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Search Results: 1 - 10 of 529 matches for " Teruyuki Hirano "
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Characterizing Earth-like Planets Using a Combination of High-Dispersion Spectroscopy and High-Contrast Instruments: Doppler-shifted Water and Oxygen Lines
Hajime Kawahara,Teruyuki Hirano
Physics , 2014,
Abstract: Future radial velocity, astrometric, and direct-imaging surveys will find nearby Earth-sized planets within the habitable zone in the near future. How can we search for water and oxygen in those nontransiting planets? We show that a combination of high-dispersion spectroscopic and coronagraphic techniques is a promising technique to detect molecular lines imprinted in the scattered light of Earth-like planets (ELPs). In this method, the planetary signals are spectroscopically separated from telluric absorption by using the Doppler shift. Assuming a long observing campaign (a 10-day exposure) using a high-dispersion spectrometer (R=50,000) with speckle suppression on a 30-m telescope, we simulate the spectra from ELPs around M dwarfs (whose stellar effective temperature is 2750-3750 K) at 5 pc. Performing a cross-correlation analysis with the spectral template of the molecular lines, we find that raw contrasts of $10^{-4}$ and $10^{-5}$ (using Y, J, and H bands) are required to detect water vapor at the 3 $\sigma$ and 16 $\sigma$ levels, respectively, for $T_\star$=3000 K. The raw contrast of $10^{-5}$ is required for a 6 $\sigma$ detection of the oxygen 1.27 $\mu$m band. We also examine possible systematics, incomplete speckle subtraction, and the correction for telluric lines. When those are not perfect, a telluric water signal appears in the cross-correlation function. However, we find the planetary signal is separated from that resulting from the velocity difference. We also find that the intrinsic water lines in the Phoenix spectra are too weak to affect the results for water detection. We conclude that a combination of high-dispersion spectroscopy and high-contrast instruments can be a powerful means to characterize ELPs in the extremely large telescope era.
First Evidence of a Retrograde Orbit of Transiting Exoplanet HAT-P-7b
Norio Narita,Bun'ei Sato,Teruyuki Hirano,Motohide Tamura
Physics , 2009, DOI: 10.1093/pasj/61.5.L35
Abstract: We present the first evidence of a retrograde orbit of the transiting exoplanet HAT-P-7b. The discovery is based on a measurement of the Rossiter-McLaughlin effect with the Subaru HDS during a transit of HAT-P-7b, which occurred on UT 2008 May 30. Our best-fit model shows that the spin-orbit alignment angle of this planet is \lambda = -132.6 (+10.5, -16.3) degrees. The existence of such a retrograde planet have been predicted by recent planetary migration models considering planet-planet scattering processes or the Kozai migration. Our finding provides an important milestone that supports such dynamic migration theories.
Characterization of the KOI-94 System with Transit Timing Variation Analysis: Implication for the Planet-Planet Eclipse
Kento Masuda,Teruyuki Hirano,Atsushi Taruya,Makiko Nagasawa,Yasushi Suto
Physics , 2013, DOI: 10.1088/0004-637X/778/2/185
Abstract: The KOI-94 system is a closely-packed, multi-transiting planetary system discovered by the Kepler space telescope. It is known as the first system that exhibited a rare event called a "planet-planet eclipse (PPE)," in which two planets partially overlap with each other in their double-transit phase. In this paper, we constrain the parameters of the KOI-94 system with an analysis of the transit timing variations (TTVs). Such constraints are independent of the radial velocity (RV) analysis recently performed by Weiss and coworkers, and valuable in examining the reliability of the parameter estimate using TTVs. We numerically fit the observed TTVs of KOI-94c, KOI-94d, and KOI-94e for their masses, eccentricities, and longitudes of periastrons, and obtain the best-fit parameters including $m_{\rm c} = 9.4_{-2.1}^{+2.4} M_{\oplus}$, $m_{\rm d} = 52.1_{-7.1}^{+6.9} M_{\oplus}$, $m_{\rm e} = 13.0_{-2.1}^{+2.5} M_{\oplus}$, and $e \lesssim 0.1$ for all the three planets. While these values are mostly in agreement with the RV result, the mass of KOI-94d estimated from the TTV is significantly smaller than the RV value $m_{\rm d} = 106 \pm 11 M_{\oplus}$. In addition, we find that the TTV of the outermost planet KOI-94e is not well reproduced in the current modeling. We also present analytic modeling of the PPE and derive a simple formula to reconstruct the mutual inclination of the two planets from the observed height, central time, and duration of the brightening caused by the PPE. Based on this model, the implication of the results of TTV analysis for the time of the next PPE is discussed.
