We report trigonometric parallax measurements of 22?GHz H2O masers in two massive star-forming regions from Very Long Baseline Array observations as part of the Bar and Spiral Structure Legacy Survey. The distances of kpc to W49N (G043.16+0.01) and kpc to G048.60+0.02 locate them in a distant section of the Perseus arm near the solar circle in the first Galactic quadrant. This allows us to locate accurately the inner portion of the Perseus arm for the first time. Combining the present results with sources measured in the outer portion of the arm in the second and third quadrants yields a global pitch angle of 95 ± 13 for the Perseus arm. We have found almost no H2O maser sources in the Perseus arm for 50° ? 80°, suggesting that this ≈6 kpc section of the arm has little massive star formation activity.
展开▼
