Identification of Young Stellar Variables with KELT for K2 II: The Upper Scorpius Association

TL;DR

This study demonstrates that long-term ground-based photometry from KELT effectively complements space-based data like K2, enabling comprehensive analysis of young star variability, including rotation and activity cycles, over 5.5 years.

Contribution

It introduces a 5.5-year KELT dataset for Upper Scorpius members, showing its effectiveness in identifying stellar rotation and variability not captured by short-term space observations.

Findings

KELT data accurately recovers K2-identified periodic signals.

Long-term KELT monitoring reveals variability related to circumstellar material.

Ground-based surveys are vital for understanding full young star variability.

Abstract

High-precision photometry from space-based missions such as K2 and TESS enables detailed studies of young star variability. However, because space-based observing campaigns are often short (e.g., 80 days for K2), complementary long-baseline photometric surveys are critical for obtaining a complete understanding of young star variability, which can change on timescales of minutes to years. We therefore present and analyze light curves of members of the Upper Scorpius association made over 5.5 years by the ground-based Kilodegree Extremely Little Telescope (KELT), which complement the high-precision observations of this region taken by K2 during its Campaigns~2 and 15. We show that KELT data accurately identify the periodic signals found with high-precision K2 photometry, demonstrating the power of ground-based surveys in deriving stellar rotation periods of young stars. We also use KELT data to identify sources exhibiting variability that is likely related to circumstellar material and/or stellar activity cycles; these signatures are often unseen in the short-term K2 data, illustrating the importance of long-term monitoring surveys for studying the full range of young star variability. We provide the KELT light curves as electronic tables in an ongoing effort to establish legacy time-series datasets for young stellar clusters.