Use the table and the Hertzsprung-Russell diagram to answer the question.

| Star | Luminosity (compared to Sun) | Temperature (K) |
|---|---|---|
| Vega | 40 | 9,600 |
| Altair | 10 | 7,700 |
| The Sun | 1 | 5,800 |
| 61 Cygni A | 0.15 | Estimate this value |
| Proxima Centauri | 0.0017 | 3,000 |
Estimate the surface temperature of the star 61 Cygni A.