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

Do Antidepressants Improve the Quality of Life and Decrease the Severity of Symptoms in Patients with Irritable Bowel Syndrome?

Objective: The objective of this selective EBM review is to determine whether or not the use of antidepressants improves the quality of life and decreases the severity of symptoms in patients with IBS. Study Design: Review of three English language, double-blind, randomized controlled trials published in 2009. Data sources: Randomized controlled trials comparing the use of three different antidepressants to a controlled placebo were found on PubMed, OVID and the Cochrane database. Outcome(s) Measured: Primary end point was overall bowel symptom score at the end of twelve weeks. Secondary end points include individual BSS for each irritable bowel syndrome subset, constipation, pain, or discomfort. Other secondary end points assessed adequate relief of symptoms, IBS-quality of life, and rectal sensitivity. Outcomes were measured through the use of questionnaires. Results: Three randomized controlled trials were included in this review. The study by Abdul-Baki H. indicated that imipramine was superior to treating IBS when compared to placebo, making this the only therapy evaluated in this review to be effective. Study by Ladabaum U. indicated that citalopram was less effective than placebo. Study by Saito Y. determined that St. John’s Wort was less effective than placebo in decreasing symptoms of IBS. Conclusions: The results of the study using imipramine concluded that the drug was effective in reducing symptoms and improving quality of life for patients with IBS. The other two studies concluded that the therapy drugs were less effective than the placebo in treating symptoms of IBS. The population studied in some of the studies was not very large and one study had a majority of females which are factors that should be changed in future studies

Dispersion of Magnetic Fields in Molecular Clouds. III

We apply our technique on the dispersion of magnetic fields in molecular clouds to high spatial resolution Submillimeter Array polarization data obtained for Orion KL in OMC-1, IRAS 16293, and NGC 1333 IRAS 4A. We show how one can take advantage of such high resolution data to characterize the magnetized turbulence power spectrum in the inertial and dissipation ranges. For Orion KL we determine that in the inertial range the spectrum can be approximately fitted with a power law k^-(2.9\pm0.9) and we report a value of 9.9 mpc for {\lambda}_AD, the high spatial frequency cutoff presumably due to turbulent ambipolar diffusion. For the same parameters we have \sim k^-(1.4\pm0.4) and a tentative value of {\lambda}_AD \simeq 2.2 mpc for NGC 1333 IRAS 4A, and \sim k^-(1.8\pm0.3) with an upper limit of {\lambda}_AD < 1.8 mpc for IRAS 16293. We also discuss the application of the technique to interferometry measurements and the effects of the inherent spatial filtering process on the interpretation of the results.Comment: 25 pages, 9 figures; accepted for publication in The Astrophysical Journa

The Removal of Artificially Generated Polarization in SHARP Maps

We characterize the problem of artificial polarization for the Submillimeter High Angular Resolution Polarimeter (SHARP) through the use of simulated data and observations made at the Caltech Submillimeter Observatory (CSO). These erroneous, artificial polarization signals are introduced into the data through misalignments in the bolometer sub-arrays plus pointing drifts present during the data-taking procedure. An algorithm is outlined here to address this problem and correct for it, provided that one can measure the degree of the sub-array misalignments and telescope pointing drifts. Tests involving simulated sources of Gaussian intensity profile indicate that the level of introduced artificial polarization is highly dependent upon the angular size of the source. Despite this, the correction algorithm is effective at removing up to 60% of the artificial polarization during these tests. The analysis of Jupiter data taken in January 2006 and February 2007 indicates a mean polarization of 1.44%+/-0.04% and 0.95%+/-0.09%, respectively. The application of the correction algorithm yields mean reductions in the polarization of approximately 0.15% and 0.03% for the 2006 and 2007 data sets, respectively.Comment: 19 pages, 7 figure

Dispersion of Magnetic Fields in Molecular Clouds. I

We describe a method for determining the dispersion of magnetic field vectors about large-scale fields in turbulent molecular clouds. The method is designed to avoid inaccurate estimates of magnetohydrodynamic or turbulent dispersion - and help avoiding inaccurate estimates of field strengths - due to large-scale, non-turbulent field structure when using the well-known method of Chandrasekhar and Fermi. Our method also provides accurate, independent estimates of the turbulent to large-scale magnetic field strength ratio. We discuss applications to the molecular clouds OMC-1, M17, and DR21(Main).Comment: 19 pages, 2 figures, 1 table, accepted for publication in the Ap

