investigators want to distinguish between two suspects: a giant planet and a celestial object called a brown dwarf. Brown dwarfs are more massive than planets, but less massive than the smallest stars. They are thought to form as stars do. For decades brown dwarfs have posed a problem for scientists: how to distinguish low-mass brown dwarfs from especially massive planets? Mass alone isn't enough to tell the difference between the two, Schlaufman said.
... Giant planets such as Jupiter are almost always found orbiting stars that have more iron than our sun. Brown dwarfs are not so discriminating ... he has proposed that objects in excess of 10 Jupiter mass should be considered brown dwarfs, not planets.
Johns Hopkins Scientist Proposes New Definition of a Planet | Johns Hopkins University
From observation of brown dwarf stars in other solar systems, they appear to look and have atmospheres similar to our gas giants Saturn and Jupiter.
The iron rain you refer to was the conclusion of a study from 2006; evidence was found that at the temperatures of the star they were looking at, the iron they detected in its atmosphere should be forming liquid droplets and raining down towards the surface of the star.
What kinds of dwarf star are there? | Astroquizzical
Why iron stars? Is it just what we can interpret from our current data? What other factors are there for physically being more Jupiter like than a so called more failed star like? Are they all just variations of electrically active plasma planets?