Upvote:1
While the proposed duration is less than three months, it would seem to be within the long-term visa categories that your partially-paid affiliation with the Institute is covered. Found in the BLS Useful Links box, select Long Term Visa Click here for Long Term Visa Application, and it takes you to the requirements to obtain a temporary residence visa to work and conduct research in Spain.
In addition to the application, passport, photos, police record and medical certificate, you would be expected to include the invitation Instituto de AstrofΓsica de Canarias which sets forth the purpose, terms, and length of your affiliation with it.