Detection of Stars Within ~0.8 in of Kepler Objects of Interest

Creators: Kolbl, Rea; Marcy, Geoffrey W.; Isaacson, Howard; Howard, Andrew W.

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 a 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 signal-to-noise 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 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 × 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 KOI showing spectroscopic evidence of a secondary star.

Additional Information

© 2015 American Astronomical Society. Received 2014 May 7. Accepted 2014 September 19. Published 2014 December 15. We thank John Johnson for the CalTech Keck Telescope time to obtain many of the spectra of the KOIs. We also thank John Brewer and Debra Fischer for their preliminary estimates of the stellar parameters for the Specmatch library stars, as their parameters are an improvement over the values in Valenti & Fischer (2005), with a published paper in preparation. G. Marcy, the Alberts Chair at UC Berkeley, would like to thank Marilyn and Watson Alberts for funding that made this research possible. We also thank the John Templeton Foundation and NASA grant NNX11AK04A for funding this research. We thank the government of the Republic of Slovenia and its Slovene Human Resources and Scholarship Fund and its Ad futura programme that helps fund R. Kolbl. Kepler was competitively selected as the 10th NASA Discovery mission. Funding for this mission is provided by the NASA Science Mission Directorate. 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 Keck Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors would like to thank the many people who gave so generously of their time to make the NASA Kepler mission a success. All spectra used in this paper are available at the Keck Observatory Archive. All Kepler data products are available to the public at the Mikulski Archive for Space Telescopes http://stdatu.stsci.edu/kepler and the spectra and their products are made available at the NExSci Exoplanet Archive and its CFOP website: http://exoplanetarchive.ipac.caltech.edu We thank the many observers who contributed to the measurements reported here. We gratefully acknowledge the efforts and dedication of the Keck Observatory staff, especially Scott Dahm, Hien Tran, and Grant Hill for support of HIRES, and Greg Wirth for support of remote observing. This work made use of the SIMBAD database (operated at CDS, Strasbourg, France) and NASAʼs Astrophysics Data System Bibliographic Services. This research has made use of the NASA Exoplanet Archive, which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program. Finally, the authors wish to extend special thanks to those of Hawaiian ancestry on whose sacred mountain of Mauna Kea we are privileged to be guests. Without their generous hospitality, the Keck observations presented herein would not have been possible.

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Erratum - Kolbl_2015_AJ_149_89.pdf

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