Detection of Stars within $\sim$0.8 arcseconds of Kepler Objects of Interest

TL;DR

This paper introduces an algorithm to detect faint secondary stars in high-resolution spectra, enhancing the identification of close stellar companions and background stars near Kepler objects of interest.

Contribution

The paper presents a novel spectral analysis method capable of identifying secondary stars as faint as 1% of the primary's brightness in high-resolution spectra.

Findings

Detected 63 secondary stars among 1160 Kepler objects of interest.

Able to identify companions as faint as 1% relative brightness.

Provided limits on undetected companion brightness.

Abstract

We present an algorithm to search for the faint spectrum of a second star mixed with the spectrum of a brighter star in high resolution spectra. We model optical stellar spectra as the sum of two input spectra drawn from a vast library of stars throughout the H-R diagram. From typical spectra having resolution of R=60,000, we are able to detect companions as faint as 1% relative to the primary star in approximately the V and R bandpasses of photometry. We are also able to find evidence for triple and quadruple systems, given that any additional companions are sufficiently bright. The precise threshold percentage depends on the SNR of the spectrum and the properties of the two stars. For cases of non-detection, we place a limit on the brightness of any potential companions. This algorithm is useful for detecting both faint orbiting companions and background stars that are angularly close to a foreground target star. The size of the entrance slit to the spectrometer, 0.87 x 3 arcsec (typically), sets the angular domain within which the second star can be detected. We analyzed Keck-HIRES spectra of 1160 California Kepler Survey objects of interest (KOI) searching for the secondary spectra, with the two goals of alerting the community to two possible host stars of the transiting planet and to dilution of the light curve. We report 63 California Kepler Survey objects of interest showing spectroscopic evidence of a secondary star.