APOD: Palomar 12 (2015 Feb 19)

[geckzilla]

The fastest way to assess Hubble data is almost always the Hubble Legacy Archive. Entering Pal 12 as the target shows two series of images, 26 July 2003 and 21 May 2006. Both used the Advanced Camera for Surveys.

I did not try the Hubble Legacy Archive (HLA) because when I have occasionally done for other objects I found there always seemed far too many results that made it difficult to find information.

Sometimes that's unavoidable with a well-studied object but for most things you can simply reduce the search radius to something very tiny like .0001 and then untick all of the cameras you know weren't used. I don't think HubbleSite or ESA are reluctant to share the dates the images were taken but the Hubble Heritage site in particular is really just a pretty pictures site and the press release part of HubbleSite (NewsCenter) typically provides the most info (including exposure time). ESA's spacetelescope.org provides a medium amount of info but not quite as much as NewsCenter. There are some press releases that only ESA does and that's when you'll find it a little harder to get the details.

The HLA is the best, though. You should use any excuse you can come up with to pay it a visit.

[DavidLeodis]

Thanks for your help geckzilla. Your "The HLA is the best, though. You should use any excuse you can come up with to pay it a visit" made me .

[BDanielMayfield]

Palomar 12 is a most open looking globular. Does it really have enough stars now to be considered a true globular? I mean, look at it, you can see right through it to distant galaxies in the background, even at it's very center.

I don't doubt that this cluster once was a globular, but over time it must have lost a great many stars. Just as it has been tidally striped from its original galaxy, many stars must have been striped from it. It now is an open cluster heading toward complete dispersal.

It appears to have thousands of members, and has enough of a gravitational field to maintain a spherical structure with a strong radial density gradient. Its stars were not lost to evaporation (as occurs with all globulars) but to a (presumably) singular tidal disruption event. I expect what remains has the stars tightly bound and any further loss will be only by evaporation, which with a low density structure like this is very slow. This isn't an open cluster, or even close to being one, and should survive for billions of years yet, barring another close encounter with a galaxy.

Thanks. I shouldn't have stated my opinion so assertively.