Perhaps because the Drimmel/Poggio selection I usually use is contaminated with some A-type stars? The Quintana catalog attempts to include all the OB stars within 1 kpc (although I notice that it does not include the highly reddened Bajamar star that ionizes the North American nebula). - ThreadSky

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galaxymap.bsky.social • 3 days ago

Perhaps because the Drimmel/Poggio selection I usually use is contaminated with some A-type stars? The Quintana catalog attempts to include all the OB stars within 1 kpc (although I notice that it does not include the highly reddened Bajamar star that ionizes the North American nebula).

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galaxymap.bsky.social•3 days ago

As in my previous maps there is no obvious spiral structure and in this map there is not even a clear density gap between the inner and outer galaxy. The Milky Way is not a grand design spiral galaxy.

galaxymap.bsky.social•3 days ago

The large low density region beyond Ori OB1, which is visible in all of my density maps, is much larger in this map. I have labelled it the California shell because it is the location of the California nebula and the California molecular cloud. (Credit: Remidone, Wikimedia Commons).

galaxymap.bsky.social•3 days ago

There is also the beginning of another somewhat well known low density region, the Vela shell, at the bottom of the map and I have also labelled several smaller low density regions (I made up the names of the Ara and Vulpecula shells based on the constellations in those directions).

galaxymap.bsky.social•3 days ago

One of the most striking results from the Gaia mission is that star clusters are only the most obvious star density features and these are the mountain peaks that are located within a complex density topography with the equivalent of mountain ranges, foothills, uplands, lowlands etc.

galaxymap.bsky.social•3 days ago

I am curious to see future research about the odd star clusters that do *not* exist within a larger density structure but instead erupt within very low density regions, like NGC 1647 or IC 4665. These remind me of the volcanic islands that suddenly appear in the Pacific Ocean. How did they form?

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