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  • Other Sources  (17)
  • 1
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    OGLE-2016-BLG-1469L: Microlensing Binary Composed of Brown Dwarfs (2017)
    In:  Other Sources
    Details
    Publication Date: 2019-05-24
    Description: We report the discovery of a binary composed of two brown dwarfs, based on the analysis of the micro lensing event OGLE-2016-BLG-1469. Thanks to the detection of both finite-source and micro lens-parallax effects, we are able to measure both the masses M(sub 1) ~ 0.05 Solar Mass and M(sub 2) ~ 0.01 Solar Mass, and the distance D(sub L) ~ 4.5 kpc, as well as the projected separation a(sub perpendicular) ~ 0.33 au. This is the third brown-dwarf binary detected using the micro lensing method, demonstrating the usefulness of micro lensing in detecting field brown-dwarf binaries with separations of less than 1 au.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN64792 , The Astrophysical Journal (ISSN 0004-637X) (e-ISSN 1538-4357); 843; 1; 59
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  • 2
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    An Isolated Microlens Observed from K2, Spitzer, and Earth (2017)
    In:  Other Sources
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    Publication Date: 2019-06-12
    Description: We present the result of microlensing event MOA-2016-BLG-290, which received observations from the two-wheel Kepler (K2), Spitzer, as well as ground-based observatories. A joint analysis of data from K2 and the ground leads to two degenerate solutions of the lens mass and distance. This degeneracy is effectively broken once the (partial) Spitzer light curve is included. Altogether, the lens is found to be an extremely low-mass star or brown dwarf (77(sup +34)(sub -23) M(sub J)) located in the Galactic bulge (6.8 0.4 kpc). MOA-2016-BLG-290 is the first microlensing event for which we have signals from three well-separated (~1 au) locations. It demonstrates the power of two-satellite microlensing experiment in reducing the ambiguity of lens properties, as pointed out independently by S. Refsdal and A. Gould several decades ago.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN64721 , Astrophysical Journal Letters (ISSN 2041-8205) (e-ISSN 2041-8213); 849; 2; L31
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  • 3
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    Faint-Source-Star Planetary Microlensing: The Discovery of the Cold Gas-Giant Planet OGLE-2014-BLG-0676Lb (2016)
    In:  CASI
    Details
    Publication Date: 2019-06-20
    Description: We report the discovery of a planet OGLE-2014-BLG-0676Lb via gravitational microlensing. Observations for the lensing event were made by the following groups: Microlensing Observations in Astrophysics; Optical Gravitational Lensing Experiment; Wise Observatory; RoboNETLas Cumbres Observatory Global Telescope; Microlensing Network for the Detection of Small Terrestrial Exoplanets; and -FUN. All analyses of the light-curve data favoura lens system comprising a planetary mass orbiting a host star. The most-favoured binary lens model has a mass ratio between the two lens masses of (4.78 +/- 0.13) 10(exp -3). Subject to some important assumptions, a Bayesian probability density analysis suggests the lens system comprises a 3.09(+1.02/-1.12) MJ planet orbiting a 0.62(+0.20/-0.22) solar mass host star at a deprojected orbital separation of 4.40(+2.16/-1.46) au. The distance to the lens system is 2.22(+0.96/-0.83) kpc. Planet OGLE-2014-BLG-0676Lb provides additional data to the growing number of cool planets discover redusing gravitational microlensing against which planetary formation theories may be tested. Most of the light in the baseline of this event is expected to come from the lens and thus high-resolution imaging observations could confirm our planetary model interpretation.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN64724 , GSFC-E-DAA-TN42195 , Monthly Notices of the Royal Astronomical Society (ISSN 0035-8711 ) (e-ISSN 1365-2966); 466; 3; 2710-2717
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  • 4
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    Pathway to the Galactic Distribution of Planets: Combined Spitzer and Ground-Based Microlens Parallax Measurements of 21 Single-Lens Events (2015)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: We present microlens parallax measurements for 21 (apparently) isolated lenses observed toward the Galactic bulge that were imaged simultaneously from Earth and Spitzer, which was approximately 1 Astronomical Unit west of Earth in projection. We combine these measurements with a kinematic model of the Galaxy to derive distance estimates for each lens, with error bars that are small compared to the Sun's galactocentric distance. The ensemble therefore yields a well-defined cumulative distribution of lens distances. In principle, it is possible to compare this distribution against a set of planets detected in the same experiment in order to measure the Galactic distribution of planets. Since these Spitzer observations yielded only one planet, this is not yet possible in practice. However, it will become possible as larger samples are accumulated.
