100 research outputs found
Magnetic Fields in Molecular Clouds: The Blastpol and Blast-Tng Experiments
The Balloon-borne Large Aperture Submillimeter Telescope for Polarimetry (BLASTPol) was a suborbital experiment designed to map magnetic fields in order to study their role in star formation processes. BLASTPol made detailed polarization maps of a number of molecular clouds during its successful flight from Antarctica in 2012. The data reduction and analysis efforts over the three years following the flight have produced a number of important scientific results. The next-generation BLAST instrument (BLAST-TNG) will build off the success of the previous experiment and continue its role as a unique instrument and a test bed for new technologies. With a 16-fold increase in mapping speed, BLAST-TNG will make larger and deeper maps. Major improvements include a 2.5 m carbon fiber mirror that is 40% wider than the BLASTPol mirror and more than 3000 polarization sensitive detectors. BLAST-TNG will observe in the same three bands as BLASTpol at 250, 350, and 500 microns. The telescope will serve as a pathfinder project for microwave kinetic inductance detector (MKID) technology, as applied to feedhorn coupled submillimeter detector arrays. The liquid helium cooled cryostat will have a 28-day hold time and will utilize a closed-cycle 3He refrigerator to cool the detector arrays to 270 mK. This will enable a detailed mapping of more targets with higher polarization resolution than any other submillimeter experiment to date. My thesis describes the 2012 instrument and results while also outlining the motivation for BLAST-TNG and the instrumental design and initial testing
PROTOCALC: an artificial calibrator source for CMB telescopes
Cosmic Microwave Background experiments need to measure polarization
properties of the incoming radiation very accurately to achieve their
scientific goals. As a result of that, it is necessary to properly characterize
these instruments. However, there are not natural sources that can be used for
this purpose. For this reason, we developed the PROTOtype CALibrator for
Cosmology, PROTOCALC, which is a calibrator source designed for the 90GHz band
of these telescopes. This source is purely polarized and the direction of the
polarization vector is known with an accuracy better than 0.1deg. This source
flew for the first time in May 2022 showing promising resultComment: Presented at SPIE Astronomical Telescopes + Instrumentation 202
Star Formation in a Strongly Magnetized Cloud
We study star formation in the Center Ridge 1 (CR1) clump in the Vela C giant
molecular cloud, selected as a high column density region that shows the lowest
level of dust continuum polarization angle dispersion, likely indicating that
the magnetic field is relatively strong. We observe the source with the ALMA
7m-array at 1.05~mm and 1.3~mm wavelengths, which enable measurements of dust
temperature, core mass and astrochemical deuteration. A relatively modest
number of eleven dense cores are identified via their dust continuum emission,
with masses spanning from 0.17 to 6.7 Msun. Overall CR1 has a relatively low
compact dense gas fraction compared with other typical clouds with similar
column densities, which may be a result of the strong magnetic field and/or the
very early evolutionary stage of this region. The deuteration ratios, Dfrac, of
the cores, measured with N2H+(3-2) and N2D+(3-2) lines, span from 0.011 to
0.85, with the latter being one of the highest values yet detected. The level
of deuteration appears to decrease with evolution from prestellar to
protostellar phase. A linear filament, running approximately parallel with the
large scale magnetic field orientation, is seen connecting the two most massive
cores, each having CO bipolar outflows aligned orthogonally to the filament.
The filament contains the most deuterated core, likely to be prestellar and
located midway between the protostars. The observations permit measurement of
the full deuteration structure of the filament along its length, which we
present. We also discuss the kinematics and dynamics of this structure, as well
as of the dense core population.Comment: 20 pages, 15 figures, submitted to ApJ, comments welcom
The Simons Observatory: Magnetic Shielding Measurements for the Universal Multiplexing Module
The Simons Observatory (SO) includes four telescopes that will measure the
temperature and polarization of the cosmic microwave background using over
60,000 highly sensitive transition-edge bolometers (TES). These multichroic TES
bolometers are read out by a microwave RF SQUID multiplexing system with a
multiplexing factor of 910. Given that both TESes and SQUIDs are susceptible to
magnetic field pickup and that it is hard to predict how they will respond to
such fields, it is important to characterize the magnetic response of these
systems empirically. This information can then be used to limit spurious
signals by informing magnetic shielding designs for the detectors and readout.
This paper focuses on measurements of magnetic pickup with different magnetic
shielding configurations for the SO universal multiplexing module (UMM), which
contains the SQUIDs, associated resonators, and TES bias circuit. The magnetic
pickup of a prototype UMM was tested under three shielding configurations: no
shielding (copper packaging), aluminum packaging for the UMM, and a
tin/lead-plated shield surrounding the entire dilution refrigerator 100 mK cold
stage. The measurements show that the aluminum packaging outperforms the copper
packaging by a shielding factor of 8-10, and adding the tin/lead-plated 1K
shield further increases the relative shielding factor in the aluminum
configuration by 1-2 orders of magnitude.Comment: 7 pages, 4 figure, conference proceedings submitted to the Journal of
Low Temperature Physic
The effects of inclination on a two stage pulse tube cryocooler for use with a ground based observatory
Abstract Ground-based observatories across a wide range of wavelengths implement cryogenic cooling techniques to increase the sensitivity of instruments and enable low temperature detector technologies. Commercial pulse tube cryocoolers (PTCs) are frequently used to provide 40 K and 4 K stages as thermal shells in scientific instruments. However, PTC operation is dependent on gravity, giving rise to changes in cooling capacity over the operational tilt range of pointed telescopes. We present a study of the performance of a two stage PTC with a cooling capacity of 1.8 W at 4.2 K and 50 W at 45 K (Cryomech PT420-RM) from 0 - 55 ° away from vertical to probe capacity as a function of angle over a set of realistic thermal loading conditions. Our study provides a method to extract temperature estimates given predicted thermal loading conditions across the angular range sampled. We then discuss the design implications for current and future tilted cryogenic systems
The Simons Observatory: A fully remote controlled calibration system with a sparse wire grid for cosmic microwave background telescopes
For cosmic microwave background (CMB) polarization observations, calibration
of detector polarization angles is essential. We have developed a fully remote
controlled calibration system with a sparse wire grid that reflects linearly
polarized light along the wire direction. The new feature is a
remote-controlled system for regular calibration, which has not been possible
in sparse wire grid calibrators in past experiments. The remote control can be
achieved by two electric linear actuators that load or unload the sparse wire
grid into a position centered on the optical axis of a telescope between the
calibration time and CMB observation. Furthermore, the sparse wire grid can be
rotated by a motor. A rotary encoder and a gravity sensor are installed on the
sparse wire grid to monitor the wire direction. They allow us to achieve
detector angle calibration with expected systematic error of .
The calibration system will be installed in small-aperture telescopes at Simons
Observatory
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
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