are given
by nu I_nu (nW m-2 sr-1) < 75, < 32, 25 +- 8, and 13 +- 3 at 60, 100, 140, and
240 microns, respectively. Our residuals have not been subjected to a detailed
anisotropy test, so our CIB results do not supersede those of Hauser et al. We
derive upper limits on the 100 micron emissivity of the ionized medium that are
typically about 40% of the 100 micron emissivity of the neutral atomic medium.
This low value may be caused in part by a lower dust-to-gas mass ratio in the
ionized medium than in the neutral medium, and in part by a shortcoming of
using H-alpha intensity as a tracer of far infrared emission.Comment: 38 pages, 8 figures. Accepted for publication in Ap
Insulin clearance and the incidence of type 2 diabetes in Hispanics and African Americans: the IRAS Family Study.
ObjectiveWe aimed to identify factors that are independently associated with the metabolic clearance rate of insulin (MCRI) and to examine the association of MCRI with incident type 2 diabetes in nondiabetic Hispanics and African Americans.Research design and methodsWe investigated 1,116 participants in the Insulin Resistance Atherosclerosis Study (IRAS) Family Study with baseline examinations from 2000 to 2002 and follow-up examinations from 2005 to 2006. Insulin sensitivity (S(I)), acute insulin response (AIR), and MCRI were determined at baseline from frequently sampled intravenous glucose tolerance tests. MCRI was calculated as the ratio of the insulin dose over the incremental area under the curve of insulin. Incident diabetes was defined as fasting glucose ≥126 mg/dL or antidiabetic medication use by self-report.ResultsWe observed that S(I) and HDL cholesterol were independent positive correlates of MCRI, whereas fasting insulin, fasting glucose, subcutaneous adipose tissue, visceral adipose tissue, and AIR were independent negative correlates (all P < 0.05) at baseline. After 5 years of follow-up, 71 (6.4%) participants developed type 2 diabetes. Lower MCRI was associated with a higher risk of incident diabetes after adjusting for demographics, lifestyle factors, HDL cholesterol, indexes of obesity and adiposity, and insulin secretion (odds ratio 2.01 [95% CI 1.30-3.10], P = 0.0064, per one-SD decrease in loge-transformed MCRI).ConclusionsOur data showed that lower MCRI predicts the incidence of type 2 diabetes
Measurement of a Magnetic Field in a Leading Arm High Velocity Cloud
Using a recent catalogue of extragalactic Faraday rotation derived from the
NRAO VLA Sky Survey we have found an agreement between Faraday rotation
structure and the HI emission structure of a High Velocity Cloud (HVC)
associated with the Leading Arm of the Magellanic System. We suggest that this
morphological agreement is indicative of Faraday rotation through the HVC.
Under this assumption we have used 48 rotation measures through the HVC,
together with estimates of the electron column density from H-\alpha\
measurements and QSO absorption lines to estimate a strength for the
line-of-sight component of the coherent magnetic field in the HVC of >
6 {\rm \mu G}B_{r}/B_{||} < 0.8$, which suggests that the random field does not dominate
over the coherent field as it does in the Magellanic Clouds from which this HVC
likely originates.Comment: 17 pages, 3 figure
Detection of a Large Arc of Ionized Hydrogen Far Above the Cas OB6 Association: A Superbubble Blowout into the Galactic Halo?
