545 research outputs found
Construction and Measurements of an Improved Vacuum-Swing-Adsorption Radon-Mitigation System
In order to reduce backgrounds from radon-daughter plate-out onto detector
surfaces, an ultra-low-radon cleanroom is being commissioned at the South
Dakota School of Mines and Technology. An improved vacuum-swing-adsorption
radon mitigation system and cleanroom build upon a previous design implemented
at Syracuse University that achieved radon levels of
0.2Bqm. This improved system will employ a better pump and
larger carbon beds feeding a redesigned cleanroom with an internal HVAC unit
and aged water for humidification. With the rebuilt (original) radon mitigation
system, the new low-radon cleanroom has already achieved a 300
reduction from an input activity of Bqm to a
cleanroom activity of Bqm.Comment: 5 pages, 4 figures, Proceedings of Low Radioactivity Techniques (LRT)
2015, Seattle, WA, March 18-20, 201
Abundant cyanopolyynes as a probe of infall in the Serpens South cluster-forming region
We have detected bright HC7N J = 21-20 emission toward multiple locations in
the Serpens South cluster-forming region using the K-Band Focal Plane Array at
the Robert C. Byrd Green Bank Telescope. HC7N is seen primarily toward cold
filamentary structures that have yet to form stars, largely avoiding the dense
gas associated with small protostellar groups and the main central cluster of
Serpens South. Where detected, the HC7N abundances are similar to those found
in other nearby star forming regions. Toward some HC7N `clumps', we find
consistent variations in the line centroids relative to NH3 (1,1) emission, as
well as systematic increases in the HC7N non-thermal line widths, which we
argue reveal infall motions onto dense filaments within Serpens South with
minimum mass accretion rates of M ~ 2-5 M_sun Myr^-1. The relative abundance of
NH3 to HC7N suggests that the HC7N is tracing gas that has been at densities n
~ 10^4 cm^-3, for timescales t < 1-2 x 10^5 yr. Since HC7N emission peaks are
rarely co-located with those of either NH3 or continuum, it is likely that
Serpens South is not particularly remarkable in its abundance of HC7N, but
instead the serendipitous mapping of HC7N simultaneously with NH3 has allowed
us to detect HC7N at low abundances in regions where it otherwise may not have
been looked for. This result extends the known star-forming regions containing
significant HC7N emission from typically quiescent regions, like the Taurus
molecular cloud, to more complex, active environments.Comment: 19 pages, 13 figures, accepted to MNRAS. Version with full resolution
figures available at http://www.dunlap.utoronto.ca/~friesen/Friesen_HC7N.pd
Determining the Mass of Dark Matter Particles with Direct Detection Experiments
In this article I review two data analysis methods for determining the mass
(and eventually the spin-independent cross section on nucleons) of Weakly
Interacting Massive Particles with positive signals from direct Dark Matter
detection experiments: a maximum likelihood analysis with only one experiment
and a model-independent method requiring at least two experiments.
