Sakurai's Object: characterising the near-infrared CO ejecta between 2003 and 2007

TL;DR

This study analyzes near-infrared observations of Sakurai's Object from 2003 to 2007, revealing details about CO ejecta, their composition, velocity, and thermal evolution, indicating complex processes beyond stellar radiation influence.

Contribution

It provides the first detailed characterization of CO ejecta and their properties in Sakurai's Object over several years, highlighting the ejecta's origin and thermal behavior.

Findings

CO ejecta mass estimated at 2.2e-6 to 2.7e-6 solar masses

High-velocity wind of 500 km/s detected

Significant cooling and weakening of CO bands observed

Abstract

We present observations of Sakurai's Object obtained at 1-5um between 2003 and 2007. By fitting a radiative transfer model to an echelle spectrum of CO fundamental absorption features around 4.7um, we determine the excitation conditions in the line-forming region. We find 12C/13C~3.5, consistent with CO originating in ejecta processed by the very late thermal pulse, rather than in the pre-existing planetary nebula. We demonstrate the existence of 2.2e-6<M<2.7e-6 Msun of CO ejecta outside the dust, forming a high-velocity wind of 500+/-80 km/s. We find evidence for significant weakening of the CO band and cooling of the dust around the central star between 2003 and 2005. The gas and dust temperatures are implausibly high for stellar radiation to be the sole contributor.