Observations and Analysis of High-Resolution Magnetic Field Structures in Molecular Clouds

Recent high-angular-resolution (up to 0.7") dust polarization observations toward star forming regions are summarized. With the Sub-Millimeter Array, the emission from the dense structures is traced and resolved. The detected magnetic field morphologies vary from hourglass-like structures to isolated patches depending on the evolutionary stage of the source. These observed features have also served as a testbed to develop new analysis methods, with a particular focus on quantifying the role of the magnetic field in the star formation process.Comment: 4 pages, 2 figures; To appear in Proceedings of Magnetic Fields in the Universe: From Laboratory and Stars to Primordial Structures Aug. 21st - 27th 2011, Zakopane, Poland Eds. M. Soida, K. Otmianowska-Mazur, E.M. de Gouveia Dal Pino & A. Lazaria

Dust continuum and Polarization from Envelope to Cores in Star Formation: A Case Study in the W51 North region

We present the first high-angular resolution (up to 0.7", ~5000 AU) polarization and thermal dust continuum images toward the massive star-forming region W51 North. The observations were carried out with the Submillimeter Array (SMA) in both the subcompact (SMA-SubC) and extended (SMA-Ext) configurations at a wavelength of 870 micron. W51 North is resolved into four cores (SMA1 to SMA4) in the 870 micron continuum image. The associated dust polarization exhibits more complex structures than seen at lower angular resolution. We analyze the inferred morphologies of the plane-of-sky magnetic field (B_bot) in the SMA1 to SMA4 cores and in the envelope using the SMA-Ext and SMA-SubC data. These results are compared with the B_bot archive images obtained from the CSO and JCMT. A correlation between dust intensity gradient position angles (phi_{nabla I}) and magnetic field position angles (phi_B) is found in the CSO, JCMT and both SMA data sets. This correlation is further analyzed quantitatively. A systematically tighter correlation between phi_{nabla I} and phi_B is found in the cores, whereas the correlation decreases in outside-core regions. Magnetic field-to-gravity force ratio (Sigma_B) maps are derived using the newly developed polarization - intensity gradient method by Koch, Tang & Ho 2012. We find that the force ratios tend to be small (Sigma_B <= 0.5) in the cores in all 4 data sets. In regions outside of the cores, the ratios increase or the field is even dominating gravity (Sigma_B > 1). This possibly provides a physical explanation of the tightening correlation between phi_{nabla I} and phi_B in the cores: the more the B field lines are dragged and aligned by gravity, the tighter the correlation is. Finally, we propose a schematic scenario for the magnetic field in W51 North to interpret the four polarization observations at different physical scales.Comment: Accepted for publication in ApJ. 10 pages. 7 figure

The circumstellar disk of AB Aurigae: evidence for envelope accretion at late stages of star formation?

The circumstellar disk of AB Aurigae has garnered strong attention owing to the apparent existence of spirals at a relatively young stage and also the asymmetric disk traced in thermal dust emission. However, the physical conditions of the spirals are still not well understood. The origin of the asymmetric thermal emission is unclear. We observed the disk at 230 GHz (1.3 mm) in both the continuum and the spectral line ^12CO J=2-1 with IRAM 30-m, the Plateau de Bure interferometer, and the Submillimeter Array to sample all spatial scales from 0.37" to about 50". To combine the data obtained from these telescopes, several methods and calibration issues were checked and discussed. The 1.3 mm continuum (dust) emission is resolved into inner disk and outer ring. Molecular gas at high velocities traced by the CO line is detected next to the stellar location. The inclination angle of the disk is found to decrease toward the center. On a larger scale, based on the intensity weighted dispersion and the integrated intensity map of ^12CO J=2-1, four spirals are identified, where two of them are also detected in the near infrared. The total gas mass of the 4 spirals (M_spiral) is 10^-7 < M_spiral < 10^-5 M_sun, which is 3 orders of magnitude smaller than the mass of the gas ring. Surprisingly, the CO gas inside the spiral is apparently counter-rotating with respect to the CO disk, and it only exhibits small radial motion. The wide gap, the warped disk, and the asymmetric dust ring suggest that there is an undetected companion with a mass of 0.03 M_sun at a radius of 45 AU. Although an hypothetical fly-by cannot be ruled out, the most likely explanation of the AB Aurigae system may be inhomogeneous accretion well above or below the main disk plane from the remnant envelope, which can explain both the rotation and large-scale motions detected with the 30-m image.Comment: 17 pages, 13 figures, accepted for publication in A&A journal. Typos are correcte

A study of the relation between inflation and exchange rates in the Fiji Islands: a cointegration and vector error correction approach

The main purpose of this study is to examine the effects of the exchange rates, international prices, and the demand shocks on inflation in Fiji. How the domestic inflation in a pegged exchange rate system is aligned with international price shocks is an important monetarist idea, and this is tested in this study. This study employs annual data from 1975 to 2010. The multivariate cointegration tests are done after the unit root tests, and further, the Vector Error Correction (VEC) model shows that the changes in Fiji’s CPI are Granger caused by the long-term trends in all other variables, and the CPI in Australia, and devaluation-year dummies are used as exogenous variables in the VEC model, and the changes in exchange rate and changes in demand shocks are the independent variables but made endogenous in the VEC model. The impulse response function also shows that due to the exchange rate depreciation, inflation has increased for many years in Fiji. The policy implication of our study is that as a monetary policy instrument, the flexibility of the exchange rate policy is indispensable for Fiji to appropriately absorb the international supply and price shocks

A study of the pass - through effects of exchange rates and international prices shocks on inflation in the Fiji Islands

The main purpose of this study is to examine the effects of the exchange rates,international prices, and the demand shocks on inflation in Fiji Island. The study covers the annual data from 1975 to 2010.The variables are transformed into changes/per cent and then Ordinary Least Squares methodology (OLS) is used. The appropriateness of the OLS assumptions is tested including the normality of the residuals, autocorrelations,heteroskedasticity and functional forms. The main findings are that the Fijian dollar depreciation increases, the international price shocks in the form of Australian consumer prices increase, the Keynesian demand shocks increase, and the devaluation events increase the consumer price inflation in Fiji. As a monetary policy instrument the flexibility of the exchange rate policy is indispensable for Fiji to absorb appropriately the international supply and price shocks. We have been able to include the international supply shocks, the domestic demand shocks, the exchange rates, and devaluation dummies in our model. Though we have used a simple OLS model, the originality of our study is the comprehensiveness of the theoretical variables in our model. This study will have an important implication for the small open economy of Fiji especially its exchange rate policy

Dom Stabiliteitspact

Aanvankelijk vervulde het Stabiliteitspact een nuttige functie: duidelijke regels waarborgden de monetaire integratie. Door de vergrijzing en de conjuncturele verslechtering is het Pact aan herziening toe. Meer ruimte voor stabilisatiebeleid en het mede beschouwen van de pensioensituatie zijn belangrijker dan strikte naleving van het Pact omwille van geloofwaardigheid