11 research outputs found
The balloon-borne large-aperture submillimeter telescope for polarimetry: BLAST-Pol
The Balloon-borne Large Aperture Submillimeter Telescope for Polarimetry
(BLAST-Pol) is a suborbital mapping experiment designed to study the role
played by magnetic fields in the star formation process. BLAST-Pol is the
reconstructed BLAST telescope, with the addition of linear polarization
capability. Using a 1.8 m Cassegrain telescope, BLAST-Pol images the sky onto a
focal plane that consists of 280 bolometric detectors in three arrays,
observing simultaneously at 250, 350, and 500 um. The diffraction-limited
optical system provides a resolution of 30'' at 250 um. The polarimeter
consists of photolithographic polarizing grids mounted in front of each
bolometer/detector array. A rotating 4 K achromatic half-wave plate provides
additional polarization modulation. With its unprecedented mapping speed and
resolution, BLAST-Pol will produce three-color polarization maps for a large
number of molecular clouds. The instrument provides a much needed bridge in
spatial coverage between larger-scale, coarse resolution surveys and narrow
field of view, and high resolution observations of substructure within
molecular cloud cores. The first science flight will be from McMurdo Station,
Antarctica in December 2010.Comment: 14 pages, 9 figures Submitted to SPIE Astronomical Telescopes and
Instrumentation Conference 201
Comparison of prestellar core elongations and large-scale molecular cloud structures in the Lupus 1 region
Turbulence and magnetic fields are expected to be important for regulating molecular cloud formation and evolution. However, their effects on sub-parsec to 100 parsec scales, leading to the formation of starless cores, are not well understood. We investigate the prestellar core structure morphologies obtained from analysis of the Herschel-SPIRE 350 mum maps of the Lupus I cloud. This distribution is first compared on a statistical basis to the large-scale shape of the main filament. We find the distribution of the elongation position angle of the cores to be consistent with a random distribution, which means no specific orientation of the morphology of the cores is observed with respect to the mean orientation of the large-scale filament in Lupus I, nor relative to a large-scale bent filament model. This distribution is also compared to the mean orientation of the large-scale magnetic fields probed at 350 mum with the Balloon-borne Large Aperture Telescope for Polarimetry during its 2010 campaign. Here again we do not find any correlation between the core morphology distribution and the average orientation of the magnetic fields on parsec scales. Our main conclusion is that the local filament dynamics---including secondary filaments that often run orthogonally to the primary filament---and possibly small-scale variations in the local magnetic field direction, could be the dominant factors for explaining the final orientation of each core
Instrumental performance and results from testing of the BLAST-TNG receiver, submillimeter optics, and MKID arrays
Polarized thermal emission from interstellar dust grains can be used to map
magnetic fields in star forming molecular clouds and the diffuse interstellar
medium (ISM). The Balloon-borne Large Aperture Submillimeter Telescope for
Polarimetry (BLASTPol) flew from Antarctica in 2010 and 2012 and produced
degree-scale polarization maps of several nearby molecular clouds with
arcminute resolution. The success of BLASTPol has motivated a next-generation
instrument, BLAST-TNG, which will use more than 3000 linear polarization
sensitive microwave kinetic inductance detectors (MKIDs) combined with a 2.5m
diameter carbon fiber primary mirror to make diffraction-limited observations
at 250, 350, and 500 m. With 16 times the mapping speed of BLASTPol,
sub-arcminute resolution, and a longer flight time, BLAST-TNG will be able to
examine nearby molecular clouds and the diffuse galactic dust polarization
spectrum in unprecedented detail. The 250 m detector array has been
integrated into the new cryogenic receiver, and is undergoing testing to
establish the optical and polarization characteristics of the instrument.
BLAST-TNG will demonstrate the effectiveness of kilo-pixel MKID arrays for
applications in submillimeter astronomy. BLAST-TNG is scheduled to fly from
Antarctica in December 2017 for 28 days and will be the first balloon-borne
telescope to offer a quarter of the flight for "shared risk" observing by the
community.Comment: Presented at SPIE Millimeter, Submillimeter, and Far-Infrared
Detectors and Instrumentation for Astronomy VIII, June 29th, 201
The Atacama Cosmology Telescope: Two-Season ACTPol Spectra and Parameters
We present the temperature and polarization angular power spectra measured by
the Atacama Cosmology Telescope Polarimeter (ACTPol). We analyze night-time
data collected during 2013-14 using two detector arrays at 149 GHz, from 548
deg of sky on the celestial equator. We use these spectra, and the spectra
measured with the MBAC camera on ACT from 2008-10, in combination with Planck
and WMAP data to estimate cosmological parameters from the temperature,
polarization, and temperature-polarization cross-correlations. We find the new
ACTPol data to be consistent with the LCDM model. The ACTPol
temperature-polarization cross-spectrum now provides stronger constraints on
multiple parameters than the ACTPol temperature spectrum, including the baryon
density, the acoustic peak angular scale, and the derived Hubble constant.
