David T. F. Weldrake

Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts, United States

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Publications (22)46.79 Total impact

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    ABSTRACT: Compared to bright star searches, surveys for transiting planets against fainter (V=12-18) stars have the advantage of much higher sky densities of dwarf star primaries, which afford easier detection of small transiting bodies. Furthermore, deep searches are capable of probing a wider range of stellar environments. On the other hand, for a given spatial resolution and transit depth, deep searches are more prone to confusion from blended eclipsing binaries. We present a powerful mitigation strategy for the blending problem that includes the use of image deconvolution and high resolution imaging. The techniques are illustrated with Lupus-TR-3 and very recent IR imaging with PANIC on Magellan. The results are likely to have implications for the CoRoT and KEPLER missions designed to detect transiting planets of terrestrial size.
    Proceedings of the International Astronomical Union 04/2009;
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    ABSTRACT: We present the results of a deep, wide-field transit survey targeting "Hot Jupiter" planets in the Lupus region of the Galactic plane conducted over 53 nights concentrated in two epochs separated by a year. Using the Australian National University 40-inch telescope at Siding Spring Observatory (SSO), the survey covered a 0.66 deg2 region close to the Galactic plane (b = 11°) and monitored a total of 110,372 stars (15.0 ≤ V ≤ 22.0). Using difference imaging photometry, 16,134 light curves with a photometric precision of σ < 0.025 mag were obtained. These light curves were searched for transits, and four candidates were detected that displayed low-amplitude variability consistent with a transiting giant planet. Further investigations, including spectral typing and radial velocity measurements for some candidates, revealed that of the four, one is a true planetary companion (Lupus-TR-3), two are blended systems (Lupus-TR-1 and 4), and one is a binary (Lupus-TR-2). The results of this successful survey are instructive for optimizing the observational strategy and follow-up procedure for deep searches for transiting planets, including an upcoming survey using the SkyMapper telescope at SSO.
    The Astronomical Journal 04/2009; 137(5):4368. · 4.97 Impact Factor
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    ABSTRACT: The EPOCh (Extrasolar Planet Observation and Characterization) component of the NASA EPOXI mission used the HRI camera aboard the Deep Impact spacecraft to observe seven transiting exoplanet systems from January through August 2008. The majority of these targets were each observed nearly continuously for several weeks at a time. We searched these high-precision time series for additional planets in these systems, which could be revealed either directly through their photometry transits, or indirectly through the variations these second planets induce on the times of transit of the previously known planet. In the case of one EPOXI target, the M-dwarf planetary system GJ 436, the presence of a second planet is perhaps indicated by the residual orbital eccentricity of the known hot Neptune companion. We will present current upper limits for the putative planet GJ 436c, and well as results for other targets.
    01/2009;
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    David T. F. Weldrake, Penny D. Sackett
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    ABSTRACT: We present a fast, efficient, and easy-to-apply computational method for the detection of planetary transits in large photometric data sets. The code was specifically produced to analyze an ensemble of 21,950 stars in the globular cluster 47 Tuc for the photometric signature indicative of a transiting hot Jupiter planet, the results of which are the subject of a separate paper. Using cross-correlation techniques and Monte Carlo-tested detection criteria, each photometric time series is compared with a database of transit models of appropriate depth and duration. The algorithm recovers transit signatures with high efficiency while maintaining a low false-detection probability, even in rather noisy data. The code has been optimized, and with a 3 GHz machine is capable of analyzing and producing candidate transits for 10,000 stars in 24 hr. We illustrate our algorithm by describing its application to our large 47 Tuc data set, for which the algorithm produced a weighted-mean transit recoverabilty spanning 85%-25% for orbital periods of 1-16 days (half the temporal span of the data set), despite gaps in the time series caused by the weather and observing the duty cycle. The code is easily adaptable and is currently designed to accept time series data produced using difference imaging analysis.
