The O-Type Star α Cam

Invitation to join an Observation Campaign on α Cam


The O star α Cam is bright (V = 4.3), located at DEC=66 degrees, and therefore easily accessible for Northern observers. It a very good target for moderate instruments. α Cam is a magnetic candidate star (one of very few). The strongest confirmation of being magnetic would be if an accurate period could be determined. Therefore, the prime goal is to determine the rotation period of the star, which is likely between 4 and 5 days. Previous data did not allow to determine sufficient accuracy. In practice this means that the duration should be at least 10 or 20 rotation periods, i.e. at least one month, preferably 2 months.
All wind affected lines (all H, He I and He II) vary significantly on timescales of hours, especially H-alpha shows obvious variations. See here March 2022.

There are at least two reasons to observe alf Cam.

Scientific reason:
The importance to determine a better period of alpha Cam is that it is a magnetic candidate star. There are only a handful of magnetic O stars known, so determining an accurate period would give indirect evidence of the presence of a magnetic field.

Aesthetic reason:
Our observations in March 2022 are to sparsely in time to see the H-alpha mountain changing its slope. An observation session of say 5 days with a higher rate say 3 hours would be helpful.


Observe at least H-alpha.

  • R ≥ 8000
  • SNR ≥ 200
  • Normally you have to average spectra to achieve this SNR
    we need a header entry containing middle of observation in UTC.
  • Don't normalise.
  • Don't remove tellurics.
  • Don't apply heliocentric correction.
  • Store your spectrum in the BAA Spectroscopy Database. Object name is alf Cam.
Echelle spectra are highly welcome.

To support the scientific campaign one spectrum a night should do because we cover 6 timezones. This campaign can start immediately if the clouds vanish and may last as long as you are fine with it.

The aesthetic campaign needs good weather in more timezones at once and if possible four spectra per night. Maybe we should start it in the group Astronomical Spectroscopy where you find us under the topic The O-type star alfa Cam.

Last modified: 2022 Sep 30