When preparing your presentation, keep the background of your audience in mind. Make sure you include enough background material that the talk is understandable to your fellow physics/astro master students, who may have a background very different from your own!
The instructors can be consulted for suggestions regarding the topics, but it is your own responsibility to make sure your have chosen a topic in time to get the presentation ready for the assigned slot. If you are not ready in time, this will count as a failed attempt.