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J/AJ/153/117     KOIs companions from high-resolution imaging    (Hirsch+, 2017)

Assessing the effect of stellar companions from high-resolution imaging of Kepler Objects of Interest. Hirsch L.A., Ciardi D.R., Howard A.W., Everett M.E., Furlan E., Saylors M., Horch E.P., Howell S.B., Teske J., Marcy G.W. <Astron. J., 153, 117-117 (2017)> =2017AJ....153..117H (SIMBAD/NED BibCode)
ADC_Keywords: Planets ; Stars, double and multiple ; Photometry Keywords: binaries: visual - planets and satellites: detection - planets and satellites: fundamental parameters - techniques: high angular resolution - techniques: photometric Abstract: We report on 176 close (<2'') stellar companions detected with high-resolution imaging near 170 hosts of Kepler Objects of Interest (KOIs). These Kepler targets were prioritized for imaging follow-up based on the presence of small planets, so most of the KOIs in these systems (176 out of 204) have nominal radii <6R. Each KOI in our sample was observed in at least two filters with adaptive optics, speckle imaging, lucky imaging, or the Hubble Space Telescope. Multi-filter photometry provides color information on the companions, allowing us to constrain their stellar properties and assess the probability that the companions are physically bound. We find that 60%-80% of companions within 1'' are bound, and the bound fraction is >90% for companions within 0.5''; the bound fraction decreases with increasing angular separation. This picture is consistent with simulations of the binary and background stellar populations in the Kepler field. We also reassess the planet radii in these systems, converting the observed differential magnitudes to a contamination in the Kepler bandpass and calculating the planet radius correction factor, XR=Rp(true)/Rp(single). Under the assumption that planets in bound binaries are equally likely to orbit the primary or secondary, we find a mean radius correction factor for planets in stellar multiples of XR=1.65. If stellar multiplicity in the Kepler field is similar to the solar neighborhood, then nearly half of all Kepler planets may have radii underestimated by an average of 65%, unless vetted using high-resolution imaging or spectroscopy. Description: We report on 176 close (<2'') stellar companions detected with high-resolution imaging near 170 hosts of Kepler Objects of Interest (KOIs). Our sample consists of 170 stellar hosts of Kepler Objects of Interest (KOIs) observed with various high-resolution imaging campaigns. This sample was drawn from the overall sample of KOI stars observed with high-resolution imaging, described in the imaging compilation paper by Furlan et al. 2017 (Cat. J/AJ/153/71). We choose targets for this study by requiring that at least one companion was detected within 2'', and that the companion was detected in two or more filters, providing color information. We choose the 2'' separation limit to include all companions falling on the same Kepler pixel as the primary KOI host star. Furlan et al. 2017 (Cat. J/AJ/153/71) details the observations and measured differential magnitudes (Δm=m2-m1) for stars with high-resolution imaging, including our target systems. Each companion within 2'' must have at least two measured Δm values from the full set of filters used for follow-up observations, in order to be included in our sample. These filters include J-band, H-band, and K-band from adaptive optics imaging from the Keck/NIRC2, Palomar/PHARO, Lick/IRCAL, and MMT/Aries instruments; 562, 692 and 880nm filters from the Differential Speckle Survey Instrument (DSSI) at the Gemini North and WIYN telescopes; i and z bands from the AstraLux lucky imaging campaign at the Calar Alto 2.2m telescope; and LP600 and i bands from Palomar/RoboAO. We also include seeing-limited observations in the U-, B-, and V-bands from the UBV survey (Everett et al.) and "secure" detections (noise probability <10%) in the J-band from the UKIRT Kepler field survey. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table1.dat 79 176 Observed companions of the KOI host sample table2.dat 63 169 *Radius correction factors notes.dat 336 40 Notes
Note on table2.dat: Radius corrections for planets and planet candidates in the stellar KOI sample.