    The Astrophysical Journal 12/2008; 620(2):1033. · 6.73 Impact Factor
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    ABSTRACT: We present a strong case for a transiting hot Jupiter planet identified during a single-field transit survey toward the Lupus Galactic plane. The object, Lupus-TR-3b, transits a V = 17.4 K1 V host star every 3.91405 days. Spectroscopy and stellar colors indicate a host star with effective temperature 5000 ± 150 K, with a stellar mass and radius of 0.87 ± 0.04 M☉ and 0.82 ± 0.05 R☉, respectively. Limb-darkened transit fitting yields a companion radius of 0.89 ± 0.07 RJ and an orbital inclination of 88.3−0.8+1.3 deg. Magellan 6.5 m MIKE radial velocity measurements reveal a 2.4 σ K = 114 ± 25 m s−1 sinusoidal variation in phase with the transit ephemeris. The resulting mass is 0.81 ± 0.18 MJ and density 1.4 ± 0.4 g cm−3. Y-band PANIC image deconvolution reveals a V ≥ 21 red neighbor 0.4'' away which, although highly unlikely, we cannot conclusively rule out as a blended binary with current data. However, blend simulations show that only the most unusual binary system can reproduce our observations. This object is very likely a planet, detected from a highly efficient observational strategy. Lupus-TR-3b constitutes the faintest ground-based detection to date, and one of the lowest mass hot Jupiters known.
    The Astrophysical Journal 12/2008; 675(1):L37. · 6.73 Impact Factor
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    ABSTRACT: EPOXI (EPOCh + DIXI) is a NASA Discovery Program Mission of Opportunity using the Deep Impact flyby spacecraft. From January through August 2008, the EPOCh (Extrasolar Planet Observation and Characterization) Science Investigation used the HRI camera to gather precise, rapid cadence photometric time series of stars with known exoplanets in edge-on orbits. One of the EPOCh science goals is a search for additional planets at larger orbital radii in these systems. Such planets would be revealed either through the variations they induce on the times of transit of the known exoplanet in front of the parent star, or directly through the photometric transit of the second planet itself. I will describe our techniques for searching for additional planets orbiting the EPOCh targets, and for placing limits on their physical sizes. This search is especially interesting in the case of the GJ 436 system, since the eccentricity of the known Neptune-mass planet may point to the presence of a second planetary companion. Using our EPOCh observations for this system, we have the sensitivity to detect a planet as small as the Earth, even if the planet produces only a single transit event.
    08/2008; 40:385.
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    ABSTRACT: The NASA Discovery mission EPOXI, utilizing the Deep Impact flyby spacecraft, comprises two phases: EPOCh (Extrasolar Planet Observation and Characterization) and DIXI (Deep Impact eXtended Investigation). With EPOCh, we use the 30-cm high resolution visible imager to obtain ultraprecise photometric light curves of known transiting planet systems. We will analyze these data for evidence of additional planets, via transit timing variations or transits; for planetary moons or rings; for detection of secondary eclipses and the constraint of geometric planetary albedos; and for refinement of the system parameters. Over a period of four months, EPOCh observed four known transiting planet systems, with each system observed continuously for several weeks. Here we present an overview of EPOCh, including the spacecraft and science goals, and preliminary photometry results. Comment: 7 pages, 5 figures. To appear in the Proceedings of the 253rd IAU Symposium: "Transiting Planets", May 2008, Cambridge, MA
    Proceedings of the International Astronomical Union 07/2008;
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    Daniel D. R. Bayliss, Penny D. Sackett, David T. F. Weldrake
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    ABSTRACT: SuperLupus is a deep transit survey monitoring a Galactic Plane field in the Southern hemisphere. The project is building on the successful Lupus Survey, and will double the number of images of the field from 1700 to 3400, making it one of the longest duration deep transit surveys. The immediate motivation for this expansion is to search for longer period transiting planets (5-8 days) and smaller radii planets. It will also provide near complete recovery for the shorter period planets (1-3 days). In March, April, and May 2008 we obtained the new images and work is currently in progress reducing these new data. Comment: 3 pages, 2 figures, to appear in the Proceedings of IAU Symposium 253, 2008: Transiting Planets
    Proceedings of the International Astronomical Union 07/2008;
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    ABSTRACT: EPOXI (EPOCh + DIXI) is a NASA Discovery Program Mission of Opportunity using the Deep Impact flyby spacecraft. The EPOCh (Extrasolar Planet Observation and Characterization) Science Investigation will gather photometric time series of known transiting exoplanet systems from January through August 2008. Here we describe the steps in the photometric extraction of the time series and present preliminary results of the first four EPOCh targets.