The Wisconsin H-Alpha Mapper (WHAM) Northern Sky Survey has revealed a loop
of H II reaching 1300 pc from the Galactic midplane above the Cas OB6
association in the Perseus sprial arm. This enormous feature surrounds and
extends far above the "W4 Chimney" identified by Normandeau et al. and appears
to be associated with the star formation activity near the W3/W4/W5 H II region
complex. The existence of this ionized structure suggests that past episodes of
massive star formation have cleared the H I from an enormous volume above the
Perseus arm, allowing Lyman continuum photons from O stars near the Galactic
midplane to reach into the halo.Comment: 12 pages, 2 figures, accepted for publication in ApJ (Letters
miRNAs are essential for survival and differentiation of newborn neurons but not for expansion of neural progenitors during early neurogenesis in the mouse embryonic neocortex
Neurogenesis during the development of the mammalian cerebral cortex involves a switch of neural stem and progenitor cells from proliferation to differentiation. To explore the possible role of microRNAs (miRNAs) in this process, we conditionally ablated Dicer in the developing mouse neocortex using Emx1-Cre, which is specifically expressed in the dorsal telencephalon as early as embryonic day (E) 9.5. Dicer ablation in neuroepithelial cells, which are the primary neural stem and progenitor cells, and in the neurons derived from them, was evident from E10.5 onwards, as ascertained by the depletion of the normally abundant miRNAs miR-9 and miR-124. Dicer ablation resulted in massive hypotrophy of the postnatal cortex and death of the mice shortly after weaning. Analysis of the cytoarchitecture of the Dicer-ablated cortex revealed a marked reduction in radial thickness starting at E13.5, and defective cortical layering postnatally. Whereas the former was due to neuronal apoptosis starting at E12.5, which was the earliest detectable phenotype, the latter reflected dramatic impairment of neuronal differentiation. Remarkably, the primary target cells of Dicer ablation, the neuroepithelial cells, and the neurogenic progenitors derived from them, were unaffected by miRNA depletion with regard to cell cycle progression, cell division, differentiation and viability during the early stage of neurogenesis, and only underwent apoptosis starting at E14.5. Our results support the emerging concept that progenitors are less dependent on miRNAs than their differentiated progeny, and raise interesting perspectives as to the expansion of somatic stem cells
Assessment of hazard metrics for predicting field benthic invertebrate toxicity in the Detroit River, Ontario, Canada
Numerical sediment quality guidelines (SQGs) are frequently used to interpret site specific sediment chemistry and predict potential toxicity to benthic communities. These SQGs are useful for a screening line of evidence (LOE) that can be combined with other LOEs in a full weight of evidence (WOE) assessment of impacted sites. Three common multi-chemical hazard quotient methods (PEC-Qavg, PEC-Qmet and PEC-Qsum) and a novel (Hazard Score; HZD) approach were used in conjunction with a consensus based set of SQGs to evaluate the ability of different scoring metrics to predict the biological effects of sediment contamination under field conditions. Multivariate analyses were first used to categorize river sediments into distinct habitats based on a set of physicochemical parameters to include gravel, low and high flow sand and silt. For high flow sand and gravel, no significant dose-response relationships between numerically dominant species and various toxicity metric scores were observed. Significant dose-response relationships were observed for Chironomid abundances and toxicity scores in low flow sand and silt habitats. For silt habitats the HZD scoring metric provided the best predictor of Chironomid abundances compared to various PEC-Q methods according to goodness of fit tests. For low flow sand habitats, PEC-Qsum followed by HZD, provided the best predictors of Chironomid abundance. Differences in apparent Chironomid toxicity between the two habitats suggest habitat specific differences in chemical bioavailability and indicator taxa sensitivity. Using an index of biological integrity (IBI) method, the HZD, PEC-Qavg and PEC-Qmet approaches provided reasonable correlations with calculated IBI values in both silt and low flow sand habitats but not for gravel or high flow sands. Computation differences between the various multi-chemical toxicity scoring metrics and how this contributes to bias in different estimates of chemical mixture toxicity scores are discussed and compared
A New Spin on Galactic Dust
We present a new puzzle involving Galactic microwave emission and attempt to
resolve it. On one hand, a cross-correlation analysis of the WHAM H-alpha map
with the Tenerife 10 and 15 GHz maps shows that the well-known DIRBE correlated
microwave emission cannot be dominated by free-free emission. On the other
hand, recent high resolution observations in the 8-10 GHz range with the Green
Bank 140 ft telescope by Finkbeiner et al. failed to find the corresponding 8
sigma signal that would be expected in the simplest spinning dust models. So
what physical mechanism is causing this ubiquitous dust-correlated emission? We
argue for a model predicting that spinning dust is the culprit after all, but
that the corresponding small grains are well correlated with the larger grains
seen at 100 micron only on large angular scales. In support of this grain
segregation model, we find the best spinning dust template to involve higher
frequency maps in the range 12-60 micron, where emission from transiently
heated small grains is important. Upcoming CMB experiments such as ground-based
interferometers, MAP and Planck LFI with high resolution at low frequencies
should allow a definitive test of this model.Comment: Minor revisions to match accepted ApJ version. 6 pages, 4 figs. Color
figures and more foreground information at
http://www.hep.upenn.edu/~angelica/foreground.html#spin or from
[email protected]
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