2,733 research outputs found
Probing The Multiphase Interstellar Medium Of The Dwarf Starburst Galaxy NGC 625 With FUSE Spectroscopy
We present new FUSE spectroscopy of the dwarf starburst galaxy NGC 625. These
observations probe multiple phases of the interstellar medium, including the
coronal, ionized, neutral and molecular gas. This nearby (D = 3.9 +/- 0.2 Mpc)
system shows a clear detection of outflowing coronal gas as traced by OVI 1032
Angstrom absorption. The centroid of the OVI profile is blueshifted with
respect to the galaxy systemic velocity by ~ 30 km/sec, suggesting a
low-velocity outflow. The implied OVI velocity extent is found to be 100 +/- 20
km/sec, which is fully consistent with the detected HI outflow velocity found
in radio synthesis observations. We detect multiple lines of diffuse H2
absorption from the ISM of NGC 625; this is one of only a few extragalactic
systems with FUSE detections of H2 lines in the Lyman and Werner bands. We find
a potential abundance offset between the neutral and nebular gas that exceeds
the errors on the derived column densities. Since such an offset has been found
in multiple dwarf galaxies, we discuss the implications of a lower-metallicity
halo surrounding the central star forming regions of dwarf galaxies. The
apparent offset may be due to saturation of the observed OI line, and higher
S/N observations are required to resolve this issue.Comment: ApJ, in press; full-resolution version may be obtained at
http://www.astro.umn.edu/~cannon/n625.fuse.p
Implementing a participatory model of micro health insurance among rural poor with evidence from Nepal
This paper reports on two voluntary, contributory, contextualised, community-based health insurance (CBHI) schemes, launched in Dhading and Banke (Nepal) in 2011. The implementation followed a four-stage process: initiating (baseline survey), involving (awareness generation and engaging community in benefit-package-design), launch (enrolment and training of selected community members) and post-launch (viable claims ratio, settled within satisfactory time, sustainable affiliation). Both schemes were successful on four key parameters: effective planning; affiliation (grew from 0 to ∼10,000) and renewals (>65 per cent); claims ratio (∼50 per cent); and promptness of claim settlement (∼23 days). This model succeeded in implementing CBHI with zero premium subsidies or subsidised health-care costs. The successful operation relied in large part on the fact that members trust that they can enforce this contract. Considerable insurance education and capacity development is necessary before the launch of the CBHI, and for sustainable operations as well as for scaling
The Case of AB Aurigae's Disk in Polarized Light: Is There Truly a Gap?
Using the NICMOS coronagraph, we have obtained high-contrast 2.0 micron
imaging polarimetry and 1.1 micron imaging of the circumstellar disk around AB
Aurigae on angular scales of 0.3-3 arcsec (40-550 AU). Unlike previous
observations, these data resolve the disk in both total and polarized
intensity, allowing accurate measurement of the spatial variation of
polarization fraction across the disk. Using these observations we investigate
the apparent "gap" in the disk reported by Oppenheimer et al. 2008. In
polarized intensity, the NICMOS data closely reproduces the morphology seen by
Oppenheimer et al., yet in total intensity we find no evidence for a gap in
either our 1.1 or 2.0 micron images. We find instead that region has lower
polarization fraction, without a significant decrease in total scattered light,
consistent with expectations for back-scattered light on the far side of an
inclined disk. Radiative transfer models demonstrate this explanation fits the
observations. Geometrical scattering effects are entirely sufficient to explain
the observed morphology without any need to invoke a gap or protoplanet at that
location.Comment: Accepted to ApJ Letter
Histological and MRI brain atlas of the common shrew, Sorex araneus, with brain region-specific gene expression profiles
Towards an Intelligent Tutor for Mathematical Proofs
Computer-supported learning is an increasingly important form of study since
it allows for independent learning and individualized instruction. In this
paper, we discuss a novel approach to developing an intelligent tutoring system
for teaching textbook-style mathematical proofs. We characterize the
particularities of the domain and discuss common ITS design models. Our
approach is motivated by phenomena found in a corpus of tutorial dialogs that
were collected in a Wizard-of-Oz experiment. We show how an intelligent tutor
for textbook-style mathematical proofs can be built on top of an adapted
assertion-level proof assistant by reusing representations and proof search
strategies originally developed for automated and interactive theorem proving.
The resulting prototype was successfully evaluated on a corpus of tutorial
dialogs and yields good results.Comment: In Proceedings THedu'11, arXiv:1202.453
The Recent Evolution of the Dwarf Starburst Galaxy NGC 625 from Hubble Space Telescope Imaging
New HST/WFPC2 imaging of the dwarf starburst galaxy NGC 625 is presented.
