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

Creators: Teske, Johanna K.; Everett, Mark E.; Hirsch, Lea; Furlan, Elise; Horch, Elliott P.; Howell, Steve B.; Ciardi, David R.; Gonzales, Erica; Crepp, Justin R.

Abstract

Kepler planet candidates require both spectroscopic and imaging follow-up observations to rule out false positives and detect blended stars. Traditionally, spectroscopy and high-resolution imaging have probed different host star companion parameter spaces, the former detecting tight binaries and the latter detecting wider bound companions as well as chance background 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 effective temperatures (T_(eff)) 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 1σ errors. In 3/11 cases the companion T_(eff) values agree within 1σ errors, and in 2/11 cases the companion F_B/F_A values agree within 1σ 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 that the spectroscopic deblending technique has for finding very close-in companions (θ ≾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 (θ ≥0."02–0."05) that are missed by the spectroscopic technique, provide additional information for characterizing the companion and its potential contamination (e.g., position angle, separation, magnitude differences), 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.

Additional Information

© 2015 The American Astronomical Society. Received 2015 May 19; accepted 2015 August 25; published 2015 October 12. The authors acknowledge the support of many people and programs that made this work possible. This paper includes data collected by the Kepler Mission. Funding for the mission is provided by the NASA Science Mission directorate. Most of the data presented here is made available to the community for download at the Kepler CFOP,15 a service of the NASA Exoplanet Archive. These data include imaging-based separations and Δm values, tabulated sensitivity curves for each of the speckle observations, and KOI stellar parameters. M. E. Everett received support through NASA Agreement NNX1-3AB60A. The WIYN speckle imaging data presented here were based on observations at Kitt Peak National Observatory, National Optical Astronomy Observatory (NOAO 2010B-0241, 2011A-0130, 2013B-0115; PI: Howell), which is operated by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation. The Gemini speckle imaging observations were obtained as part of the programs GN-2013B-Q-87 and GN-2014B-Q-21 (PI: Howell) at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), Ministério da Ciência, Tecnologia e Inovação (Brazil) and Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina). We are very grateful for the excellent support of the Gemini administration and support staff who helped make the visiting instrument program possible and the DSSI observing run a great success. Some of the data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation. We thank the referee for their thoughtful comments and edits that improved the paper. Finally, the authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. The authors are honored to be permitted to conduct observations on Iolkam Du'ag (Kitt Peak), a mountain within the Tohono O'odham Nation with particular significance to the Tohono O'odham. Facilities: Gemini:Gillett (DSSI), Keck:II (NIRC2), WIYN (DSSI)

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