I would only think about being involved as an author if I was actively contributing to a paper. If you conceptualized and wrote up the dissertation yourself, and you don't need supervisor input to help you craft and publish (some students do prefer this) then there's no reason to include them.

I also don't get your second question, as long as the data is yours to publish (and not someone else's as part of a larger project where they have overall ownership) then just submit your paper there without emailing and they will see if they think the 'fit' is right.

If this is part of your MA Dissertation then the data you collected belongs to the university and you will need permission to publish. Your supervisor may require some sort of recognition before agreeing. Go back and look at your handbook to check who you need to talk to.

In my field it's normal for the supervisor of a project to be added as author so I'd check with them.

as I supervisor (sciences) I would be furious if an ex-MSc student tried to publish work done in their MSc without telling me. If a student wants to publish work, I will do all I can do suppor them. but it is not appropriate to publish data collected under my supervision without at least discussing the publication strategy with me.

Parietal I have the same kind of approach and I'm a social sciences academic.

But the landscape is very different between social and physical/natural sciences. For a start, students don't use any equipment or consumables that 'belong' to me/my lab.

However, my approach is that I've had a key input into the theoretical ideas and empirical execution of projects and, therefore, I should be an author on paper. We should be training students (BA, MA and PhD) to be scholars and learning how to co-author is an important part of that. I would take my grievances high if I've worked with a colleague on a project to the same level as with an MA student and I didn't get an authorship. I don't see why we should treat students any different.

However, this might also be about career stage. I'm junior so I need to co-author papers to get my publication record up. However, my PhD supervisor who's a massive cheese in the field said he didn't want to be on my papers because he wanted me to make a statement with them alone. He didn't need the papers at all.

From what you have said, your work does rely heavily on Prof X's work and presumably quite a bit on your supervisor's input in which case I agree approaching at least your supervisor about publishing is sensible.

It is also not really hurting you to add them as an author unless you need a sole authored publication for some reason.

I have published my Masters dissertation without any supervisor as author, as they were a 'caretaker' supervisor as the main one was on sabbatical, I only met them once before any work was started, and I completed the entire thing without them, gaining a high mark, so there really was no intellectual input whatsoever. I have had UG students (rarely) who have done similar, and where I have really contributed nothing, but this is very rare and in most cases, co-authorship is more appropriate.

This is partly a disciplinary divide though. In the field I originally came from, everything is co-authored, people conceive of themselves in teams and as 'training' Masters and PhD's in their way of thinking/methods, however this has often been abused and it was still common when I started out for the junior person to go as second author and the most senior professor as first, even when they had contributed next to nothing. I protested against this and refused to conceptualize or write any paper where I was not first author.

In the discipline in which I now sit, sole authorship is extremely common and people tend to think of themselves giving a hand up to Masters/PhD but not training them, more giving them the space to develop themselves intellectually. There is therefore more of an argument for sole authorship, although the danger of this is that actually you end up contributing quite a lot for no recognition and I've pulled back from doing this and do ask now if students would like to co-author in return for a more substantial effort on my part, or 'go it alone' in return for a brief read.