Author
Tim Natusch
Other affiliations: Ohio State University
Bio: Tim Natusch is an academic researcher from Auckland University of Technology. The author has contributed to research in topics: Gravitational microlensing & Planet. The author has an hindex of 37, co-authored 147 publications receiving 5399 citations. Previous affiliations of Tim Natusch include Ohio State University.
Papers published on a yearly basis
Papers
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TL;DR: In this paper, the authors presented the first measurement of the planet frequency beyond the "snow line," for the planet-to-star mass-ratio interval during 2005-2008 microlensing events during the survey-plus-follow-up high-magnification channel.
Abstract: We present the first measurement of the planet frequency beyond the "snow line," for the planet-to-star mass-ratio interval –4.5 200) microlensing events during 2005-2008. The sampled host stars have a typical mass M_(host) ~ 0.5 M_⊙, and detection is sensitive to planets over a range of planet-star-projected separations (s ^(–1)_(max)R_E, s_(max)R_E), where R_E ~ 3.5 AU(M_(host)/M_⊙)^(1/2) is the Einstein radius and s_(max) ~ (q/10^(–4.3))^(1/3). This corresponds to deprojected separations roughly three times the "snow line." We show that the observations of these events have the properties of a "controlled experiment," which is what permits measurement of absolute planet frequency. High-magnification events are rare, but the survey-plus-follow-up high-magnification channel is very efficient: half of all high-mag events were successfully monitored and half of these yielded planet detections. The extremely high sensitivity of high-mag events leads to a policy of monitoring them as intensively as possible, independent of whether they show evidence of planets. This is what allows us to construct an unbiased sample. The planet frequency derived from microlensing is a factor 8 larger than the one derived from Doppler studies at factor ~25 smaller star-planet separations (i.e., periods 2-2000 days). However, this difference is basically consistent with the gradient derived from Doppler studies (when extrapolated well beyond the separations from which it is measured). This suggests a universal separation distribution across 2 dex in planet-star separation, 2 dex in mass ratio, and 0.3 dex in host mass. Finally, if all planetary systems were "analogs" of the solar system, our sample would have yielded 18.2 planets (11.4 "Jupiters," 6.4 "Saturns," 0.3 "Uranuses," 0.2 "Neptunes") including 6.1 systems with two or more planet detections. This compares to six planets including one two-planet system in the actual sample, implying a first estimate of 1/6 for the frequency of solar-like systems.
381 citations
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Ohio State University1, University of Notre Dame2, University of Warsaw3, Tel Aviv University4, Lawrence Livermore National Laboratory5, Princeton University6, University of Concepción7, University of Cambridge8, Chungbuk National University9, Korea Astronomy and Space Science Institute10, Nagoya University11, Massey University12, University of Auckland13, University of Canterbury14, Victoria University of Wellington15, Konan University16, University of Manchester17, Vaughn College of Aeronautics and Technology18, University of Exeter19, Centre national de la recherche scientifique20, Liverpool John Moores University21, University of St Andrews22, University of Tasmania23, Paul Sabatier University24, Dartmouth College25, University of Oxford26
TL;DR: Two planets with masses that could not have been detected with other techniques are identified; their discovery from only six confirmed microlensing planet detections suggests that solar system analogs may be common.
Abstract: Searches for extrasolar planets have uncovered an astonishing diversity of planetary systems, yet the frequency of solar system analogs remains unknown. The gravitational microlensing planet search method is potentially sensitive to multiple-planet systems containing analogs of all the solar system planets except Mercury. We report the detection of a multiple-planet system with microlensing. We identify two planets with masses of ∼0.71 and ∼0.27 times the mass of Jupiter and orbital separations of ∼2.3 and ∼4.6 astronomical units orbiting a primary star of mass ∼0.50 solar mass at a distance of ∼1.5 kiloparsecs. This system resembles a scaled version of our solar system in that the mass ratio, separation ratio, and equilibrium temperatures of the planets are similar to those of Jupiter and Saturn. These planets could not have been detected with other techniques; their discovery from only six confirmed microlensing planet detections suggests that solar system analogs may be common.