These data, 80% complete to V and I magnitudes of 26.0 and 25.3, respectively,
allow us to study the recent star formation history of NGC 625. We derive a tip
of the red giant branch (TRGB) distance modulus of 27.95+/-0.07, corresponding
to a distance of 3.89+/-0.22 Mpc, and a location on the far side of the
Sculptor Group. NGC 625 has a well-defined radial stellar population gradient,
evidenced by a central concentration of young MS stars and an RGB/AGB ratio
that increases with galactocentric distance. The prominent AGB is very red, and
RGB stars are detected far from the central star forming regions. Using H Alpha
and H Beta narrow band imaging and previous optical spectroscopy we identify
substantial and varying internal extinction (A_V = 0.0 to 0.6 mag) associated
with the central active star formation regions. To better understand the
effects of internal extinction on the analysis of young stellar populations,
synthetic models are presented which, for the first time, examine and account
for this effect. Using the luminous blue helium burning stars, we construct a
simple model of the recent (< 100 Myr) star formation in which an elevated but
declining star formation rate has been present over this entire period. This is
at odds with the presence of spectroscopic W-R features in the major star
formation region which imply a short duration (<= 5 Myr) for the recent
starburst. This suggests that starbursts displaying W-R features are not
necessarily all of a short duration. Finally, we speculate on the possible
causes of the present burst of star formation in this apparently isolated
galaxy, and compare it to other nearby, well-studied dwarf starburst systems.Comment: 56 pages, including 15 figures (2 in color). Scheduled to appear in
AJ, December, 2003. Full-resolution version may be obtained at
http://www.astro.umn.edu/~Cannon/n625.p
Formation and Evolution of Planetary Systems (FEPS): Properties of Debris Dust around Solar-type Stars
We present Spitzer photometric (IRAC and MIPS) and spectroscopic (IRS low
resolution) observations for 314 stars in the Formation and Evolution of
Planetary Systems (FEPS) Legacy program. These data are used to investigate the
properties and evolution of circumstellar dust around solar-type stars spanning
ages from approximately 3 Myr to 3 Gyr. We identify 46 sources that exhibit
excess infrared emission above the stellar photosphere at 24um, and 21 sources
with excesses at 70um. Five sources with an infrared excess have
characteristics of optically thick primordial disks, while the remaining
sources have properties akin to debris systems. The fraction of systems
exhibiting a 24um excess greater than 10.2% above the photosphere is 15% for
ages < 300 Myr and declines to 2.7% for older ages. The upper envelope to the
70um fractional luminosity appears to decline over a similar age range. The
characteristic temperature of the debris inferred from the IRS spectra range
between 60 and 180 K, with evidence for the presence of cooler dust to account
for the strength of the 70um excess emission. No strong correlation is found
between dust temperature and stellar age. Comparison of the observational data
with disk models containing a power-law distribution of silicate grains suggest
that the typical inner disk radius is > 10 AU. Although the interpretation is
not unique, the lack of excess emission shortwards of 16um and the relatively
flat distribution of the 24um excess for ages <300~Myr is consistent with
steady-state collisional models.Comment: 85 pages, 18 figures, 4 tables; accepted for publication in ApJ
High-precision photometry by telescope defocussing. III. The transiting planetary system WASP-2
We present high-precision photometry of three transits of the extrasolar
planetary system WASP-2, obtained by defocussing the telescope, and achieving
point-to-point scatters of between 0.42 and 0.73 mmag. These data are modelled
using the JKTEBOP code, and taking into account the light from the
recently-discovered faint star close to the system. The physical properties of
the WASP-2 system are derived using tabulated predictions from five different
sets of stellar evolutionary models, allowing both statistical and systematic
errorbars to be specified. We find the mass and radius of the planet to be M_b
= 0.847 +/- 0.038 +/- 0.024 Mjup and R_b = 1.044 +/- 0.029 +/- 0.015 Rjup. It
has a low equilibrium temperature of 1280 +/- 21 K, in agreement with a recent
finding that it does not have an atmospheric temperature inversion. The first
of our transit datasets has a scatter of only 0.42 mmag with respect to the
best-fitting light curve model, which to our knowledge is a record for
ground-based observations of a transiting extrasolar planet.Comment: Accepted for publication in MNRAS. 9 pages, 3 figures, 10 table
System size and centrality dependence of the balance function in A + A collisions at sqrt s NN = 17.2 GeV
Electric charge correlations were studied for p+p, C+C, Si+Si and centrality selected Pb+Pb collisions at sqrt s_NN = 17.2$ GeV with the NA49 large acceptance detector at the CERN-SPS. In particular, long range pseudo-rapidity correlations of oppositely charged particles were measured using the Balance Function method. The width of the Balance Function decreases with increasing system size and centrality of the reactions. This decrease could be related to an increasing delay of hadronization in central Pb+Pb collisions
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