A preliminary theoretical line-blanketed model solar photosphere

Solar Physics - A preliminary theoretical solar model is presented that produces closer agreement with observation than has been heretofore possible. The qualitative advantages and shortcomings of...     

Photospheric limb-darkening signatures of global structure variations

Observations of short-term irradiance variations and consideration of mechanisms of the solar activity cycle suggest the possibility of long-term variation of the solar flux. Since the limb darkening is sensitive to effective temperature and convective efficiency, observations of the solar limb darkening may provide a useful means to detect and study long-term global variations. The limb-darkening responses to impulsive variation (in depth) of the source function, to effective temperature variation, and to convection variations are presented. For the variations considered, the limb-darkening variation is approximately linearly proportional to the associated parameters. The minimum detectable amplitude of those parametric variations is derived as a function of observational noise. Given our demonstrated errors of observation, single-parameter sensitivies are 3 K for effective temperature variation and 0.007 for local mixing-length variation for year to year changes at 99% confidence.     

Status of the physics of substellar objects project

A full understanding of the properties of substellar objects is one of the major challenges facing astrophysics. Since their discovery in 1995, hundreds of brown dwarfs and extrasolar planets have been discovered. While these discoveries have enabled important comparisons with theory, observational progress has been much more rapid than the theoretical understanding of cool atmospheres. The reliable determination of mass, abundances, gravities and temperatures is not yet possible. The key problem is that substellar objects emit their observable radiation in the infrared region of the spectrum where our knowledge of atomic, molecular and line broadening data is poor. Here we report on the status of our PoSSO (Physics of SubStellar Objects) project. In order to understand brown dwarfs and extrasolar planets increasing more like those in our solar system, we are studying a wide range of processes. Here we give an update on the project and sketch an outline of atoms, molecules and processes requiring study. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effects of line blanketing on the solar windows

The increasingly high flux predicted to the violet of 4500 Å by many model solar atmospheres stands in contradiction to the observations. Since one possible cause of the disagreement is that the solar windows by which the observed continuum is established might be obscured by line wings, we have made detailed calculations of these narrow spectral regions. With the exception of a few windows affected by the wings of Balmer lines, those redward of the Balmer discontinuity appear free of line blanketing. Even the assumption that the ultraviolet continuum is depressed 5% by unseen lines not included in our calculations leaves substantial disagreements between the models and observations. The discrepancies could perhaps be explained by a veil of weak lines across the ultraviolet spectrum.Our calculations indicate that the windows become narrower at shorter wavelengths. Many of the ambiguities to the violet of 3600 Å would be resolved if spectrophotometric tracings with a band pass of 10 mÅ were available.