Triple stars on planetary scales: Formation of compact hierarchical triples

Compact hierarchical triples (CHTs) are triple stars where the tertiary is in an orbit of period less than 1000 d. In other words, you can fit three solar-mass main-sequence stars between the Sun and Jupiter. These systems were thought to be rare, but we are discovering more of these systems recently (currently ~600 systems), thanks to space-based missions like TESS, Kepler, and GAIA. In our work, we use eclipse timing and radial velocities of double-lined eclipsing binaries to discover and characterise these systems. We then use spectroscopic and systemic parameters from our work and the literature to understand the effects of metallicity and dynamics on the formation processes. We find that the formation channels are similar to those of close binaries, but how the systems evolve might vary a lot depending on their initial architectures and, therefore, also impact the final states that we see in observations. A bigger sample can help us understand the effect of dynamics in their subsequent evolution.