    Proceedings of the International Astronomical Union 04/2008; 4:470 - 473.
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    David T. F. Weldrake, Daniel D. R. Bayliss
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    ABSTRACT: We have conducted a wide-field photometric survey in a single 52' × 52' field towards the Lupus Galactic Plane in an effort to detect transiting Hot Jupiter planets. The data set also led to the detection of 494 field variables, all of which are new discoveries. This paper presents an overview of the project, along with the total catalog of variables, which comprises 190 eclipsing binaries (of contact, semi-contact, and detached configurations), 51 miscellaneous pulsators of various types, 237 long-period variables (P >= 2 d), 11 delta Scuti stars, 4 field RR Lyrae (3 disk and 1 halo) and 1 irregular variable. Our survey provides a complete catalog of W UMa eclipsing binaries in the field to V = 18.8, which display a Gaussian period distribution of 0.277 ± 0.036 d. Several binary systems are likely composed of equal-mass M-dwarf components and others display evidence of mass transfer. We find 17 candidate blue stragglers and one binary that has the shortest period known, 0.2009 d (V = 20.9). The frequency of eclipsing binaries (all types) is found to be 1.7 ± 0.4 × 10-3 per star, substantially higher (by a factor of 3-10) than previously determined in the halos of the globular clusters 47 Tuc and omega Cen. This indicates that cluster dynamics aid mass segregation and binary destruction.
    The Astronomical Journal 01/2008; · 4.97 Impact Factor
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    David T. F. Weldrake, Penny D. Sackett, Terry J Bridges
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    ABSTRACT: We present the results of a deep, wide-field search for transiting hot Jupiter (HJ) planets in the globular cluster omega Centauri. As a result of a 25 night observing run with the ANU 40 inch (1 m) telescope at Siding Spring Observatory, a total of 109,726 stellar time series composed of 787 independent data points were produced with differential photometry in a 52'×52' (0.75 deg2) field centered on the cluster core, but extending well beyond. Taking into account the size of transit signals as a function of stellar radius, 45,406 stars have suitable photometric accuracy (<=0.045 mag to V=19.5) to search for transits. Of this sample, 31,000 stars are expected to be main-sequence cluster members. All stars, both cluster and foreground, were subjected to a rigorous search for transit signatures; none were found. Extensive Monte Carlo simulations based on our actual data set allow us to determine the sensitivity of our survey to planets with radii ~1.5 RJup and thus place statistical upper limits on their occurrence frequency F. Smaller planets are undetectable in our data. At 95% confidence, the frequency of very hot Jupiters (VHJs) with periods P satisfying 1 day<P<3 days can be no more than FVHJ<1/1040 in omega Cen. For HJs and VHJs distributed uniformly over the orbital period range 1 day<P<5 days, FVHJ+HJ<1/600. Our limits on large, short-period planets are comparable to those recently reported for other Galactic fields, despite being derived with less telescope time.
