As a second - ascent giant brightens, the star's outer gas layers become unstable, and it may begin to «valve» its outgoing radiative energy by pulsating which also changes its brightness. (solstation.com)
While we have four inner rocky planets and four outer gas giants, many other systems have «hot Jupiters» very close to their star. (newscientist.com)
The swelling of the star's outer gas envelope also cools the surface, however, which makes the star look redder. (solstation.com)