Statistical equilibrium equations for trace elements in stellar atmospheres

The conditions of thermodynamic equilibrium, local thermodynamic equilibrium, and statistical equilibrium are discussed in detail. The equations of statistical equilibrium and the supplementary equations are shown together with the expressions for radiative and collisional rates with the emphasize on the solution for trace elements.Comment: presented at the workshop held in Nice, France, 30.7.-4.8.2007, to appear in Non-LTE Line Formation for Trace Elements in Stellar Atmospheres, R. Monier et al. eds., EAS Publ.Se

Model atmospheres of sub-stellar mass objects

We present an outline of basic assumptions and governing structural equations describing atmospheres of substellar mass objects, in particular the extrasolar giant planets and brown dwarfs. Although most of the presentation of the physical and numerical background is generic, details of the implementation pertain mostly to the code CoolTlusty. We also present a review of numerical approaches and computer codes devised to solve the structural equations, and make a critical evaluation of their efficiency and accuracy.Comment: 31 pages, 10 figure

Black hole singularity in AdS/CFT

We present a short review of hep-th/0306170. In the context of AdS/CFT correspondence, we explore what information from behind the horizon of the bulk black hole geometry can be found in boundary CFT correlators. In particular, we argue that the CFT correlators contain distinct, albeit subtle, signals of the black hole singularity.Comment: 7 pages, 2 figures, AMSLaTeX (ws-procs9x6.cls included). Presented at QTS3 (Cincinnati, Ohio, Sept. 10-14, 2003

Holographic insights and puzzles

The talk is composed of two parts, both set within the AdS/CFT context. In the first part, I discuss holographic insight into strongly coupled field theory in a black hole background. I conjecture two new gravitational solutions, dubbed black funnels and black droplets, which describe two distinct deconfined phases in the field theory at finite temperature. I also briefly mention puzzles associated with an analogous set-up in a rotating black hole background. In the second part of the talk, I discuss time-dependent states in a CFT on flat spacetime background, exemplified by the conformal soliton flow. Here I focus on puzzles regarding the nature of entropy in time-evolving states and its holographic dual.Comment: 23 pages, 9 figures; prepared for the Proceedings of the XVIth European Workshop on String Theory, Madrid, Spain, June 14-18 201

A Systematic Study of Departures from Chemical Equilibrium in the Atmospheres of Substellar Mass Objects

We present a systematic study of the spectral consequences of departures from chemical equilibrium in the atmospheres of L and T dwarfs, and for even cooler dwarfs. The temperature/pressure profiles of the non-equilibrium models are fully consistent with the non-equilibrium chemistry. Our grid of non-equilibrium models includes spectra for effective temperatures from 200 K to 1800 K, three surface gravities, four possible values of the coefficient of eddy diffusion in the radiative zone, and three different CO/CH$_4$ chemical reaction prescriptions. We find that the non-equilibrium overabundance of CO translates into flux suppressions in the M ($\sim4-$5 $\mu$m) band of at most $\sim$40% between effective temperatures of 600 and 1800 K. The effect is largest around $T_{\rm eff} \approx 1100$ K. The underabundance of ammonia due to non-equilibrium chemistry translates into flux enhancements of no more than $\sim$20% for the $T_{\rm eff}$ range from 300 to 1800 K, with the largest effects at the lowest values of $T_{\rm eff}$. The magnitude of the departure from chemical equilibrium increases with decreasing gravity, with increasing eddy diffusion coefficient, and with decreasing speed of the CO/CH$_4$ reaction. Though these effects are modest, they lead to better fits with the measured T dwarf spectra. Furthermore, the suppression in the M band due to non-equilibrium enhancements in the CO abundance disappears below $\sim$500 K, and is only partial above $\sim$500 K, preserving the M band flux as a useful diagnostic of cool atmospheres and maintaining its importance for searches for brown dwarfs cooler than T dwarfs.Comment: Accepted to the Astrophysical Journal; 21 figures in a total of 26 emulateapj page