The Rise and Fall of the Eclipsing Binary HS Hydrae

TL;DR

This study combines over a century of data to analyze the evolution of eclipses in HS Hydrae, confirming their recent disappearance and predicting their return around 2195, illustrating rapid inclination changes caused by a third star.

Contribution

It provides the first comprehensive long-term analysis of HS Hydrae's eclipse evolution using historic photographic plates and recent space-based data, confirming the cessation and future reappearance of eclipses.

Findings

Eclipses in HS Hydrae have ceased as of recent observations.

Eclipses are predicted to reappear around the year 2195.

The system's inclination changes are driven by a third star.

Abstract

HS Hydrae is a short period eclipsing binary (P_orb=1.57 day) that belongs to a rare group of systems observed to have rapidly changing inclinations. This evolution is due to a third star on an intermediate orbit, and results in significant differences in eclipse depths and timings year-to-year. Zasche & Paschke (2012) revealed that HS Hydrae's eclipses were rapidly fading from view, predicting they would cease around 2022. Using 25 days of photometric data from Sector 009 of the Transiting Exoplanet Survey Satellite (TESS), we find that the primary eclipses for HS Hydrae were only 0.00173+/-0.00007 mag in depth in March 2019. This data from TESS likely represents the last eclipses detected from HS Hydrae. We also searched the Digitization of the Harvard Astronomical Plate Collection (DASCH) archive for historic data from the system. With a total baseline of over 125 years, this unique combination of data sets - from photographic plates to precision space-based photometry - allows us to trace the emergence and decay of eclipses from HS Hydrae, and further constrain its evolution. Recent TESS observations from Sector 035 confirm that eclipses have ceased for HS Hya, and we estimate they will begin again in 2195.