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

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

Submillimeter Polarimetry with PolKa, a reflection-type modulator for the APEX telescope

Imaging polarimetry is an important tool for the study of cosmic magnetic fields. In our Galaxy, polarization levels of a few up to $\sim$10\% are measured in the submillimeter dust emission from molecular clouds and in the synchrotron emission from supernova remnants. Only few techniques exist to image the distribution of polarization angles, as a means of tracing the plane-of-sky projection of the magnetic field orientation. At submillimeter wavelengths, polarization is either measured as the differential total power of polarization-sensitive bolometer elements, or by modulating the polarization of the signal. Bolometer arrays such as LABOCA at the APEX telescope are used to observe the continuum emission from fields as large as \sim0\fdg2 in diameter. %Here we present the results from the commissioning of PolKa, a polarimeter for Here we present PolKa, a polarimeter for LABOCA with a reflection-type waveplate of at least 90\% efficiency. The modulation efficiency depends mainly on the sampling and on the angular velocity of the waveplate. For the data analysis the concept of generalized synchronous demodulation is introduced. The instrumental polarization towards a point source is at the level of $\sim0.1$\%, increasing to a few percent at the $-10$db contour of the main beam. A method to correct for its effect in observations of extended sources is presented. Our map of the polarized synchrotron emission from the Crab nebula is in agreement with structures observed at radio and optical wavelengths. The linear polarization measured in OMC1 agrees with results from previous studies, while the high sensitivity of LABOCA enables us to also map the polarized emission of the Orion Bar, a prototypical photon-dominated region

Non-Zeeman circular polarization of CO rotational lines in SNR IC 443

Context. We study interstellar magnetic fields by measuring the polarization in molecular spectral lines and thermal emission of dust. Aims. We report detection of non-Zeeman circular polarization and linear polarization levels of up to 1% in the ^(12)CO spectral line emission in a shocked molecular clump around the supernova remnant (SNR) IC 443. We examine our polarization results to confirm that the circular polarization signal in CO lines is caused by a conversion of linear to circular polarization, consistent with anisotropic resonant scattering. In this process background, linearly polarized CO emission interacts with similar foreground molecules aligned with the ambient magnetic field and scatters at a transition frequency. The difference in phase shift between the orthogonally polarized components of this scattered emission can cause a transformation of linear to circular polarization. Methods. We compared linear polarization maps from the dust continuum, which were obtained with PolKa at APEX, and ^(12)CO (J = 2 → 1) and (J = 1 → 0) from the IRAM 30-m telescope. We found no consistency between the two sets of polarization maps. We then reinserted the measured circular polarization signal in the CO lines across the source to the corresponding linear polarization signal to test whether the linear polarization vectors of the CO maps were aligned with those of the dust before this linear to circular polarization conversion. Results. After the flux correction for the two transitions of the CO spectral lines, the new polarization vectors for both CO transitions aligned with the dust polarization vectors, establishing that the non-Zeeman CO circular polarization is due to a linear to circular polarization conversion

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)

Study on the properties of piezoelectric materials and manganese-based oxide perovskites /

Perovskite type piezoelectric and manganese oxide materials have gained a lot of attention in the field of device engineering. Lead zirconium titananium oxide (PbZri.iTiiOa or PZT) is a piezoelectric material widely used as sensors and actuators. Miniaturization of PZTbased devices will not only perfect many existing products, but also opens doors to new applications. Lanthanum manganese oxides Lai-iAiMnOa (A-divalent alkaline earth such as Sr, Ca or Ba) have been intensively studied for their colossal magnetoresistance (CMR) properties that make them applicable in memory cells, magnetic and pressure sensors. In this study, we fabricate PZT and LSMO(LCMO) heterostructures on SrTiOa substrates and investigate their temperature dependency of resistivity and magnetization as a function of the thickness of LSMO(LCMO) layer. The microstructure of the samples is analysed through TEM. In another set of samples, we study the effect of application of an electric field across the PZT layer that acts as an external pressure on the manganite layer. This verifies the correlation of lattice distortion with transport and magnetic properties of the CMR materials

Ambipolar diffusion and turbulent magnetic fields in molecular clouds

We review the introduction and development of a novel method for the characterization of magnetic fields in star-forming regions. The technique is based on the comparison of spectral line profiles from coexistent neutral and ion molecular species commonly detected in molecular clouds, sites of star formation. Unlike other methods used to study magnetic fields in the cold interstellar medium, this ion/neutral technique is not based on spin interactions with the field. Instead, it relies on and takes advantage of the strong cyclotron coupling between the ions and magnetic fields, thus exposing what is probably the clearest observational manifestation of magnetic fields in the cold, weakly ionized gas that characterizes the interior of molecular clouds. We will show how recent development and modeling of the ensuing ion line narrowing effect leads to a determination of the ambipolar diffusion scale involving the turbulent component of magnetic fields in star-forming regions, as well as the strength of the ordered component of the magnetic field