The effect of rotation on the spectrum of Vega

TL;DR

This paper reanalyzes Vega's composition considering its rapid rotation, revealing complex spectral line shapes, a peculiar abundance pattern, and implications for its mass and age, challenging previous assumptions.

Contribution

It introduces a detailed spectral synthesis of Vega using a Roche model, highlighting the impact of rotation on spectral features and stellar parameters.

Findings

Vega's spectral lines are more complex than previously thought.

Vega exhibits a peculiar abundance pattern similar to \\W Bootis stars.

Rotation affects ionization states minimally but necessitates full stellar mixing.

Abstract

The discovery that Vega is a rapidly rotating pole-on star has raised a number of questions about this fundamental standard, including such issues as its composition, and in turn its mass and age. We report here a reanalysis of Vega's composition. A full spectral synthesis based on the Roche model derived earlier from NPOI interferometry is used. We find the line shapes in Vega's spectrum to be more complex than just flat-bottomed, which have been previously reported; profiles range from slightly self-reversed to simple ``V'' shapes. A high SNR spectrum, obtained by stacking spectra from the ELODIE archive, shows excellent agreement with the calculations, provided we add about 10 km/s of macroturbulence to the predicted spectra. From the abundance analysis, we find that Vega shows the peculiar abundance pattern of a \W Bootis star as previously suggested. We investigate the effects of rotation on the deduced abundances and show that the dominant ionization states are only slightly affected compared to analyses using non-rotating models. We argue that the rapid rotation requires the star be fully mixed. The composition leads to masses and particularly ages that are quite different compared to what are usually assumed.