Large-field CO(1--0) observations toward the Galactic historical supernova remnants: a large cavity around Tycho's supernova remnant

The investigation of the interaction between the supernova remnants (SNRs) and interstellar gas is not only necessary to improve our knowledge of SNRs, but also to understand the nature of the progenitor systems. As a part of the Milky Way Imaging Scroll Painting CO line survey (MWISP), we study the interstellar gas surrounding the Galactic historical SNRs, using the PMO 13.7-meter telescope. In this work, we present large-field (3$^\circ$$\times$2$^\circ$) and high-sensitivity CO(1-0) molecular line observations toward Tycho's SNR. The CO observations reveal, from the outside in, large molecular clouds, stream-like structures, and an inner rim around Tycho's SNR. We derived the basic properties (column density, mass, and kinematics) of these objects based on the CO observations. The large molecular clouds individually show an arc toward the remnant center, outlining a large cavity with radii of $\sim$0.3$^\circ$$\times$0.6$^\circ$ (or 13 pc $\times$27 pc at a distance of 2.5 kpc) around the remnant. The CO line broadenings and asymmetries detected in the surrounding clouds, the observed expansion of the cavity, in concert with enhanced $^{12}$CO(2-1)/(1-0) intensity ratio detected in previous studies, suggest the interaction of the large cavity with a wind in the region. After excluding the scenario of a large bubble produced by bright massive stars, we suggest that the large cavity could be explained by accretion wind from the progenitor system of Tycho's supernova. Nevertheless, the possibility of the random distribution of a large cavity around Tycho's SNR cannot be ruled out thus far. Further observations are needed to confirm the physical association of the large cavity with Tycho's SNR.Comment: 15 pages, 9 figures, updated according to the A&A proo

Trade Agreements and Economic Growth

This paper studies the growth effects of regional trade agreements (RTAs), taking into account the WTO participation of RTA members. Assuming smaller preference margins of RTAs for WTO members than non-members, I show in a model a stronger growth effect of RTAs for non-WTO members than that for WTO members. Based on a comprehensive set of 270 RTAs and a large panel dataset covering 177 countries over the period of 1960-2007, the regression results show that RTAs promote growth for non-WTO members, while their growth effect is insignificantly different from zero for WTO members. This implies that the complementarity between the two approaches of trade liberalization in promoting economic growth is so far limited

SMA CO(2-1) Observations of CG30: A Protostellar Binary System with a High-Velocity Quadrupolar Molecular Outflow

We present interferometric observations in the 12CO (2-1) line and at 1.3 mm dust continuum of the low-mass protostellar binary system in the cometary globule CG30, using the Submillimeter Array. The dust continuum images resolve two compact sources (CG30N and CG30S), with a linear separation of ~8700 AU and total gas masses of ~1.4 and ~0.6 M_sun, respectively. With the CO images, we discover two high-velocity bipolar molecular outflows, driven by the two sources. The two outflows are nearly perpendicular to each other, showing a quadrupolar morphology. The northern bipolar outflow extends along the southeast (redshifted, with a velocity up to ~23 km/s) and northwest (blueshifted, velocity up to ~30 km/s) directions, while the southern pair has an orientation from southwest (blueshifted, velocity up to 13 km/s) to northeast (redshifted, velocity up to ~41 km/s). The outflow mass of the northern pair, driven by the higher mass source CG30N, is ~9 times larger than that of the southern pair. The discovery of the quadrupolar molecular outflow in the CG30 protobinary system, as well as the presence of other quadrupolar outflows associated with binary systems, demonstrate that the disks in (wide) binary systems are not necessarily co-aligned after fragmentation.Comment: 12 pages, 3 figures, to be published by ApJL in October 200

Satellite Observed Aerosol Optical Thickness and Trend around Megacities in the Coastal Zone

Nearly 30-year aerosol optical thickness (AOT) climate data record (CDR) derived from the operational satellite observations of National Ocean and Atmospheric Administration (NOAA) Advanced Very High Resolution Radiometer (AVHRR) is used to study the AOT trends over seventeen megacities in the coast zone (MCCZ). Linear trends are derived from monthly and seasonal mean AOT in the past three decades and used in the analysis. The results indicate the following: (1) AOT around a MCCZ in fast developing countries has relatively high value and a positive trend with a confidence level generally above 95%; (2) AOT around a MCCZ in industrialized countries has relatively low value and a negative trend with a confidence level generally above 95%; (3) AOT values and their trends show distinct seasonal variations in MCCZ, which can be explained somewhat by the seasonal variations of meteorological conditions. AOT trend is an effective index for examining the efficacy of air pollution control policies implemented for these megacities

Testing Conflicting Political Economy Theories: Full-Fledged versus Partial-Scope Regional Trade Agreements

We apply a duration analysis to test the conflicting predictions of the median voter model and the lobbying model using panel data on regional trade agreement (RTA) formation. Our results show that the pro-labor prediction of the median voter model is supported by the full-fledged free trade areas and customs unions (FTAs/CUs), while the pro-capital prediction of the lobbying model is supported by the partial-scope preferential trade arrangements among developing countries. This finding holds better for the country pairs with more different capital-labor ratios as a result of the stronger distributional effects of RTAs. The support for the median voter model (lobbying model) is stronger when the two countries in a pair have left-oriented (right-oriented) governments. I also find stronger support for the median voter model for the subset of FTAs/CUs with service coverage and stronger support for the lobbying model for countries that place higher weight on political contribution

GATT/WTO Promotes Trade Strongly: Sample Selection and Model Specification

Some recent empirical studies examine the impact of the GATT/WTO on trade. This paper investigates the sample selection bias and the gravity model specification issues in the literature. First, the GATT/WTO not only makes existing trading partners trade more at the intensive margin, but also creates new trading relationships at the extensive margin. Most existing papers exclude zero trade observations and hence ignore the extensive margin. Secondly, due to the violation of some maintained assumptions, the traditional log-linear gravity regressions fail to uncover the role of the GATT/WTO even at the intensive margin. Using a large bilateral panel dataset including zero trade flows and a more appropriate econometric method, this paper finds that the GATT/WTO has been very effective in promoting world trade at both the intensive and extensive margins