The only way to catch them is if they decloak or if you bump into them and decloak them. They will decloak when using a wormhole or if they try to hack something. Since Helios’s (Heliai?) have no combat capabilities, the only sites they typically run are the ones with no rats like the pirate faction ones, so that kind of narrows it down.
The way most explorer hunters do it is they scan down all the sites in the system (beforehand), and make “perches” 200-1000km outside a cosmic signature site by dropping a bookmark while warping in. When the target decloaks at one of these sites to start hacking the cans, you can figure out where they are with D scan and then warp to the perch, wait until they start hacking, then warp to the can and surprise.
Occasionally, you can catch one on a wormhole but it’s really hard. You either need to bump/decloak them and hope you can catch them before they warp off, or they can sometimes become befuddled by wormhole polarity mechanics, or if you have a Maulus navy/remote sensor boosting buddy you can try to lock them before they recloak when coming out of the wormhole but it’s hit-or-miss. You could also employ the use of a bubble to make it easier to ram decloak them.