The Michigan Astronomy department admits students to the program, and not to individual professors. This ensures that you are not obligated to work with a specific faculty or on a specific topic, and have a lot of freedom and flexibility in choosing your topic (and/or switching advisors). I think this is one of the strengths of the department! Here is a link to the department's application page.
There's no need to email me prior to your application.
The following advice is not necessarily Michigan-specific:
Make sure your personal and academic statements are well written. Ask other people to read them (preferably people at higher career stage such as graduate students, postdocs, or one of your professors), and take their feedback seriously.
Showcase the research that you've done, explain your contribution, and demonstrate a good understanding of your research. If you presented your work in any form, make sure to highlight that.
Spend some time with the department's website and do your "homework". Comment on how the department is going to be a good fit for you (rbeyond a specific research group)
Show that you understand the level of challenge that grad school will be, and reflect on what in your life and school experiences prepared you for overcoming obstacles.
Finally, admissions committees find that the most useful letters of recommendation come from people who know the student well and give information beyond what's already in your transcript.
Good luck!