Name/Affiliation: Jeff A. Valenti (STScI)
Generating Asymmetric Line Profiles with 1D Models
Dynamic 3D stellar atmosphere models have been in use for 3 decades, increasing in sophistication until today they represent the state of the art. For practical reasons, the vast majority of investigators (including me) still use static 1D model atmospheres, despite many published warnings from the 3D community. For static 1D model atmospheres, synthetic line profiles are symmetric about line center. Observed solar and stellar line profiles are markedly asymmetric. Line profiles reflected about line center differ from the original profile by 1% of the continuum for moderately strong lines. Inability to model line asymmetries is the largest error in static 1D model atmospheres, leaving aside atomic data errors that also affect 3D models. This suggests that the static assumption may be the main weakness of typical 1D studies, rather than the plane parallel approximation. We generate asymmetric line profiles with 1D models by relaxing the static assumption in Spectroscopy Made Easy (SME). Initially, we combine a warm ascending component and a cool descending component. Unlike most previous studies (but see Frutiger et al. 2000; Borrero and Bellot Rubio 2002), we allow vertical velocity to be a function of depth in the atmosphere. With these additional useful degrees of freedom, we dramatically improve agreement between observed and synthetic line profiles. We quantify how opacity smearing in a kinematic 1D model affects microturbulence, macroturbulence, line equivalent width, and abundance. More study is needed to relate physical results from dynamic 3D models to the parameters of kinematic 1D models, which are likely remain a useful approximation for another decade at least.