Is Dust Forming on the Red Giant Branch in 47 Tuc?

Boyer, Martha L., van Loon, Jacco Th., McDonald, Iain, Gordon, Karl D., Babler, Brian, Block, Miwa, Bracker, Steve, Engelbracht, Charles, Hora, Joe, Indebetouw, Remy, Meade, Marilyn, Meixner, Margaret, Misselt, Karl, Sewilo, Marta, Shiao, Bernie, & Whitney, Barbara
2010, The Astrophysical Journal Letters, 711, L99

Using Spitzer Infrared Array Camera (IRAC) observations from the SAGE-SMC Legacy program and archived Spitzer IRAC data, we investigate dust production in 47 Tuc, a nearby massive Galactic globular cluster. A previous study detected infrared excess, indicative of circumstellar dust, in a large population of stars in 47 Tuc, spanning the entire red giant branch (RGB). We show that those results suffered from effects caused by stellar blending and imaging artifacts and that it is likely that no stars below ≈1 mag from the tip of the RGB are producing dust. The only stars that appear to harbor dust are variable stars, which are also the coolest and most luminous stars in the cluster.


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