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Table 3.
Best-fit results of the spiral arm parameters for the present-day OCs and the regressed OCs.
| Age groups | 0−20 Myr | 20−40 Myr | 40−60 Myr | 60−80 Myr | 80−100 Myr |
|---|---|---|---|---|---|
| Regress to: | 20 MYA | 40 MYA | 60 MYA | 80 MYA | |
| Pitch angle: φ (degree) | |||||
| Sgr–Car Arm | 16.2 ± 0.4 | 16.3 ± 1.0 | 16.2 ± 1.1 | 16.2 ± 1.0 | 16.0 ± 1.0 |
| Local Arm | 10.8 ± 0.6 | 10.8 ± 0.9 | 10.5 ± 1.0 | 10.5 ± 0.9 | 10.6 ± 1.0 |
| Perseus Arm | 9.6 ± 0.8 | 9.3 ± 0.9 | 9.5 ± 0.9 | 9.6 ± 0.9 | 9.5 ± 1.0 |
| Arm width: w (kpc) | |||||
| Sgr–Car Arm | 0.27 ± 0.02 | 0.24 ± 0.09 | 0.24 ± 0.09 | 0.25 ± 0.09 | 0.25 ± 0.10 |
| Local Arm | 0.24 ± 0.06 | 0.28 ± 0.03 | 0.20 ± 0.05 | 0.23 ± 0.10 | 0.22 ± 0.09 |
| Perseus Arm | 0.33 ± 0.03 | 0.29 ± 0.09 | 0.29 ± 0.09 | 0.30 ± 0.10 | 0.31 ± 0.10 |
Notes. For each of the spiral arms near the Sun, we list its best-fit pitch angle (φ) and arm width (w), including their 1σ errors. Sgr–Car: Sagittarius-Carina Arm; MYA: million years ago.
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