An independent distance estimate to the AGB star R Sculptoris

Abstract

For the carbon AGB star R Sculptoris, the uncertain distance significantly affects the interpretation of observations regarding the evolution of the stellar mass loss during and after the most recent thermal pulse. We aim to provide a new, independent measurement of the distance to R Sculptoris, reducing the absolute uncertainty of the distance estimate to this source. R Scl is a semi-regular pulsating star, surrounded by a thin shell of dust and gas created during a thermal pulse approximately 2000 years ago. The stellar light is scattered by the dust particles in the shell at a radius of 19 arcsec. The variation in the stellar light affects the amount of dust-scattered light with the same period and amplitude ratio, but with a phase lag that depends on the absolute size of the shell. We measured this phase lag by observing the star R Scl and the dust-scattered stellar light from the shell at five epochs between June - December 2017. By observing in polarised light, we imaged the shell in the plane of the sky, removing any uncertainty due to geometrical effects. The phase lag gives the absolute size of the shell, and together with the angular size of the shell directly gives the absolute distance to R Sculptoris. We measured a phase lag between the stellar variations and the variation in the shell of 40.0 +/- 4.0 days. The angular size of the shell is measured to be 19.1 arcsec +/- 0.7 arcsec. Combined, this gives an absolute distance to R Sculptoris of 361 +/- 44 pc. We independently determined the absolute distance to R Scl with an uncertainty of 12%. The estimated distance is consistent with previous estimates, but is one of the most accurate distances to the source to date. In the future, using the variations in polarised, dust-scattered stellar light, may offer an independent possibility to measure reliable distances to AGB stars.

arXiv commentaccepted by A&A, 8 pages, 8 figures

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Cited by in corpus (2)

• Distance estimates for AGB stars from parallax measurements
• Locating dust and molecules in the inner circumstellar environment of R~Sculptoris with MATISSE