Signature of Differential Rotation in Sun-as-a-Star Ca II K Measurements

TL;DR

This study demonstrates that solar surface differential rotation can be detected from disk-integrated Ca II K measurements even during solar minima, using a robust analysis method applicable to other stars.

Contribution

The paper introduces a technique to identify differential rotation signatures in Sun-as-a-star Ca II K data during low activity periods, enhancing the analysis of stellar rotation.

Findings

SDR signatures are detectable during solar minima.

Method applied to ISS Ca II K data reveals SDR during Cycle 23 and 24.

Technique is adaptable to other stellar photometric data.

Abstract

The characterization of solar surface differential rotation (SDR) from disk-integrated chromospheric measurements has important implications for the study of differential rotation and dynamo processes in other stars. Some chromospheric lines, such as Ca II K, are very sensitive to the presence of activity on the disk and are an ideal choice for investigating SDR in Sun-as-a star observations. Past studies indicate that when the activity is low, the determination of Sun's differential rotation from integrated-sunlight measurements becomes uncertain. However, our study shows that using the proper technique, SDR can be detected from these type of measurements even during periods of extended solar minima. This paper describes results from the analysis of the temporal variations of Ca II K line profiles observed by the Integrated Sunlight Spectrometer (ISS) during the declining phase of Cycle 23 and the rising phase of Cycle 24, and discusses the signature of SDR in the power spectra computed from time series of parameters derived from these profiles. The described methodology is quite general, and could be applied to photometric time series of other Main-Sequence stars for detecting differential rotation.