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Naito H.,Nagoya University | Mizoguchi S.,Sendai Astronomical Observatory | Arai A.,Kyoto Sangyo University | Tajitsu A.,Japan National Astronomical Observatory | And 9 more authors.
Astronomy and Astrophysics | Year: 2012

We present optical (B, V, R c, I c and y) and near-infrared (J, H, and K s) photometric and spectroscopic observations of a classical nova V1280 Scorpii for five years from 2007 to 2011. Our photometric observations show a declining event in optical bands shortly after the maximum light, which took about 250 days to recover. This event was most probably caused by dust formation. The event was accompanied by a short (∼30 days) re-brightening episode (∼2.5 mag in V), which suggests that there had been some re-ignition of the surface nuclear burning. After 2008, the y band observations show a very long plateau at around y = 10.5 for more than 1000 days until April 2011 (∼1500 days after the maximum light). The nova had taken a very long time (∼50 months) to enter the nebular phase, according to a clear detection of both [O III] 4959 and 5007 and is still continuing to generate the wind caused by H-burning. This finding suggests that historically V1280 Sco is evolving at its slowest ever measured rate. The interval from the maximum light (2007 February 16) to the beginning of the nebular phase is longer than any previously known slow novae: V723 Cas (18 months), RR Pic (10 months), or HR Del (8 months). It suggests that the mass of a white dwarf in the V1280 Sco system might be 0.6 M ⊙ or lower. The distance, based on our measurements of the expansion velocity combined with the directly measured size of the dust shell, is estimated to be 1.1 ± 0.5 kpc. © 2012 ESO.

Yamamoto K.,Osaka University | Matsuo T.,Kyoto University | Shibai H.,Osaka University | Itoh Y.,Nishi Harima Astronomical Observatory | And 53 more authors.
Publications of the Astronomical Society of Japan | Year: 2013

We carried out an imaging survey for extrasolar planets around stars in the Pleiades (125 Myr, 135 pc) in the H and KS bands using HiCIAO combined with adaptive optics, AO188, on the Subaru telescope. We found 13 companion candidates fainter than 14.5 mag in the H band around 9 stars. Five of these 13 were confirmed to be background stars by measurement of their proper motion. One was not found in the second epoch observation, and thus was not a background or companion object. One had multi-epoch images, but the precision of its proper motion was not sufficient to conclude whether it was a background object. Four other candidates are waiting for second-epoch observations to determine their proper motion. Finally, the remaining two were confirmed to be 60MJ brown dwarf companions orbiting around HD 23514 (G0) and HII 1348 (K5), respectively, as had been reported in previous studies. In our observations, the average detection limit for a point source was 20.3 mag in the H band beyond 1:005 from the central star. On the basis of this detection limit, we calculated the detection efficiency to be 90% for a planet with 6 to 12 Jovian masses and a semi-major axis of 50-1000 AU. For this reason we extrapolated the distribution of the planet mass and the semi-major axis derived from radial velocity observations, and adopted the planet evolution model Baraffe et al. (2003, A&A, 402, 701). Since there was no detection of a planet, we estimated the frequency of such planets to be less than 17.9% (2) around one star of the Pleiades cluster. © 2013. Astronomical Society of Japan.

Iijima T.,Astronomical Observatory of Padua | Naito H.,Nishi Harima Astronomical Observatory | Naito H.,Nagoya University
Astronomy and Astrophysics | Year: 2011

The spectral evolution of the classical nova V2468 Cygni (Nova Cyg 2008) was monitored at Asiago Astrophysical Observatory in Italy and at Nishi-Harima Astronomical Observatory in Hyogo Japan from soon after the discovery in March 2008 to the end of 2009. The notable peculiarities in the spectra of this nova were the asymmetric and variable profiles of its emission lines. The emission-line profiles of H I varied in the early decline stage in 2008, while their profiles were nearly stable in 2009. On the other hand, large variations in the profiles of the emission lines of [O III], [Fe VII], and He II were observed in 2009. In the spectrum obtained on 2009 October 15, the red parts of the emission lines of [O III] strengthened with respect to the profiles in September, while the red parts of the lines of He II and [Fe VII] faded. The emission lines of [Fe VII] 5721 and [Fe VII] + [Ca V] 6087 exhibited convex profiles on 2009 September 27 and 28 in a similar way to the other lines, while only these lines had concave profiles on October 26 and 29. It seems to be difficult to explain the variations in the emission-line profiles with any known model of nova shells. The absolute magnitude at light maximum and the distance to the nova are estimated to be MV = -8.8±0.3 mag and d = 5.5±0.8 kpc. Using the intensities of H I, He I, and He II lines observed in September 2009, we estimated the helium abundance in number to be N(He) = 0.20±0.01, and the mass of the ejecta to be 1.7±1 × 10 -5 M⊙. A very broad emission line from 3790 Å to 3850 Å was detected in the spectrum obtained on 2009 July 21. We propose that the multiple lines of [Fe V] 3F, 3839.3, 3794.9, 3851.3, 3819.9 etc. suddenly strengthened at that time, but the cause of this phenomenon is not known. © 2010 ESO.