341 citations
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Nagoya University1, University of Notre Dame2, Massey University3, University of Warsaw4, Royal Society5, University of St Andrews6, Centre national de la recherche scientifique7, Ohio State University8, Lawrence Livermore National Laboratory9, Institute for Advanced Study10, University of Auckland11, University of Canterbury12, Victoria University of Wellington13, Konan University14, College of Industrial Technology15, Institut d'Astrophysique de Paris16, University of Tasmania17, University of Chile18, National Institute for Space Research19, Liverpool John Moores University20, European Southern Observatory21, University of Stuttgart22, Ames Research Center23, University of the Free State24, University of Rijeka25, University of Vienna26, Niels Bohr Institute27, NASA Exoplanet Science Institute28, Space Telescope Science Institute29, Las Cumbres Observatory Global Telescope Network30, Heidelberg University31, University of Concepción32, Texas A&M University33, Chungbuk National University34, Korea Astronomy and Space Science Institute35, Auckland University of Technology36
TL;DR: The OGLE-2007-BLG-368Lb with a planet-star mass ratio of q = [9.5 ± 2.1] × 10^(-5] via gravitational microlensing was discovered in real-time thanks to the high cadence of the Microlensing Observations in Astrophysics survey and intensive followup observations.
Abstract: We present the discovery of a Neptune-mass planet OGLE-2007-BLG-368Lb with a planet-star mass ratio of q = [9.5 ± 2.1] × 10^(-5) via gravitational microlensing. The planetary deviation was detected in real-time thanks to the high cadence of the Microlensing Observations in Astrophysics survey, real-time light-curve monitoring and intensive follow-up observations. A Bayesian analysis returns the stellar mass and distance at M_l = 0.64^(+0.21)_(–0.26) M_☉ and D_l = 5.9^(+0.9)_(–1.4) kpc, respectively, so the mass and separation of the planet are M_p = 20^(+7)_(–8) M_⊕ and a = 3.3^(+1.4)_(–0.8) AU, respectively. This discovery adds another cold Neptune-mass planet to the planetary sample discovered by microlensing, which now comprises four cold Neptune/super-Earths, five gas giant planets, and another sub-Saturn mass planet whose nature is unclear. The discovery of these 10 cold exoplanets by the microlensing method implies that the mass ratio function of cold exoplanets scales as dN_(pl)/d log q ∝ q^(–0.7±0.2) with a 95% confidence level upper limit of n < –0.35 (where dN_(pl)/d log q ∝ q^n). As microlensing is most sensitive to planets beyond the snow-line, this implies that Neptune-mass planets are at least three times more common than Jupiters in this region at the 95% confidence level.
253 citations
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TL;DR: A Neptune-mass planet OGLE-2007-BLG-368Lb with a planet-star mass ratio of q=[9.5 +/- 2.1] x 10^{-5} via gravitational microlensing was discovered in real-time thanks to the high cadence of the MOA survey and intensive follow-up observations as mentioned in this paper.
Abstract: We present the discovery of a Neptune-mass planet OGLE-2007-BLG-368Lb with a planet-star mass ratio of q=[9.5 +/- 2.1] x 10^{-5} via gravitational microlensing. The planetary deviation was detected in real-time thanks to the high cadence of the MOA survey, real-time light curve monitoring and intensive follow-up observations. A Bayesian analysis returns the stellar mass and distance at M_l = 0.64_{-0.26}^{+0.21} M_\sun and D_l = 5.9_{-1.4}^{+0.9} kpc, respectively, so the mass and separation of the planet are M_p = 20_{-8}^{+7} M_\oplus and a = 3.3_{-0.8}^{+1.4} AU, respectively. This discovery adds another cold Neptune-mass planet to the planetary sample discovered by microlensing, which now comprise four cold Neptune/Super-Earths, five gas giant planets, and another sub-Saturn mass planet whose nature is unclear. The discovery of these ten cold exoplanets by the microlensing method implies that the mass ratio function of cold exoplanets scales as dN_{\rm pl}/d\log q \propto q^{-0.7 +/- 0.2} with a 95% confidence level upper limit of n < -0.35 (where dN_{\rm pl}/d\log q \propto q^n). As microlensing is most sensitive to planets beyond the snow-line, this implies that Neptune-mass planets are at least three times more common than Jupiters in this region at the 95% confidence level.
217 citations
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University of Würzburg1, University of Erlangen-Nuremberg2, Goddard Space Flight Center3, University of Maryland, Baltimore County4, The Catholic University of America5, Radboud University Nijmegen6, Istituto Nazionale di Fisica Nucleare7, University of Padua8, Commonwealth Scientific and Industrial Research Organisation9, Auckland University of Technology10, University of Trieste11, University of Tasmania12, Hartebeesthoek Radio Astronomy Observatory13, University of Valencia14, Max Planck Society15, University of California, Los Angeles16
TL;DR: In this paper, the IceCube neutrino telescope in the South Pole has observed several high-energy neutrinos of undetermined origin from blazar PKS B1424-418.
