The limb-darkened Arcturus; Imaging with the IOTA/IONIC interferometer

TL;DR

This study used interferometry to analyze Arcturus's limb darkening and brightness distribution, confirming atmospheric models and setting limits on potential companions and asymmetries.

Contribution

First high-resolution interferometric imaging of Arcturus in the H band, validating atmospheric models and providing detailed brightness and limb darkening measurements.

Findings

Achromatic power law models fit the brightness distribution well

Derived Rosseland diameter of 21.05±0.21 mas and T_eff=4295±26 K

No companion detected with an upper brightness ratio limit of 8e-4

Abstract

This paper is an H band interferometric examination of Arcturus, a star frequently used as a spatial and spectral calibrator. Using the IOTA 3 telescope interferometer, we performed spectro-interferometric observation (R~35) of Arcturus. Atmospheric models and prescriptions were fitted to the data to derive the brightness distribution of the photosphere. Image reconstruction was also obtained using two software algorithms: Wisard and Mira. An achromatic power law proved to be a good model of the brightness distribution, with a limb darkening compatible with the one derived from atmospheric model simulations using our Marcs model. A Rosseland diameter of 21.05+/-0.21 was derived, corresponding to an effective temperature of T_eff=4295+/-26 K. No companion was detected from the closure phases, with an upper limit on the brightness ratio of 8e-4 at 1AU. Dynamic range at such distance from the photosphere was established at 1.5e-4 (1sigma rms). An upper limit of 1.7e-3 was also derived for the level of brightness asymmetries present on the photosphere.