The chromospherically active binary star EI Eridani II. Long-term Doppler imaging

TL;DR

This study presents 11 years of Doppler imaging of the active binary star EI Eridani, revealing persistent spot patterns and complex activity that do not directly correlate with photometric cycles, challenging simple spot-cycle models.

Contribution

It provides the longest Doppler imaging dataset for EI Eridani, showing persistent spot morphology and complex activity patterns over a decade.

Findings

No correlation between spot parameters and activity cycle.

Persistent polar spot observed across all images.

Variable activity near high latitudes with spot appendages.

Abstract

Data from 11 years of continuous spectroscopic observations of the active RS CVn-type binary star EI Eridani - gained at NSO/McMath-Pierce, KPNO/Coude Feed and during the MUSICOS 98 campaign - were used to obtain 34 Doppler maps in three spectroscopic lines for 32 epochs, 28 of which are independent of each other. Various parameters are extracted from our Doppler maps: average temperature, fractional spottedness, and longitudinal and latitudinal spot-occurrence functions. We find that none of these parameters show a distinct variation nor a correlation with the proposed activity cycle as seen from photometric long-term observations. This suggests that the photometric brightness cycle may not necessarily be due to just a cool spot cycle. The general morphology of the spot pattern remains persistent over the whole period of 11 years. A large cap-like polar spot was recovered from all our images. A high degree of variable activity was noticed near latitudes of approx. 60-70 degrees where the appendages of the polar spot emerged and dissolved.