Evidence of asymmetries in the Aldebaran photosphere from multi-wavelength lunar occultations

TL;DR

This study used multi-wavelength lunar occultations to analyze Aldebaran's photosphere, revealing potential asymmetries and surface spots that vary with wavelength and over time, challenging simple symmetric models.

Contribution

It provides evidence of asymmetries in Aldebaran's photosphere using multi-epoch, multi-wavelength lunar occultation data, suggesting surface spots influence brightness profiles.

Findings

Indications of asymmetric brightness profiles.

Wavelength and time-dependent asymmetries observed.

Surface spots likely cause observed asymmetries.

Abstract

We have recorded three lunar occultations of Aldebaran (AlfTau) at different telescopes and using various band-passes, from the ultraviolet to the far red. The data have been analyzed using both model-dependent and model-independent methods. The derived uniform-disc angular diameter values have been converted to limb-darkened values using model atmosphere relations, and are found in broad agreement among themselves and with previous literature values. The limb-darkened diameter is about 20.3 milliarcseconds on average . However, we have found indications that the photospheric brightness profile of Aldebaran may have not been symmetric, a finding already reported by other authors for this and for similar late-type stars. At the sampling scale of our brightness profile, between one and two milliarcsecond, the uniform and limb-darkened disc models may not be a good description for Aldebaran. The asymmetries appear to differ with wavelength and over the 137 days time span of our measurements. Surface spots appear as a likely explanation for the differences between observations and the models.