Magnetic Fields and Infall Motions in NGC 1333 IRAS 4

We present single-dish 350 micron dust continuum polarimetry as well as HCN and HCO+ J=4-3 rotational emission spectra obtained on NGC 1333 IRAS 4. The polarimetry indicates a uniform field morphology over a 20" radius from the peak continuum flux of IRAS 4A, in agreement with models of magnetically supported cloud collapse. The field morphology around IRAS 4B appears to be quite distinct however, with indications of depolarization observed towards the peak flux of this source. Inverse P-Cygni profiles are observed in the HCN J=4-3 line spectra towards IRAS 4A, providing a clear indication of infall gas motions. Taken together, the evidence gathered here appears to support the scenario that IRAS 4A is a cloud core in a critical state of support against gravitational collapse.Comment: 23 pages, 6 figures, 2 table

Dispersion of Magnetic Fields in Molecular Clouds. II.

We expand our study on the dispersion of polarization angles in molecular clouds. We show how the effect of signal integration through the thickness of the cloud as well as across the area subtended by the telescope beam inherent to dust continuum measurements can be incorporated in our analysis to correctly account for its effect on the measured angular dispersion and inferred turbulent to large-scale magnetic field strength ratio. We further show how to evaluate the turbulent magnetic field correlation scale from polarization data of sufficient spatial resolution and high enough spatial sampling rate. We apply our results to the molecular cloud OMC-1, where we find a turbulent correlation length of δ ≈ 16 mpc, a turbulent to large-scale magnetic field strength ratio of approximately 0.5, and a plane-of-the-sky large-scale magnetic field strength of approximately 760 μG

Dispersion of Magnetic Fields in Molecular Clouds. IV - Analysis of Interferometry Data

We expand on the dispersion analysis of polarimetry maps toward applications to interferometry data. We show how the filtering of low spatial frequencies can be accounted for within the idealized Gaussian turbulence model, initially introduced for single-dish data analysis, to recover reliable estimates for correlation lengths of magnetized turbulence, as well as magnetic field strengths (plane-of-the-sky component) using the Davis–Chandrasekhar–Fermi method. We apply our updated technique to TADPOL/CARMA data obtained on W3(OH), W3 Main, and DR21(OH). For W3(OH), our analysis yields a turbulence correlation length δ ≃ 19 mpc, a ratio of turbulent-to-total magnetic energy 〈B〉_^2_t/〈B^2〉 ≃ 0.58, and a magnetic field strength B_0 ~ 1.1 mG for W3 Main δ ≃ 22mpc, 〈B_t^2〉/〈B^2〉 ≃ 0.74, and B_0 ~ 0.7 mG while for DR21(OH) δ ≃ 12 mpc, 〈B_t^2〉/〈B^2〉 ≃ 0.70, and B_0 ~ 1.2 mG

ALMA observations of dust polarization and molecular line emission from the Class 0 protostellar source Serpens SMM1

We present high angular resolution dust polarization and molecular line observations carried out with the Atacama Large Millimeter/submillimeter Array (ALMA) toward the Class 0 protostar Serpens SMM1. By complementing these observations with new polarization observations from the Submillimeter Array (SMA) and archival data from the Combined Array for Research in Millimeter-wave Astronomy (CARMA) and the James Clerk Maxwell Telescopes (JCMT), we can compare the magnetic field orientations at different spatial scales. We find major changes in the magnetic field orientation between large (~0.1 pc) scales -- where the magnetic field is oriented E-W, perpendicular to the major axis of the dusty filament where SMM1 is embedded -- and the intermediate and small scales probed by CARMA (~1000 AU resolution), the SMA (~350 AU resolution), and ALMA (~140 AU resolution). The ALMA maps reveal that the redshifted lobe of the bipolar outflow is shaping the magnetic field in SMM1 on the southeast side of the source; however, on the northwestern side and elsewhere in the source, low velocity shocks may be causing the observed chaotic magnetic field pattern. High-spatial-resolution continuum and spectral-line observations also reveal a tight (~130 AU) protobinary system in SMM1-b, the eastern component of which is launching an extremely high-velocity, one-sided jet visible in both CO(2-1) and SiO(5-4); however, that jet does not appear to be shaping the magnetic field. These observations show that with the sensitivity and resolution of ALMA, we can now begin to understand the role that feedback (e.g., from protostellar outflows) plays in shaping the magnetic field in very young, star-forming sources like SMM1.Comment: 15 pages, 6 figures, 4 tables, 1 appendix. Accepted for publication in the Astrophysical Journal. Materials accessible in the online version of the (open-access) ApJ article include the FITS files used to make the ALMA image in Figure 1(d), and a full, machine-readable version of Table