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Wright J.T.,Pennsylvania State University | Eastman J.D.,Las Cumbres Observatory Global Telescope | Eastman J.D.,University of California at Santa Barbara
Publications of the Astronomical Society of the Pacific | Year: 2014

The goal of this paper is to establish the requirements of a barycentric correction with an rms of ≲1 cm s-1, which is an order of magnitude better than necessary for the Doppler detection of true Earth analogs (∼9 cm s-1). We describe the theory and implementation of accounting for the effects on precise Doppler measurements of motion of the telescope through space, primarily from rotational and orbital motion of the Earth, and the motion of the solar system with respect to target star (i.e., the “barycentric correction"). We describe the minimal algorithm necessary to accomplish this and how it differs from a naïve subtraction of velocities (i.e., a Galilean transformation). We demonstrate the validity of code we have developed from the California Planet Survey code via comparison with the pulsar timing package, TEMPO2. We estimate the magnitude of various terms and effects, including relativistic effects, and the errors associated with incomplete knowledge of telescope position, timing, and stellar position and motion. We note that chromatic aberration will create uncertainties in the time of observation, which will complicate efforts to detect true Earth analogs. Our code is available for public use and validation. © 2014. The Astronomical Society of the Pacific. All rights reserved. Source


French K.D.,University of Arizona | Arcavi I.,Las Cumbres Observatory Global Telescope | Arcavi I.,University of California at Santa Barbara | Zabludoff A.,University of Arizona
Astrophysical Journal Letters | Year: 2016

Tidal Disruption Events (TDEs) are transient events observed when a star passes close enough to a supermassive black hole to be tidally destroyed. Many TDE candidates have been discovered in host galaxies whose spectra have weak or no line emission yet strong Balmer line absorption, indicating a period of intense star formation that has recently ended. As such, TDE host galaxies fall into the rare class of quiescent Balmer-strong galaxies. Here, we quantify the fraction of galaxies in the Sloan Digital Sky Survey (SDSS) with spectral properties like those of TDE hosts, determining the extent to which TDEs are over-represented in such galaxies. Galaxies whose spectra have Balmer absorption HδA ? σ(HδA) > 4 Å (where σ(HδA) is the error in the Lick HδA index) and H? emission equivalent width (EW) < 3 Å have had a strong starburst in the last ∼Gyr. They represent 0.2% of the local galaxy population, yet host 3 of 8 (37.5%) optical/UV-selected TDE candidates. A broader cut, HδA > 1.31 Å and H? EW < 3 Å, nets only 2.3% of SDSS galaxies, but 6 of 8 (75%) optical/UV TDE hosts. Thus, quiescent Balmerstrong galaxies are over-represented among the TDE hosts by a factor of 33-190. The high-energy-selected TDE Swift J1644 also lies in a galaxy with strong Balmer lines and weak Hα emission, implying a >80 enhancement in such hosts and providing an observational link between the γ/X-ray-bright and optical/UV-bright TDE classes. © 2016. The American Astronomical Society. All rights reserved. Source


Brown T.M.,Las Cumbres Observatory Global Telescope | Latham D.W.,Harvard - Smithsonian Center for Astrophysics | Everett M.E.,U.S. National Optical Astronomy Observatories | Esquerdo G.A.,Harvard - Smithsonian Center for Astrophysics
Astronomical Journal | Year: 2011

We describe the photometric calibration and stellar classification methods used by the Stellar Classification Project to produce the Kepler Input Catalog (KIC). The KIC is a catalog containing photometric and physical data for sources in the Kepler mission field of view; it is used by the mission to select optimal targets. Four of the visible-light (g, r, i, z) magnitudes used in the KIC are tied to Sloan Digital Sky Survey magnitudes; the fifth (D51) is an AB magnitude calibrated to be consistent with Castelli & Kurucz (CK) model atmosphere fluxes. We derived atmospheric extinction corrections from hourly observations of secondary standard fields within the Kepler field of view. For these filters and extinction estimates, repeatability of absolute photometry for stars brighter than magnitude 15 is typically 2%. We estimated stellar parameters {T eff, log (g), log (Z), E B - V} using Bayesian posterior probability maximization to match observed colors to CK stellar atmosphere models. We applied Bayesian priors describing the distribution of solar-neighborhood stars in the color-magnitude diagram, in log (Z), and in height above the galactic plane. Several comparisons with samples of stars classified by other means indicate that for 4500K ≤T eff ≤ 6500 K, our classifications are reliable within about 200 K and 0.4 dex in log (g) for dwarfs, with somewhat larger log (g) uncertainties for giants. It is difficult to assess the reliability of our log (Z) estimates, but there is reason to suspect that it is poor, particularly at extreme T eff. Comparisons between the CK models and observed colors are generally satisfactory with some exceptions, notably for stars cooler than 4500K. Of great importance for the Kepler mission, for T eff ≤ 5400 K, comparison with asteroseismic results shows that the distinction between main-sequence stars and giants is reliable with about 98% confidence. Larger errors in log (g) occur for warmer stars, for which our filter set provides inadequate gravity diagnostics. The KIC is available through the MAST data archive. © 2011. The American Astronomical Society. All rights reserved. Source


Desert J.-M.,Harvard - Smithsonian Center for Astrophysics | Charbonneau D.,Harvard - Smithsonian Center for Astrophysics | Fortney J.J.,University of California at Santa Cruz | Madhusudhan N.,Princeton University | And 11 more authors.
Astrophysical Journal, Supplement Series | Year: 2011

This paper reports the detection and the measurements of occultations of the two transiting hot giant exoplanets Kepler-5b and Kepler-6b by their parent stars. The observations are obtained in the near-infrared with Warm-Spitzer Space Telescope and at optical wavelengths by combining more than a year of Kepler photometry. The investigation consists of constraining the eccentricities of these systems and of obtaining broadband emergent photometric data for individual planets. For both targets, the occultations are detected at the 3σ level at each wavelength with mid-occultation times consistent with circular orbits. The brightness temperatures of these planets are deduced from the infrared observations and reach T Spitzer = 1930 ± 100 K and T Spitzer = 1660 ± 120 K for Kepler-5b and Kepler-6b, respectively. We measure optical geometric albedos Ag in the Kepler bandpass and find Ag = 0.12 ± 0.04 for Kepler-5b and A g = 0.11 ± 0.04 for Kepler-6b, leading to upper an limit for the Bond albedo of A B ≤ 0.17 in both cases. The observations for both planets are best described by models for which most of the incident energy is redistributed on thedayside, with only less than 10% of the absorbed stellar flux redistributed to the nightside of these planets. © 2011. The American Astronomical Society. All rights reserved. Source


Christensen-Dalsgaard J.,University of Aarhus | Kjeldsen H.,University of Aarhus | Brown T.M.,Las Cumbres Observatory Global Telescope | Gilliland R.L.,US Space Telescope Science Institute | And 7 more authors.
Astrophysical Journal Letters | Year: 2010

In addition to its great potential for characterizing extra-solar planetary systems, the Kepler Mission is providing unique data on stellar oscillations. A key aspect of Kepler asteroseismology is the application to solar-like oscillations of main-sequence stars. As an example, we here consider an initial analysis of data for three stars in the Kepler field for which planetary transits were known from ground-based observations. For one of these, HAT-P-7, we obtain a detailed frequency spectrum and hence strong constraints on the stellar properties. The remaining two stars show definite evidence for solar-like oscillations, yielding a preliminary estimate of their mean densities. © 2010. The American Astronomical Society. All rights reserved. Source

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