    Keywords: Astronomy; Astrophysics
    Type: GSFC-E-DAA-TN34952 , The Astrophysical Journal; 804; 1 20; 1-25
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  • 5
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    OGLE-2013-BLG-1761Lb: A Massive Planet around an MK Dwarf (2017)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: We report the discovery and the analysis of the planetary microlensing event, OGLE-2013-BLG-1761. There are some degenerate solutions in this event because the planetary anomaly is only sparsely sampled. However, the detailed light curve analysis ruled out all stellar binary models and shows the lens to be a planetary system. There is the so-called close wide degeneracy in the solutions with the planet host mass ratio of q approx.(7.0+/-2.0) x 10(exp -3) and q approx.(8.1+/-2.6) x 10(exp -3) with the projected separation in Einstein radius units of s = 0.95 (close) and s = 1.18(wide), respectively. The microlens parallax effect is not detected, but the finite source effect is detected. Our Bayesian analysis indicates that the lens system is located -D(sub L) = 6.9(+ 1.0 -1.2)kpc away from us and the host star is an M/K dwarf with amass of M(sub L) = 0.33(+ 0.32- 1.9)Stellar Mass orbited by a super-Jupiter mass planet with a mass of m(sub p) = 2.7(+ 2.5 - 1.5) M(sub Jup) at the projected separation of a(sub l) = 1.8(+ 0.5 -0.5)au. The preference of the large lens distance in the Bayesian analysis is due to the relatively large observed source star radius. The distance and other physical parameters may be constrained by the future high-resolution imaging by large ground telescopes or HST. If the estimated lens distance is correct, then this planet provides another sample for testing the claimed deficit of planets in the Galactic bulge.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN45581 , GSFC-E-DAA-TN64725 , The Astronomical Journal (ISSN 0004-6256) (e-ISSN 1538-3881); 154; 1; 1-8
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  • 6
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    Swift J045106.8-694803: A Highly Magnetised Neutron Star in the Large Magellanic Cloud (2013)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: We report the analysis of a highly magnetised neutron star in the Large Magellanic Cloud (LMC). The high mass X-ray binary pulsar Swift J045106.8-694803 has been observed with Swift X-ray telescope (XRT) in 2008, The Rossi X-ray Timing Explorer (RXTE) in 2011 and the X-ray Multi-Mirror Mission - Newton (XMM-Newton) in 2012. The change in spin period over these four years indicates a spin-up rate of 5.010.06 s/yr, amongst the highest observed for an accreting pulsar. This spin-up rate can be accounted for using Ghosh and Lambs (1979) accretion theory assuming it has a magnetic field of (1.2 +/= 0.20/0.7) x 10(exp 14) Gauss. This is over the quantum critical field value. There are very few accreting pulsars with such high surface magnetic fields and this is the first of which to be discovered in the LMC. The large spin-up rate is consistent with Swift Burst Alert Telescope (BAT) observations which show that Swift J045106.8-694803 has had a consistently high X-ray luminosity for at least five years. Optical spectra have been used to classify the optical counterpart of Swift J045106.8-694803 as a B0-1 III-V star and a possible orbital period of 21.631 +/- 0.005 days has been found from MACHO optical photometry.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN7991
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  • 7
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    The Lowest Mass Ratio Planetary Microlens: OGLE 2016BLG1195Lb (2017)
    In:  CASI
    Details
    Publication Date: 2019-06-11
    Description: We report discovery of the lowest mass ratio exoplanet to be found by the microlensing method in the light curve of the event OGLE 2016 BLG1195. This planet revealed itself as a smalldeviation from a microlensing single lens profile from an examination of the survey data. Theduration of the planetary signal is ~ 2.5 h. The measured ratio of the planet mass to its hos tstar is q = 4.2 0.7 x 10 -5(exp). We further estimate that the lens system is likely to comprise a cold ~3 Earth mass planet in an ~2 au wide orbit around a 0.2 Solar mass star at an overall distance of 7.1 kpc.
