David P. Bennett

Publications (8)12.05 Total impact

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  Available from: Kouji Ohnishi

  Article: Measurements of Transit Timing Variations for WASP-5b

  Akihiko Fukui, Norio Narita, Paul J. Tristram, Takahiro Sumi, Fumio Abe, Yoshitaka Itow, Denis J. Sullivan, Ian A. Bond, Teruyuki Hirano, Motohide Tamura, [......], Kenta Nishimoto, Kouji Ohnishi, Kengo Omori, Yvette Perrott, Nicholas Rattenbury, Toshiharu Saito, Ljiljana Skuljan, Daisuke Suzuki, Winston L. Sweatman, Kohei Wada
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  ABSTRACT: We have observed 7 new transits of the 'hot Jupiter' WASP-5b using a 61 cm telescope located in New Zealand, in order to search for transit timing variations (TTVs) which can be induced by additional bodies existing in the system. When combined with other available photometric and radial velocity (RV) data, we find that its transit timings do not match a linear ephemeris; the best fit \chi^2 values of 32.2 with 9 degrees of freedom indicates that a marginal TTV signal has been observed at a confidence level of 99.982 %, or 3.7 \sigma. The standard deviation of the TTVs is as large as 70 s, and if this is real, it cannot be explained by other effects than that due to an additional body or bodies. We put the upper limit on the RV amplitude due to the possible secondary body as 21 m s^{-1}, which corresponds to its mass of 22-70 M_{Earth} over the period ratio from 0.2 to 5.0. From the TTVs data, using the numerical simulations, we place more stringent limits down to 2 M_{Earth} near 1:2 and 2:1 MMRs at the 3 \sigma level, assuming that the two planets are co-planer. We also put the upper limit on Trojan mass as 43 M_{Earth} (3 \sigma) using both RV and photometric data. Further follow-up photometric and spectroscopic observations will be required to confirm the reality of the TTV signal. Results such as these will provide important information for the migration mechanisms of planetary systems. Comment: 27 pages, 6 figures, 7 tables, submitted to PASJ
  09/2010;
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  Available from: Szymon Kozlowski

  Article: A Second Method to Photometrically Align Multi-Site Microlensing Light Curves: Source Color in Planetary Event MOA-2007-BLG-192

  Andrew Gould, Subo Dong, David P. Bennett, Ian A. Bond, Andrzej Udalski, Szymon Kozlowski
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  ABSTRACT: At present, microlensing light curves from different telescopes and filters are photometrically aligned by fitting them to a common model. We present a second method based on photometry of common field stars. If two spectral responses are similar (or the color of the source is known) then this technique can resolve important ambiguities that frequently arise when predicting the future course of the event, and that occasionally persist even when the event is over. Or if the spectral responses are different, it can be used to derive the color of the source when that is unknown. We present the essential elements of this technique and apply it to the case of MOA-2007-BLG-192, an important planetary event for which the system may be a terrestrial planet orbiting a brown dwarf or very low mass star. The refined estimate of the source color that we derive here, V-I=2.36 +- 0.03, will aid in making the estimate of the lens mass more precise. Comment: 16 pages including 3 figures. Submitted to ApJ
  10/2009;
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  Available from: ArXiv

  Article: The Demographics of Extrasolar Planets Beyond the Snow Line with Ground-based Microlensing Surveys

  B. Scott Gaudi, J. P. Beaulieu, David P. Bennett, Ian A. Bond, Subo Dong, Andrew Gould, Cheongho Han, Byeong-Gon Park, Takahiro Sumi
  [show abstract] [hide abstract]
  ABSTRACT: In the currently-favored paradigm of planet formation, the location of the snow line in the protoplanetary disk plays a crucial role. Determining the demographics of planets beyond the snow line of stars of various masses is thus essential for testing this model. Microlensing is sensitive to planets that are generally inaccessible to other methods, and in particular is most sensitive to cool planets at or beyond the snow line, including very low-mass (i.e. terrestrial) planets. Hence, microlensing is uniquely suited and so essential for a comprehensive study of this region. Microlensing is also sensitive to planets orbiting low-mass stars, free-floating planets, planets in the Galactic bulge and disk, and even planets in external galaxies. These planets can also provide critical constraints on models of planet formation. Although microlensing searches have so far detected only a handful of planets, these have already changed our understanding of planet formation beyond the snow line. Next generation microlensing surveys, which would be sensitive to tens of "cold Earths" in this region, are well advanced in design conception and are starting initial practical implementation.
  04/2009;
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  Available from: arxiv.org

