Both sentences are correct but they both have their short comings. The first one puts part of the accusative object into the Nachfeld. This is never a good idea as the accusative object is usually very relevant and defining for the predicate as a whole.
Ich habe gestern meine Mutter gesehen und meinen Vater.
This is still processable but in your example the second of the elements that are coordinated using sowie is incredibly long. The idea of passive is strong enough to carry over but we do expect another verb at the end that would bring us closure.
The second sentence is not very nice because the second element is so long and layered (something for the something of something between something using something) that we might forget that we're in a passive construct. Or at least we have to concentrate to carry over the tension up to the final verb. By the way, it doesn't matter whether there is und or sowie. They're synonyms here.
So... closing the verb after the first element is bad, closing it after the second is bad too.
Can we solve this? I think not.
We could just introduce another verb and use that.
[...] Außerdem werden Doppelsterne vorgestellt sowie eine Methode zur Messung der Entferung zwischen massearmen Sternen mittels Ultraschallwellen erklärt/skizziert/eingeführt/präsentiert.
This is a bit ... well... it sounds patched. Like a "Praktikant" wrote it.
A similar option is bringing back the werden :
[...] Außerdem werden Doppelsterne vorgestellt, und eine Methode zur Messung der Entferung zwischen massearmen Sternen mittels Ultraschallwellen wird erklärt.
This sounds less patchy but it sounds redundant and stiff.
Or we could turn around the elements:
[...] Außerdem werden eine Methode zur Messung der Entferung zwischen massearmen Sternen mittels Ultraschallwellen sowie Doppelsterne vorgestellt.
This is easier to process because the werden tells us that the method is not going to be the only object and we're set up for a second element. But it also sounds weird. Doppelsterne sounds really lame here, to me. They are given no room to shine (no pun intended)
So, whatever we try to fix it, I always find it less than perfect writing.
I think the main problem is that the 2 objects don't fit well. One is very long and layed, the other is just a word. That makes them unbalanced. Also, one is a method, while the other is a phenomenon of nature. It is like saying
Es werden ein paar Vulkane sowie eine Methode zur Altersbestimmung von Fossilien vorgestellt.
It's just kind of random.