Daniel Irvin Rather, Jr.  was born on October 31, 1931, in Wharton County, Texas, the son of Daniel Irvin Rather, Sr., a ditch digger, and the former Byrl Veda Page. The Rathers moved to Houston, where Dan attended Love Elementary School and Hamilton Middle School. He graduated in 1950 from John H. Reagan High School in Houston. In 1953, he earned a bachelor's degree in journalism from Sam Houston State University where he was editor of the school newspaper, The Houstonian.

On September 8, 2004, Rather reported on 60 Minutes Wednesday that a series of memos critical of President George W. Bush's Texas Air National Guard service record had been discovered in the personal files of Lt. Bush's former commanding officer, Lt. Col. Jerry B. Killian. Once copies of the documents were made available on the Internet, their authenticity was quickly called into question. Much of this was based on the fact that the documents were proportionally printed and displayed using other modern typographic conventions usually unavailable on military typewriters of the 1970s. The font used on the documents has characteristics that exactly match standard font features of Microsoft Word. This led to claims that the memos were forgeries. The accusations then spread over the following days into mainstream media outlets including The Washington Post, The New York Times, and the Chicago Sun-Times.  Rather and CBS initially defended the story, insisting that the documents had been authenticated by experts. CBS was contradicted by some of the experts it originally cited, and later reported that its source for the documents - former Texas Army National Guard officer Lt. Col. Bill Burkett - had misled the network about how he had obtained them.  On September 20, CBS retracted the story. Rather stated, "If I knew then what I know now, I would not have gone ahead with the story as it was aired, and I certainly would not have used the documents in question." The controversy has been referred to by some as "Memogate" and "Rathergate."  Following an investigation commissioned by CBS, CBS fired story producer Mary Mapes and asked three other producers connected with the story to resign. Many believe Rather's retirement was hastened by this incident. On September 20, 2007, Rather was interviewed on Larry King Live commenting "Nobody has proved that they were fraudulent, much less a forgery. ... The truth of this story stands up to this day."

Using a quote from the above article, answer the following question: What were the Killian documents?
a series of memos critical of President George W. Bush's Texas Air National Guard service record