Special status of some physicists in France This is a question specific to France.

Permanent positions at the university typically are either research only or research and teaching. For the latter, positions are "maître de conférences" (assistant professor) and "professeur des universités" (full professor). In both cases, you are affiliated to one (or two) disciplinar "sections" listed here. Several are related to physics : 28, 29, 30, 60...

However, there exists other permanent positions called "physicien" (physicist), which belong to a different, separate "corps", see here.

How is that so and what is the difference ?
This other kind of permanent position is very specific to a few fields of science such as astronomy, geology and probably a few other ones.

While usual permanent positions (such as something-professor) imply research and teaching, these positions add a new commitment : "observation service". 1/3 of the time should be dedicated to operate big equipments (telescope for example) for gathering and analysing data that will be useful to the community. For astronomy it implies missions on telescope sites for instance.