The Star α Cam

Parameters of α Cam
(1) Sìmon-Dìaz,2014, (2) Sota,2011, (3) Gaia DR3, (4) Repolust,2004 (5) Holgado,2018
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
Interferometric Observation

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: 2022 Aug 01