Aavso paper Session I sunday Sunday, May 22, 2011, 9: 30 am – 12: 00 pm

227

Results From Kepler

Poster Session

Essex Ballroom

227.01

8:00 AM - 7:00 PM

In February 2011, the Kepler team announced the discovery of 1235 planet candidates. The majority of the candidates have radii smaller than Neptune and orbital periods less than fifty days. Although these data are preliminary and some candidates may prove to be astrophysical false positives, this sample of planet candidates is large enough to probe the underlying distribution of planets as a function of planetary radius, semimajor axis, and host star spectral type. We approach this problem by considering a variety of underlying distributions and assigning planets according to those distributions to the stars listed in the Kepler Input Catalog. We simulate the likelihood of detecting a transit of each planet around its assigned host star, accounting for the geometric probability of transit, the transit duration, and the number of transits that would be observed during the first year of the Kepler mission assuming square root of N improvement with the number of transits. We require a signal to noise ratio of 7 for detection as required by the Kepler team for inclusion in the list of Kepler Objects of Interest in the February data release, and we reject any underlying distribution of planets that differs significantly from the Kepler data. CDD acknowledges support from the National Science Foundation Graduate Research Fellowship Program.

227.02

8:00 AM - 7:00 PM

We present photometry of 4 transits of the exoplanet WASP-4b, each with a precision of approximately 500 ppm and a time sampling of 40-60s. During two of the transits we observed a short-lived, low-amplitude anomaly that we interpret as the occultation of a starspot by the planet. We also find evidence for a pair of similar anomalies in previously published photometry. The recurrence of these anomalies suggests that the stellar rotation axis is nearly aligned with the orbital axis, or else the star spot would not have remained on the transit chord. By analyzing the timings of the anomalies we find the sky-projected stellar obliquity to be 1^{+12}_{-14} degrees. This result is consistent with (and more constraining than) a recent observation of the Rossiter-McLaughlin effect. It suggests that the planet migration mechanism preserved the initially low obliquity, or else that tidal evolution has realigned the system. We discuss future applications of this method using data from the Kepler satellite, which will allow spin-orbit alignment to be probed for many other exoplanets.

227.03

Following up Kepler Objects of Interest Using Adaptive Optics Images

Elisabeth R. Adams¹, A. K. Dupree¹, C. Kulesa², D. W. McCarthy², Kepler Science Team
¹SAO, ²U. of Arizona.

8:00 AM - 7:00 PM

With the recent announcement of over 1200 candidate transiting planets, the Kepler space mission has an enormous need for high-quality follow-up observations, both to confirm the planetary nature of its candidates and to accurately measure their characteristics. The pixel size for Kepler images is just under 4", which means that close companion stars could dilute the signal from the target star, leading to an underestimate of the planetary parameters, or even a false positive detection. High-resolution images are thus vital to either detect potential contaminants or to rule out their presence with high confidence.

227.04

8:00 AM - 7:00 PM

We have observed about 200 targets in Kepler Cycle 1/2 Guest Observer programs. The sample of active star candidates was selected primarily using GALEX colors, and the Kepler light curves have revealed a rich variety of variability. Rotational modulation (typical periods a few days) due to starspots over the multi-year timeline of the Kepler observations will permit us to measure surface differential rotation and stellar magnetic cycles. On shorter timescales, the Kepler data show dramatic evidence of stellar pulsations across much of the HR diagram. Our selection criteria yielded a sample of magnetically active G and K dwarfs, which might show solar-like pulsations. It also yielded subsamples of several well-known pulsators (e.g., Delta Scuti stars) as well as pulsators that currently defy easy classification. We are systematically classifying and analyzing the pulsating stars in the our Kepler GO program. We are particularly interested in using pulsations to probe the interior properties of active G and K dwarfs, while the starspots serve as a probe of the convection zone and surface layers. We will present summary results for several different types of pulsation, and we will provide a detailed asteroseismic analysis of those stars in our sample that were observed to have both pulsations and magnetic activity.

227.05

8:00 AM - 7:00 PM

We report on preliminary results from our Kepler Cycle 2 GO program to observe low mass stars at high cadence (one observation per minute). The outstanding fidelity of the Kepler light curves reveals both starspot modulation and a large number of stellar flares. We investigate the flare amplitude, frequency and energy distributions and relate these to the better-known nearby flare stars in the solar neighborhood.

227.06

NGC 6811: An Intermediate-age Cluster In The Kepler Field

Kenneth Janes¹, S. Barnes², S. Meibom³, S. Hoq^1
1Boston Univ., ²Lowell Observatory, ³Center for Astrophysics.

8:00 AM - 7:00 PM

NGC 6811 is one of four open clusters located in the Kepler spacecraft field of view. We have observed the cluster on several occasions with the 1.08-meter Hall and 1.83-meter Perkins telescopes at Lowell Observatory. A well-defined main sequence and red giant "clump" are clearly visible in the color-magnitude diagram; several of the red clump stars have velocities consistent with cluster membership. We have analyzed the data from two photometric nights (one night with each telescope) and we derive the following parameters for the cluster: E(B-V) = 0.04 ± 0.04, (m-M)_o = 11.0 ± 0.2 and log(age) = 9.05 ± 0.10, all assuming a slightly metal-poor composition. We are continuing our analysis with additional photometry.

227.07

8:00 AM - 7:00 PM

We present a Bayesian Maximum A Posteriori (MAP) approach to systematic error removal in Kepler photometric data, in which a subset of highly correlated stars is used to establish the range of “reasonable” robust fit parameters, and hence mitigate the loss of astrophysical signal and noise injection on transit time scales (<3d), which afflict Least Squares (LS) fitting. A numerical and empirical approach is taken where the Bayesian Prior PDFs are generated from fits to the light curve distributions themselves versus an analytical approach, which uses a Gaussian fit to the Priors. Along with the systematic effects there are also Sudden Pixel Sensitivity Dropouts (SPSDs) resulting in abrupt steps in the light curves that should be removed. A joint fitting technique is therefore presented that simultaneously applies MAP and SPSD removal. The concept will be illustrated in detail by applying MAP to publicly available Kepler data, and give an overview of its application to all Kepler data collected through the present. We show that the light curve correlation matrix after treatment is diagonal, and present diagnostics such as correlation coefficient histograms, singular value spectra, and principal component plots. The benefits of MAP is shown applied to variable stars with RR Lyrae, harmonic, chaotic, and eclipsing binary waveforms, and examine the impact of MAP on transit waveforms and detectability of transiting planets. We conclude with a discussion of current work on selecting input vectors for the design matrix, generating the Prior PDFs and suppressing high-frequency noise injection with Bandpass Filtering. Funding for this work is provided by the NASA Science Mission Directorate.