Investigation of Kepler Objects of Interest Stellar Parameters from Observed Transit Durations

The Kepler mission discovery of candidate transiting exoplanets (KOIs) enables a plethora of ensemble analysis of the architecture and properties of exoplanetary systems. We compare the observed transit durations of KOIs to a synthetic distribution generated from the known eccentricities of radial velocity (RV) discovered exoplanets. We find that the Kepler and RV distributions differ at a statistically significant level. We identify three related systematic trends that are likely due to errors in stellar radii, which in turn affect the inferred exoplanet radii and the distribution thereof, and prevent a valid analysis of the underlying ensemble eccentricity distribution. First, 15% of KOIs have transit durations >20% longer than the transit duration expected for an edge-on circular orbit, including 92 KOIs with transit durations >50% longer, when only a handful of such systems are expected. Second, the median transit duration is too long by up to ~25%. Random errors of <50% in the stellar radius are not adequate to account for these two trends, and they are present for all spectral types in the Kepler sample. We identify that incorrect estimates of stellar metallicity and extinction could account for these anomalies, rather than astrophysical effects such as eccentric exoplanets improbably transiting near apastron. Third, we find that the median transit duration is correlated with stellar radius, when no such trend is expected. All three effects are still present, although less pronounced, when considering only multiple transiting KOI systems which are thought to have a low false positive rate. Improved stellar parameters for KOIs are necessary for the validity of future ensemble tests of exoplanetary systems found by Kepler.Comment: PASP, in pres

Astro2020 Science White Paper Community Endorsement of the National Academies “Exoplanet Science Strategy” and “Astrobiology Strategy for the Search for Life in the Universe” Reports

The National Academies “Exoplanet Science Strategy” (ESS) and “Astrobiology Strategy for the Search for Life in the Universe” (AbS) reports present timely and consensus assessments of the current status, priorities and recommendations of the exoplanet and astrobiology science communities. We are signing our support for the findings and recommendations contained in the ESS and AbS as representing our consensus input to the Astrophysics 2020 decadal survey

A Spitzer Study of Debris Disks in the Young Nearby Cluster NGC 2232: Icy Planets Are Common around ~1.5-3 M☉ Stars

We describe Spitzer IRAC and MIPS observations of the nearby 25 Myr old open cluster NGC 2232. Combining these data with ROSAT All-Sky Survey observations, proper motions, and optical photometry/spectroscopy, we construct a list of highly probable cluster members. We identify one A-type star, HD 45435, that has definite excess emission at 4.5-24 μm indicative of debris from terrestrial planet formation. We also identify 2-4 late-type stars with possible 8 μm excesses and 8 early-type stars with definite 24 μm excesses. Constraints on the dust luminosity and temperature suggest that the detected excesses are produced by debris disks. From our sample of B and A stars, stellar rotation appears to be correlated with 24 μm excess, a result that would be expected if massive primordial disks evolve into massive debris disks. To explore the evolution of the frequency and magnitude of debris around A-type stars, we combine our results with data for other young clusters. The frequency of debris disks around A-type stars appears to increase from ~25% at 5 Myr to ~50%-60% at 20-25 Myr. Older A-type stars have smaller debris disk frequencies: ~20% at 50-100 Myr. For these ages, the typical level of debris emission increases from 5 to 20 Myr and then declines. Because 24 μm dust emission probes icy planet formation around A-type stars, our results suggest that the frequency of icy planet formation is ηi ≳ 0.5-0.6. Thus, most A-type stars (≈1.5-3 M☉) produce icy planets

A Young Planetary-Mass Object in the ρ Oph Cloud Core

We report the discovery of a young planetary-mass brown dwarf in the ρ Oph cloud core. The object was identified as such with the aid of a 1.5-2.4 μm low-resolution spectrum obtained using the NIRC instrument on the Keck I telescope. Based on the COND model, the observed spectrum is consistent with a reddened (A_V ~ 15-16) brown dwarf whose effective temperature is in the range 1200-1800 K. For an assumed age of 1 Myr, comparison with isochrones further constrains the temperature to ~1400 K and suggests a mass of ~2-3 Jupiter masses. The inferred temperature is suggestive of an early T spectral type, which is supported by spectral morphology consistent with weak methane absorption. Based on its inferred distance (~100 pc) and the presence of overlying visual absorption, it is very likely to be a ρ Oph cluster member. In addition, given the estimated spectral type, it may be the youngest and least massive T dwarf found so far. Its existence suggests that the initial mass function for the ρ Oph star-forming region extends well into the planetary-mass regime

The Peculiar Periodic YSO WL 4 in ρ Ophiuchus

We present the discovery of 130.87 day periodic near-infrared flux variability for the Class II T Tauri star WL 4 (= 2MASS J16271848-2429059, ISO-Oph 128). Our data are from the 2MASS Calibration Point Source Working Database, and constitute 1580 observations in J, H and K_s of a field in ρ Ophiuchus used to calibrate the 2MASS All-Sky Survey. We identify a light curve for WL 4 with eclipse amplitudes of ~0.4 mag lasting more than one-quarter the period, and color variations in J-H and H-K_s, of ~0.1 mag. The long period cannot be explained by stellar rotation. We propose that WL 4 is a triple YSO system, with an inner binary orbital period of 130.87 days. We posulate that we are observing each component of the inner binary alternately being eclipsed by a circum-binary disk with respect to our line of sight. This system will be useful in investigating terrestrial zone YSO disk properties and dynamics at ~1 Myr

Period Error Estimation for the Kepler Eclipsing Binary Catalog

The Kepler Eclipsing Binary Catalog (KEBC) describes 2165 eclipsing binaries identified in the 115 deg^2 Kepler Field based on observations from Kepler quarters Q0, Q1, and Q2. The periods in the KEBC are given in units of days out to six decimal places but no period errors are provided. We present the PEC (Period Error Calculator) algorithm, which can be used to estimate the period errors of strictly periodic variables observed by the Kepler Mission. The PEC algorithm is based on propagation of error theory and assumes that observation of every light curve peak/minimum in a long time-series observation can be unambiguously identified. The PEC algorithm can be efficiently programmed using just a few lines of C computer language code. The PEC algorithm was used to develop a simple model that provides period error estimates for eclipsing binaries in the KEBC with periods less than 62.5 days: log σ P ≈ – 5.8908 + 1.4425(1 + log P), where P is the period of an eclipsing binary in the KEBC in units of days. KEBC systems with periods ≥62.5 days have KEBC period errors of ~0.0144 days. Periods and period errors of seven eclipsing binary systems in the KEBC were measured using the NASA Exoplanet Archive Periodogram Service and compared to period errors estimated using the PEC algorithm