2018AJ....155...68W

The Apache Point Observatory Galactic Evolution Experiment (APOGEE) has observed ∼600 transiting exoplanets and exoplanet candidates from Kepler (Kepler Objects of Interest, KOIs), most with >=18 epochs. The combined multi-epoch spectra are of high signal-to-noise ratio (typically >=100) and yield precise stellar parameters and chemical abundances. We first confirm the ability of the APOGEE abundance pipeline, ASPCAP, to derive reliable [Fe/H] and effective temperatures for FGK dwarf stars-the primary Kepler host stellar type-by comparing the ASPCAP-derived stellar parameters with those from independent high-resolution spectroscopic characterizations for 221 dwarf stars in the literature. With a sample of 282 close-in (P 100 days) KOIs observed in the APOGEE KOI goal program, we find a correlation between orbital period and host star [Fe/H] characterized by a critical period, P_crit=8.3_–4.1^+0.1 days, below which small exoplanets orbit statistically more metal-enriched host stars. This effect may trace a metallicity dependence of the protoplanetary disk inner radius at the time of planet formation or may be a result of rocky planet ingestion driven by inward planetary migration. We also consider that this may trace a metallicity dependence of the dust sublimation radius, but we find no statistically significant correlation with host T_eff and orbital period to support such a claim.