  Article: Systematic Analysis of 22 Microlensing Parallax Candidates

  Shawn Poindexter, Cristina Afonso, David P. Bennett, Jean-Francois Glicenstein, Andrew Gould, Michał K. Szymański, and Andrzej Udalski
  [show abstract] [hide abstract]
  ABSTRACT: We attempt to identify all microlensing parallax events for which the parallax fit improves Δχ2 > 100 relative to a standard microlensing model. We outline a procedure to identify three types of discrete degeneracies (including a new one that we dub the "ecliptic degeneracy") and find many new degenerate solutions in 16 previously published and six unpublished events. Only four events have one unique solution, and the other 18 events have a total of 44 solutions. Our sample includes three previously identified black hole (BH) candidates. We consider the newly discovered degenerate solutions and determine the relative likelihood that each of these is a BH. We find that the lens of event MACHO-99-BLG-22 is a strong BH candidate (78%), event MACHO-96-BLG-5 is a marginal BH candidate (37%), and MACHO-98-BLG-6 is a weak BH candidate (2.2%). The lens of event OGLE-2003-BLG-84 may be a Jupiter-mass free-floating planet candidate based on a weak 3 σ detection of finite-source effects. We find that event MACHO-179-A is a brown dwarf candidate within ~100 pc of the Sun, mostly due to its very small projected Einstein radius, E = 0.23 ± 0.05 AU. As expected, these microlensing parallax events are biased toward lenses that are heavier and closer than average. These events were examined for xallarap (or binary-source motion), which can mimic parallax. We find that 23% of these events are strongly affected by xallarap.
  The Astrophysical Journal 12/2008; 633(2):914. · 6.02 Impact Factor
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  Available from: ArXiv

  Article: Ground-based Microlensing Surveys

  Andrew Gould, B. Scott Gaudi, David P. Bennett
  [show abstract] [hide abstract]
  ABSTRACT: Microlensing is a proven extrasolar planet search method that has already yielded the detection of four exoplanets. These detections have changed our understanding of planet formation ``beyond the snowline'' by demonstrating that Neptune-mass planets with separations of several AU are common. Microlensing is sensitive to planets that are generally inaccessible to other methods, in particular cool planets at or beyond the snowline, very low-mass (i.e. terrestrial) planets, planets orbiting low-mass stars, free-floating planets, and even planets in external galaxies. Such planets can provide critical constraints on models of planet formation, and therefore the next generation of extrasolar planet searches should include an aggressive and well-funded microlensing component. When combined with the results from other complementary surveys, next generation microlensing surveys can yield an accurate and complete census of the frequency and properties of planets, and in particular low-mass terrestrial planets.
  05/2007;
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  Available from: ArXiv

