So ARE authors sexy? Frankly, I am quite happy to leave this off the job description, and it's definitely not a core requirement. If you put 'sexy author' into Google image, you get Paul Auster, Neil Gaiman, Zadie Smith and Penelope Cruz. Now, call me picky, but the only person who really qualifies in that list is the madly beautiful Zadie Smith. Auster and Gaiman are defined as 'sexy' because they look perfectly fine and are writers. Penelope Cruz is only in the list because she comes up under 'sexy' anything.
Of course, an author's perceived 'sexiness' also can also depend on what they write. Danger and macho-ness seem to do the trick (if you are Ernest Hemingway) or being edgy and naughty (if you are the young Martin Amis, though at the time he was assisted by looking a bit like Mick Jagger). Actually writing about sex isn't necessary. I have put a bit of shagging in my latest book, but not because I wanted to be sexy. I only take my characters' clothes off when it is absolutely necessary for the plot.