@echo0o , your employer needs the W-9 because you are employed by them -- that is what IRS requires ( a Tax ID). As far as the residency status and exclusion of earned income -- these depend on your visa under which you were admitted. Thus if you are a H-B visa holder then you are generally not treated as a researcher - you are an employee thus you will get W-2 and your salary may not be excludable. Please consult with your school --- a researcher is usually under J- visa. They may have to make sure that IRS will regard you as a researcher for tax purposes.
