How should I refer to a professor as a undergrad TA?
This has a cultural element so it varies. Some places tend to be quite formal and others not so. My perspective is the US.
But as an undergrad you probably shouldn't make assumptions and use a title until told otherwise. Of course, you can also ask.
I normally expected my undergrad and even master's students to be fairly formal as I think a certain separation is helpful to them since it is occasionally necessary to be an authority figure. But I accepted things like &quot;doc&quot; or Dr. B&quot; from those who worked closely with me.
When I was in the PhD program I was the only one who called many of the faculty by their first names (not my advisor, though). My fellow students (also TAs) were all more formal, but I was a special case, joining at an older age with a young faculty. I insisted my own doctoral students called me by my given name. But many of them resisted, wanting to be more formal.
But, if you are working closely with a faculty member it is good to just ask.