1082 open cluster locations

[t00fri]

I always find that my Perl skills tend to fall off very rapidly when I don't use the language for a couple of weeks...

Don't worry, after ~30 years of a PERL love affair it won't happen anymore . But sometimes I note that my PERL sounds a bit "antique", since quite a few things didn't exist when I learned it.

Fridger

[t00fri]

I just wanted to point out that the rendering of open clusters may require some different techniques than the ones we're using now for galaxies and what you're developing for globulars.

Of course, see e.g. here:
viewtopic.php?f=10&t=12421&start=22

Here's an interesting resource:
http://www.astro.iag.usp.br/%7Ewilton/tabUCAC.html

These are lists of stars in various clusters, with membership probabilities for each. For 6705, there are over 1200 records, though the membership probability for many of them is quite low. Perhaps it would be possible to use these as follows:

- Filter out stars with membership probability below some threshold
- Assign each star a distance based on the distance to the center of the cluster plus a random offset based on the distance of the star from the center of the cluster and the apparent distribution of stars in the cluster
- Spectral type would have to be derived from the UCAC magnitude and 2MASS J, H, and K magnitudes in the cluster--not sure how difficult this is.

--Chris

Yes that's essentially the way I am having in mind.

There is usually enough "separation power" to define a transition boundary: on the one hand it's characterized by catalog parameters of open clusters and on the other hand by the faint star data of star catalogs in the cluster neighborhood. Parameters like cluster concentration and richness will have good filtering power. I guess that should be about sufficient (in a statistical sense).

Star distance is no problem (on a statistical basis at least), given the known cluster distance.

There is spectral information about the open clusters in the catalog.

Fridger

[t00fri]

Let me go on a bit about what is on my mind:

Open clusters have a great range of "morphology". On the one hand there are many looking as rich as M 11, e.g. NGC 2158
,
or NGC 3603


on the other hand, there are many that mainly consist of a hand full of relatively bright stars over the faint field star background.



One major task is to establish a good criterion from the cluster catalog parameters and the explicit field star data in the cluster neighborhood, for how to merge the resulting information visually.

The clusters with just a few bright stars and no dense "core" should almost completely be contained in the usual star catalogs. Certainly for M 11 type clusters, this is quite different.

Another rendering issue is the color. Most open clusters are young: generally less than a few hundred million years old.

Yes there are great differences to globular clusters: the loose structures of open clusters contain anywhere from a few dozen to a few thousand stars, hence that number is an important ingredient! The brightest stars are mostly blue in colour
(center of NGC 3603):


unlike the conspicuous orange bright "red giants" of globular clusters.

Open clusters are irregular in shape and there is a great range in size (1-20 pc);

Unlike globulars, the distribution of open clusters is concentrated about the galactic plane. Many of the younger clusters contain gas and dust.

++++++++++++++++++
So altogether there seem to be quite a few challenges to render the diversity of open clusters from the given characteristics.
++++++++++++++++++

Fridger

[chris]

An experiment with using symbols to indicate the positions of open clusters. The sizes of the circles are the apparent sizes of the clusters. The view is a little crowded because there's no culling based on apparent brightness or size:

opencluster-symbols.jpg

--Chris

[ajtribick]

I also note the information display in the top left describes these as "Cluster" rather than "Open cluster".

[t00fri]

An experiment with using symbols to indicate the positions of open clusters. The sizes of the circles are the apparent sizes of the clusters. The view is a little crowded because there's no culling based on apparent brightness or size:

--Chris

Yes, that's how we did it in XEphem > 10 years ago.

Fridger

[Cham]

Interesting. I like this idea (showing clusters size with circles). IMO, the label darkness could be dependant on the cluster's size.

[t00fri]

Interesting. I like this idea (showing clusters size with circles). IMO, the label darkness could be dependant on the cluster's size.

As I wrote above, OpenClusters are irregular in shape and vary greatly in concentration. Hence a circular marker is rather misleading as a size indicator.

But why not, it saves us a lot of work

Fridger

[chris]

Interesting. I like this idea (showing clusters size with circles). IMO, the label darkness could be dependant on the cluster's size.

As I wrote above, OpenClusters are irregular in shape and vary greatly in concentration. Hence a circular marker is rather misleading as a size indicator.

But why not, it saves us a lot of work

I think that there is some misunderstanding here. I was not proposing using circles as the sole means of showing open clusters. Rather, I was suggesting that we show symbols in addition to labels for open clusters (and possibly other deep sky objects as well.) I see three advantages:

• an extra visual cue for distinguishing object types.
  
• clearer indication of the location of the object (the alignment of the label text with respect to the object position isn't always obvious)
  
• extra information about the object: apparent size

How the various deep sky objects are rendered is independent of their labeled representation.

--Chris

[t00fri]

Interesting. I like this idea (showing clusters size with circles). IMO, the label darkness could be dependant on the cluster's size.

As I wrote above, OpenClusters are irregular in shape and vary greatly in concentration. Hence a circular marker is rather misleading as a size indicator.

But why not, it saves us a lot of work

I think that there is some misunderstanding here. I was not proposing using circles as the sole means of showing open clusters. Rather, I was suggesting that we show symbols in addition to labels for open clusters (and possibly other deep sky objects as well.) I see three advantages:

• an extra visual cue for distinguishing object types.
  
• clearer indication of the location of the object (the alignment of the label text with respect to the object position isn't always obvious)
  
• extra information about the object: apparent size

How the various deep sky objects are rendered is independent of their labeled representation.

--Chris

Of course! Agreed...

Fridger

[abramson]

An experiment with using symbols to indicate the positions of open clusters. The sizes of the circles are the apparent sizes of the clusters.

Nice. I imagine that selecting a cluster, with this symbols activated, and right-click-dragging to move around from several ly away, may be a good visualization of the stars belonging to the cluster.

Guillermo

[chris]

I also note the information display in the top left describes these as "Cluster" rather than "Open cluster".

Time to fix that . . .

--Chris