UV Spectral Synthesis of Vega

TL;DR

This study demonstrates that Vega's UV spectrum can be accurately modeled using LTE atmosphere models and a comprehensive line list, revealing detailed surface abundances and testing stellar atmosphere modeling capabilities.

Contribution

First detailed UV spectral synthesis of Vega using LTE models and a new line list, deriving surface abundances and testing modeling accuracy for early A-stars.

Findings

Vega's UV spectrum fits well with LTE synthetic spectra.

Surface abundances for 17 elements were determined.

Modeling confirms the utility of UV spectra in stellar analysis.

Abstract

We show that the UV spectrum (1280-3200 A) of the "superficially normal" A-star Vega, as observed by the IUE satellite at a resolution comparable to the star's rotational broadening width, can be fit remarkably well by a single-temperature synthetic spectrum based on LTE atmosphere models and a newly constructed UV line list. If Vega were a normal, equator-on, slow-rotating star, then its spectrum and our analysis would indicate a temperature of Teff ~ 9550 K, surface gravity of log g ~ 3.7, general surface metallicity of [m/H] ~ -0.5, and a microturbulence velocity of v(turb) ~ 2.0 km/s. Given its rapid rotation and nearly pole-on orientation, however, these parameters must be regarded as representing averages across the observed hemisphere. Modeling the complex UV line spectrum has allowed us to determine the specific surface abundances for 17 different chemical elements, including CNO, the light metals, and the iron group elements. The resultant abundance pattern agrees in general with previous results, although there is considerable scatter in the literature. Despite its peculiarities, Vega has turned out to provide a powerful test of the extent of our abilities to model the atmospheric properties of the early A-stars, particularly the detailed UV line spectrum. The value of the measurements from this pilot study will increase as this analysis is extended to more objects in the rich high-dispersion IUE data archive, including both normal and peculiar objects.