Sirius IV

Sirius IV was the fourth planet in the Sirius star system. In the early 22nd century, the planet belonged to United Earth and was the site of the Cochrane Research Facility. 

History
When Malcolm Reed was an Earth Starfleet cadet, he participated in a tour of cadets to visit the Cochrane Research Facility. When the facility's reactor exploded, twenty Humans died slowly from radiation poisoning, including Cadet John Mayhill.