Exploring the water and carbon monoxide shell around Betelgeuse with VLTI/AMBER

TL;DR

This study uses VLTI/AMBER interferometry to analyze Betelgeuse's atmosphere, detecting water vapor and CO molecules in a MOLsphere extending beyond the photosphere, confirming previous findings.

Contribution

First detailed interferometric analysis of Betelgeuse's MOLsphere using medium spectral resolution data revealing molecular distribution and atmospheric structure.

Findings

Detected water vapor and CO molecules in Betelgeuse's atmosphere.

Derived the size, temperature, and column densities of the MOLsphere.

Confirmed the MOLsphere extends to about 1.3 times the star's photospheric radius.

Abstract

We present the results of the analysis of our recent interferometric observations of Betelgeuse, using the AMBER instrument of the VLTI. Using the medium spectral resolution mode ($R \sim 1500$) we detected the presence of the water vapour and carbon monoxide (CO) molecules in the H and K bands. We also derived the photospheric angular diameter in the continuum. By analysing the depth of the molecular lines and the interferometric visibilities, we derived the column densities of the molecules, as well as the temperature and the size of the corresponding regions in the atmosphere of Betelgeuse (the MOLsphere) using a single shell model around the photosphere. Our results confirm the findings by Perrin \et al\ (\cite{Perrin2004}) and Ohnaka \et al\ (\cite{Ohnaka2011}) that the H$_2$O and CO molecules are distributed around Betelgeuse in a MOLsphere extending to approximately 1.3 times the star's photospheric radius.