Table 2.
Best-fit parameters of nearby spiral arms using HMSFR masers and OCs of different age groups.
| Arm | φ | Rref | βref | Arm width | |
|---|---|---|---|---|---|
| (deg) | (kpc) | (deg) | (kpc) | ||
| Sagittarius-Carina | 17.1 ± 1.6 | 6.04 ± 0.09 | 24 | 0.27 ± 0.04 | |
| HMSFR masers | Local | 11.4 ± 1.9 | 8.26 ± 0.05 | 9 | 0.31 ± 0.05 |
| Perseus | 10.3 ± 1.4 | 8.87 ± 0.13 | 40 | 0.35 ± 0.06 | |
| Sagittarius-Carina | 16.2 ± 0.4 | 6.72 ± 0.07 | 2 | 0.27 ± 0.02 | |
| YOCs (< 20 Myr) | Local | 10.8 ± 0.6 | 8.18 ± 0.06 | 6 | 0.24 ± 0.06 |
| Perseus | 9.6 ± 0.8 | 9.42 ± 0.04 | 20 | 0.33 ± 0.03 | |
| Sagittarius-Carina | 15.7 ± 0.5 | 6.80 ± 0.07 | 2 | 0.30 ± 0.03 | |
| OCs (20−60 Myr) | Local | 10.7 ± 0.8 | 8.24 ± 0.07 | 6 | 0.31 ± 0.03 |
| Perseus | 9.0 ± 1.0 | 9.45 ± 0.06 | 20 | 0.36 ± 0.04 | |
| Sagittarius-Carina | 15.2 ± 0.5 | 6.79 ± 0.07 | 2 | 0.33 ± 0.04 | |
| OCs (60−100 Myr) | Local | 8.9 ± 0.9 | 8.09 ± 0.06 | 5 | 0.40 ± 0.03 |
| Perseus | 9.0 ± 0.9 | 9.43 ± 0.07 | 20 | 0.39 ± 0.05 | |
Notes. For each spiral arm, the best-fit pitch angle (φ), initial radius (Rref), reference Galactocentric azimuth angle (βref), and arm width are listed. The OCs are divided into three subsamples: (1) YOCs (< 20 Myr, 633 clusters); (2) OCs with ages from 20 to 60 Myr (334 clusters); and (3) OCs with ages from 60 to 100 Myr (262 clusters).
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