Mining Planet Search Data for Binary Stars: The $\psi^1$ Draconis system

TL;DR

This paper demonstrates how existing long-term planet search data can be repurposed to detect and characterize binary star companions, revealing a new low-mass companion to $raconis A using spectral analysis.

Contribution

The study introduces a cross-correlation spectral analysis method to identify binary companions in existing planet search data, enabling detection of close-in stellar companions previously difficult to observe.

Findings

Detected a new low-mass companion to $raconis A with a 20-year orbit.

Measured the companion's mass as approximately 0.70 solar masses.

Showed the method's potential for identifying binary stars in radial velocity data.

Abstract

Several planet-search groups have acquired a great deal of data in the form of time-series spectra of several hundred nearby stars with time baselines of over a decade. While binary star detections are generally not the goal of these long-term monitoring efforts, the binary stars hiding in existing planet search data are precisely the type that are too close to the primary star to detect with imaging or interferometry techniques. We use a cross-correlation analysis to detect the spectral lines of a new low-mass companion to $\psi^1$ Draconis A, which has a known roughly equal-mass companion at ${\sim}680$ AU. We measure the mass of $\psi^1$ Draconis C as $M_2 = 0.70 \pm 0.07 M_{\odot}$, with an orbital period of ${\sim}20$ years. This technique could be used to characterize binary companions to many stars that show large-amplitude modulation or linear trends in radial velocity data.