    The Astrophysical Journal 01/2008; · 6.73 Impact Factor
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    ABSTRACT: We report the detection of a giant planet candidate in a close binary system. This result was obtained from the follow-up radial velocity (RV) measurements of MACHO 120.22303.5389 (MAESTRO-1), a planetary transit candidate from the MACHO project. From the stellar spectra we determined the fundamental stellar parameters and derived a primary mass of 1.36 Mo. The spectroscopic observations show a short-period
    Fischer, D ; Rasio, F. A.; Thorsett, S. E. ; Wolszczan, A.: Extreme Solar Systems, ASP, 113-115 (2008). 01/2008;
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    ABSTRACT: We present the results of a comprehensive search for stellar variability in the globular cluster 47 Tucanae. Using the Mount Stromlo 40 inch (1 m) telescope at Siding Spring Observatory and a combined V + R filter, we have detected 100 variable stars across a 52' × 52' field centered on the cluster. The main aim of this project is to search for transiting "hot Jupiter" planets in this cluster, the results of which shall be discussed in a separate paper. Here we present the V + R light curves and preliminary investigations of the detected variable stars, which comprise 28 eclipsing binaries (21 contact binaries and 7 detached systems), 45 RR Lyrae stars (41 of which belong to the Small Magellanic Cloud and 4 seemingly to the Galactic halo), and 20 K-giant long-period variables (LPVs). We also detected four δ Scuti stars, one type I Cepheid, and one type II Cepheid. One variable appears to be a possible dust-enshrouded SMC star with a short-period pulsation. Of these 100 variables, 69 are new discoveries. Our eclipsing binary sample indicates a clear radial segregation in period and includes two binaries that are seemingly orbited by low-luminosity stellar companions. One RR Lyrae star shows a Blazhko effect with remarkable regularity. Those variables previously known are cross-identified with a study by Kaluzny and coworkers. In agreement with previous studies, this work shows that the relative frequency of detectable variable stars (particularly contact binaries) in 47 Tuc is very low compared to other studied regions. Distance moduli of 18.93±0.24 for the Small Magellanic Cloud and 13.14±0.25 for 47 Tuc have been estimated from our sample and are in agreement with values previously published. The total database presented here contains V and I photometry for 43,067 47 Tuc field stars (13.0 ≤ V ≤ 21.0), along with 33 night V + R light curves and astrometry for 109,866 stars (14.5 ≤ V ≤ 22.5).
    The Astronomical Journal 12/2007; 128(2):736. · 4.97 Impact Factor
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    David T. F. Weldrake
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    ABSTRACT: Star clusters provide an excellent opportunity to study the role of environment on determining the frequencies of short period planets. They provide a large sample of stars which can be imaged simultaneously, with a common distance, age and pre-determined physical parameters. This allows the search to be tailor-made for each specific cluster. Several groups are attempting to detect transiting planets in open clusters. Three previous surveys have also targeted the two brightest globular clusters. No cluster survey has yet detected a planet. This contribution presents a brief overview of the field, highlighting the pros and cons of performing such a search, and presents the expected and current results, with implications for planetary frequencies in regions of high stellar density and low metallicity.
    10/2007;
  • C. Afonso, D. Weldrake, T. Henning
    07/2007;
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    David T. F. Weldrake, Johny Setiawan, Patrick Weise, Thomas Henning
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    ABSTRACT: We present preliminary results on the radial velocity follow-up of a planetary transit candidate (P=2.43d, V=15.4) detected during the MACHO project. The photometry is consistent with a grazing transit of an object with radius >=1.8RJ orbiting a K dwarf star, and is the brightest best candidate detected from MACHO. Results from the 2.2m MPG/ESO telescope and FEROS (R=48,000) in May 2006 display an apparent radial velocity variation with amplitude ~650m/s with the same period as the transit, and a solar-type primary. This is consistent with an orbiting companion of mass ~4MJ. However, further observations display an additional secondary long-period variation with amplitude of several km/s, indicating the presence of a third body. The system is likely a low mass eclipsing binary orbiting the solar-type primary. Further observations are planned to fully characterize the system.
    01/2007;
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    David T. F. Weldrake, Penny D. Sackett, Terry J Bridges
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    ABSTRACT: We have performed a large ground-based search for transiting Hot Jupiter planets in the outer regions of the globular clusters 47 Tucanae and omega Centauri. The aim was to help understand the role that environmental effects play on Hot Jupiter formation and survivability in globular clusters. Using the ANU 1m telescope and a 52' X 52' field, a total of 54,000 solar-type stars were searched for transits in both clusters with fully tested transit-finding algorithms. Detailed Monte Carlo simulations were performed to model the datasets and calculate the expected planet yields. Seven planets were expected in 47 Tuc, and five in omega Cen. Despite a detailed search, no planet-like candidates were identified in either cluster. Combined with previous theoretical studies of planet survivability, and the HST null result in the core of 47 Tuc, the lack of detections in the uncrowded outer regions of both clusters indicates that stellar metallicity is the dominant factor inhibiting Hot Jupiter formation in the cluster environment.
