Showing papers by "Yoshiyuki Watase published in 1997"
Lawrence Livermore National Laboratory1, University of California, Berkeley2, Wellington Management Company3, Australian National University4, University of California, Davis5, Victoria University of Wellington6, Space Telescope Science Institute7, University of Washington8, University of Notre Dame9, Nagoya University10, University of California, San Diego11, University of Canterbury12, Tel Aviv University13, University of Tokyo14, Tokai University15, KEK16, University of Auckland17, University of Colorado Boulder18, Kyoto University19, University of California, Santa Barbara20, European Southern Observatory21, California Institute of Technology22, Dominion Astrophysical Observatory23, University of Oxford24
TL;DR: In this article, the authors present an analysis of MACHO Alert 95-30, a dramatic microlensing event toward the Galactic bulge whose peak magnification departs significantly from the standard point-source micro-lensing model.
Abstract: We present analysis of MACHO Alert 95-30, a dramatic gravitational microlensing event toward the Galactic bulge whose peak magnification departs significantly from the standard point-source microlensing model Alert 95-30 was observed in real time by the Global Microlensing Alert Network (GMAN), which obtained densely sampled photometric and spectroscopic data throughout the event We interpret the light-curve fine structure as indicating transit of the lens across the extended face of the source star This signifies resolution of a star several kiloparsecs distant We find a lens angular impact parameter θmin/θsource = 0715 ± 0003 This information, along with the radius and distance of the source, provides an additional constraint on the lensing system Spectroscopic and photometric data indicate the source is a M4 III star of radius 61 ± 12 R☉, located on the far side of the bulge at ~9 kpc We derive a lens angular velocity, relative to the source, of 215 ± 29 km s-1 kpc-1, where the error is dominated by uncertainty in the angular size of the source star Likelihood analysis yields a median lens mass of 067 -->+ 253−046 M☉, located with 80% probability in the Galactic bulge at a distance of 693 -->+ 156−225 kpc If the lens is a main-sequence star, we can include constraints on the lens luminosity This modifies our estimates to Mlens=053 -->+ 052−035 M☉ and Dlens=657 -->+ 099−225 kpc Spectra taken during the event show that the absorption-line equivalent widths of Hα and the TiO bands near 6700 A vary, as predicted for microlensing of an extended source This is most likely due to center-to-limb variation in the stellar spectral lines The observed spectral changes further support our microlensing interpretation These data demonstrate the feasibility of using microlensing limb crossings as a tool to probe stellar atmospheres directly
168 citations
TL;DR: In this article, the authors present an analysis of MACHO Alert 95-30, a dramatic gravitational microlensing event towards the Galactic bulge whose peak magnification departs significantly from the standard point-source micro-lensing model.
Abstract: We present analysis of MACHO Alert 95-30, a dramatic gravitational microlensing event towards the Galactic bulge whose peak magnification departs significantly from the standard point-source microlensing model. Alert 95-30 was observed in real-time by the Global Microlensing Alert Network (GMAN), which obtained densely sampled photometric and spectroscopic data throughout the event. We interpret the light-curve ``fine structure'' as indicating transit of the lens across the extended face of the source star. This signifies resolution of a star several kpc distant. We find a lens angular impact parameter theta_{min}/theta_{source} = 0.715 +/- 0.003. This information, along with the radius and distance of the source, provides an additional constraint on the lensing system. Spectroscopic and photometric data indicate the source is an M4 III star of radius 61 +/- 12 Rsun, located on the far side of the bulge at 9 kpc. We derive a lens angular velocity, relative to the source, of 21.5 +/- 4.9 km/s/kpc, where the error is dominated by uncertainty in the source radius. Likelihood analysis yields a median lens mass of 0.67{+2.53}{-0.46} Msun, located with 80% probability in the Galactic bulge at a distance of 6.93{+1.56}{-2.25} kpc. If the lens is a main-sequence star, we can include constraints on the lens luminosity. This modifies our estimates to M_lens = 0.53{+0.52}{-0.35} Msun and D_lens = 6.57{+0.99}{-2.25} kpc. Spectra taken during the event show that the absorption line equivalent widths of H alpha and the TiO bands near 6700 A vary, as predicted for microlensing of an extended source. This is most likely due to center-to-limb variation in the stellar spectral lines. These data demonstrate the feasibility of using microlensing limb crossings as a tool to probe stellar atmospheres directly.
