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

TL;DR

This paper uses Spitzer mid-infrared photometry to analyze the properties of cold brown dwarfs, revealing color trends and estimating their masses and ages, which enhances understanding of these planet-like objects.

Contribution

It provides new mid-infrared color data for brown dwarfs and applies models to estimate their masses and ages, improving characterization of the coldest brown dwarfs.

Findings

H-[4.5] color is a sensitive temperature indicator.

Mid-infrared colors help constrain mass and age.

Color trends are established for L0 to T10 dwarfs.

Abstract

Mid-infrared data, including Spitzer warm-IRAC [3.6] and [4.5] 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_eff) drops from 800 K to 400 K, the fraction of flux emitted beyond 3 microns increases rapidly, from about 40% to >75%. This rapid increase makes a color like H-[4.5] 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 & Marley to investigate the masses and ages of 13 very late-type T dwarfs, which have H-[4.5] > 3.2 and T_eff ~ 500 K to 750 K.