The Submillimeter Polarization Spectrum of M17

We present 450 {\mu}m polarimetric observations of the M17 molecular cloud obtained with the SHARP polarimeter at the Caltech Submillimeter Observatory. Across the observed region, the magnetic field orientation is consistent with previous submillimeter and far-infrared polarization measurements. Our observations are centered on a region of the molecular cloud that has been compressed by stellar winds from a cluster of OB stars. We have compared these new data with previous 350 {\mu}m polarimetry and find an anti-correlation between the 450 to 350 {\mu}m polarization magnitude ratio and the ratio of 21 cm to 450 {\mu}m intensity. The polarization ratio is lower near the east end of the studied region where the cloud is exposed to stellar winds and radiation. At the west end of the region, the polarization ratio is higher. We interpret the varying polarization spectrum as evidence supporting the radiative alignment torque (RAT) model for grain alignment, implying higher alignment efficiency in the region that is exposed to a higher anisotropic radiation field.Comment: 24 pages, 10 figure

A Wideband Profiled Corrugated Horn for Multichroic Applications

A wideband profiled corrugated feedhorn was developed for multichroic applications. This feedhorn features a return loss of better than -25 dB and cross polarization peaks below -30 dB, over a fractional bandwidth of greater than 50%. Its performance is close to that of the ring-loaded corrugated feedhorn; however, the design presented is much easier to fabricate at millimeter wavelengths

A Low Cross-Polarization Smooth-Walled Horn with Improved Bandwidth

Corrugated feed horns offer excellent beam symmetry, main beam efficiency, and cross-polar response over wide bandwidths, but can be challenging to fabricate. An easier-to-manufacture smooth-walled feed is explored that approximates these properties over a finite bandwidth. The design, optimization and measurement of a monotonically-profiled, smooth-walled scalar feedhorn with a diffraction-limited approximately 7 degrees full width at half maximum (FWHM) is presented. The feed was demonstrated to have low cross polarization (<-30 dB) across the frequency range 33-45 GHz (30% fractional bandwidth). A return loss better than -28 dB was measured across the band

The Cosmology Large Angular Scale Surveyor (CLASS): 40 GHz Optical Design

The Cosmology Large Angular Scale Surveyor (CLASS) instrument will measure the polarization of the cosmic microwave background at 40, 90, and 150 GHz from Cerro Toco in the Atacama desert of northern Chile. In this paper, we describe the optical design of the 40 GHz telescope system. The telescope is a diffraction limited catadioptric design consisting of a front-end Variable-delay Polarization Modulator (VPM), two ambient temperature mirrors, two cryogenic dielectric lenses, thermal blocking filters, and an array of 36 smooth-wall scalar feedhorn antennas. The feed horns guide the signal to antenna-coupled transition-edge sensor (TES) bolometers. Polarization diplexing and bandpass definition are handled on the same microchip as the TES. The feed horn beams are truncated with 10 dB edge taper by a 4 K Lyot-stop to limit detector loading from stray light and control the edge illumination of the front-end VPM. The field-of-view is 19 deg x 14 deg with a resolution for each beam on the sky of 1.5 deg. FWHM

Photoactivation of Cu Centers in Metal-Organic Frameworks for Selective CO2 Conversion to Ethanol.

CO2 hydrogenation to ethanol is of practical importance but poses a significant challenge due to the need of forming one C-C bond while keeping one C-O bond intact. CuI centers could selectively catalyze CO2-to-ethanol conversion, but the CuI catalytic sites were unstable under reaction conditions. Here we report the use of low-intensity light to generate CuI species in the cavities of a metal-organic framework (MOF) for catalytic CO2 hydrogenation to ethanol. X-ray photoelectron and transient absorption spectroscopies indicate the generation of CuI species via single-electron transfer from photoexcited [Ru(bpy)3]2+-based ligands on the MOF to CuII centers in the cavities and from Cu0 centers to the photoexcited [Ru(bpy)3]2+-based ligands. Upon light activation, this Cu-Ru-MOF hybrid selectively hydrogenates CO2 to EtOH with an activity of 9650 μmol gCu-1 h-1 under 2 MPa of H2/CO2 = 3:1 at 150 °C. Low-intensity light thus generates and stabilizes CuI species for sustained EtOH production

CLASS Angular Power Spectra and Map-Component Analysis for 40 GHz Observations through 2022

Measurement of the largest angular scale ($\ell < 30$) features of the cosmic microwave background (CMB) polarization is a powerful way to constrain the optical depth to reionization, $\tau$, and search for the signature of inflation through the detection of primordial $B$-modes. We present an analysis of maps covering nearly 75% of the sky made from the ground-based $40\,\mathrm{GHz}$ channel of the Cosmology Large Angular Scale Surveyor (CLASS) from August 2016 to May 2022. Using fast front-end polarization modulation from the Atacama Desert in Chile, we show this channel achieves higher sensitivity than the analogous frequencies from satellite measurements in the range $10 < \ell < 100$. After a final calibration adjustment, noise simulations show the CLASS linear (circular) polarization maps have a white noise level of $125 \,(130)\,\mathrm{\mu K\, arcmin}$. We measure the Galaxy-masked $EE$ and $BB$ spectra of diffuse synchrotron radiation and compare to space-based measurements at similar frequencies. In combination with external data, we expand measurements of the spatial variations of the synchrotron spectral energy density (SED) to include new regions of the sky and measure the faint diffuse SED in the harmonic domain. We place a new upper limit on a background of circular polarization in the range $5 < \ell < 125$ with the first bin showing $D_\ell < 0.023$ $\mathrm{\mu K^2_{CMB}}$ at 95% confidence. These results establish a new standard for recovery of the largest-scale CMB polarization from the ground and signal exciting possibilities when the higher sensitivity and higher frequency CLASS channels are included in the analysis.Comment: 36 pages, 24 figures, 6 tables. Submitted to The Astrophysical Journa