Should I feel obligated to include my advisor as coauthor?
I am a mathematician, but I did co-author a paper published in a chemistry journal. The paper was co-authored by seven people from the lab where I worked at the time:  two mathematicians, two physicists, two chemists and an engineer (the lab director). I understood (and still understand) only the math part of the paper, I am sure that non-mathematicians, including the lab director, do not understand the math part. Nevertheless, certainly, there were no objections to including all seven people as co-authors.