    01/2007;
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    David T. F. Weldrake, Penny D. Sackett, Terry J Bridges
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    ABSTRACT: We present a variable star catalog of an extensive ground-based wide-field variability survey in the globular cluster omega Centauri. Using the Australian National University 40 inch (1 m) telescope at Siding Spring Observatory, the cluster was observed with a 52'×52' (0.75 deg2) field for 25 nights. A total of 187 variable stars were identified in the field, 81 of which are new discoveries. This work comprises the widest field variability survey yet undertaken for this cluster. Here we present the V+R light curves and preliminary analysis of the detected variable stars, comprising 58 eclipsing binaries, 69 RR Lyrae stars, 36 long-period variables (P>=2 days), and 24 miscellaneous pulsators including 15 SX Phoenicis stars and two type II Cepheids. Analysis of the eclipsing binary radial distribution has revealed an apparent lack of binaries in the 8'-15' range, perhaps indicating two separate binary populations. Four detached binaries have short periods (<2.5 days) and are likely composed of low-mass M-dwarf components, useful for testing stellar evolution models. One further detached system has a period of 0.8 days, and due to the blueness of the system could be composed of white dwarf stars. Analysis of the RR Lyrae sample has produced a reddening-corrected distance modulus (also accounting for metallicity spread) for the cluster of 13.68+/-0.27, a result consistent with previously published values. This paper also presents a total stellar database comprising V and I photometry (with astrometry better than 0.25") for 203,892 stars with 12.0<=V<=21.0 and 25 night V+R light curves for 109,726 stars (14.0<=V<=22.0) for both the cluster and the field.
    The Astronomical Journal 01/2007; · 4.97 Impact Factor
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    ABSTRACT: A 52'X52' field in the Lupus Galactic plane was observed with the ANU 1m telescope for 53 nights during 2005 and 2006 in a search for transiting Hot Jupiter planets. A total of 2200 images were obtained. We have sampled 120,000 stars via differential photometry, of which ~26,000 have sufficient photometric accuracy (<=2.5%) with which to perform a search for transiting planets. Ongoing analysis has led to the identification of three candidates. We present an overview of the project, including the results of radial velocity analysis performed on the first candidate (Lupus-TR-1) with the 4m AAT telescope. The third candidate, Lupus-TR-3 (P=3.914d, V~16.5), is a particularly strong case for a giant planet of 1.0-1.2RJ orbiting a solar-like primary star with a near central transit. Further observations are planned to determine its nature.
    12/2006;
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    ABSTRACT: The search for extrasolar planets is nowadays one of the most promising science drivers in Astronomy. The radial velocity technique proved to be successful in planet hunting, harvesting more than a hundred planets to date. In these last recent years, the transit method has come to fruition, with the detection of seven Jupiter-mass extrasolar transiting planets in close-in orbits ({ AU). Currently, the radius of planets can only be determined from transiting planets, representing the principal motivation and strength of this technique. The MPIA is presently building the Large Area Imager (LAIWO) for the 1m telescope in the Wise Observatory, Israel. LAIWO will have a field of view of one square degree. An intensive search for extra-solar planets will be performed with the 1m Wise telescope, together with the 1.2m MONET telescope in Texas. We will monitor three fields at a given time during three years and more than 200 nights per year. We expect several dozens of extra-solar planets.
    Proceedings of the International Astronomical Union 01/2005;

Publication Stats

165 Citations
46.79 Total Impact Points

Institutions

  • 2008–2009
    • Harvard-Smithsonian Center for Astrophysics
      • Smithsonian Astrophysical Observatory
      Cambridge, Massachusetts, United States
  • 2007–2008
    • Max Planck Institute for Astronomy
      Heidelburg, Baden-Württemberg, Germany
  • 2004–2008
    • Australian National University
      • Research School of Astronomy & Astrophysics
      Canberra, Australian Capital Territory, Australia