Local Spiral Structure Traced by Red Clump Stars

Using the cross-matched data of Gaia EDR3 and the Two Micron All Sky Survey Point Source Catalog, a sample of RC stars with parallax accuracies better than 20% is identified and used to reveal the nearby spiral pattern traced by old stars. As shown in the overdensity distribution of RC stars, there is an arc-like feature extending from l similar to 90 degrees to similar to 243 degrees, which passes close to the Sun. This feature is probably an arm segment traced by old stars, indicating the galaxy potential in the vicinity of the Sun. With a comparison to the spiral arms depicted by young objects, we found that there are considerable offsets between the two different components of the Galactic spiral arms. The spiral arm traced by RC stars tends to have a larger pitch angle, and hence a more loosely wound pattern.