Positioning a small sun (or at least, a kinda sunlike object) in the middle of a habitat is great if you want to provide heat and light to a large area or volume. Given the scale of your ship (150 people) this kind of setup seems somewhat wasteful, and waste is very much not something you want or can even afford if you're flying between stars. Space is big, as the good book says, and you want to still be alive (or at least, have your descendants be alive) at the end of the trip.
So, the main problem here is colour temperature. Our sun is a toasty 5800K, though our daylight colour temperatures on earth are more like 4800K. In either case, the temperatures are quite above the melting point of our most refractory (and theoretical) materials like hafnium-carbon-nitrogen (melting point somewhere above 4400K). That makes building your sun a bit tricky, if it is just something that's heated up by a nuclear fire til it produces a cheery glow then it will be liquid. And you certainly don't want to expose people directly to the distinctly uncheery glow of a nuclear reaction, which is likely to involve unhealthy amounts of UV, xrays, gamma rays and fast neutrons which are bad even for just dumb matter, let alone living things or electronics. Of course, having a liquid or plasma light source could work given enough scifi wizardry... careful confinement with electromagnetic fields, perhaps, and careful deployment of vortices of cool buffering gas and so on. Seems a bit of a hazardous thing to have near a habitat though, to be honest.
What you probably want, then, are giant light and heat emitters... big arrays of incandescent or fluorescent lights, basically. Maybe they're pumped directly by the radiation of a nuclear reactor underneath, or maybe secondarily by high energy electron beams making use of the massive voltages a fusion reactor might output, or maybe just boring old electricity. As elements wear out, they can be replaced or refilled or repaired or recycled as necessary, possibly by automated systems.
Given that you're illuminating a ring, one neat design for a light-emitting structure is a solid of revolution formed from a compound parabolic concentrator. It might look a little like this in cross section:
The coloured cylinder in the middle is the light source, the rest is the reflector. This ensures that light is efficiently cast upon the ring, but there's no wastage. There's more information on this idea here, also the source for the above image. The edges of the reflector can be tethered to the edges of the ring, like spokes on a bicycle wheel. These spokes might be more or less invisible from the ring itself, given that the structure doesn't need to be accelerated, they don't need to be super substantial.