Starspots - Transit Depth Relation of the Evaporating Planet Candidate KIC 12557548b
Hajime Kawahara,Teruyuki Hirano,Kenji Kurosaki,Yuichi Ito,Masahiro Ikoma
Physics , 2013, DOI: 10.1088/2041-8205/776/1/L6
Abstract: Violent variation of transit depths and an ingress-egress asymmetry of the transit light curve discovered in KIC 12557548 have been interpreted as evidences of a catastrophic evaporation of atmosphere with dust (M_p gtrsim 1 M_oplus/Gyr) from a close-in small planet. To explore what drives the anomalous atmospheric escape, we perform time-series analysis of the transit depth variation of Kepler archival data for ~ 3.5 yr. We find a ~ 30% periodic variation of the transit depth with P1 = 22.83 pm 0.21 days, which is within the error of the rotation period of the host star estimated using the light curve modulation, Prot = 22.91 pm 0.24 days. We interpret the results as evidence that the atmospheric escape of KIC 12557548b correlates with stellar activity. We consider possible scenarios that account for both the mass loss rate and the correlation with stellar activity. X-ray and ultraviolet (XUV)-driven evaporation is possible if one accepts a relatively high XUV flux and a high efficiency for converting the input energy to the kinetic energy of the atmosphere. Star-planet magnetic interaction is another possible scenario though huge uncertainty remains for the mass loss rate.
Distal migration of a floating carotid thrombus in a patient using oral contraceptives: a case report
Masaki Watanabe, Takahisa Mori, Keisuke Imai, Hajime Izumoto, Teruyuki Hirano, Makoto Uchino
Journal of Medical Case Reports , 2009, DOI: 10.4076/1752-1947-3-8389
Abstract: A 48-year-old woman using oral contraceptives suffered from dysarthria and gait disturbance. Examinations, including ultrasound and cerebral arteriogram, revealed a floating thrombus at the left carotid bifurcation with no stenosis. Despite antithrombotic therapy, the floating carotid thrombus migrated to the ipsilateral middle cerebral artery, resulting in a severe stroke.Some floating thrombi are resistant to conservative therapy and have a risk of distal migration, which may cause a major stroke in the acute stage.Carotid endarterectomy (CEA) is the standard treatment for extracranial carotid occlusive diseases. However, determining a more appropriate therapy, surgery or medical management, for treating a floating thrombus in the carotid artery is controversial. Some reports have recommended conservative therapy such as antithrombotic drugs [1,2], while others have diagnosed the floating thrombus as a critical lesion and recommended aggressive therapy, including emergent CEA [3]. In this report, we describe the distal migration of a floating carotid thrombus to the ipsilateral middle cerebral artery despite intensive antithrombotic therapy.A 48-year-old Asian woman with dysmenorrhea and taking oral contraceptives (Edulen, ethinylestradiol 50 μg, ethynodiol acetate 1000 μg) for 6 months suddenly developed difficulty in speech at 7 p.m. on 25 September 2003. Her symptoms resolved in a few minutes. A re-attack of the difficulty in speech and unsteadiness in walking occurred on October 1, and she was admitted to our hospital. Her mother and grandfather had a medical history of cerebral infarction; however, the details were unclear. The patient had been a cigarette smoker (20/day) since 1999.A physical examination revealed no disturbance of consciousness or cognitive dysfunction, but mild weakness in her right leg was demonstrated. The patient was assessed and was graded with a score of 2 on the National Institutes of Health Stroke Scale (NIHSS). An immediate brain co