Shidatsu M.,Kyoto University | Ueda Y.,Kyoto University | Nakahira S.,Japan Aerospace Exploration Agency | Done C.,Durham University | And 13 more authors.
Astrophysical Journal | Year: 2013

We report the results from X-ray studies of the newly discovered black hole candidate MAXI J1305-704 based on Suzaku and Swift observations in the low/hard and high/soft states, respectively. The long Suzaku observation shows two types of clear absorption dips, both of which recur on a dip interval of 9.74 ± 0.04 hr, which we identify with the orbital period. There is also partially ionized absorption in the nondip (persistent) emission in both the high/soft state and, very unusually, the low/hard state. However, this absorption (in both states) has substantially lower ionization than that seen in other high inclination systems, where the material forms a homogeneous disk wind. Here instead the absorption is most likely associated with clumpy, compact structures associated with the dipping material, which we see uniquely in this source likely because we view it at a very large inclination angle. A large inclination angle is also favored, together with a low black hole mass, to explain the high disk temperature seen in the fairly low luminosity high/soft state, as Doppler boosting enhances the disk temperature at high inclination. The disk radius inferred from these data is significantly smaller than that of the soft component seen in the low/hard state, supporting models where the disk is truncated at low luminosities. We find, however, that the lack of variability power on timescales of ∼50 s in the Suzaku low/hard state data is difficult to explain, even with a low-mass black hole. © 2013. The American Astronomical Society. All rights reserved..

Kim M.-J.,Yonsei University | Kim M.-J.,Korea Astronomy and Space Science Institute | Choi Y.-J.,Korea Astronomy and Space Science Institute | Moon H.-K.,Korea Astronomy and Space Science Institute | And 7 more authors.
Astronomy and Astrophysics | Year: 2013

Context. Near-Earth asteroid 162173 (1999 JU3) is a potential target of two asteroid sample return missions, not only because of its accessibility but also because of the first C-type asteroid for exploration missions. The lightcurve-related physical properties of this object were investigated during the 2011 - 2012 apparition. Aims. We aim to confirm the physical parameters useful for JAXA's Hayabusa 2 mission, such as rotational period, absolute magnitude, and phase function. Our data complement previous studies that did not cover low phase angles. Methods. With optical imagers and 1-2 m class telescopes, we acquired the photometric data at different phase angles. We independently derived the rotational lightcurve and the phase curve of the asteroid. Results. We have analyzed the lightcurve of 162173 (1999 JU3), and derived a synodic rotational period of 7.625 ± 0.003 h, the axis ratio a/b = 1.12. The absolute magnitude HR = 18.69 ± 0.07 mag and the phase slope of G = -0.09 ± 0.03 were also obtained based on the observations made during the 2011-2012 apparition. These physical properties are in good agreement with the previous results obtained during the 2007-2008 apparition. © ESO 2013.

Matsuo T.,Kyoto University | Murakami N.,Hokkaido University | Kotani T.,Japan National Astronomical Observatory | Kawahara H.,University of Tokyo | And 20 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2014

We propose a new high contrast imager for Kyoto 4m segmented telescope called SEICA (Second-generation Exoplanet Imager with Coronagraphic Adaptive optics), aiming at detection and characterization of selfluminous gas giants within 10AU around nearby stars. SEICA is aggressively optimized for high performance at very small inner working angle, 10-6 detection contrast at 0".1 in 1-hour integration. We start the on-sky commissioning test in 2016 and the science observations in 2017. Since it is the first time to realize the highcontrast imaging on the segmented telescope, SEICA is an important step toward future high contrast sciences on Extremely Large Telescopes (ELTs). This paper presents an overall of the SEICA program and the conceptual design for ultimate performance under given atmospheric conditions. © 2014 SPIE.