    Keywords: Lunar and Planetary Science and Exploration
    Type: GSFC-E-DAA-TN64722 , Monthly Notices of the Royal Astronomical Society; 469; 2434–2440
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  • 8
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    The Optical Gravitational Lensing Experiment (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: The technical features are described of the Optical Gravitational Lensing Experiment, which aims to detect a statistically significant number of microlensing events toward the Galactic bulge. Clusters of galaxies observed during the 1992 season are listed and discussed and the reduction methods are described. Future plans are addressed.
    Keywords: ASTRONOMY
    Type: Acta Astronomica (ISSN 0001-5237); 42; 4; p. 253-284.
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  • 9
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    The First Neptune Analog or Super-Earth with a Neptune-Like Orbit: MOA-2013-BLG-605Lb (2016)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: We present the discovery of the first Neptune analog exoplanet or super-Earth with a Neptune-like orbit, MOA- 2013-BLG-605Lb. This planet has a mass similar to that of Neptune or a super-Earth and it orbits at 9 approximately 14 times the expected position of the snow line, a(sub snow), which is similar to Neptunes separation of 11 a(sub snow) from the Sun. The planet/host-star mass ratio is q = (3.6 +/- 0.7) 10(exp 4) and the projected separation normalized by the Einstein radius is s = 2.39 +/- 0.05. There are three degenerate physical solutions and two of these are due to a new type of degeneracy in the microlensing parallax parameters, which we designate "the wide degeneracy." The three models have (i) a Neptune-mass planet with a mass of M(sub p) = 21(+6/-7)(M) orbiting a low-mass M-dwarf with a mass of M(sub h) = 0.19(+0.05/-0.06 (solar mass)), (ii) a mini-Neptune with M(sub p) = 7.9(+1.8/-1.5)(M)) orbiting a brown dwarf host with M(sub h) = 0.068(+0.019/-0.011(solar mass)), and (iii) a super-Earth with M(sub p) = 3.2(+0.5/-0.3(M)) orbiting a low-mass brown dwarf host with M(sub h) = 0.025(+0.005/-0.004)(solar mass)), which is slightly favored. The 3D planet-host separations are 4.6(+4.7/-1.2)au, 2.1(+1.0/-0.2)au, and 0.94(+0.67/-0.02)au, which are 8.9(+10.5/-1.4)m 12(+7/-1), or 14(+11/-1) times larger than a(sub snow) for these models, respectively. Keck adaptive optics observations confirm that the lens is faint. This discovery suggests that low-mass planets with Neptune-like orbits are common. Therefore processes similar to the one that formed Neptune in our own solar system or cold super-Earths may be common in other solar systems.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN34130 , The Astrophysical Journal; 825; 2; 112
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  • 10
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    The First Circumbinary Planet Found by Microlensing: OGLE-2007-BLG-349L(AB)c (2016)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: We present the analysis of the first circumbinary planet microlensing event, OGLE-2007-BLG-349. This event has a strong planetary signal that is best fit with a mass ratio of q approx. = 3.410(exp 4), but there is an additional signal due to an additional lens mass, either another planet or another star. We find acceptable light-curve fits with two classes of models: two-planet models (with a single host star) and circumbinary planet models. The light curve also reveals a significant microlensing parallax effect, which constrains the mass of the lens system to be M(sub L) approx. = 0.7 Stellar Mass. Hubble Space Telescope (HST) images resolve the lens and source stars from their neighbors and indicate excess flux due to the star(s) in the lens system. This is consistent with the predicted flux from the circumbinary models, where the lens mass is shared between two stars, but there is not enough flux to be consistent with the two-planet, one-star models. So, only the circumbinary models are consistent with the HST data. They indicate a planet of mass m(sub c) = 80 +/- 13 Stellar Mass, orbiting a pair of M dwarfs with masses of M(sub A) = 0.41+/- 0.07 and M(sub B) = 0.30 +/- 0.07, which makes this the lowest-mass circumbinary planet system known. The ratio of the separation between the planet and the center of mass to the separation of the two stars is approx.40, so unlike most of the circumbinary planets found by Kepler, the planet does not orbit near the stability limit.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN37484 , GSFC-E-DAA-TN42328 , The Astronomical Journal (e-ISSN 1538-3881); 152; 125; 14pp
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