A reversible lesion of the corpus callosum splenium with adult influenza-associated encephalitis/encephalopathy: a case report
En Kimura, Sadahisa Okamoto, Yuji Uchida, Tomoo Hirahara, Tokunori Ikeda, Teruyuki Hirano, Makoto Uchino
Journal of Medical Case Reports , 2008, DOI: 10.1186/1752-1947-2-220
Abstract: A previously healthy 35-year-old man presented with acute progressive tetraplegia, transcortical motor aphasia and a mild decrease in his consciousness during his recovery after receiving oseltamivir phosphate treatment, and influenza type A antiviral medication. The initial magnetic resonance imaging study at day 1 showed symmetrical diffuse lesions in the white matter and a lesion on the central portion of the corpus callosum splenium. These findings had resolved on follow-up studies at day 8 and day 146. His neurological deficits mostly recovered within 12 hours following methylprednisolone pulse therapy. The levels of interleukin-6 and interleukin-10 in his blood and cerebrospinal fluid were initially elevated, but rapidly decreased to normal levels by day 8.It is important for clinicians to recognize that even in adulthood, the subcortical encephalopathy observed during the therapeutic treatment for influenza type A infection can occur in conjunction with a reversible lesion of the corpus callosum, which may recover quickly. In addition, the cytokine storm in the blood system and the corticospinal cavity may play an important role in the etiology of the disease process.Influenza virus-associated encephalitis/encephalopathy (IAEE) [1-4] is known to have a poor prognosis in childhood, especially in children under the age of 5 years. An acute necrotizing encephalopathy, Reye's syndrome, hemorrhagic shock and encephalopathy are the most feared and often fatal complications in IAEE [5,6]. Although there has been a great improvement in therapeutic approaches, the rates of mortality (31.8%) and disability (27.7%) are still quite high. Recently, the number of patients in Japan with childhood IAEE has increased [3,7], although the number of adult case reports remains small. Pathogenically, IAEE is suggested to be a pro-inflammatory cytokine-related disease [8]. Cytokine levels in serum and cerebrospinal fluid (CSF) are markedly increased in the majority of severe IAEE c
Spin-Orbit Alignment of the TrES-4 Transiting Planetary System and Possible Additional Radial Velocity Variation
Norio Narita,Bun'ei Sato,Teruyuki Hirano,Joshua N. Winn,Wako Aoki,Motohide Tamura
Physics , 2010, DOI: 10.1093/pasj/62.3.653
Abstract: We report new radial velocities of the TrES-4 transiting planetary system, including observations of a full transit, with the High Dispersion Spectrograph of the Subaru 8.2m telescope. Modeling of the Rossiter-McLaughlin effect indicates that TrES-4b has closely aligned orbital and stellar spin axes, with $\lambda = 6.3^{\circ} \pm 4.7^{\circ}$. The close spin-orbit alignment angle of TrES-4b seems to argue against a migration history involving planet-planet scattering or Kozai cycles, although there are two nearby faint stars that could be binary companion candidates. Comparison of our out-of-transit data from 4 different runs suggest that the star exhibits radial velocity variability of $\sim$20 ms^-1 in excess of a single Keplerian orbit. Although the cause of the excess radial velocity variability is unknown, we discuss various possibilities including systematic measurement errors, starspots or other intrinsic motions, and additional companions besides the transiting planet.