Uncertainties and caveats of these methods will also be discussed.Comment: 24 pages, 10 figures, 1 reference added, typos fixed, published
version, to appear in the NJP Focus Issue on "Dark Matter and Particle
Physics
The COMPLETE Nature of the Warm Dust Ring in Perseus
The Perseus molecular cloud complex is a ~30pc long chain of molecular clouds
most well-known for the two star-forming clusters NGC1333 and IC348 and the
well-studied outflow source in B5. However, when studied at mid- to
far-infrared wavelengths the region is dominated by a ~10pc diameter shell of
warm dust, likely generated by an HII region caused by the early B-star
HD278942. Using a revised calibration technique the COMPLETE team has produced
high-sensitivity temperature and column-density maps of the Perseus region from
IRAS Sky Survey Atlas (ISSA) 60 and 100um data. In this paper, we combine the
ISSA based dust-emission maps with other observations collected as part of the
COMPLETE Survey, along with archival H-alpha and MSX observations. Molecular
line observations from FCRAO and extinction maps constructed by applying the
NICER method to the 2MASS catalog provide independent estimates of the ``true''
column-density of the shell. H-alpha emission in the region of the shell
confirms that it is most likely an HII region located behind the cloud complex,
and 8um data from MSX indicates that the shell may be interacting with the
cloud. Finally, the two polarisation components previously seen towards
background stars in the region can be explained by the association of the
stronger component with the shell. If confirmed, this would be the first
observation of a parsec-scale swept-up magnetic field.Comment: Accepted by ApJ. Figures have been compressed - full resolution
version available at http://cfa-www.harvard.edu/COMPLETE/results.htm
Constraining Radon Backgrounds in LZ
The LZ dark matter detector, like many other rare-event searches, will suffer
from backgrounds due to the radioactive decay of radon daughters. In order to
achieve its science goals, the concentration of radon within the xenon should
not exceed Bq/kg, or 20 mBq total within its 10 tonnes. The LZ
collaboration is in the midst of a program to screen all significant components
in contact with the xenon. The four institutions involved in this effort have
begun sharing two cross-calibration sources to ensure consistent measurement
results across multiple distinct devices. We present here five preliminary
screening results, some mitigation strategies that will reduce the amount of
radon produced by the most problematic components, and a summary of the current
estimate of radon emanation throughout the detector. This best estimate totals
mBq, sufficiently low to meet the detector's science goals.Comment: Low Radioactivity Techniques (LRT) 2017 Workshop Proceedings. 6
pages; 3 figure
Evidence for dust evolution within the Taurus Complex from Spitzer images
We present Spitzer images of the Taurus Complex (TC) and take advantage of
the sensitivity and spatial resolution of the observations to characterize the
diffuse IR emission across the cloud. This work highlights evidence of dust
evolution within the translucent sections of the archetype reference for
studies of quiescent molecular clouds. We combine Spitzer 160 um and IRAS 100
um observations to produce a dust temperature map and a far-IR dust opacity map
at 5' resolution. The average dust temperature is about 14.5K with a dispersion
of +/-1K across the cloud. The far-IR dust opacity is a factor 2 larger than
the average value for the diffuse ISM. This opacity increase and the
attenuation of the radiation field (RF) both contribute to account for the
lower emission temperature of the large grains. The structure of the TC
significantly changes in the mid-IR images that trace emission from PAHs and
VSGs. We focus our analysis of the mid-IR emission to a range of ecliptic
latitudes where the zodiacal light residuals are small. Within this cloud area,
there are no 8 and 24 um counterparts to the brightest 160 um emission
features. Conversely, the 8 and 24 um images reveal filamentary structure that
is strikingly inconspicuous in the 160 um and extinction maps. The IR colors
vary over sub-parsec distances across this filamentary structure. We compare
the observed colors with model calculations quantifying the impact of the RF
intensity and the abundance of stochastically heated particles on the dust SED.
To match the range of observed colors, we have to invoke variations by a factor
of a few of both the interstellar RF and the abundance of PAHs and VSGs. We
conclude that within this filamentary structure a significant fraction of the
dust mass cycles in and out the small size end of the dust size distribution.Comment: 43 pages, 13 figures, accepted for publication in Ap
TMC-1C: an accreting starless core
We have mapped the starless core TMC-1C in a variety of molecular lines with
the IRAM 30m telescope. High density tracers show clear signs of
self-absorption and sub-sonic infall asymmetries are present in N2H+ (1-0) and
DCO+ (2-1) lines. The inward velocity profile in N2H+ (1-0) is extended over a
region of about 7,000 AU in radius around the dust continuum peak, which is the
most extended ``infalling'' region observed in a starless core with this
tracer. The kinetic temperature (~12 K) measured from C17O and C18O suggests
that their emission comes from a shell outside the colder interior traced by
the mm continuum dust. The C18O (2-1) excitation temperature drops from 12 K to
~10 K away from the center. This is consistent with a volume density drop of
the gas traced by the C18O lines, from ~4x10^4 cm^-3 towards the dust peak to
~6x10^3 cm^-3 at a projected distance from the dust peak of 80" (or 11,000 AU).
