Spectroscopic Observation of BE Star - 4 Hercules

4 Hercules is a mag 5.75 star which is a known BE star with an edge on circumstellar disk. I made a spectroscopic observation of this star last night 20/21 April. I have written up a little report including the method used to calculate the rotational velocity of the circumstellar disk.

www.webtreatz.com/index.php/articles/34-...f-be-star-4-hercules

Dave.

Nice work Dave. Its not so long ago that the first pioneers were making discoveries like this for the first time. It must feel pretty good.
I'm amazed the H alpha line is split so much, I always imagined the shift was small. Intuitively, I would expect a central peak from the main star and a shoulder on each side due to the surrounding disk. Interesting stuff......
A magnetic field can also split emission lines(Zeeman effect?). I wonder if there are any objects in the sky that show magnetic effects?

John one of the places the zeeman effect is most pronounced is in sunspots. Depending on the strength of the local magnetic field it is possible to see this as a broadening or even splitting of some of the lines. In order to do this I will have to wait until I have an appropriate solar filter for the C14.

johnomahony wrote: Intuitively, I would expect a central peak from the main star and a shoulder on each side due to the surrounding disk.

John, I missed this bit in your reply. Normally you would expect to see an absorption rather than an emission in the H-Alpha region from the main star itself. However in BE stars like this the absorption line is overwhelmed by the emission lines from the circumstellar disk.

Dave - good to see some results.

Question though: if the accretion disc is not edge on to the observer wont this tend to skew the results such that rotation appears slower than it really is? Therefore what we measure here is a lower-bound on what the actual rotation speed is?

Mark C

Mark, your right. However the orientation of the accretion disk has a huge impact on the HA profile. For example if the disk was face on the we would see a central peak in emission with no shifting at all. Also some accretion disks rotate so fast that material is being ejected in every direction this creates a very broad emission line.

In short if the disk was say at 45degrees, the central 'trough' would only extend half way to the base, as it becomes more and more face on the central depression in the profile disappears. In this case we can see the center of the profile extending all the way to the base and the classic 'wings' (slight but broad absorptions flanking either side) which all put together clearly describes a classic edge on profile.

I hope to gather some more examples of BE stars once the skies permit.

Dave.