  Article: Discovery of a Very Bright, Nearby Gravitational Microlensing Event

  B. Scott Gaudi, Joseph Patterson, David S. Spiegel, Thomas Krajci, R. Koff, G. Pojmanski, Subo Dong, Andrew Gould, Jose L. Prieto, Cullen H. Blake, [......], David P. Bennett, Joshua S. Bloom, David Boyd, Pierre de Ponthiere, N. Mirabal, Christopher W. Morgan, Ronald R. Remillard, T. Vanmunster, R. Mark Wagner, Linda C. Watson
  [show abstract] [hide abstract]
  ABSTRACT: We report the serendipitous detection of a very bright, very nearby microlensing event. In late October 2006, an otherwise unremarkable A0 star at a distance ~1 kpc (GSC 3656-1328) brightened achromatically by a factor of nearly 40 over the span of several days and then decayed in an apparently symmetrical way. We present a light curve of the event based on optical photometry from the Center for Backyard Astrophysics and the All Sky Automated Survey, as well as near-infrared photometry from the Peters Automated Infrared Imaging Telescope. This light curve is well-fit by a generic microlensing model. We also report optical spectra, and Swift X-ray and UV observations that are consistent with the microlensing interpretation. We discuss and reject alternative explanations for this variability. The lens star is probably a low-mass star or brown dwarf, with a relatively high proper motion of >20 mas/yr, and may be visible using precise optical/infrared imaging taken several years from now. A modest, all-sky survey telescope could detect ~10 such events per year, which would enable searches for very low-mass planetary companions to relatively nearby stars. Comment: 11 pages, 5 figures. Accepted to ApJ, to appear in the May 1, 2008 issue (v678). Minor changes. Data available upon request
  The Astrophysical Journal 03/2007; · 6.02 Impact Factor
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  Available from: ArXiv

  Article: Characterization of Gravitational Microlensing Planetary Host Stars

  David P. Bennett, Jay Anderson, B. Scott Gaudi
  [show abstract] [hide abstract]
  ABSTRACT: The gravitational microlensing light curves that reveal the presence of extrasolar planets generally yield the planet-star mass ratio and separation in units of the Einstein ring radius. The microlensing method does not require the detection of light from the planetary host star. This allows the detection of planets orbiting very faint stars, but it also makes it difficult to convert the planet-star mass ratio to a value for the planet mass. We show that in many cases, the lens stars are readily detectable with high resolution space-based follow-up observations in a single passband. When the lens star is detected, the lens-source relative proper motion can also be measured, and this allows the masses of the planet and its host star to be determined and the star-planet separation can be converted to physical units. Observations in multiple passbands provide redundant information, which can be used to confirm this interpretation. For the recently detected super-Earth planet, OGLE-2005-BLG-169Lb, we show that the lens star will definitely be detectable with observations by the Hubble Space Telescope (HST) unless it is a stellar remnant. Finally, we show that most planets detected by a space-based microlensing survey are likely to orbit host stars that will be detected and characterized by the same survey.
  11/2006;
• Source

  Available from: arxiv.org

  Article: Identification of the OGLE-2003-BLG-235/MOA-2003-BLG-53 Planetary Host Star

  David P. Bennett, Jay Anderson, Ian A. Bond, Andrzej Udalski, Andrew Gould
  [show abstract] [hide abstract]
  ABSTRACT: We present the results of HST observations of the host star for the first definitive extrasolar planet detected by microlensing. The light curve model for this event predicts that the lens star should be separated from the source star by ~6mas at the time of the HST images. If the lens star is a late G, K or early M dwarf, then it will be visible in the HST images as an additional source of light that is blended with the source image. Unless the lens and source have exactly the same colors, its presence will also be revealed by a systematic shift between centroids of the source plus lens in different filter bands. The HST data indicates both of these effects: the HST source that matches the position of the source star is 0.21 magnitudes brighter in the ACS/HRC-F814W filter than the microlensing model predicts, and there is an offset of ~0.7mas between the centroid of this source in the F814W and F435W filter bands. We conclude the planetary host star has been detected in these HST images, and this identification of the lens star enables a complete solution of the lens system. The lens parameters are determined with a Bayesian analysis, averaging over uncertainties in the measured parameters, interstellar extinction, and allowing for the possibility of a binary companion to the source star. This yields a stellar mass of M_* = 0.63(+0.07/-0.09) M_solar and a planet mass of M_p = 2.6 (+0.8/-0.6) M_Jup at an orbital separation of 4.3 (+2.5/-0.8) AU. Thus, the lens system resembles our own Solar System, with a planet of ~3 Jupiter-masses in a Jupiter-like orbit around a star of two-thirds of a Solar mass. These conclusions can be tested with future HST images, which should reveal a broadening of the blended source-plus-lens point spread function due to the relative lens-source proper motion. Comment: 11 pages, with 3 figures. to appear in ApJ Lett (Aug 20 issue)
  06/2006;