Phil James' talk and galaxies in h-alpha

[DRatledge]

Following on from Professor Phil James' talk last night and what resulted from taking H-alpha images of galaxies then is it possible to do something similar from Lancashire? Not really but we can image galaxies in H-alpha. The relatively nearby big bright ones can record well. Below are two of the easiest that I took with an h-alpha filter a few years ago - M82 and M51. They are totally different and M82 is regarded as a starburst galaxy.

[DRatledge]

M33 is another that records very well in H-alpha. This was taken with a Canon DSLR + h-alpha filter and 4 inch apo. NGC 604 is the very bright nebula towards its top left.

[rwilkinson]

Do you have the full-spectrum versions of those images for comparison?

And I wonder if the bandwidth of the H-alpha filter makes a big difference to the data?
I see that Baader make two grades of filters with bandwidths of 35 & 7nm, whereas the high-end Chroma ones have a bandwidth of just 3nm.
But I suppose that the professional 'scopes have custom (maybe temp-controlled?) filters with even narrower bandwidths.

[DRatledge]

Ross,
These should be approximately the same scale.
I used a bandwidth of 6 and 7. The wider ones are really for wide-angle lenses. When you go narrower than 6 then you lose out on NII emission which is very close. The filter should be referred to as an h-alpha + (NII) and I think Phil's images actually quoted that. Narrower than 6 starts to get seriously expensive rather than just plain expensive.

[rwilkinson]

Thanks David, in those colour images the "hydrogen hot-spots" do show up nicely in the context of the overall galactic structures.