NEW YORK—On a chilly evening earlier this week, a group of well-heeled American art aficionados — dealers and collectors — streamed into Christie’s spacious James Christie Room. Some of them had been in the same room the previous week, for the auction house’s biannual evening sale of modern and contemporary art, to witness auctioneer Christopher Burge triumphantly hammer down a sprawling David Hockney painting for $7.9 million, and some would return to the room two days later for the house’s sale of American paintings, drawings, and sculptures, estimated to sell for considerably more modest sums.

But on this night the space bore none of the trappings of an auction — the raised lectern, the banks of Christie’s minions frantically taking telephone bids, the illuminated board displaying hammer prices in a dizzying litany of currencies. Instead, it had been transformed into a darkened theater, with seats arrayed around a makeshift stage above which a screen flickered with images of paintings by Georgia O’Keeffe, and photographs of O’Keeffe and her photographer and art-dealer husband, Alfred Stieglitz.

The room changes had been made for an unusually star-studded event — for an auction house, at least. As a benefit for the Georgia O’Keeffe Museum in Santa Fe, with tickets starting at $250, actors Joan Allen (familiar from movies like The Bourne Ultimatum, and Oliver Stone’s Nixon), Sam Waterston (of Law and Order fame, but also known for films like The Killing Fields and Woody Allen’s Hannah and Her Sisters), and Marsha Mason (a veteran of the stage and screen, and also once a semi-regular on the TV show Frasier) would read excerpts from letters between O’Keeffe (played by Allen) and Stieglitz (played by Waterston). Also read were a few early ones between a young O’Keeffe and an artist friend, Anita Pollitzer, played by Mason, who served as narrator as well.

The O’Keeffe-Stieglitz letters packed a particular frisson for O’Keeffe fans and, for that matter, anyone with a prurient interest in love affairs conducted through written correspondence. As Barbara Buhler Lynes, editor of an edition of O’Keeffe’s letters, explained before the reading, O’Keeffe had stipulated in her will that the letters remain unopened (except by a few very select scholars) at Yale’s Beinecke Library for 10 years after her death. They have been viewable only since 2006, and many of those performed by Allen and Waterston were being read for the very first time.

Some surprising details emerged. O’Keeffe, known to most as the unflappable doyenne of American modernism, was downright flirtatious in some of her early letters to Stieglitz. In one of them, before they’d begun their affair, she suggestively described to the older dealer (23 years her senior) how she felt when she painted herself in the nude (“I feel broiled, not all done in the middle.”). But the reading reached its dramatic peak much later in their relationship, with Stieglitz pining for O’Keeffe during one of her many trips out West. In his loneliness, he starts to sound raving, even King Lear–like: “I’ve grown ages in a moment ... a heart bleeding to death, feeling it is not loved anymore.”

As O’Keeffe, Allen was alternately coy and commanding, bringing to the role some of the same verve she brought to the 2005 flick The Upside of Anger, in which she played opposite Kevin Costner as an enraged mother of four abandoned by her husband. Waterston, as Stieglitz, veered from gruff bluster to stern and serious art criticism, and to an elderly man’s whining neediness. Allen may have captured O’Keeffe’s tone, but with her long, glossy blond hair and her svelte physique, she was hardly a dead ringer for the gypsyish Georgia, known for her trademark bandannas and her skin leathered by the Southwest sun. (One imagines Allen will be duly transformed for her role as O’Keeffe in an upcoming biopic, to air on Lifetime in September.) Waterston, on the other hand, with his salt-and-pepper hair and his spectacles poised on the tip of his nose, bore an eerie resemblance to the redoubtable Stieglitz.