Identifying Bound Stellar Companions to Kepler

Identifying Bound Stellar Companions to Kepler

Identifying Bound Stellar Companions to Kepler Exoplanet Host Stars With Speckle Imaging Collaborators: Nicole Hess Patrick Thayer, Elliott Horch SCSU, James Davidson, UVA, Southern Connecticut State Brian Baptista, Aerospace Corp. University Steve Howell, NASA Ames Mark Everett, NOAO Are Kepler double stars gravitationally bound? • Horch+ 2014: A statistical approach using the TRILEGAL galaxy model and Raghavan statistics for binaries. Based on separation and magnitude difference, line-of-sight companions have different characteristics than bound companions, and the majority of companions detected via speckle imaging fit the profile of bound companions. • Matson+ 2018 shows a similar result for companions to K2 planet hosts. Are Kepler double stars BOUND gravitationally bound? • Hirsch+ 2017: Use photometry derived from high-resolution imaging to do isochrone fitting. If the companion can be fit by the same isochrone, the system is coeval and therefore likely to be bound. Common Proper Motion as Another Test • Wittrock+ 2016. HD 2638 is a common proper motion pair. Speckle observations, with well-calibrated astrometry over 3 years is used to confirm this. • High proper motion: (-107 mas/yr, -223 mas/yr) Easy! Proper Motions of the Kepler Binary Sample Speckle Imaging t=0.00s t=0.05s t=0.10s t=0.15s DSSI Astrometric Precision at WIYN • Horch+ 2017. 2-3 mas precision per observation at WIYN; about 1 mas at Gemini. Astrometry from Speckle Data Kepler 1 Kepler 907 Step 1: Identify secondary in a rudimentary reconstructed image produced by the data reduction pipeline. V=11.25, Δm=4 V=11.16, Δm=1 Astrometry from Speckle Data Kepler 907 - Data Kepler 907 - Fit Step 2: Perform a fringe fit in the Fourier domain to get final relative astrometry and photometry. Kepler-13 (KOI 13) Kepler-14 (KOI 98) Kepler-449 (KOI 270) KOI-984 KOI-5578 Kepler-1002 (KOI 1890) Kepler-450 (KOI 279) Brief Comparison with Hirsch et al. Star Time Rel. Proper Phot. This work Comment Baseline Motion Motion Analysis (yr) (mas/yr) (mas/yr) (Hirsch et al) KOI 13 5.4 3.0 10.2 Bound Bound? Very little relative motion. KOI 98 5.3 1.8 17.4 Bound Bound Very little relative motion. KOI 270 5.8 2.2 45.4 Unbound Bound Inclination near 90 degrees? KOI 984 5.8 7.7 21.1 Unbound Unbound Large relative motion. KOI 1890 2.7 4.9 15.1 Bound Unbound? Rel. motion mostly in θ. KOI 5578 2.3 4.0 10.2 Uncertain Bound? Modest rel. motion. Conclusion and What’s Next? • High-Precision astrometry is possible using speckle imaging techniques even on very close binary systems. Well-calibrated astrometry makes this p • Can identify common proper motion pairs in observations dating back to 2010. • A couple of systems we have studied appear to show some relative motion. • More work to do to finish the entire sample. Further observations will be needed in some cases. • K2 will provide another opportunity for this methodology. Systems are closer, and therefore a given angular separation means a smaller physical separation. N.M.H. and E.P.H. would like to thank the Research and Scholarship Advisory Committee and the Provost’s Office at Southern Connecticut State University for supporting this work with an SCSU undergraduate research grant. Some of the observations in the paper made use of the NN-EXPLORE Exoplanet and Stellar Speckle Imager (NESSI). NESSI was funded by the NASA Exoplanet Exploration Program and the NASA Ames Research Center. NESSI was built at the Ames Research Center by Steve B. Howell, Nic Scott, Elliott P. Horch, and Emmett Quigley. .

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