A Comparison of Spectroscopic versus Imaging Techniques for Detecting Close Companions to Kepler Objects of Interest

TL;DR

This study compares spectroscopic deblending and imaging techniques for detecting close stellar companions to Kepler planet hosts, highlighting their complementary strengths and limitations in identifying and characterizing these companions.

Contribution

It provides a direct comparison of two methods for companion detection, demonstrating the advantages of spectroscopic deblending for very close-in companions and imaging for wider separations.

Findings

Spectroscopic deblending is effective for detecting very close-in companions ($ heta \\lesssim$0.02-0.05")

Imaging techniques detect wider companions ($ heta \\geq$0.02-0.05") missed by spectroscopy

Combining both methods reveals higher-order multiples in planet-hosting systems.

Abstract

(Abbreviated) Kepler planet candidates require both spectroscopic and imaging follow-up observations to rule out false positives and detect blended stars. [...] In this paper, we examine a sample of 11 Kepler host stars with companions detected by two techniques -- near-infrared adaptive optics and/or optical speckle interferometry imaging, and a new spectroscopic deblending method. We compare the companion Teff and flux ratios (F_B/F_A, where A is the primary and B is the companion) derived from each technique, and find no cases where both companion parameters agree within 1sigma errors. In 3/11 cases the companion Teff values agree within 1sigma errors, and in 2/11 cases the companion F_B/F_A values agree within 1sigma errors. Examining each Kepler system individually considering multiple avenues (isochrone mapping, contrast curves, probability of being bound), we suggest two cases for which the techniques most likely agree in their companion detections (detect the same companion star). Overall, our results support the advantage the spectroscopic deblending technique has for finding very close-in companions ($\theta \lesssim$0.02-0.05") that are not easily detectable with imaging. However, we also specifically show how high-contrast AO and speckle imaging observations detect companions at larger separations ($\theta \geq$0.02-0.05") that are missed by the spectroscopic technique, provide additional information for characterizing the companion and its potential contamination (e.g., PA, separation, $\Delta$m), and cover a wider range of primary star effective temperatures. The investigation presented here illustrates the utility of combining the two techniques to reveal higher-order multiples in known planet-hosting systems.