Multi-epoch Optical Images of IRC+10216 Tell About the Central Star And the Adjacent Environment

TL;DR

This study uses multi-epoch Hubble images and Gaia data to analyze the central star IRC+10216, revealing dust distribution, stellar motion, and wind velocities, providing insights into its circumstellar environment and variability.

Contribution

It presents a detailed multi-epoch analysis of IRC+10216 combining Hubble imaging and Gaia astrometry, offering new insights into dust, stellar motion, and wind dynamics.

Findings

Detection of a red, dusty feature at the star's position in 2016.

Measurement of the star's transverse wind velocity as approximately 12.5 km/s.

Identification of a porous envelope influencing brightness variations.

Abstract

Six images of IRC+10216 taken by the Hubble Space Telescope at three epochs in 2001, 2011, and 2016 are compared in the rest frame of the central carbon star. An accurate astrometry has been achieved with the help of Gaia Data Release 2. The positions of the carbon star in the individual epochs are determined using its known proper motion, defining the rest frame of the star. In 2016, a local brightness peak with compact and red nature is detected at the stellar position. A comparison of the color maps between 2016 and 2011 epochs reveals that the reddest spot moved along with the star, suggesting a possibility of its being the dusty material surrounding the carbon star. Relatively red, ambient region is distributed in an $\Omega$ shape and well corresponds to the dusty disk previously suggested based on near-infrared polarization observations. In a larger scale, differential proper motion of multiple ring-like pattern in the rest frame of the star is used to derive the average expansion velocity of transverse wind components, resulting in $\sim$ 12.5 km s$^{-1}$ ($d$/123 pc), where $d$ is the distance to IRC+10216. Three dimensional geometry is implied from its comparison with the line-of-sight wind velocity determined from half-widths of submillimeter emission line profiles of abundant molecules. Uneven temporal variations in brightness for different searchlight beams and anisotropic distribution of extended halo are revisited in the context of the stellar light illumination through a porous envelope with postulated longer-term variations for a period of $\lesssim10$ years.