Abstract: The IceCube neutrino telescope in the South Pole has observed several high-energy neutrinos of undetermined origin. Could the third detected PeV event be from blazar PKS B1424–418?
216 citations
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1,288 citations
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TL;DR: In 2014, the Science Definition Team (SDT) of the Wide Field Infrared Survey Telescope (WFIRST) mission presented a design reference mission (DRM) for an implementation of WFIRST using one of the 2.4m, Hubble-quality telescopes recently made available to NASA as discussed by the authors.
Abstract: This report describes the 2014 study by the Science Definition Team (SDT) of the Wide-Field Infrared Survey Telescope (WFIRST) mission. It is a space observatory that will address the most compelling scientific problems in dark energy, exoplanets and general astrophysics using a 2.4-m telescope with a wide-field infrared instrument and an optical coronagraph. The Astro2010 Decadal Survey recommended a Wide Field Infrared Survey Telescope as its top priority for a new large space mission. As conceived by the decadal survey,
WFIRST would carry out a dark energy science program, a microlensing program to
determine the demographics of exoplanets, and a general observing program
utilizing its ultra wide field. In October 2012, NASA chartered a Science
Definition Team (SDT) to produce, in collaboration with the WFIRST Study Office
at GSFC and the Program Office at JPL, a Design Reference Mission (DRM) for an
implementation of WFIRST using one of the 2.4-m, Hubble-quality telescope
assemblies recently made available to NASA. This DRM builds on the work of the
earlier WFIRST SDT, reported by Green et al. (2012) and the previous WFIRST-2.4
DRM, reported by Spergel et. (2013). The 2.4-m primary mirror enables a mission
with greater sensitivity and higher angular resolution than the 1.3-m and 1.1-m
designs considered previously, increasing both the science return of the
primary surveys and the capabilities of WFIRST as a Guest Observer facility.
The addition of an on-axis coronagraphic instrument to the baseline design
enables imaging and spectroscopic studies of planets around nearby stars.
1,009 citations
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TL;DR: A review of the current knowledge of the occurrence of planets around other stars, their orbital distances and eccentricities, the orbital spacings and mutual inclinations in multi-planet systems, the orientation of the host star's rotation axis, and the properties of planets in binary-star systems can be found in this paper.
Abstract: The basic geometry of the Solar System—the shapes, spacings, and orientations of the planetary orbits—has long been a subject of fascination as well as inspiration for planet-formation theories. For exoplanetary systems, those same properties have only recently come into focus. Here we review our current knowledge of the occurrence of planets around other stars, their orbital distances and eccentricities, the orbital spacings and mutual inclinations in multiplanet systems, the orientation of the host star's rotation axis, and the properties of planets in binary-star systems.
824 citations
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TL;DR: The discovery of an extraterrestrial diffuse flux of high-energy neutrinos, announced by IceCube in 2013, has characteristic properties that hint at contributions from extragalactic sources, although the individual sources remain as yet unidentified.
Abstract: INTRODUCTION Neutrinos are tracers of cosmic-ray acceleration: electrically neutral and traveling at nearly the speed of light, they can escape the densest environments and may be traced back to their source of origin. High-energy neutrinos are expected to be produced in blazars: intense extragalactic radio, optical, x-ray, and, in some cases, γ-ray sources characterized by relativistic jets of plasma pointing close to our line of sight. Blazars are among the most powerful objects in the Universe and are widely speculated to be sources of high-energy cosmic rays. These cosmic rays generate high-energy neutrinos and γ-rays, which are produced when the cosmic rays accelerated in the jet interact with nearby gas or photons. On 22 September 2017, the cubic-kilometer IceCube Neutrino Observatory detected a ~290-TeV neutrino from a direction consistent with the flaring γ-ray blazar TXS 0506+056. We report the details of this observation and the results of a multiwavelength follow-up campaign. RATIONALE Multimessenger astronomy aims for globally coordinated observations of cosmic rays, neutrinos, gravitational waves, and electromagnetic radiation across a broad range of wavelengths. The combination is expected to yield crucial information on the mechanisms energizing the most powerful astrophysical sources. That the production of neutrinos is accompanied by electromagnetic radiation from the source favors the chances of a multiwavelength identification. In particular, a measured association of high-energy neutrinos with a flaring source of γ-rays would elucidate the mechanisms and conditions for acceleration of the highest-energy cosmic rays. The discovery of an extraterrestrial diffuse flux of high-energy