148 citations
University of Tsukuba1, Tohoku University2, Tokyo Metropolitan University3, University of Toyama4, Naruto University of Education5, Osaka University6, Kyoto University7, Tohoku Gakuin University8, Hiroshima University9, University of Helsinki10, Okayama University11, Ehime University12, International Christian University13, University of Miyazaki14, Kobe University15, KEK16, Niigata University17, Kogakuin University18, National University Corporation Tsukuba University of Technology19
TL;DR: The cross section of the γγ → p p reaction was measured at two-photon center-of-mass energy (Wγγ) between 2.2 and 3.3 GeV, using the twophoton process at an e+e− collider, TRISTAN as mentioned in this paper.
22 citations
University of Tsukuba1, Tokyo Metropolitan University2, Tohoku University3, University of Toyama4, Osaka University5, Kyoto University6, Tohoku Gakuin University7, Kobe University8, Hiroshima University9, University of Helsinki10, Okayama University11, International Christian University12, University of Miyazaki13, Kogakuin University14, National University Corporation Tsukuba University of Technology15, Naruto University of Education16
TL;DR: In this article, a model-independent scattering-angle distribution is extracted from the measurement, which is in good agreement with the prediction of the standard electroweak theory, after unfolding the photon-radiation effect.
Abstract: Bhabha scattering at a center-of-mass energy of 57.77 GeV has been measured using the VENUS detector at KEK TRISTAN. The precision is better than 1% in scattering angle regions of |cos\ensuremath{\theta}|\ensuremath{\leqslant}0.743 and 0.822\ensuremath{\leqslant}cos\ensuremath{\theta}\ensuremath{\leqslant}0.968. A model-independent scattering-angle distribution is extracted from the measurement. The distribution is in good agreement with the prediction of the standard electroweak theory. The sensitivity to underlying theories is examined, after unfolding the photon-radiation effect. The ${\mathit{q}}^{2}$ dependence of the photon vacuum polarization, frequently interpreted as a running of the QED fine-structure constant, is directly observed with a significance of three standard deviations. The ${\mathit{Z}}^{0}$ exchange effect is clearly seen when the distribution is compared with the prediction from QED (photon exchanges only). The agreement with the standard theory leads us to constraints on extensions of the standard theory. In all quantitative discussions, correlations in the systematic error between angular bins are taken into account by employing an error matrix technique.
13 citations
Osaka University1, Tohoku University2, University of Tsukuba3, Kyushu University4, Tokyo Metropolitan University5, University of Toyama6, Naruto University of Education7, Kyoto University8, Tohoku Gakuin University9, Kobe University10, Hiroshima University11, University of Helsinki12, Okayama University13, University of Tokyo14, Ehime University15, International Christian University16, University of Miyazaki17, Niigata University18, Kogakuin University19, National University Corporation Tsukuba University of Technology20
TL;DR: In this article, the average polarization of τ leptons in the reaction e+e− → τ+τ− has been measured using a TRISTAN at the center-of-mass energy of 58 GeV.
4 citations
Tohoku University1, University of Tsukuba2, Tokyo Metropolitan University3, University of Toyama4, Naruto University of Education5, Osaka University6, Kyoto University7, Tohoku Gakuin University8, Kobe University9, Hiroshima University10, University of Helsinki11, Okayama University12, Ehime University13, International Christian University14, University of Miyazaki15, Niigata University16, Kogakuin University17, National University Corporation Tsukuba University of Technology18
3 citations
Journal Article•
Hiroshima National College of Maritime Technology1, Tohoku University2, University of Tsukuba3, Tokyo Metropolitan University4, University of Toyama5, Osaka University6, Kyoto University7, Tohoku Gakuin University8, Kobe University9, Okayama University10, International Christian University11, Niigata University12, Kogakuin University13, Naruto University of Education14
1 citations