37 575 Mit Kavli Institute For Astrophysics And Space Research

Cambridge, MA, United States

37 575 Mit Kavli Institute For Astrophysics And Space Research

Cambridge, MA, United States
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Tran K.,Kavli Institute for Astrophysics and Space Research | Levine A.,37 575 Mit Kavli Institute For Astrophysics And Space Research | Rappaport S.,Kavli Institute for Astrophysics and Space Research | Borkovits T.,Baja Astronomical Observatory | And 5 more authors.
Astrophysical Journal | Year: 2013

We report a study of the eclipse timing variations in contact binary systems, using long-cadence lightcurves from the Kepler archive. As a first step, observed minus calculated (O-C) curves were produced for both the primary and secondary eclipses of some 2000 Kepler binaries. We find ∼390 short-period binaries with O-C curves that exhibit (1) random walk-like variations or quasi-periodicities, with typical amplitudes of ±200-300 s, and (2) anticorrelations between the primary and secondary eclipse timing variations. We present a detailed analysis and results for 32 of these binaries with orbital periods in the range of 0.35 ± 0.05 days. The anticorrelations observed in their O-C curves cannot be explained by a model involving mass transfer, which, among other things, requires implausibly high rates of ∼0.01 MȮ yr-1. We show that the anticorrelated behavior, the amplitude of the O-C delays, and the overall random walk-like behavior can be explained by the presence of a starspot that is continuously visible around the orbit and slowly changes its longitude on timescales of weeks to months. The quasi-periods of ∼50-200 days observed in the O-C curves suggest values for k, the coefficient of the latitude dependence of the stellar differential rotation, of ∼0.003-0.013. © 2013. The American Astronomical Society. All rights reserved.


Rappaport S.,Massachusetts Institute of Technology | Swift J.,California Institute of Technology | Levine A.,37 575 Mit Kavli Institute For Astrophysics And Space Research | Joss M.,Massachusetts Institute of Technology | And 8 more authors.
Astrophysical Journal | Year: 2014

We have searched the Kepler light curves of ∼3900 M-star targets for evidence of periodicities that indicate, by means of the effects of starspots, rapid stellar rotation. Several analysis techniques, including Fourier transforms, inspection of folded light curves, "sonograms," and phase tracking of individual modulation cycles, were applied in order to distinguish the periodicities due to rapid rotation from those due to stellar pulsations, eclipsing binaries, or transiting planets. We find 178 Kepler M-star targets with rotation periods, P rot, of <2 days, and 110 with P rot < 1 day. Some 30 of the 178 systems exhibit two or more independent short periods within the same Kepler photometric aperture, while several have 3 or more short periods. Adaptive optics imaging and modeling of the Kepler pixel response function for a subset of our sample support the conclusion that the targets with multiple periods are highly likely to be relatively young physical binary, triple, and even quadruple M star systems. We explore in detail the one object with four incommensurate periods all less than 1.2 days, and show that two of the periods arise from one of a close pair of stars, while the other two arise from the second star, which itself is probably a visual binary. If most of these M-star systems with multiple periods turn out to be bound M stars, this could prove a valuable way discovering young hierarchical M-star systems; the same approach may also be applicable to G and K stars. The ∼5% occurrence rate of rapid rotation among the ∼3900 M star targets is consistent with spin evolution models that include an initial contraction phase followed by magnetic braking, wherein a typical M star can spend several hundred Myr before spinning down to periods longer than 2 days. © 2014. The American Astronomical Society. All rights reserved..


Rappaport S.,Kavli Institute for Astrophysics and Space Research | Deck K.,Kavli Institute for Astrophysics and Space Research | Levine A.,37 575 Mit Kavli Institute For Astrophysics And Space Research | Borkovits T.,Baja Astronomical Observatory | And 7 more authors.
Astrophysical Journal | Year: 2013

We present the results of a search through the photometric database of Kepler eclipsing binaries looking for evidence of hierarchical triple-star systems. The presence of a third star orbiting the binary can be inferred from eclipse timing variations. We apply a simple algorithm in an automated determination of the eclipse times for all 2157 binaries. The "calculated" eclipse times, based on a constant period model, are subtracted from those observed. The resulting O-C (observed minus calculated times) curves are then visually inspected for periodicities in order to find triple-star candidates. After eliminating false positives due to the beat frequency between the ∼1/2 hr Kepler cadence and the binary period, 39 candidate triple systems were identified. The periodic O-C curves for these candidates were then fit for contributions from both the classical Roemer delay and so-called physical delay, in an attempt to extract a number of the system parameters of the triple. We discuss the limitations of the information that can be inferred from these O-C curves without further supplemental input, e.g., ground-based spectroscopy. Based on the limited range of orbital periods for the triple-star systems to which this search is sensitive, we can extrapolate to estimate that at least 20% of all close binaries have tertiary companions. © 2013. The American Astronomical Society. All rights reserved..


Sanchis-Ojeda R.,Massachusetts Institute of Technology | Rappaport S.,Massachusetts Institute of Technology | Winn J.N.,Massachusetts Institute of Technology | Kotson M.C.,University of Hawaii at Manoa | And 2 more authors.
Astrophysical Journal | Year: 2014

We present the results of a survey aimed at discovering and studying transiting planets with orbital periods shorter than one day (ultra-short-period, or USP, planets), using data from the Kepler spacecraft. We computed Fourier transforms of the photometric time series for all 200,000 target stars, and detected transit signals based on the presence of regularly spaced sharp peaks in the Fourier spectrum. We present a list of 106 USP candidates, of which 18 have not previously been described in the literature. This list of candidates increases the number of planet candidates with orbital periods shorter than about six hours from two to seven. In addition, among the objects we studied, there are 26 USP candidates that had been previously reported in the literature which do not pass our various tests. All 106 of our candidates have passed several standard tests to rule out false positives due to eclipsing stellar systems. A low false positive rate is also implied by the relatively high fraction of candidates for which more than one transiting planet signal was detected. By assuming these multi-transit candidates represent coplanar multi-planet systems, we are able to infer that the USP planets are typically accompanied by other planets with periods in the range 1-50 days, in contrast with hot Jupiters which very rarely have companions in that same period range. Another clear pattern is that almost all USP planets are smaller than 2 R ⊕, possibly because gas giants in very tight orbits would lose their atmospheres by photoevaporation when subject to extremely strong stellar irradiation. Based on our survey statistics, USP planets exist around approximately (0.51 ± 0.07)% of G-dwarf stars, and (0.83 ± 0.18)% of K-dwarf stars. © 2014. The American Astronomical Society. All rights reserved..

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