I want study bse astrophysics or bse astronomy does IIST offer this courses
No IIST don't offer BSc Astrophysics/Astronomy course. Although the institute offers MS Astronomy and Astrophysics which a student can pursue by qualifying GATE examination after a MSc Physics/BTech degree which you can see by visiting the official website.
The courses offered in the UG level on the basis of JEE Advanced are:
B.Tech Aerospace Engineering
B.Tech Avionics
B.Tech Engineering Physics Dual Degree
To know more about IIST you may visit the link below:
For official website visit the link below:
https://www.iist.ac.in/
To know more about Astrophysics visit the link below:
https://www.careers360.com/courses/astrophysics-course
I hope this answer helps. All the very best for your future endeavors!