Unit | Ref | ||

Spectral Type | O9 Ia | 1 | |

RA | 04:54:03.011 | h:m:s | 2 |

Dec | +66:20:33.58 | d:m:s | 2 |

Parallax | 0.59 | mas | 3 |

\(M_v\) | -7.00 | mag | 4 |

\(v_r\) | 10 | km/s | 5 |

M_{★} |
36.7 | M_{☉} |
4 |

R_{★} |
32.5 | R_{☉} |
4 p.352 |

\(T_\mathrm{eff}\) | 29.5 | kK | 4 |

\(v\sin i\) | 100 | km/s | 4 |

\(v_\infty\) | 1550 | km/s | 4 |

\(\dot{M}\) | \(6\cdot 10^{-6}\) | M_{☉}/yr |
4 |

In the 2010s the CHARA Array on Mount Wilson was used to observe O-type stars. As with Black Bodies there is a realtionship between the effective temperature \(T_{eff}\), angular diameter \(\theta\) and extinction corrected bolometric flux \(f_{bol}\):

\[f_{bol}=\frac{1}{4}\theta^2\sigma T_{eff}^4\]Their best fit results in \(T_{eff}=28.0\pm1.5\,\mathrm{kK}\) and \(\theta=0.256\pm0.014\,\mathrm{mas}\). You get \(f_{bol}\) from model calculations [Gordon,2018].

Now let's try to calculate the stellar radius of α Cam.

With the star's distance \(d\) and its angular diameter \(\theta\) we can get the star's
true diameter \(D\).
\[\frac{D}{2d\pi} = \frac{\theta}{360^\circ}\]
To get the distance we take the trigonometric parallax from Gaia. There are three data
releases DR1, DR2 and DR3. The data differ significantly.

DR2 \(\mathrm{parallax}=1.3686\pm0.3297\,\mathrm{mas}\)

DR3 \(\mathrm{parallax}=0.5916\pm0.1333\,\mathrm{mas}\).

Distances from this values are

\(d(\mathrm{DR2})=2383\pm574\,\mathrm{ly}\)

\(d(\mathrm{DR3})=5513\pm1198\,\mathrm{ly}\).

After all the diameter of α Cam is between 20 D_{☉} and
50 D_{☉}.

Last modified: 2023 Jan 13