I asked the same question a few months(ish?) back. All that I've found in Official Fluff is the scant references in the 5th edition SM dex, which states the "Novamarines are scattered throughout the galaxy and not fought together as a Chapter since M37" and "Task force Septus" is "under attack by chaos renegades believe dto be in the Employ of Huron Black Heart (p. 25, 31).
Other than that, there is a very sparce entry at the Lexicanum and I hear they were mentioned back in the days of Rogue Trader.
So, it seems, it's up to us to turn them into a table top and fan fluff reality. It's interesting you locked in on the star theme and decided to represent it by the plasma cannon, as I came up with the same. Here's what I typed up for my own benefit:
“These stars belong to the Emperor!”
Based on Honorium in the Ultima Segmentum, the Novamarine Chapter was founded by the Ultramarines subsequent to the promulgation of the Codex Astartes. Over its millennia of service, the Chapter has been instrumental in a number of major engagements, including the 13th Black Crusade, the Badab War, and the Damocles Crusade.
The Chapter specializes in operating in total vacuum and low gravity environments, self-tasked to protect Imperial shipping lanes, outposts on moons and asteroids, and to assault enemy orbital defenses not vulnerable to the Imperial Navy. The Novamarines represent their pride in frequenting these especially arduous battlefields by incorporating an eclipsed star in their Chapter Symbol.
Although the Novamarines fight where and how threats demand, the widespread need for their combat specialty has scattered the Chapter across the galaxy, rarely assembled in groups above company strength. For this reason, it is rare for the Chapter to fight together as a whole, the last incidence of which was in the early years of M37.
The delicate combat environments in which the Novamarines specialize make close quarter fighting impractical and confer severe limitations on the use of armored units. Therefore, the Chapter exploits the flexible agility of power armored Space Marines and ranged combat, especially energy weapons, the low kickback of which make them ideal for low gravity warfare.
While the Chapter has increasingly adopted a more flexible order of battle, Novamarine forces continue reflect their doctrinal heritage and continues to eschew hand-to-hand combat, deploy Terminators and Devastators instead of heavy armor, and strongly prefer plasma weapons and lascannons.
The Novamarine Chapter organization observes the Codex Astartes, diverging in superficial and minor ways.
Instead of being represented by color, company attachment is denoted by non-roman numerals displayed on the right knee. First company is not assigned a numeral.
While squad-type insignias apply the symbols prescribed in the Codex, squad attachment is denoted by a colored stripe on the left knee.
The Chapter frequently operates in Task Forces. Task Force attachments are denoted on the weapon casings by a symbol specific to that Task Force.
PS: have any pics?