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- 저자 : Beichman, C. (검색결과 11 건)
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Shvartzvald, Y.,Bryden, G.,Gould, A.,Henderson, C. B.,Howell, S. B.,Beichman, C. American Institute of Physics 2017 The Astronomical journal Vol.153 No.2
<P>Optical microlensing surveys are restricted from detecting events near the Galactic plane and center, where the event rate is thought to be the highest due to the high optical extinction of these fields. In the near-infrared (NIR), however, the lower extinction leads to a corresponding increase in event detections and is a primary driver for the wavelength coverage of the WFIRST microlensing survey. During the 2015 and 2016 bulge observing seasons, we conducted NIR microlensing surveys with UKIRT in conjunction with and in support of the Spitzer and Kepler microlensing campaigns. Here, we report on five highly extinguished (A(H) = 0.81-1.97), low-Galactic latitude (-0.98 <= b <= -0.36) microlensing events discovered from our 2016 survey. Four of them were monitored with an hourly cadence by optical surveys but were not reported as discoveries, likely due to the high extinction. Our UKIRT surveys and suggested future NIR surveys enable the first measurement of the microlensing event rate in the NIR. This wavelength regime overlaps with the bandpass of the filter in which the WFIRST microlensing survey will conduct its highest-cadence observations, making this event rate derivation critically important for optimizing its yield.</P>
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OGLE-2017-BLG-1130: The First Binary Gravitational Microlens Detected from <i>Spitzer</i> Only
Wang, Tianshu,Calchi Novati, S.,Udalski, A.,Gould, A.,Mao, Shude,Zang, W.,Beichman, C.,Bryden, G.,Carey, S.,Gaudi, B. S.,Henderson, C. B.,Shvartzvald, Y.,Yee, J. C.,Mró,z, P.,Poleski, R.,Skowron American Astronomical Society 2018 The Astrophysical journal Vol.860 No.1
<P>We analyze the binary gravitational microlensing event OGLE-2017-BLG-1130 (mass ratio q similar to 0.45), the first published case in which the binary anomaly was detected only by the Spitzer Space Telescope. This event provides strong evidence that some binary signals can be missed by observations from the ground alone but detected by Spitzer. We therefore invert the normal procedure, first finding the lens parameters by fitting the space-based data and then measuring the microlensing parallax using ground-based observations. We also show that the normal four-fold space-based degeneracy in the single-lens case can become a weak eight-fold degeneracy in binary-lens events. Although this degeneracy is resolved in event OGLE-2017-BLG-1130, it might persist in other events.</P>
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<i>SPITZER</i>MICROLENS MEASUREMENT OF A MASSIVE REMNANT IN A WELL-SEPARATED BINARY
Shvartzvald, Y.,Udalski, A.,Gould, A.,Han, C.,Bozza, V.,Friedmann, M.,Hundertmark, M.,Beichman, C.,Bryden, G.,Novati, S. Calchi,Carey, S.,Fausnaugh, M.,Gaudi, B. S.,Henderson, C. B.,Kerr, T.,Pogge, R. IOP Publishing 2015 The Astrophysical journal Vol.814 No.2
<P>We report the detection and mass measurement of a binary lens OGLE-2015-BLG-1285La, b, with the more massive component having M-1 > 1.35M(circle dot) (80% probability). A main-sequence star in this mass range is ruled out by limits on blue light, meaning that a primary in this mass range must be a neutron star (NS) or black hole (BH). The system has a projected separation r(perpendicular to) = 6.1 +/- 0.4 AU and lies in the Galactic bulge. These measurements are based on the 'microlens parallax' effect, i.e., comparing the microlensing light curve as seen from Spitzer, which lay at 1.25 AU projected from Earth, to the light curves from four ground-based surveys, three in the optical and one in the near-infrared. Future adaptive optics imaging of the companion by 30 m class telescopes will yield a much more accurate measurement of the primary mass. This discovery both opens the path and defines the challenges to detecting and characterizing BHs and NSs in wide binaries, with either dark or luminous companions. In particular, we discuss lessons that can be applied to future Spitzer and Kepler K2 microlensing parallax observations.</P>
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Han, C.,Udalski, A.,Gould, A.,Zhu, Wei,Street, R. A.,Yee, J. C.,Beichman, C.,Bryden, C.,Novati, S. Calchi,Carey, S.,Fausnaugh, M.,Gaudi, B. S.,Henderson, Calen B.,Shvartzvald, Y.,Wibking, B.,Szyma American Astronomical Society 2016 The Astrophysical journal Vol.828 No.1
