DSpace collection: 期刊論文

WIDGET: System Performance and GRB Prompt Optical Observations

Tue, 27 Mar 2012 10:13:29 GMT

title: WIDGET: System Performance and GRB Prompt Optical Observations abstract: The WIDeField telescope for Gamma-ray burst Early Timing (WIDGET) is used for a fully automated, ultrawide-field survey aimed at detecting the prompt optical emission associated with Gamma-ray Bursts (GRBs). WIDGET surveys the HETE-2 and Swift/BAT pointing directions, covering a total field of view of 62 x 62 every 10 secounds using a unfiltered system. This monitoring survey allows the exploration of optical emission before the gamma-ray trigger. The unfiltered magnitude is well converted to the SDSS r' system at a 0.1 mag level. Since 2004, WIDGET has made a total of ten simultaneous and one pre-trigger GRB observations. The efficiency of synchronized observations with HETE-2 is four-times better than that of Swift. There has been no bright optical emission similar to that from GRB 080319B. A statistical analysis implies that GRB 080319B is a rare event. This paper summarizes the design and operation of the WIDGET system and the simultaneous GRB observations obtained with this instrument.

Whole Earth Telescope observations of the subdwarf B star KPD 1930+2752: a rich, short-period pulsator in a close binary

Tue, 27 Mar 2012 10:13:23 GMT

title: Whole Earth Telescope observations of the subdwarf B star KPD 1930+2752: a rich, short-period pulsator in a close binary abstract: KPD 1930+2752 is a short-period pulsating subdwarf B (sdB) star. It is also an ellipsoidal variable with a known binary period of 2.3 h. The companion is most likely a white dwarf and the total mass of the system is close to the Chandresekhar limit. In this paper, we report the results of Whole Earth Telescope (WET) photometric observations during 2003 and a smaller multisite campaign of 2002. From 355 h of WET data, we detect 68 pulsation frequencies and suggest an additional 13 frequencies within a crowded and complex temporal spectrum between 3065 and 6343 mu Hz (periods between 326 and 157 s). We examine pulsation properties including phase and amplitude stability in an attempt to understand the nature of the pulsation mechanism. We examine a stochastic mechanism by comparing amplitude variations with simulated stochastic data. We also use the binary nature of KPD 1930+2752 for identifying pulsation modes via multiplet structure and a tidally induced pulsation geometry. Our results indicate a complicated pulsation structure that includes short-period (approximate to 16 h) amplitude variability, rotationally split modes, tidally induced modes and some pulsations which are geometrically limited on the sdB star.

Transit timing variation and activity in the WASP-10 planetary system star

Tue, 27 Mar 2012 10:13:19 GMT

title: Transit timing variation and activity in the WASP-10 planetary system star abstract: Transit timing analysis may be an effective method of discovering additional bodies in extrasolar systems that harbour transiting exoplanets. The deviations from the Keplerian motion, caused by mutual gravitational interactions between planets, are expected to generate transit timing variations of transiting exoplanets. In 2009, we collected nine light curves of eight transits of the exoplanet WASP-10b. Combining these data with those published, we have found that transit timing cannot be explained by a constant period but by a periodic variation. Simplified three-body models, which reproduce the observed variations of timing residuals, were identified by numerical simulations. We have found that the configuration with an additional planet with a mass of similar to 0.1 M(J) and an orbital period of similar to 5.23 d, located close to the outer 5 : 3 mean motion resonance, is the most likely scenario. If the second planet is a transiter, the estimated flux drop will be similar to 0.3 per cent and can be observed with a ground-based telescope. Moreover, we present evidence that the spots on the stellar surface and the rotation of the star affect the radial-velocity curve, giving rise to a spurious eccentricity of the orbit of the first planet. We argue that the orbit of WASP-10b is essentially circular. Using the gyrochronology method, the host star was found to be 270 +/- 80 Myr old. This young age can explain the large radius reported for WASP-10b.

Trajectory of HAYABUSA Reentry Determined from Multisite TV Observations

Tue, 27 Mar 2012 10:13:17 GMT

title: Trajectory of HAYABUSA Reentry Determined from Multisite TV Observations abstract: The asteroid explorer HAYABUSA reentered into the Earth's atmosphere on 2010 June 13. We made simultaneous TV (television) observations at seven ground sites in order to calculate the trajectories of HAYABUSA and its sample return capsule (SRC), which both reentered into the atmosphere. Our TV observations showed that, after HAYABUSA reentered the atmosphere, the beginning time of its light emission on video was 13:51:57.4 UT at a height of 101.0 +/- 0.2 km. The end time was 13:52:42.0 UT at a height of 38.6 +/- 0.2 km. The initial velocity at the beginning was 12.1 +/- 0.3 km s(-1), and the entry angle was 9 degrees. After identifying SRC as separated light emission independent of the mother spacecraft, we analyzed the trajectory of SRC from a height of 52.9 km to 35.7 km based on video images. The actual trajectory of the capsule, determined from the TV observations, was almost the same as the predicted trajectory in terms of the position, velocity, and time. We then calculated the fall spots of the SRC heat shields from the rnultisite TV observations.