See also: J/AJ/152/8 : Impact of multiplicity on planetary systems I. (Kraus+, 2016) J/ApJ/822/86 : False positive prob. for Q1-Q17 DR24 KOIs (Morton+, 2016) J/ApJ/784/45 : Kepler's multiple planet candidates. III. (Rowe+, 2014) J/ApJS/211/2 : Revised stellar prop. of Q1-16 Kepler targets (Huber+, 2014) J/ApJS/210/25 : Transit timing variation for planetary pairs. II. (Xie, 2014) J/ApJS/210/1 : Asteroseismic study of solar-type stars (Chaplin+, 2014) J/ApJS/208/22 : Transit timing variation for 12 planetary pairs (Xie, 2013) J/ApJS/204/24 : Kepler planetary candidates. III. (Batalha+, 2013) J/ApJ/779/188 : Spectra of nearby late K and M Kepler stars (Mann+, 2013) J/ApJ/767/127 : Asteroseismic solutions for 77 Kepler stars (Huber+, 2013) J/ApJ/750/L37 : Stellar parameters of low-mass KOIs (Muirhead+, 2012) J/other/Nat/486.375 : Stellar parameters of KOI stars (Buchhave+, 2012) J/ApJS/190/1 : A survey of stellar families (Raghavan+, 2010) Byte-by-byte Description of file: table1.dat
Bytes Format Units Label Explanations
1- 4 I4 --- KOI Kepler Object of Interest (KOI) number (1) 6 A1 --- m_KOI [BC] Companion identifier (B or C) (1) 8- 11 F4.2 arcsec Sep [0.04/2] Separation (companion relative to primary) (1) 13- 16 F4.2 arcsec e_Sep [0.05/0.15] Uncertainty in Sep (1) 18- 23 F6.2 deg PA [1.7/357.8] Position angle (companion relative to primary), from North through East (1) 25- 28 F4.2 deg e_PA [1/5.16] Uncertainty in PA (1) 30- 34 F5.2 mag Dmag [-0.3/6.9]? Magnitude difference, Kepler band (ΔKp) (2) 36- 39 F4.2 mag e_Dmag [0/1.31]? Uncertainty in Dmag (2) 41- 45 F5.2 --- Coff [0/30.1] Average color offset, in σ unit (3) 47- 51 F5.2 --- e_Coff [0.07/24.2]? Uncertainty in Coff, in σ (3) 53- 60 E8.2 % Bckg [6.54e-06/10.9]? Background probability (4) 62- 66 F5.2 % Bound [0.94/18.64]? System bound probability (4) 68- 76 A9 --- System System designation (either Bound, Unbound, or Uncertain) (3) 78- 79 A2 --- Note Notes on system (5)
Note (1): From the imaging compilation paper of Furlan et al. 2017 (Cat. J/AJ/153/71). It is important to note that the term "companion" is used here to describe any star detected angularly nearby a KOI host star. It is not used to imply physical association. Instead, we will refer to physical binary or multiple systems as "bound" companions, and unphysical, line-of-sight alignments as "unbound" or "background" companions. Note (2): The magnitude difference in the Kepler bandpass between the primary and companion, taken from Furlan et al. 2017 (Cat. J/AJ/153/71), submitted for uncertain and unbound companions, and from this paper's isochrone models for the bound companions. Note (3): The Color Offset (Coff) indicates the difference, in units of the model and measurement uncertainty σ, between the modeled and observed colors of the companion. Better agreement means the companion is more likely to be physically bound. The error quoted for color offset is the standard deviation of the color offset, which describes the variation in the color offset among several different filter pairs. Systems with only a single color measurement have no reported standard deviation. Systems with poor agreement have higher color offset standard deviation, and are likely to be reclassified as "Uncertain" for the Designation. Note (4): Background probability and bound probability refer to the analysis using TRILEGAL galaxy models (Girardi et al. 2005A&A...436..895G) and solar neighborhood stellar multiplicity statistics (Raghavan et al. 2010, Cat. J/ApJS/190/1) respectively, as described in Section 3.2. Note (5): Notes on additional companions to individual systems, marked with letters, are from Appendix A.
