The Unhurried Universe: A Continued Search for Long Term Variability in ASAS-SN

TL;DR

This study searches over 5.6 million isolated sources in the ASAS-SN survey for long-term brightness variability over a decade, identifying 426 slowly-varying systems, many of which are newly discovered or exhibit complex behaviors.

Contribution

The paper presents a large-scale search for long-term variability in a vast dataset, identifying new variable sources and classifying their diverse behaviors over ten years.

Findings

426 slowly-varying systems identified

200 are new variable discoveries

62% show shorter-term periodic variability

Abstract

We search a sample of 5,685,060 isolated sources in the All Sky Automated Survey for SuperNovae (ASAS-SN) with 14.5<g<15 mag for slowly varying sources with brightness changes larger than ~0.03 mag/year over 10 years. We find 426 slowly-varying systems. Of these systems, 200 are identified as variables for the first time, 226 are previously classified as variables, and we find equal numbers of sources becoming brighter and fainter. Previously classified systems were mostly identified as semi-regular variables (SR), slow irregular variables (L), or unknown (MISC or VAR), as long time scale variability does not fit into a standard class. Much like Petz & Kochanek 2025, the sources are scattered across the color magnitude diagram and can be placed into 5 groups that exhibit distinct behaviors. There are also six AGN. There are 262 candidates (~62 percent) that also show shorter time scale periodic variability, mostly with periods longer than 10 days. The variability of 66 of these candidates may be related to dust. Combining the new slow variable candidates with the candidates from Petz & Kochanek 2025, we have found a total of 1208 slow variables.