Troubling a Star (ISBN  ) is the last full-length novel in the Austin family series by Madeleine L'Engle.
 The young adult suspense thriller, published in 1994, reunites L'Engle's most frequent protagonist, Vicky Austin, with Adam Eddington, both of whom become enmeshed in international intrigue as they travel separately to Antarctica.
 The story takes place several months after the end of "A Ring of Endless Light", the novel in which Vicky and Adam first met.
Madeleine L'Engle ( ; Camp, November 29, 1918 – September 6, 2007 ) was an American writer who wrote young adult fiction, including "A Wrinkle in Time" and its sequels: "A Wind in the Door", "A Swiftly Tilting Planet", "Many Waters" and "An Acceptable Time".
 Her works reflect both her Christian faith and her strong interest in science.
A Ring of Endless Light is a 2002 Disney Channel Original Movie based on the Madeleine L'Engle book of the same name filmed on location in Australia, and starring Mischa Barton in the main lead role.
 It is one of two Disney adaptations of novels by Madeleine L'Engle, the other being "A Wrinkle in Time".
 In the U.S. it was aired on August 23, 2002.
A Live Coal in the Sea, written by Madeleine L'Engle and published in 1996, is the sequel to "Camilla Dickinson" (also published as "Camilla"), one of L'Engle's earliest novels.
 While "Camilla Dickinson" was written for a young adult audience, "A Live Coal in the Sea" is an adult novel.
 It continues the story of Camilla Dickinson as a college student, her marriage, her family and the problems that follow.
 The story is told by an aged Camilla to her granddaughter, who is seeking answers about her family.
A Wind in the Door is a young adult science fantasy novel by Madeleine L'Engle.
 It is a companion book to "A Wrinkle in Time", and part of the Time Quintet.
A Wrinkle in Time is a science fantasy novel written by American writer Madeleine L'Engle, first published in 1963, and in 1979 with illustrations by Leo and Diane Dillon.
 The book won the Newbery Medal, Sequoyah Book Award, and Lewis Carroll Shelf Award, and was runner-up for the Hans Christian Andersen Award.
 It is the first book in L'Engle's Time Quintet, which follows the Murry and O'Keefe families.
The Arm of the Starfish is a young adult novel by Madeleine L'Engle, first published in 1965.
 It is the first novel featuring Polly O'Keefe and the O'Keefe family, a generation after the events of "A Wrinkle in Time" (1962).
 The plot concerning advanced regeneration research puts this novel in the science fiction genre, but it could also be described as a mystery thriller.
Dan Simmons (born April 4, 1948) is an American science fiction and horror writer.
 He is the author of the Hyperion Cantos and the Ilium/Olympos cycles, among other works which span the science fiction, horror, and fantasy genres, sometimes within a single novel.
 A typical example of Simmons' intermingling of genres is "Song of Kali" (1985), winner of World Fantasy Award.
 He also writes mysteries and thrillers, some of which feature the continuing character Joe Kurtz.
Calvin O'Keefe is a major character in Madeleine L'Engle's "Time Quartet" series of books, and, as "Dr. Calvin O'Keefe", an important character in her O'Keefe series of young adult novels.
 In an interview released on the DVD of the TV adaptation of "A Wrinkle in Time", L'Engle describes Calvin as "the boy that we all, all us girls want to meet.
 Not all of us are lucky enough to meet a Calvin, but I was.
 And I married mine."
Charles Wallace Murry is a major character in Madeleine L'Engle's Time Quintet series of young adult science fiction novels.
 He is first introduced in L'Engle's "A Wrinkle in Time" as the youngest sibling of the protagonist, Meg Murry, and accompanying her on her adventures alongside Calvin O'Keefe.

Question: Which writer, Dan Simmons or Madeleine L'Engle, is known for young adult fiction, including "A Wrinkle in Time"?
Answer: Madeleine L'Engle