<P>We present a combined analysis of the observations of the gravitational microlensing event OGLE-2015-BLG-0479 taken both from the ground and by the Spitzer Space Telescope. The light curves seen from the ground and from space exhibit a time offset of similar to 13 days between the caustic spikes, indicating that the relative lens-source positions seen from the two places are displaced by parallax effects. From modeling the light curves, we measure the space-based microlens parallax. Combined with the angular Einstein radius measured by analyzing the caustic crossings, we determine the mass and distance of the lens. We find that the lens is a binary composed of two G-type stars with masses of similar to 1.0 M-circle dot and similar to 0.9 M-circle dot located at a distance. of similar to 3 kpc. In addition, we are able to constrain the complete orbital parameters of the lens thanks to the precise measurement of the microlens parallax derived from the joint analysis. In contrast to the binary event OGLE-2014-BLG-1050, which was also observed by Spitzer, we find that the interpretation of OGLE-2015-BLG-0479 does not suffer from the degeneracy between (+/-, +/-) and (+/-, -/+) solutions, confirming that the four-fold parallax degeneracy in single-lens events collapses into the two-fold degeneracy for the general case of binary-lens events. The location of the blend in the color-magnitude diagram is consistent with the lens properties, suggesting that the blend is the lens itself. The blend is bright enough for spectroscopy and thus this possibility can be checked from future follow-up observations.</P>
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OGLE-2016-BLG-1266: A Probable Brown Dwarf/Planet Binary at the Deuterium Fusion Limit
Albrow, M. D.,Yee, J. C.,Udalski, A.,Novati, S. Calchi,Carey, S.,Henderson, C. B.,Beichman, C.,Bryden, G.,Gaudi, B. S.,Shvartzvald, Y.,Szymań,ski, M. K.,Mró,z, P.,Skowron, J.,Poleski, R.,So American Astronomical Society 2018 The Astrophysical journal Vol.858 No.2
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An Earth-mass Planet in a 1 au Orbit around an Ultracool Dwarf
Shvartzvald, Y.,Yee, J. C.,Novati, S. Calchi,Gould, A.,Lee, C.-U.,Beichman, C.,Bryden, G.,Carey, S.,Gaudi, B. S.,Henderson, C. B.,Zhu, W.,Albrow, M. D.,Cha, S.-M.,Chung, S.-J.,Han, C.,Hwang, K.-H.,Jun American Astronomical Society 2017 ASTROPHYSICAL JOURNAL LETTERS - Vol.840 No.1
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Zhu (祝伟,), Wei,Udalski, A.,Gould, A.,Dominik, M.,Bozza, V.,Han, C.,Yee, J. C.,Novati, S. Calchi,Beichman, C. A.,Carey, S.,Poleski, R.,Skowron, J.,Kozłowski, S.,Mró,z, P.,Pietrukowicz, P.,P IOP Publishing 2015 The Astrophysical journal Vol.805 No.1
<P>We report the first mass and distance measurements of a caustic-crossing binary system OGLE-2014-BLG-1050 L using the space-based microlens parallax method. Spitzer captured the second caustic. crossing of the event, which occurred similar to 10 days before that seen from Earth. Due to the coincidence that the source-lens relative motion was almost parallel to the direction of the binary-lens axis, the fourfold degeneracy, which was known before only to occur in single-lens events, persists in this case, leading to either a lower-mass (0.2 and 0.07 M-circle dot) binary at similar to 1.1 kpc or a higher-mass (0.9 and 0.35 M-circle dot) binary at similar to 3.5 kpc. However, the latter solution is strongly preferred for reasons including blending and lensing probability. OGLE-2014-BLG-1050 L demonstrates the power of microlens parallax in probing stellar and substellar binaries.</P>
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Shvartzvald, Y.,Li, Z.,Udalski, A.,Gould, A.,Sumi, T.,Street, R. A.,Novati, S. Calchi,Hundertmark, M.,Bozza, V.,Beichman, C.,Bryden, G.,Carey, S.,Drummond, J.,Fausnaugh, M.,Gaudi, B. S.,Henderson, C. American Astronomical Society 2016 The Astrophysical journal Vol.831 No.2
<P>Simultaneous observations of microlensing events from multiple locations allow for the breaking of degeneracies between the physical properties of the lensing system, specifically by exploring different regions of the lens plane and by directly measuring the 'microlens parallax.' We report the discovery of a 30-65M(J) brown dwarf orbiting a K dwarf in the microlensing event OGLE-2015-BLG-1319. The system is located at a distance of similar to 5 kpc toward the Galactic Bulge. The event was observed by several ground-based groups as well as by Spitzer and Swift, allowing a measurement of the physical properties. However, the event is still subject to an eight-fold degeneracy, in particular the well-known close-wide degeneracy, and thus the projected separation between the two lens components is either similar to 0.25 au or similar to 45 au. This is the first microlensing event observed by Swift, with the UVOT camera. We study the region of microlensing parameter space to which Swift is sensitive, finding that though Swift could not measure the microlens parallax with respect to ground-based observations for this event, it can be important for other events. Specifically, it is important for detecting nearby brown dwarfs and free-floating planets in high magnification events.</P>
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