Adding the new data to planck temperature data tightens the limits on damping
tail parameters, for example reducing the joint uncertainty on the number of
neutrino species and the primordial helium fraction by 20%.Comment: 23 pages, 25 figure
Design and Fabrication of Zwitter-Wettable Nanostructured Films
Manipulating surface properties using chemistry and roughness has led to the development of advanced multifunctional surfaces. Here, in a nanostructured polymer film consisting of a hydrophilic reservoir of chitosan/carboxymethyl cellulose capped with various hydrophobic layers, we demonstrate the role of a third design factor, water permeation rate. We use this additional design criterion to produce antifogging coatings that readily absorb water vapor while simultaneously exhibiting hydrophobic character to liquid water. These zwitter-wettable films, produced via aqueous layer-by-layer assembly, consist of a nanoscale thin hydrophobic capping layer (chitosan/Nafion) that enables water vapor to diffuse rapidly into the underlying hydrophilic reservoir rather than nucleating drops of liquid water on the surface. We characterize these novel films using a quartz crystal microbalance with dissipation monitoring (QCM-D) and via depth-profiling X-ray photoelectron spectroscopy (XPS) in addition to extensive testing for fogging/antifogging performance.1121Nsciescopu
The half wave plate rotator for the BLAST-TNG balloon-borne telescope
The Next Generation Balloon-borne Large Aperture Submillimeter Telescope (BLAST-TNG) is an experiment designed to map magnetic fields in molecular clouds in order to study their role in the star formation process. The telescope will be launched aboard a high-altitude balloon in December 2016 for a 4-week flight from McMurdo station in Antarctica. BLAST-TNG will measure the polarization of submillimeter thermal emission from magnetically aligned interstellar dust grains, using large format arrays of kinetic inductance detectors operating in three bands centered at 250, 350, and 500 microns, with sub-arcminute angular resolution. The optical system includes an achromatic Half Wave Plate (HWP), mounted in a Half Wave Plate rotator (HWPr). The HWP and HWPr will operate at 4 K temperature to reduce thermal noise in our measurements, so it was crucial to account for the effects of thermal contraction at low temperature in the HWPr design. It was also equally important for the design to meet torque requirements while minimizing the power from friction and conduction dissipated at the 4 K stage. We also discuss our plan for cold testing the HWPr using a repurposed cryostat with a Silicon Diode thermometer read out by an EDAS-CE Ethernet data acquisition system
Comparing polarized submm emission and near-infrared extinction polarization in the Vela C giant molecular cloud
We present one of largest studies to date of combined near-infrared and submillimeter linear polarization data for a giant molecular cloud. The dust polarized emission data (at 250, 350 and 500 μm) were obtained using the Balloon-borne Large Aperture Submillimeter Telescope for Polarimetry (BLASTPol) during its 2012 Antarctic flight. The near-infrared polarization, which is produced by dichroic extinction of background starlight, was measured in the I band (0.8 μm) using the Pico dos Dias Observatory in Brazil. The study targets the Vela C cloud, a conspicuous star-forming environment at a distance of approximately 700 pc, hosting HII regions, protostars, and dense filamentary structures. By studying the relationship between polarized emission and polarized absorption, we can investigate how this relates to the physical properties of dust grains. The area of overlap of the two data sets corresponds to a large fraction of the molecular cloud (approximately 1.5° × 2.0°), with hundreds of combined polarization pseudo-vectors distributed mainly along the borders of the cloud. For most sight-lines, the inferred magnetic field orientations match within 20°. Visual extinction values (AV) for near-infrared pseudo-vectors are estimated from 2MASS photometry. Based on these extinction values, we determine and correct for a small foreground contribution (~0.4%) in the near-infrared sample. We calculate the polarization efficiency ratio, defined as the polarization fraction at 500 μm divided by the polarization efficiency in the near-infrared (defined as P/AV). Models of aligned dust grains are helpful for producing predicted polarization maps from numerical simulations of turbulent molecular clouds, and the polarization efficiency ratio provides a constraint for such dust alignment models. Preliminary results show that the measured polarization efficiency ratio appears to be roughly consistent with the predictions of the Draine and Fraisse (2009) models