Improved Modeling of the Rossiter-McLaughlin Effect for Transiting Exoplanets
Teruyuki Hirano,Yasushi Suto,Joshua N. Winn,Atsushi Taruya,Norio Narita,Simon Albrecht,Bun'ei Sato
Physics , 2011, DOI: 10.1088/0004-637X/742/2/69
Abstract: We present an improved formula for the anomalous radial velocity of the star during planetary transits due to the Rossiter-McLaughlin (RM) effect. The improvement comes from a more realistic description of the stellar absorption line profiles, taking into account stellar rotation, macroturbulence, thermal broadening, pressure broadening, and instrumental broadening. Although the formula is derived for the case in which radial velocities are measured by cross-correlation, we show through numerical simulations that the formula accurately describes the cases where the radial velocities are measured with the iodine absorption-cell technique. The formula relies on prior knowledge of the parameters describing macroturbulence, instrumental broadening and other broadening mechanisms, but even 30% errors in those parameters do not significantly change the results in typical circumstances. We show that the new analytic formula agrees with previous ones that had been computed on a case-by-case basis via numerical simulations. Finally, as one application of the new formula, we reassess the impact of the differential rotation on the RM velocity anomaly. We show that differential rotation of a rapidly rotating star may have a significant impact on future RM observations.
Tidal evolution of the spin-orbit angle in exoplanetary systems
Yuxin Xue,Yasushi Suto,Atsushi Taruya,Teruyuki Hirano,Yuka Fujii,Kento Masuda
Physics , 2014, DOI: 10.1088/0004-637X/784/1/66
Abstract: The angle between the stellar spin and the planetary orbit axes (spin-orbit angle) is supposed to carry valuable information on the initial condition of the planet formation and the subsequent migration history. Indeed current observations of the Rossiter- McLaughlin effect have revealed a wide range of spin-orbit misalignments for transiting exoplanets. We examine in detail the tidal evolution of a simple system comprising a Sun-like star and a hot Jupiter adopting the equilibrium tide and the inertial wave dissipation effects simultaneously. We find that the combined tidal model works as a very efficient realignment mechanism; it predicts three distinct states of the spin-orbit angle (i.e., parallel, polar, and anti-parallel orbits) for a while, but the latter two states eventually approach the parallel spin-orbit configuration. The intermediate spin-orbit angles as measured in recent observations are difficult to be achieved. Therefore the current model cannot reproduce the observed broad distribution of the spin-orbit angles, at least in its simple form. This indicates that the observed diversity of the spin-orbit angles may emerge from more complicated interactions with outer planets and/or may be the consequence of the primordial misalignment between the proto-planetary disk and the stellar spin, which requires future detailed studies.
Measurements of Stellar Inclinations for Kepler Planet Candidates II: Candidate Spin-Orbit Misalignments in Single and Multiple-Transiting Systems
Teruyuki Hirano,Roberto Sanchis-Ojeda,Yoichi Takeda,Joshua N. Winn,Norio Narita,Yasuhiro H. Takahashi
Physics , 2014, DOI: 10.1088/0004-637X/783/1/9
Abstract: We present a test for spin-orbit alignment for the host stars of 25 candidate planetary systems detected by the {\it Kepler} spacecraft. The inclination angle of each star's rotation axis was estimated from its rotation period, rotational line broadening, and radius. The rotation periods were determined using the {\it Kepler} photometric time series. The rotational line broadening was determined from high-resolution optical spectra with Subaru/HDS. Those same spectra were used to determine the star's photospheric parameters (effective temperature, surface gravity, metallicity) which were then interpreted with stellar-evolutionary models to determine stellar radii. We combine the new sample with the 7 stars from our previous work on this subject, finding that the stars show a statistical tendency to have inclinations near 90$^\circ$, in alignment with the planetary orbits. Possible spin-orbit misalignments are seen in several systems, including three multiple-planet systems (KOI-304, 988, 2261). Ideally these systems should be scrutinized with complementary techniques---such as the Rossiter-McLaughlin effect, starspot-crossing anomalies or asteroseismology---but the measurements will be difficult owing to the relatively faint apparent magnitudes and small transit signals in these systems.
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