Observational Techniques for Detecting Planets in Binary Systems

TL;DR

This paper reviews observational techniques for detecting planets in binary star systems, focusing on methods for identifying S-type and P-type planets through astrometry, radial velocities, and eclipse timing, to better understand planet formation.

Contribution

It provides a comprehensive overview of current observational methods tailored for binary systems, highlighting differences between resolved and unresolved binaries and techniques for both S-type and P-type planets.

Findings

Different techniques are suited for resolved and unresolved binaries.

Radial velocity and eclipse timing are effective for detecting S-type and P-type planets.

Astrometric methods like differential astrometry are crucial for wide binary systems.

Abstract

Searches for planets in close binary systems explore the degree to which stellar multiplicity inhibits or promotes planet formation. There is a degeneracy between planet formation models when only systems with single stars are studied--several mechanisms appear to be able to produce such a final result. This degeneracy is lifted by searching for planets in binary systems; the resulting detections (or evidence of non-existence) of planets in binaries isolates which models may contribute to how planets form in nature. In this chapter, we consider observational efforts to detect planetary companions to binary stars in two types of hierarchical planet-binary configurations: first ``S-type'' planets which orbit just one of the stars, with the binary period being much longer than the planet's; second, ``P-type'' or circumbinary planets, where the planet simultaneously orbits both stars, and the planetary orbital period is much longer than that of the binary. The S-type planet finding techniques are different for binaries that can or cannot be spatially resolved. For wider systems, techniques reviewed include dualstar interferometric differential astrometry and precision radial velocities. Alternatively, unresolved binaries can be studied using modified dualstar "PHASES-style" differential astrometry or a modification of the radial velocity technique for composite spectra. Should a fortunately aligned--but still long period--binary be found, eclipse timing can also reveal the presence of S-type planets. Methods for detecting P-type planets include the composite-spectra variant of the radial velocity technique and eclipse timing.