SiO and H2O Maser Observations of Red Supergiants in Star Clusters Embedded in the Galactic Disk

TL;DR

This study uses SiO and H2O maser observations to analyze red supergiants in specific star clusters within the Galactic disk, revealing their velocities, distances, and surrounding molecular gas, thus providing insights into cluster properties and evolution.

Contribution

First maser observations of red supergiants in these clusters, offering new data on their velocities, distances, and molecular environment, enhancing understanding of cluster dynamics.

Findings

Detected multiple red supergiants via maser lines.

Estimated cluster distance at 5.5 kpc near the Scutum-Crux arm.

Found varying molecular gas presence indicating different gas expulsion timescales.

Abstract

We present the result of radio observations of red supergiants in the star cluster, Stephenson's #2, and candidates for red supergiants in the star clusters, Mercer et al. (2005)'s #4, #8, and #13, in the SiO and H$_2$O maser lines.The Stephenson's #2 cluster and nearby aggregation at the South-West contain more than 15 red supergiants. We detected one at the center of Stephenson's #2 and three in the south-west aggregation in the SiO maser line, and three of these 4 were also detected in the H2O maser line. The average radial velocity of the 4 detected objects is 96 km s^{-1}, giving a kinematic distance of 5.5 kpc, which locates this cluster near the base of the Scutum-Crux spiral arm. We also detected 6 SiO emitting objects associated with the other star clusters. In addition, mapping observations in the CO J=1--0 line toward these clusters revealed that an appreciable amount of molecular gas still remains around Stephenson's #2 cluster in contrast to the prototypical red-supergiant cluster, Bica et al.'s #122. It indicates that a time scale of gas expulsion differs considerably in individual clusters.