2007) at the VLBA correlation facility in Socorro, NM. The data were correlated with the DiFX 10 The observations used the same equipment setup and calibration procedures described by Xu et al. The geometry and kinematics of the arm are discussed in Section 5 and 6, and we summarize our conclusions in Section 7. We discuss how sources were assigned to the Sgr Far arm in Section 4. Parallaxes and proper motions are presented in Section 3. In Section 2 we describe the observations and data analysis. With the aim of better constraining the structure of the "far" side of the Sagittarius arm (Sgr Far, i.e., beyond the tangent point), we measured parallaxes of 13 additional maser sources. Beyond the tangent point, only four parallax measurements had been made, and those tended to have large uncertainties (>1 kpc). These contained 18 parallaxes for sources in the Sagittarius spiral arm, most of which were located closer to the Sun than the arm's tangent point at l ≈ 49° and a distance of ≈5 kpc (Wu et al. As of 2015, over 100 parallaxes had been published (Reid et al. Trigonometric parallaxes for molecular masers associated with high-mass star-forming regions (HMSFRs) from the Bar and Spiral Structure Legacy (BeSSeL) Survey and the VLBI Exploration of Radio Astrometry (VERA) project are accurately tracing the spiral structure of the Milky Way.
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