Abstract

Contributed Talk - Splinter CloseBinaries   (MW-0250)

Observing the most compact binaries with the Time Domain Telescope

Thomas Kupfer
University of Hamburg / Hamburger Sternwarte

The shortest-period compact binaries known, such as HM Cnc, complete an orbit in only about five minutes. These systems provide a unique opportunity to study the final stages of binary evolution before the components merge, but their rapid variability presents severe observational challenges. Measuring their fundamental system parameters requires phase-resolved spectroscopy with exposure times short enough to avoid phase smearing, necessitating the use of 8 m-class telescopes. The resulting readout overheads lead to substantial losses in observing efficiency, a problem that will become even more acute as the number of known ultracompact binaries increases over the coming decade. The upcoming Laser Interferometer Space Antenna (LISA) is expected to detect tens of thousands of Galactic compact binaries individually, with thousands likely to have detectable electromagnetic counterparts. Among these will be the most compact systems, with orbital periods of only a few minutes, providing an unprecedented opportunity to study the endpoints of binary evolution through joint gravitational-wave and electromagnetic observations. However, no existing or planned facility combines the aperture, flexibility, and high-cadence spectroscopic capability required to routinely characterize these sources. In this talk, I will present the concept of the Time-Domain Telescope (TDT), which will be proposed as part of ESO’s Expanding Horizons programme. TDT is envisioned as a spectroscopic facility comprising a large array of medium-sized telescopes that can operate independently or coherently as a single large-aperture telescope, delivering “a spectrum, anywhere, anytime.” I will also introduce the planned Proto-TDT demonstrator and discuss how this concept could transform time-domain spectroscopy of the most compact binaries in the era of LISA.