Spitzer IRAC Mid-Infrared Photometry of 500-750K Brown Dwarfs.

摘要

Mid-infrared data, including Spitzer warm-IRAC and photometry, is critical for understanding the cold population of brown dwarfs now being found, objects which have more in common with planets than stars. As effective temperature (T(sub eff)) drops from 800K to 400K, the fraction of flux emitted beyond 3 (mu)m increases rapidly, from about 40% to > 75%. This rapid increase makes a color like H--a very sensitive temperature indicator, and it can be combined with a gravity--and metallicity-sensitive color like H-K to constrain all three of these fundamental properties, which in turn gives us mass and age for these slowly cooling objects. Determination of mid-infrared color trends also allows better exploitation of the WISE mission by the community. We use new Spitzer Cycle 6 IRAC photometry, together with published data, to present trends of color with type for L0 to T10 dwarfs. We also use the atmospheric and evolutionary models of Saumon and Marley to investigate the masses and ages of 13 very late-type T dwarfs, which have H- > 3.2 and T(sub eff) (approx) 500K to 750K.