I'm an undergraduate student. The graduate students in my group call everyone by their first names including the advisor (who is a professor) but I still refer to the advisor as Professor ____. I was working with a graduate student and called them by their first name, but now I'm working with a post-doc so they already have their PhD/are a "doctor." Is it no longer acceptable to call them by their first name?
I would go with Doc/prof until you are told otherwise.
Most of the time, the doc will, at some point, tell you differently. Even then when in a group of undergrads or class, use the title.
Lab culture is almost always quite informal, as this one appears to be. Use his/her first name.
While Chem 101 is correct about lab culture usually being informal, it is better to earn the right to call someone by their first name than to assume it. Always use the more formal title until specifically told otherwise.
If the grad students are calling the prof by first name, I would say undergrad calling postdoc by first name is acceptable. Like the guy above me said, lab culture is usually pretty informal. Also, most postdocs have only just gotten that degree and are not yet comfortable of the formal title. Most postdocs will refer to each as Dr. so-and-so when with each other and in a totally joking way. It is kind of this self-deprecating uclture. I always went by first name as a post doc, even on the occasions I taught. Once I became a faculty member, it took a few months before hearing Dr.Stache as anything remotely normal. Once class is over I will still just have people call me by my first name.
The Stache wrote:
If the grad students are calling the prof by first name, I would say undergrad calling postdoc by first name is acceptable. Like the guy above me said, lab culture is usually pretty informal. Also, most postdocs have only just gotten that degree and are not yet comfortable of the formal title. Most postdocs will refer to each as Dr. so-and-so when with each other and in a totally joking way. It is kind of this self-deprecating uclture. I always went by first name as a post doc, even on the occasions I taught. Once I became a faculty member, it took a few months before hearing Dr.Stache as anything remotely normal. Once class is over I will still just have people call me by my first name.
^This is the case most of the time, but again, there is no harm in erring on the side of formality until told otherwise. The grad students that call the Prof by his first name are in that lab full time for years. They've earned the right to act the way they do. The OP, by contrast, sounds like an undergrad who will be there for a summer...maybe part time during the academic year. As such, he is a visitor and should show some damn respect!
I'd rather get some grief for being polite than get in trouble for being too familiar.
Refer to him in the same way he signs his emails.
Call him Sugarlips McGee?