Life in the Slow Lane: A Search for Long Term Variability in ASAS-SN

TL;DR

This study searches for long-term variability in over 9 million isolated stars, identifying 782 slowly varying systems, many of which are newly discovered, revealing diverse behaviors across different stellar populations and some active galactic nuclei.

Contribution

It introduces a large-scale search for long-term variability in a vast stellar sample, discovering numerous new variable systems and classifying their diverse behaviors over a decade.

Findings

782 slowly varying systems identified, 433 new discoveries.

Most variables are red subgiants and lower main sequence stars.

Approximately 70% of candidates show shorter period variability.

Abstract

We search a sample of 9,361,613 isolated sources with 13<g<14.5 mag for slowly varying sources. We select sources with brightness changes larger than ~ 0.03 mag/year over 10 years, removing false positives due to, for example, nearby bright stars or high proper motions. After a thorough visual inspection, we find 782 slowly varying systems. Of these systems, 433 are identified as variables for the first time and 349 are previously classified as variables. Previously classified systems were mostly identified as semi-regular variables (SR), slow irregular variables (L), spotted stars (ROT), or unknown (MISC or VAR), as long time scale variability does not fit into a standard class. The stellar sources are scattered across the CMD and can be placed into 5 groups that exhibit distinct behaviors. The largest groups are very red subgiants and lower main sequence stars. There are also a small number of AGN. There are 551 candidates (~70 percent) that also show shorter time scale periodic variability, mostly with periods longer than 10 days. The variability of 191 of these candidates may be related to dust.