I'm looking to use Guardian Circle for healing (kind of like an uber health regen rate in combat) and I have some questions about it that I was hoping you lovely people could answer:

1) Can it be dual cast? I appreciate that most master spells can't be dual cast, however the wikia page for it says http://elderscrolls.wikia.com/wiki/Guardian_Circle as does the http://www.uesp.net/wiki/Skyrim:Spells#Master_Level of the spells page on the UESP (however it does not make a mention of the spell being able to be dual cast on the http://www.uesp.net/wiki/Skyrim:Guardian_Circle oddly). Having said that the wikia also says it "requires both hands to cast" on the same page, further muddying the issue.

2) Is its duration affected by Necromage, or must you be a Necromage vampire to have greater duration? UESP http://www.uesp.net/wiki/Skyrim:Guardian_Circle, whilst the wikia http://elderscrolls.wikia.com/wiki/Guardian_Circle.

I want hard answers here, no speculation based on the effects of other spells. Thanks in advance.