neutrinos, announced by IceCube in 2013, has characteristic properties that hint at contributions from extragalactic sources, although the individual sources remain as yet unidentified. Continuously monitoring the entire sky for astrophysical neutrinos, IceCube provides real-time triggers for observatories around the world measuring γ-rays, x-rays, optical, radio, and gravitational waves, allowing for the potential identification of even rapidly fading sources. RESULTS A high-energy neutrino-induced muon track was detected on 22 September 2017, automatically generating an alert that was distributed worldwide within 1 min of detection and prompted follow-up searches by telescopes over a broad range of wavelengths. On 28 September 2017, the Fermi Large Area Telescope Collaboration reported that the direction of the neutrino was coincident with a cataloged γ-ray source, 0.1° from the neutrino direction. The source, a blazar known as TXS 0506+056 at a measured redshift of 0.34, was in a flaring state at the time with enhanced γ-ray activity in the GeV range. Follow-up observations by imaging atmospheric Cherenkov telescopes, notably the Major Atmospheric Gamma Imaging Cherenkov (MAGIC) telescopes, revealed periods where the detected γ-ray flux from the blazar reached energies up to 400 GeV. Measurements of the source have also been completed at x-ray, optical, and radio wavelengths. We have investigated models associating neutrino and γ-ray production and find that correlation of the neutrino with the flare of TXS 0506+056 is statistically significant at the level of 3 standard deviations (sigma). On the basis of the redshift of TXS 0506+056, we derive constraints for the muon-neutrino luminosity for this source and find them to be similar to the luminosity observed in γ-rays. CONCLUSION The energies of the γ-rays and the neutrino indicate that blazar jets may accelerate cosmic rays to at least several PeV. The observed association of a high-energy neutrino with a blazar during a period of enhanced γ-ray emission suggests that blazars may indeed be one of the long-sought sources of very-high-energy cosmic rays, and hence responsible for a sizable fraction of the cosmic neutrino flux observed by IceCube.
813 citations
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TL;DR: In this paper, the authors used a fraction of the guaranteed time on the ESO/HARPS spectrograph to estimate the radial velocities of 102 southern nearby M dwarfs, and then applied systematic searches for long-term trends, periodic signals, and Keplerian orbits.
Abstract: Searching for planets around stars with different masses helps us to assess the outcome of planetary formation for different initial conditions. The low-mass M dwarfs are also the most frequent stars in our Galaxy and potentially therefore, the most frequent planet hosts. Aims. We present observations of 102 southern nearby M dwarfs, using a fraction of our guaranteed time on the ESO/HARPS spectrograph. We observed for 460 h and gathered 1965 precise (~1-3 m/s) radial velocities (RVs), spanning the period from Feb. 11, 2003 to Apr. 1, 2009. Methods. For each star observed, we derive a time series and its precision as well as its variability. We apply systematic searches for long-term trends, periodic signals, and Keplerian orbits (from one to four planets). We analyze the subset of stars with detected signals and apply several diagnostics to discriminate whether the observed Doppler shifts are caused by either stellar surface inhomogeneities or the radial pull of orbiting planets. To prepare for the statistical view of our survey, we also compute the limits on possible unseen signals, and derive a first estimate of the frequency of planets orbiting M dwarfs. Results. We recover the planetary signals of 9 planets announced by our group (Gl 176 b, Gl 581 b, c, d & e, Gl 674 b, Gl 433 b, Gl 667C b, and Gl 667C c). We present radial velocities confirming that GJ 849 hosts a Jupiter-mass planet, plus a long-term radial-velocity variation. We also present RVs that precise the planetary mass and period of Gl 832b. We detect long-term RV changes for Gl 367, Gl 680, and Gl 880, which are indicative of yet unknown long-period companions. We identify candidate signals in the radial-velocity time series of 11 other M dwarfs. Spectral diagnostics and/or photometric observations demonstrate however that these signals are most probably caused by stellar surface inhomogeneities. Finally, we find that our survey is sensitive to a few Earth-mass planets for periods up to several hundred days. We derive a first estimate of the occurrence of M-dwarf planets as a function of their minimum mass and orbital period. In particular, we find that giant planets (msini = 100 − 1000 M⊕) have a low frequency (e.g. f ≲ 1% for P = 1 − 10 d and f = 0.02+0.03-0.01 for P = 10 − 100 d), whereas super-Earths (msini = 1 − 10 M⊕) are likely very abundant (f = 0.36+0.25-0.10 for P = 1 − 10 d and f = 0.52+0.50-0.16 for P = 10 − 100 d). We also obtained η⊕ = 0.41+0.54-0.13, which is the frequency of habitable planets orbiting M dwarfs (1 ≤ msini ≤ 10 M⊕). For the first time, η⊕ is a direct measure and not a number extrapolated from the statistics of more massive and/or shorter-period planets.
777 citations