THE APOGEE SPECTROSCOPIC SURVEY OFKEPLERPLANET HOSTS: FEASIBILITY, EFFICIENCY, AND FIRST RESULTS

Abstract

The Kepler mission has yielded a large number of planet candidates from among the Kepler Objects of Interest (KOIs), but spectroscopic follow-up of these relatively faint stars is a serious bottleneck in confirming and characterizing these systems. We present motivation and survey design for an ongoing project with the Sloan Digital Sky Survey III multiplexed Apache Point Observatory Galactic Evolution Experiment (APOGEE) near-infrared spectrograph to monitor hundreds of KOI host stars. We report some of our first results using representative targets from our sample, which include current planet candidates that we find to be false positives, as well as candidates listed as false positives that we do not find to be spectroscopic binaries. With this survey, KOI hosts are observed over ∼20 epochs at a radial velocity (RV) precision of 100-200 m s −1 . These observations can easily identify a majority of false positives caused by physically associated stellar or substellar binaries, and in many cases, fully characterize their orbits. We demonstrate that APOGEE is capable of achieving RV precision at the 100-200 m s −1 level over long time baselines, and that APOGEE's multiplexing capability makes it substantially more efficient at identifying false positives due to binaries than other single-object spectrographs working to confirm KOIs as planets. These APOGEE RVs enable ancillary science projects, such as studies of fundamental stellar astrophysics or intrinsically rare substellar companions. The coadded APOGEE spectra can be used to derive stellar properties (T eff , g log ) and chemical abundances of over a dozen elements to probe correlations of planet properties with individual elemental abundances.

Sloan Digital Sky Survey IV: Mapping the Milky Way, Nearby Galaxies, and the Distant Universe

“…Exoplanet host observations in Kepler fields to characterize host versus non-host properties and assess false positive rates (Fleming et al 2015). 8.…”

“…This strategy is adopted to yield detections of spectroscopic variability, most commonly velocity shifts due to binary companions with a typical radial velocity precision of ∼100-200 m s −1 . For stars observed more than the nominal three visits, it is possible to detect brown dwarf and planet mass companions (Fleming et al 2015;Troup et al 2016).…”

Target Selection for the SDSS-IV APOGEE-2 Survey

“…High-resolution, high-cadence spectroscopy can distinguish many of the "false-positive" cases from true planets (Fleming et al 2015). While the APOGEE RV precision is generally insufficient to detect planets directly, the data can identify several of the most common classes of false positives, including eclipsing binaries with grazing orbits, tertiary companions diluting binary system eclipse depths, and very low mass stars or brown dwarfs, with radii (and thus transit depths) similar to those of gas giant exoplanets but with much larger masses.…”

TOI-150: A Transiting Hot Jupiter in the TESS Southern CVZ*

“…Once TESS begins observations in the northern ecliptic hemisphere, where there is more overlap with the bulk of APOGEE-2 data, it will be possible to effectively "precover" a TESS -detection for a hot Jupiter in APOGEE-2 velocimetry. While high-precision spectroscopy is still required to derive the most precise planetary mass, APOGEE-2 data can serve to (i) vet TESS candidates for eclipsing binaries (e.g., Fleming et al 2015), (ii) provide spectroscopic parameters of the host star via ASPCAP (e.g., Wilson et al 2018), and (iii) derive masses for giant planets when sufficient APOGEE observations are available. When TESS begins northern observations in late 2019, the planned 16th data release of SDSS (DR16) will provide a large, complementary data set for validating, and in some cases confirming, exoplanets around bright stars.…”