Understanding the head plugin

Hi again forum!

I'm using head plugin since i see it is quite intuitive to have an overall sight of the cluster.
The problem is that I do no sync what I read on the docs with what I see on the browser.

It is very easy to understand data nodes... they appear as black filled circled entries followed by the shard distribution corresponding to the upper end list of indices... great! we see storage balancing!

The problem comes with the master... or the elected master? with an star icon... it is followed by a series of lines with a nomenclature like logstash-master-12345-6789 What are they?

There are also non master nodes, or non master elected nodes, or both... not sure... Why if a node is elected new master all logstash-master-12345-6789 vanish? Data becomes unreachable... but it is there on the data nodes, and health keeps green.

Best regards.