Examinando por Autor "Rojas-Ayala, B."

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    A Catalog of Cool Dwarf Targets for the Transiting Exoplanet Survey Satellite
    (Institute of Physics Publishing, 2018-04) Muirhead, P.S.; Dressing, C.D.; Mann, A.W.; Rojas-Ayala, B.; Lépine, S.; Paegert, M.; De Lee, N.; Oelkers, R.
    We present a catalog of cool dwarf targets (V - > J 2.7, T eff ≳4000 K) and their stellar properties for the upcoming Transiting Exoplanet Survey Satellite (TESS), for the purpose of determining which cool dwarfs should be observed using two minute observations. TESS has the opportunity to search tens of thousands of nearby, cool, late K- and M-type dwarfs for transiting exoplanets, an order of magnitude more than current or previous transiting exoplanet surveys, such as Kepler, K2, and ground-based programs. This necessitates a new approach to choosing cool dwarf targets. Cool dwarfs are chosen by collating parallax and proper motion catalogs from the literature and subjecting them to a variety of selection criteria. We calculate stellar parameters and TESS magnitudes using the best possible relations from the literature while maintaining uniformity of methods for the sake of reproducibility. We estimate the expected planet yield from TESS observations using statistical results from the Kepler mission, and use these results to choose the best targets for two minute observations, optimizing for small planets for which masses can conceivably be measured using follow-up Doppler spectroscopy by current and future Doppler spectrometers. The catalog is available in machine readable format and is incorporated into the TESS Input Catalog and TESS Candidate Target List until a more complete and accurate cool dwarf catalog identified by ESA's Gaia mission can be incorporated. © 2018. The American Astronomical Society. All rights reserved.
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    Planet Detectability in the Alpha Centauri System
    (Institute of Physics Publishing, 2018) Zhao, L.; Fischer, D.A.; Brewer, J.; Giguere, M.; Rojas-Ayala, B.
    We use more than a decade of radial-velocity measurements for α Cen A, B, and Proxima Centauri from the High Accuracy Radial Velocity Planet Searcher, CTIO High Resolution Spectrograph, and the Ultraviolet and Visual Echelle Spectrograph to identify the M i sin and orbital periods of planets that could have been detected if they existed. At each point in a mass-period grid, we sample a simulated, Keplerian signal with the precision and cadence of existing data and assess the probability that the signal could have been produced by noise alone. Existing data places detection thresholds in the classically defined habitable zones at about M i sin of 53 M· for a Cen A, 8.4 M· for a Cen B, and 0.47 M· for Proxima Centauri. Additionally, we examine the impact of systematic errors, or "red noise" in the data. A comparison of white- and red-noise simulations highlights quasi-periodic variability in the radial velocities that may be caused by systematic errors, photospheric velocity signals, or planetary signals. For example, the red-noise simulations show a peak above white-noise simulations at the period of Proxima Centauri b. We also carry out a spectroscopic analysis of the chemical composition of the a Centauri stars. The stars have supersolar metallicity with ratios of C/O and Mg/Si that are similar to the Sun, suggesting that any small planets in the a Cen system may be compositionally similar to our terrestrial planets. Although the small projected separation of a Cen A and B currently hampers extreme-precision radial-velocity measurements, the angular separation is now increasing. By 2019, a Cen A and B will be ideal targets for renewed Doppler planet surveys.
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    The TESS Input Catalog and Candidate Target List
    (Institute of Physics Publishing, 2018-09) Stassun, K.G.; Oelkers, R.J.; Pepper, J.; Paegert, M.; Lee, N.D.; Torres, G.; Latham, D.W.; Charpinet, S.; Dressing, C.D.; Huber, D.; Kane, S.R.; Lépine, S.; Mann, A.; Muirhead, P.S.; Rojas-Ayala, B.; Silvotti, R.; Fleming, S.W.; Levine, A.; Plavchan, P.
    The Transiting Exoplanet Survey Satellite (TESS) will be conducting a nearly all-sky photometric survey over two years, with a core mission goal to discover small transiting exoplanets orbiting nearby bright stars. It will obtain 30 minute cadence observations of all objects in the TESS fields of view, along with two-minute cadence observations of 200,000-400,000 selected stars. The choice of which stars to observe at the two-minute cadence is driven by the need to detect small transiting planets, which leads to the selection of primarily bright, cool dwarfs. We describe the catalogs assembled and the algorithms used to populate the TESS Input Catalog (TIC), including plans to update the TIC with the incorporation of the Gaia second data release in the near future. We also describe a ranking system for prioritizing stars according to the smallest transiting planet detectable, and assemble a Candidate Target List (CTL) using that ranking. We discuss additional factors that affect the ability to photometrically detect and dynamically confirm small planets, and we note additional stellar populations of interest that may be added to the final target list. The TIC is available on the STScI MAST server, and an enhanced CTL is available through the Filtergraph data visualization portal system at the URL http://filtergraph.com/tess_ctl © 2018. The American Astronomical Society. All rights reserved.