Abstract
Close, compact, hierarchical, and multiple stellar systems, i.e., multiples having an outer orbital period from months to a few years, comprise a small but continuously growing group of the triple and multiple star zoo. Many of them consist of at least one eclipsing pair of stars and, therefore, exhibit readily observable short-term dynamical interactions among the components. Thus, their dynamical and astrophysical properties can be explored with high precision. In this paper we present an overview of the history of the search for additional components around eclipsing binaries from the first serendipitous discoveries to more systematic recent studies. We describe the different observational detection methods and discuss their connections to the different kinds of astrophysical and dynamical information that can be mined from different datasets. Moreover, the connection amongst the observable phenomena and the long-term dynamics of such systems is also discussed.
Highlights
In the last years of the 19th century, in a series of papers, Chandler [1,2,3,4] investigated the nature of some ‘inequalities’ in the eclipsing periods of Algol and some other eclipsing binaries (EB)
Before the era of the exoplanet hunting space telescopes, whenever variable star observers detected quasi-sinusoidal variations in the observed versus expected mid-eclipse times of any EB, if the variations in the primary and the secondary eclipses were of opposite signs, they could assume with great certainty that their origin was dominated by apsidal motion caused by the non-spherical mass distribution of the stars
We find that ≈63% (129 of 204) of the known compact hierarchical triple stellar system (CHT) have been discovered in the last decade, through space photometry
Summary
In the last years of the 19th century, in a series of papers, Chandler [1,2,3,4] investigated the nature of some ‘inequalities’ in the eclipsing periods of Algol (noticed first by Argelander [5]) and some other eclipsing binaries (EB). Tight triples (or multiples) are not necessarily CHTs. For example, the recently known tightest triple star system is LHS 1070 (Xia et al [25]), which consists of three very low mass red dwarfs with inner and outer periods of 18.2 and 99 years, respectively, i.e., it has a period ratio of Pout/Pin = 5.4, which is close to the dynamical stability limit of Mardling & Aarseth [26]. The recently known tightest triple star system is LHS 1070 (Xia et al [25]), which consists of three very low mass red dwarfs with inner and outer periods of 18.2 and 99 years, respectively, i.e., it has a period ratio of Pout/Pin = 5.4, which is close to the dynamical stability limit of Mardling & Aarseth [26] In such a tight system, one can expect strong perturbations and, variations in the orbital elements.
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