The column density implied by the gas and dust show similar N2H+ and CO
depletion factors (f_D < 6). This can be explained with a simple scenario in
which: (i) the TMC-1C core is embedded in a relatively dense environment (H2
~10^4 cm^-3), where CO is mostly in the gas phase and the N2H+ abundance had
time to reach equilibrium values; (ii) the surrounding material (rich in CO and
N2H+) is accreting onto the dense core nucleus; (iii) TMC-1C is older than
3x10^5 yr, to account for the observed abundance of N2H+ across the core
(~10^-10 w.r.t. H2); and (iv) the core nucleus is either much younger (~10^4
yr) or ``undepleted'' material from the surrounding envelope has fallen towards
it in the past 10,000 yr.Comment: 29 pages, including 5 tables and 15 figure
An ALMA Search for Substructure, Fragmentation, and Hidden Protostars in Starless Cores in Chamaeleon I
We present an Atacama Large Millimeter/submillimeter Array (ALMA) 106 GHz
(Band 3) continuum survey of the complete population of dense cores in the
Chamaeleon I molecular cloud. We detect a total of 24 continuum sources in 19
different target fields. All previously known Class 0 and Class I protostars in
Chamaeleon I are detected, whereas all of the 56 starless cores in our sample
are undetected. We show that the Spitzer+Herschel census of protostars in
Chamaeleon I is complete, with the rate at which protostellar cores have been
misclassified as starless cores calculated as <1/56, or < 2%. We use synthetic
observations to show that starless cores collapsing following the turbulent
fragmentation scenario are detectable by our ALMA observations when their
central densities exceed ~10^8 cm^-3, with the exact density dependent on the
viewing geometry. Bonnor-Ebert spheres, on the other hand, remain undetected to
central densities at least as high as 10^10 cm^-3. Our starless core
non-detections are used to infer that either the star formation rate is
declining in Chamaeleon I and most of the starless cores are not collapsing,
matching the findings of previous studies, or that the evolution of starless
cores are more accurately described by models that develop less substructure
than predicted by the turbulent fragmentation scenario, such as Bonnor-Ebert
spheres. We outline future work necessary to distinguish between these two
possibilities.Comment: Accepted by Ap
On the direct search for spin-dependent WIMP interactions
We examine the current directions in the search for spin-dependent dark
matter. We discover that, with few exceptions, the search activity is
concentrated towards constraints on the WIMP-neutron spin coupling, with
significantly less impact in the WIMP-proton sector. We review the situation of
those experiments with WIMP-proton spin sensitivity, toward identifying those
capable of reestablishing the balance.Comment: 7 pages, 4 figure
MAMBO Mapping of Spitzer c2d Small Clouds and Cores
AIMS: To study the structure of nearby (< 500 pc) dense starless and
star-forming cores with the particular goal to identify and understand
evolutionary trends in core properties, and to explore the nature of Very Low
Luminosity Objects (< 0.1 L_sun; VeLLOs). METHODS: Using the MAMBO bolometer
array, we create maps unusually sensitive to faint (few mJy per beam) extended
(approx. 5 arcmin) thermal dust continuum emission at 1.2 mm wavelength.
Complementary information on embedded stars is obtained from Spitzer, IRAS, and
2MASS. RESULTS: Our maps are very rich in structure, and we characterize
extended emission features (``subcores'') and compact intensity peaks in our
data separately to pay attention to this complexity. We derive, e.g., sizes,
masses, and aspect ratios for the subcores, as well as column densities and
related properties for the peaks. Combination with archival infrared data then
enables the derivation of bolometric luminosities and temperatures, as well as
envelope masses, for the young embedded stars. CONCLUSIONS: (abridged) Starless
and star-forming cores occupy the same parameter space in many core properties;
a picture of dense core evolution in which any dense core begins to actively
form stars once it exceeds some fixed limit in, e.g., mass, density, or both,
is inconsistent with our data. Comparison of various evolutionary indicators
for young stellar objects in our sample (e.g., bolometric temperatures) reveals
inconsistencies between some of them, possibly suggesting a revision of some of
these indicators.Comment: Accepted to A&A. In total 46 pages, with 20 pages of tables, figures,
and appendices. High-resolution version of this article at
https://www.xythosondemand.com/home/harvard_iic/Users/jkauffma/Public/mambo_spitzer.pd
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