Okayama Astrophysical Observatory

Asakuchi, Japan

Okayama Astrophysical Observatory

Asakuchi, Japan
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Elmasli A.,Ankara University | Fossati L.,Open University Milton Keynes | Folsom C.P.,Armagh Observatory | Albayrak B.,Ankara University | Izumiura H.,Okayama Astrophysical Observatory
New Astronomy | Year: 2012

The Ursa Major group is a nearby stellar supercluster which, while not gravitationally bound, is defined by co-moving members. DD UMa is a δ Scuti star whose membership in the Ursa Major group is unclear. The objective of this study is to confirm the membership of DD UMa in the Ursa Major group, as well as perform a detailed spectral analysis of the star. Since DD UMa is a low-amplitude δ Scuti star, we performed a frequency analysis. We determined fundamental parameters, chemical abundances, and derive a mass and age for the star. For this study we observed DD UMa at the Okayama Astrophysical Observatory with the high-resolution spectrograph HIDES, between the 27th of February and the 4th March, 2009. Additional observations were extracted from the ELODIE archive in order to expand our abundance analysis. Group membership of DD UMa was assessed by examining the velocity of the star in Galactic coordinates. Pulsational frequencies were determined by examining line profile variability in the HIDES spectra. Stellar fundamental parameters and chemical abundances were derived by fitting synthetic spectra to both the HIDES and ELODIE observations. DD UMa is found to be a member of the extended stream of the Ursa Major group, based on the space motion of the star. This is supported by the chemical abundances of the star being consistent with those of Ursa Major group members. The star is found to be chemically solar, with Teff = 7450 ± 150 K and logg = 3.98 ± 0.2. We found pulsational frequencies of 9.4 and 15.0 c/d. While these frequencies are insufficient to perform an asteroseismic study, DD UMa is a good bright star candidate for future study by the BRITE-constellation. © 2011 Elsevier B.V. All rights reserved.

Darnley M.J.,Liverpool John Moores University | Henze M.,European Space Astronomy Center | Steele I.A.,Liverpool John Moores University | Bode M.F.,Liverpool John Moores University | And 21 more authors.
Astronomy and Astrophysics | Year: 2015

The Andromeda Galaxy recurrent nova M31N 2008-12a had been caught in eruption eight times. The inter-eruption period of M31N 2008-12a is ~1 yr, making it the most rapidly recurring system known, and a strong single-degenerate Type Ia supernova progenitor candidate. Following the 2013 eruption, a campaign was initiated to detect the predicted 2014 eruption and to then perform high cadence optical photometric and spectroscopic monitoring using ground-based telescopes, along with rapid UV and X-ray follow-up with the Swift satellite. Here we report the results of a high cadence multi-colour optical monitoring campaign, the spectroscopic evolution, and the UV photometry. We also discuss tantalising evidence of a potentially related, vastly-extended, nebulosity. The 2014 eruption was discovered, before optical maximum, on October 2, 2014. We find that the optical properties of M31N 2008-12a evolve faster than all Galactic recurrent novae known, and all its eruptions show remarkable similarity both photometrically and spectroscopically. Optical spectra were obtained as early as 0.26 days post maximum, and again confirm the nova nature of the eruption. A significant deceleration of the inferred ejecta expansion velocity is observed which may be caused by interaction of the ejecta with surrounding material,possibly a red giant wind. We find a low ejected mass and low ejection velocity, which are consistent with high mass-accretion rate, high mass white dwarf, and short recurrence time models of novae. We encourage additional observations, especially around the predicted time of the next eruption, towards the end of 2015. © ESO, 2015.

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.

Yilmaz M.,Ankara University | Selam S.O.,Ankara University | Sato B.,Tokyo Institute of Technology | Izumiura H.,Okayama Astrophysical Observatory | And 4 more authors.
New Astronomy | Year: 2013

A small group of collaborators was established at the end of 2007 with the objective of starting an extrasolar planet search at the TÜBITAK National Observatory of Turkey. High resolution spectra of some radial velocity standards and planet-harbouring stars have since been obtained using an iodine (I 2) absorption cell placed in front of the entrance slit of the Coude Echelle Spectrograph (CES) in the 1.5-m Russian-Turkish Telescope (RTT150). To determine precise radial velocity measurements for these stars, a new computer code was developed by one of the collaborators (MY) using an IDL (Interactive Data Language) programing platform specific to the RTT150's CES + I 2-cell data. This paper summarises the technical setup, the new code, the test observation results and the precision achieved in the radial velocity measurements. The results from radial velocity standards and planet-harbouring stars show that a precision of approximately 10 m s -1 was achieved with the CES on the RTT150 during the three years of test observations. In addition, the instrumental profile (IP) characteristics of the CES on the RTT150 in this study were derived by modelling the observed B-star + I 2 spectra. The observed instrumental profiles were a typical Gaussian shape and exhibited small variations that depended on the position on the CCD and also varied between exposures, which affected the precision of the radial velocity measurements. © 2012 Elsevier B.V. All rights reserved.

