A Nongray Theory of Extrasolar Giant Planets and Brown Dwarfs

Abstract

We present the results of a new series of non-gray calculations of the atmospheres, spectra, colors, and evolution of extrasolar giant planets (EGPs) and brown dwarfs for effective temperatures below 1300 K. This theory encompasses most of the mass/age parameter space occupied by substellar objects and is the first spectral study down to 100 K. These calculations are in aid of the multitude of searches being conducted or planned around the world for giant planets and brown dwarfs and reveal the exotic nature of the class. Generically, absorption by H 2 at longer wavelengths and H 2 O opacity windows at shorter wavelengths conspire to redistribute flux blueward. Below 1200 K, methane is the dominant carbon bearing molecule and is a universal diagnostic feature of EGP and brown dwarf spectra. We find that the primary bands in which to search are Z (∼1.05 µm), J (∼1.2 µm), H (∼1.6 µm), K (∼2.2 µm), M (∼5 µm), and N (∼10 µm), that enhancements of the emergent flux over blackbody values, in particular in the near infrared, can be by many orders of magnitude, and that the infrared colors of EGPs and brown dwarfs are much bluer than previously believed. In particular, relative to J and H, the K band flux is reduced by CH 4 and H 2 absorption. Furthermore, we derive that for T eff s below 1200 K most or all true metals are sequestered below the photosphere, that an interior radiative zone is a generic feature of substellar objects, and that clouds of H 2 O and NH 3 are formed for T eff s below ∼400 K and ∼200 K, respectively. This study is done for solar-metallicity objects in isolation and does not include the effects of stellar insolation. Nevertheless, it is a comprehensive attempt to bridge the gap between the planetary and stellar realms and to develop a non-gray theory of objects from 0.3 M J ("saturn") to 70 M J (∼0.07 M ). We find that the detection ranges for brown dwarf/EGP -3discovery of both ground-and space-based telescopes are larger than previously estimated.

Atmospheric circulation and tides of “51 Pegasus b-like” planets

“…The discovery of extrasolar planets has led to a growing list of work devoted to modeling their atmospheres (Burrows et al 1997;Seager & Sasselov 1998Goukenleuque et al 2000;Barman et al 2001). While no spectra of these objects have yet been measured, one might be encouraged by the successes obtained in the case of the similar brown dwarfs, for which theoretical models now reproduce the observations well, even in the case of low-temperature objects (T eff ∼ 1000 K or less) (e.g.…”

Do Low Luminosity Stars Matter?

“…Another source of interest in low mass stars research came from theoretical modeling of their evolution, interiors and atmospheres (Bergeron et al (1995); ; Allard et al (1997); Burrows et al (1997); Marley et al (2002); Baraffe et al (1998)). Models today are quite mature, they rapidly evolve as new observations and the required physics become available.…”

“…At the same time mature models ; Burrows et al (1997); Burrows et al (2001)), are assigning physical meanings to their observed spectral characteristics (Geballe et al (2002)). …”

Activity and Kinematics of M and L Dwarfs

“…The situation is illustrated in Figs. 1 and 2 using theoretical models [6] and a plausible temperature scale [13]. (See this volume for different views of the L dwarf temperature scale).…”