If it says Ignacio Ugartechea, that's the maker, and they have made all grades of guns, from "fairly clubby but it works, with canoe-paddle wood" to "Spanish Best." This seems like a low-to-middle-brow" gun like many AyAs and others imported to the States in the 1960s. I've only owned later Ugartecheas, but those were well, if not elegantly made--they worked just fine.
I can't tell from the photos--does this have a crossbolt? That would be a common feature of the competition of the period (AyA, Beretta "Silver Hawk", etc.). I like the scalloped reciever back and the engraving on the fences--reminds me of a Smith Ideal or a Grade 1 Ithaca, which I happen to like (many don't).
Is the "model name" perhaps really "Estrella" not "Esterella"? That would be "Star" in Spanish, a very common name for Basque- made guns, both models and trademarks. I can't remember what the Euzkadi word for star is, but the Basque makers gave up using it early in the last century in favor of the Spanish and English versions. Interarms once imported a "Star Guage" Spanish double in order to cash in on the fame of the Star brand of automatics (which they also imported), with the "implication" of great precision of a "star-guaged" barrel. Great marketing; I never thought the guns were so great. Does anyone know who actually manufactured them?