Ishiguro M.,Seoul National University | Ham J.-B.,Seoul National University | Tholen D.J.,University of Hawaii at Manoa | Elliott G.T.,University of Hawaii at Manoa | And 13 more authors.
Astrophysical Journal | Year: 2011

We present the optical observations of the Near Earth Object 107P/(4015) Wilson-Harrington during the 2009/2010 apparition taken in search of low-level comet activity. Our photometric and spectroscopic data were collected 28-86 days after the perihelion passage on 2009 October 22 in a wide range of solar phase angles of 39°-68°. A disk-integrated phase function was constructed, giving a geometric albedo of 0.055 ± 0.012, phase integral of q = 0.34, and Bond albedo of AB = 0.019. The photometric property shows a profile similar to low albedo asteroids and comet nuclei. No emission lines were found in our spectrum, giving a flat reflectance similar to low albedo asteroids. Although we could not find any evidence for cometary activity in our photometric and spectroscopic data, we found an upper limit of 0.001% on the fractional active area. We derived the upper limit of the optical depth of the dust trail and tail, 7 × 10-10. We conclude that 107P/(4015) Wilson-Harrington was completely dormant or inactive in the 2009/2010 return. © 2011 The American Astronomical Society. All rights reserved.

Ishiguro M.,Japan National Astronomical Observatory | Ishiguro M.,Seoul National University | Watanabe J.-I.,Japan National Astronomical Observatory | Sarugaku Y.,Japan Aerospace Exploration Agency | And 11 more authors.
Astrophysical Journal | Year: 2010

Based on optical and infrared observations, we study the albedo and the temperature of the dust grains associated with the spectacular 2007 outburst of Jupiter-family comet 17P/Holmes. We found that the albedo at the solar phase angle ∼ 16° was 0.03-0.12. While the color temperature around 3-4 μm was 360 ± 40K, the color temperature at 12.4 μm and 24.5 μm was ∼ 200K, which is consistent with that of a blackbody. We studied the equilibrium temperature of the dust grains at 2.44AU and found that the big discrepancy in the temperature was caused by the heterogeneity in particle size, that is, hotter components consist of submicron absorbing grains whereas colder components consist of large (≳1 μm) grains. The contemporaneous optical and mid-infrared observations suggest that the albedo and the temperature could decrease within ∼ 3 days after the outburst and stabilized at typical values of the other comets. We estimated the total mass injected into the coma by the outburst on the basis of the derived albedo and the optical magnitude for the entire dust cloud, and found that at least 4 × 1010kg (equivalent to a few meter surface layer) was removed by the initial outburst event. The derived mass suggests that the outburst is explainable by neither the exogenetic asteroidal impact nor water ice sublimation driven by solar irradiation, but by an endogenic energy source. We conclude that the outburst was triggered by the energy sources several meters or more below the nuclear surface. © 2010 The American Astronomical Society. All rights reserved.

Kuwamura S.,Kitami Institute of Technology | Yoshinoya Y.,Kitami Institute of Technology | Miura N.,Kitami Institute of Technology | Tsumuraya F.,Nishi Harima Astronomical Observatory | And 2 more authors.
Optical Review | Year: 2011

A bispectral method for astronomical speckle imaging utilizes an average speckle bispectrum of an object to derive its Fourier phase. There has been, however, a problem in conventional bispectral algorithm owing to difficulty in processing bispectral data in a four-dimensional (4D) space. In this paper, we propose an implementation to overcome this problem, where a one-dimensional (1D) object projection is reconstructed from a two-dimensional (2D) average bispectrum of speckle projections, and object projections so obtained at various angles are then tomographically combined into a 2D object image. In this tomographic approach, processes are separable into those for individual projection angles, implying that bispectral data required to be stored at a time are from 4D to 2D and computation time can be substantially reduced by parallelizing angle-by-angle processes. We have performed experiments using simulated and observed data, and have demonstrated the feasibility of the present approach with an achievable accuracy comparable to that of a conventional approach. © 2011 The Optical Society of Japan.

Kuwamura S.,Kitami Institute of Technology | Azuma Y.,Kitami Institute of Technology | Miura N.,Kitami Institute of Technology | Tsumuraya F.,Nishi Harima Astronomical Observatory | And 2 more authors.
Optical Review | Year: 2014

In astronomical speckle imaging, deconvolving a shift-and-add (SAA) image has an advantage over deconvolving noisy specklegrams, because an SAA image is an integration of many specklegrams and has a relatively enhanced signal-tonoise ratio. In this paper, to reinforce the deconvolution of a single SAA image, we propose a multiframe deconvolution applied to multiple SAA images that are obtained by diversely recombining the same set of specklegrams to have different point spread functions. We have found that such diverse SAA images can be easily produced by permuting specklegrams to be processed by SAA. The results of experiments using simulated and observational data have shown a robustness of our present approach: in the previous approach of deconvolving a single SAA frame, the resulting object estimate is apt to be influenced by the given SAA frame and the estimation sometimes fails, whereas in the present approach, a reliable object image is stably reconstructed regardless of the given SAA frames. © 2014 The Optical Society of Japan.

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