Detailed magnetic field morphology of the Vela C molecular cloud from the BLASTPol 2012 flight
In order to understand the role of magnetic fields in the process of star formation, we require detailed observations of field morphology on scales ranging from clouds to cores. However, ground based millimetre/submillimetre polarimetry is usually limited to small maps of relatively dense regions. BLASTPol, the Balloon-borne Large Aperture Sub-mm Telescope for Polarimetry, maps linear polarization at 250, 350 and 500 microns with arcminute resolution. Its high sensitivity and resolving power allow BLASTPol to bridge the gap in spatial scales between the polarization capabilities of Planck and ALMA.I will present early results from the second flight of BLASTPol, focusing on our observations of the Vela C molecular cloud, an early stage intermediate mass star forming region (d~700 pc). With thousands of independent measurements of magnetic field direction, this is the most detailed sub-mm polarization map of a GMC to date. The field we observe in this elongated cloud exhibits a coherent, large-scale ~ 90 degree bend between its high latitude and low latitude edges. I will discuss what we can learn about star formation in Vela C from the combination of BLASTPol polarization maps and velocity information from molecular line observations, and what the variation of polarization strength across the cloud can tell us about dust grain alignment in GMCs
Mapping magnetic fields in star forming regions with BLASTPol
A key outstanding question in our understanding of star formation is whether magnetic fields provide support against the gravitational collapse of their parent molecular clouds and cores. Direct measurement of magnetic field strength is observationally challenging, however observations of polarized thermal emission from dust grains aligned with respect to the local cloud magnetic field can be used to map out the magnetic field orientation in molecular clouds. Statistical comparisons between these submillimeter polarization maps and three-dimensional numerical simulations of magnetized star-forming clouds provide a promising method for constraining magnetic field strength. We present early results from a BLASTPol study of the nearby giant molecular cloud (GMC) Vela C, using data collected during a 2012 Antarctic flight. This sensitive balloon-borne polarimeter observed Vela C for 57 hours, yielding the most detailed submillimeter polarization map ever made of a GMC forming high mass stars. We find that most of the structure in p can be modeled by a power-law dependence on two quantities: the hydrogen column density and the local dispersion in magnetic field orientation. Our power-law model for p(N,S) provides new constraints for models of magnetized star-forming clouds and an important first step in the interpretation of the BLASTPol 2012 data set
BLAST-TNG: a next generation balloon-borne large aperture submillimeter polarimeter
Measurements of polarized thermal dust emission can be used to map magnetic fields in the interstellar medium. Recently, BLASTPol, the Balloon-borne Large Aperture Submillimeter Telescope for Polarimetry, has published the most detailed map ever made of a giant molecular cloud forming high-mass stars. I will present an overview of The Next Generation BLAST polarimeter (BLAST-TNG), the successor telescope to BLASTPol, which maps linearly polarized dust emission at 250, 350 and 500 μm. BLAST-TNG utilizes a 2.5-meter carbon-fiber primary mirror that illuminates focal plane arrays containing over 3,000 microwave kinetic inductance detectors. This new polarimeter has an order of magnitude increase in mapping speed and resolution compared to BLASTPol and we expect to make over 500,000 measurements of magnetic field orientation per flight. BLAST-TNG will have the sensitivity to map entire molecular cloud complexes as well as regions of diffuse high Galactic latitude dust. It also has the resolution (FWHM = 25’’ at 250 μm) necessary to trace magnetic fields in prestellar cores and dense filaments. BLAST-TNG will thus provide a crucial link between the low resolution Planck all-sky maps and the detailed but narrow field of view polarimetry capabilities of ALMA. For our first Antarctic flight in December 2017 we are putting out a call for shared-risk proposals to fill 25% of the available science time. In addition, BLAST-TNG data will be publicly released within a year of the publication of our first look papers, leaving a large legacy data set for the study of the role played by magnetic fields in the star formation process and the properties of interstellar dust