Byte-by-byte Description of file: table2.dat
Bytes Format Units Label Explanations
1- 4 I4 --- KOI [5/7587] Kepler Object of Interest (KOI) number 6 I1 --- Ncomp [1/4] Number of companions detected within 2'' (1) 8- 12 F5.2 mag Dmag2 [-0.21/7.25] Magnitude difference, Kepler band for the secondary companion (ΔKp21) 14- 17 F4.2 mag Dmag3 [0.35/7.26]? Magnitude difference, Kepler band for the tertiary companion (ΔKp31) 19- 25 F7.2 --- Planet KOI of planetary candidate or confirmed planet 27- 32 F6.3 Rgeo Rp [0.51/33.62] Previous best estimate of the planet radius (Rp) (2) 34- 38 F5.3 Rgeo e_Rp [0.04/1.95]? Uncertainty in Rp (2) 40- 51 A12 --- r_Rp Literature reference for Rp (3) 53- 57 F5.3 --- XR1 [1/1.8] Calculated radius correction factor, assuming the planet orbits the primary (XR1) (4) 59- 63 F5.3 --- XR2 [1.2/5.1]? Calculated radius correction factor, assuming the planet orbits the secondary (XR2) (4)
Note (1): Three target KOI hosts have more than 2 companions within 2'', which we include in the dilution correction analysis. These are: KOI-387 (dmag-kep-41=7.58mag); KOI-2032 (dmag-kep-41=0.32mag); and KOI-3049 (dmag-kep-41=7.48mag, dmag-kep-51=4.92mag). Only one target, KOI-652, has 2 bound companions within 2'', allowing calculation of XR3 in this system. KOI-652 has XR-3=2.657. Note (2): Previous best estimate of the planet radius, either from the Kepler pipeline for planet candidates, or from the Exoplanet Archive (http://exoplanetarchive.ipac.caltech.edu/index.html) where literature sources are given in the following column for the confirmed planets. Note (3): Literature sources for the confirmed planets are defined as follows: Morton2016 = Morton et al. 2016 (Cat. J/ApJ/822/86); Rowe2014 = Rowe et al. 2014 (Cat. J/ApJ/784/45); VanEylen2015 = Van Eylen & Albrecht (2015ApJ...808..126V); Xie2013a = Xie 2013 (Cat. J/ApJS/208/22); Xie2014 = Xie 2014 (Cat. J/ApJS/210/25). Note (4): For stellar multiple systems, the ratio of the true planet radius to the assumed single radius can be estimated as: XR=[Rp(true)/Rp(single)]=(Rt/R1)[(Ftot/Ft)1/2] (1), where: Rt and Ft = Radius and Kepler bandpass flux from the transited star; Ftot = Kepler bandpass flux from all stars within the Kepler aperture; R1 = Radius of the assumed-single primary KOI star (Ciardi et al. 2015ApJ...805...16C). Note that Equation (1) only provides an estimate of the radius correction factor for a given system (see Section 5 in the paper for more details). Without significant observational follow-up, we cannot fully assess which star in a stellar multiple system is the planet host. We therefore calculate XRn, the planet correction factor assuming the planet host star is the nth component of the system, for each of our bound systems. In all cases but one, n=1 or 2, where the planets may orbit either the primary or bound companion. An indeterminate value for XR2 indicates a system in which we have too little information to calculate the radius correction factor because the system is uncertain or unbound, and we have no accurate estimate of the companion's stellar radius.
Byte-by-byte Description of file: notes.dat
Bytes Format Units Label Explanations
1- 2 A2 --- Code Note code 4-336 A333 --- Note Notes
History: From electronic version of the journal
(End) Prepared by [AAS]; Sylvain Guehenneux [CDS] 18-Jul-2017
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