Cataloging the Praesepe Cluster: Identifying Interlopers and Binary Systems Madeline Lucey1, Natalie Gosnell1, Andrew Mann2, Stephanie Douglas3 1Colorado College, 2Columbia University, 3Center for Astrophysics

Removing Systematics from K2 Studies The repurposed Kepler mission, K2 (Howell et al., 2014), has observed clusters of varying ages, including the Praesepe cluster (600 Myr), to investigate how exoplanets form and evolve (Mann et al., 2016). In order to make strong conclusions about exoplanet formation and evolution, we need to have accurate stellar properties of the host stars. By identifying interlopers and binary systems we can remove systematic biases that would otherwise contaminate our sample. Our survey focuses on stars that are too faint for Gaia to obtain accurate radial velocity measurements.

Observations Identifying Interlopers Our observations were obtained Radial Velocities with Gaussians Membership Probabilities at the WIYN 3.5-m Telescope We calculate the probability using the Hydra spectrograph. Cluster fit: 34.40 km s-1 Membership probabilities membership by: σ = 1.10 km s-1 based off of average radial We constrain our target stars by Fcluster(v) -1 PRV (v)= only choosing those that have Field fit: 27.17 km s velocities for 87 stars. We Ffield(v)+Fcluster(v) also been observed by K2. We σ = 71.08 km s-1 find 9 stars with also focused on stars determined membership probabilities where Fcluster(v) is the value of to be members based on their below 50%. the cluster-fitted Gaussian for proper motion and photometry the radial velocity v, and (Kraus & Hillenbrand, 2007), as Ffield(v) is the value of the field- one of the goals of this research fitted Gaussian for the same is to test the accuracy of these radial velocity (Vasilevskis et membership probabilities. al. 1958).

Single-Lined Spectroscopic Binarity Double-Lined Standard Deviations of Average RV Binaries Cross-Correlation Function of a Binary We identified 7 radial velocity Spectroscopic variables. These stars have a standard Binaries deviation of their radial velocity We identified 3 double-lined measurements that is ≥ 2.25 km s-1. By spectroscopic binaries. We visual inspection, any deviation greater identified them by visually than 2.25 km s-1 is an outlier and inspecting their spectra after therefore likely to be a binary system. finding two peaks in the We expect to find more radial velocity cross-correlation function. variables as we complete our sample.

Preliminary Results Praesepe Cluster Completeness We have ≥ 1 radial velocity measurements for 93% of our sample. In our sample of 229 stars, we However, we need ≥ 3 radial velocity measurements to be 95% calculated memberships confident that the star is not a velocity variable (Mathieu 1983). We probabilities for 87 stars with have ≥ 3 radial velocity measurements for 87 stars, or 38% of our ≥ 3 radial velocity sample. measurements. So far, we identify 10 binary systems. Nine of the 87 stars are not radial Future Directions velocity members. Six out of We plan to obtain further observations at the WIYN 3.5-m these nine interlopers had been Telescope. With these observations we hope to complete identified to be cluster membership probabilities for all stars in our sample and obtain members by Kraus & orbital solutions for the binary systems. We also plan to expand Hillenbrand 2007 using our survey to other clusters, including the Pleiades. photometry and proper motion methods. These results References: suggest that photometry and Howell, S.B., et al., 2014, PASP, 126, 398 Kraus, A. L., & Hillenbrand, L. A. 2007, AJ, 134, 2340 proper motion methods falsely Mann, A. W., et al. 2016, ApJ, 818, 46 identify members ~7% of the Mathieu, R. D. 1983, PhD Thesis, California Univ., Berkeley Vasilevskis, et al. 1958, AJ, 63, 387 time. Data presented herein were obtained at the WIYN Observatory from telescope time allocated to NN-EXPLORE through the scientific partnership of the National Aeronautics and Space Administration, the National Science Foundation, and the National Optical Astronomy Observatory. This work was supported by a NASAWIYN PI Data Award, administered by the NASA Exoplanet Science Institute.