A Four-Stokes-Parameter Spectral Line Polarimeter at the Caltech Submillimeter Observatory

We designed and built a new Four-Stokes-Parameter spectral line Polarimeter (FSPPol) for the Caltech Submillimeter Observatory (CSO). The simple design of FSPPol does not include any mirrors or optical components to redirect or re-image the radiation beam and simply transmits the beam to the receiver through its retarder plates. FSPPol is currently optimized for observation in the 200-260 GHz range and measures all four Stokes parameters, I, Q, U, and V. The very low level of instrument polarization makes it possible to obtain reliable measurements of the Goldreich-Kylafis effect in molecular spectral lines. Accordingly, we measured a polarization fraction of a few percent in the spectral line wings of ^{12}\mathrm{CO} (J=2\rightarrow1) in Orion KL/IRc2, which is consistent with previous observations. We also used FSPPol to study the Zeeman effect in the N=2\rightarrow1 transition of CN in DR21(OH) for the first time. At this point we cannot report a Zeeman detection, but more observations are ongoing

Explaining Recurring Maser Flares in the ISM Through Large-scale Entangled Quantum Mechanical States

We apply Dicke's theory of superradiance introduced in 1954 to the methanol 6.7 GHz and water 22 GHz spectral lines, often detected in molecular clouds as signposts for the early stages of the star formation process. We suggest that superradiance, characterized by burst-like features taking place over a wide range of time-scales, may provide a natural explanation for the recent observations of periodic and seemingly alternating methanol and water maser flares in G107.298+5.639. Although these observations would be very difficult to explain within the context of maser theory, we show that these flares may result from simultaneously initiated 6.7-GHz methanol and 22-GHz water superradiant bursts operating on different time-scales, thus providing a natural mechanism for their observed durations and time ordering. The evidence of superradiance in this source further suggests the existence of entangled quantum mechanical states, involving a very large number of molecules, over distances up to a few kilometres in the interstellar medium.Comment: 14 pages, 3 figure

Astronomical Image Processing with Array Detectors

We address the question of astronomical image processing from data obtained with array detectors. We define and analyze the cases of evenly, regularly, and irregularly sampled maps for idealized (i.e., infinite) and realistic (i.e., finite) detectors. We concentrate on the effect of interpolation on the maps, and the choice of the kernel used to accomplish this task. We show how the normalization intrinsic to the interpolation process must be carefully accounted for when dealing with irregularly sampled grids. We also analyze the effect of missing or dead pixels in the array, and their consequences for the Nyquist sampling criterion.Comment: 31 pages, 5 figures, accepted for publication in the PAS

Observational Determination of the Turbulent Ambipolar Diffusion Scale and Magnetic Field Strength in Molecular Clouds

We study the correlation of the velocity dispersion of the coexisting molecules H13CN and H13CO+ and the turbulent energy dissipation scale in the DR21(OH) star-forming region. The down-shift of the H13CO+ spectrum relative to H13CN is consistent with the presence of ambipolar diffusion at dissipation length scales that helps the process of turbulent energy dissipation, but at a different cut-off for ions compared to the neutrals. We use our observational data to calculate a turbulent ambipolar diffusion length scale L'\simeq17 mpc and a strength of B_{pos}\simeq1.7 mG for the plane of the sky component of the magnetic field in DR21(OH)

Non-Zeeman Circular Polarization of Molecular Rotational Spectral Lines

We present measurements of circular polarization from rotational spectral lines of molecular species in Orion KL, most notably 12CO (J=2 - 1), obtained at the Caltech Submillimeter Observatory with the Four-Stokes-Parameter Spectra Line Polarimeter. We find levels of polarization of up to 1 to 2% in general, for 12CO (J=2 - 1) this level is comparable to that of linear polarization also measured for that line. We present a physical model based on resonant scattering in an attempt to explain our observations. We discuss how slight differences in scattering amplitudes for radiation polarized parallel and perpendicular to the ambient magnetic field, responsible for the alignment of the scattering molecules, can lead to the observed circular polarization. We also show that the effect is proportional to the square of the magnitude of the plane of the sky component of the magnetic field, and therefore opens up the possibility of measuring this parameter from circular polarization measurements of Zeeman insensitive molecules.Comment: 30 pages, 7 figures; accepted for publication in the Ap