A Systematic Search for Big Dippers in ASAS-SN

TL;DR

The paper tackles the challenge of identifying big-dipper stars—deep, long-lasting, non-recurrent dimming events likely caused by dusty occultations—within the ASAS-SN dataset. It develops a systematic pipeline that searches for dips with $Δg \,\ge\ 0.3$ mag in stars with $13<g<14$ mag, requiring detections in multiple cameras and keeping photometric dispersion low. The study yields 15 new long-period eclipsing-binary candidates (with 5 previously known) and 4 new dippers (with 7 known), with further classification into SDEBs, MDEBs, and dippers, aided by Gaia, WISE/2MASS, LAMOST/APOGEE, and X-ray data. These results illustrate the diversity of dimming mechanisms, from circumbinary disk eclipses to dusty occultations, and suggest avenues for scalable expansion to other surveys and enhanced automated screening.

Abstract

Dipper stars are extrinsically variable stars with deep dimming events due to extended, often dusty, structures produced by a wide range of mechanisms such as collisions, protoplanetary evolution or stellar winds. ASAS-SN has discovered 12 dipper-like objects as part of its normal operations. Here we systematically search the $\sim 5.1$ million ASAS-SN targets with $13<g<14$~mag for dippers with $Δg\ge0.3$~mag to identify 4 new candidates. We also discover 15 long-period eclipsing binary candidates. We characterized the 19 new and 12 previously discovered objects using the ASAS-SN light curves and archival multi-wavelength data. We divide them into three categories: long-period eclipsing binaries with a single eclipse (13 total), long-period eclipsing binaries with multiple eclipses (7 total) and dipper stars with dust or disk occultations (11 total).

Figures (11)

• Figure 1: Examples of false positives that were rejected during the visual inspection of possible candidates and objects rejected by our search labeled by their rejection reason. Some of the rejections are due to other types of variability, some are caused by a few bad points, and some effects are environmental. The vertical lines correspond to the dimming events detected by our pipeline. The different colors correspond to different cameras. In panels (e) and (g), the light curves are phase-folded using the period from a Lomb-Scargle periodogram Lomb_1976Scargle_1982.
• Figure 2: The Gaia CMD with the known sources and the new sources. The targets on the CMD are sorted into the categories of single-dip eclipsing binaries (SDE binaries) candidates, multi-dip eclipsing binaries (MDE binaries) candidates, and dipper candidates. The grey background stars show the first $\sim100{,}000$ stars run through our pipeline.
• Figure 3: The single-dip eclipsing binaries discussed in Section 3.1. The serendipitously found targets are shown first, followed by the targets found in this search, both ordered by right ascension. The first known target shows the light curve zoomed in on the dip, while the rest of the known targets show the full ASAS-SN light curves. The first three new targets show the light curves, zoomed in on the dips while the remaining new targets show the full ASAS-SN light curves. The zoomed in cases are to better show the shape of the events. Each different color in the light curve represents a different ASAS-SN camera. The circles (squares) are the ASAS-SN $g$ ($V$) band data.
• Figure 4: Spectral energy distributions of the dippers that have significant IR excesses. The black lines are single star SED models fit to the optical part of the SED. The effective temperature and radius of the model is reported in the upper right corner of each panel.
• Figure 5: The multi-dip eclipsing binaries. They are organized in the same way as in Figure \ref{['fig:SDE_Binaries']} and are discussed in Section 3.2.