Yanagisawa K.,Okayama Astrophysical Observatory | Kuroda D.,Okayama Astrophysical Observatory | Yoshida M.,Hiroshima University | Shimizu Y.,Okayama Astrophysical Observatory | And 4 more authors.
AIP Conference Proceedings | Year: 2010

MITSuME Okayama Telescope is an autonomous telescope with a diameter of 50 cm dedicated primarily to follow-up γ-ray bursts. The telescope has successfully been in operation since 2004. We have made 131 observations of γ-ray bursts and submitted 47 reports to GCN circulars. In this article, we present an overview of the instrumentation and scientific results obtained so far. © 2010 American Institute of Physics.

Shimono A.,University of Tokyo | Iwamuro F.,Kyoto University | Kurita M.,Kyoto University | Moritani Y.,Kyoto University | And 5 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2012

A 3.8 m segmented telescope is planned to be built at the Okayama Astrophysical Observatory by the joint program among Kyoto university, Nagoya university, NAOJ, and Nano-Optonics Energy Inc. This is the world's first optical-infrared telescope whose primary mirror is composed of "petal-shaped" segment mirrors. To investigate the best layout of the displacement sensors as well as to study the control algorithm, we have developed a simulation software for the segmented petaloid mirrors. This simulator calculates the vertical position differences between the segments at the 60 displacement sensors based on the three-dimensional movements of the 54 actuators, and enables us to test the control algorithms under various conditions including random noise on the displacement sensors, random movement errors of the actuators, and unexpected lateral shifts of the segments. The outputs of the simulator are not only the phase error of the primary mirror but also the PSF image, taking the structure function of the optical surfaces into account. Using a singular value decomposition method, we found that the 18 petal-shaped segments are controllable within the required displacement errors of 15 nm under the following three conditions: 1) the displacement measurement sensors are placed in staggered fashion between segments, 2) the displacement measurement sensors are axisymmetrically placed with respect to the optical axis, and 3) the relative lateral shift and rotation of each segment are less than 500 μm and 0.05 degree, respectively. In this report, the control algorithm, requirements for the layout of the displacement measurement sensors, and the simulated performance will be presented. © 2012 SPIE.

Otsuka M.,US Space Telescope Science Institute | Tajitsu A.,Subaru Telescope | Hyung S.,Chungbuk National University | Izumiura H.,Okayama Astrophysical Observatory
Astrophysical Journal | Year: 2010

We have performed a comprehensive chemical abundance analysis ofthe extremely metal-poor ([Ar/H] < -2) halo planetary nebula (PN) BoBn 1 based on International Ultraviolet Explorer archive data, Subaru/High-Dispersion Spectrograph spectra, VLT/UVES archive data, and Spitzer/IRS spectra We have detected over 600 lines in total and calculated ionic and elemental abundances of 13 elements using detected optical recombination lines (ORLs) and collisionally excited lines (CELs). The estimations of C, N, O, and Ne abundances from theORLs and Kr,Xe, and Ba from the CELs are done the first for this nebula, empirically and theoretically. The C, N, O, and Ne abundances from ORLs are systematically larger than those from CELs. The abundance discrepancies apart fromOcould be explained by a temperature fluctuation model, and that of O might be by a hydrogen-deficient cold component model.We have detected five fluorine and several slow neutron capture elements (the s-process). The amounts of [F/H], [Kr/H], and [Xe/H] suggest that BoBn 1 is the most F-rich among F-detected PNe and is a heavy s-process element rich PN. We have confirmed dust in the nebula that iscomposed of amorphous carbon and polycyclic aromatic hydrocarbons with a total mass of 5.8 × 10-6M⊙. The photoionization models built with non-LTE theoretical stellar atmospheres indicate that the progenitor was a 1-1.5M⊙ star that would evolve into a white dwarf with an ∼0.62M⊙ core mass and∼0.09M⊙ ionized nebula.We have measured a heliocentric radial velocity of +191.6±1.3 kms-1 and expansion velocity 2Vexp of 40.5 ± 3.3 km s -1 from an average over 300 lines. The derived elemental abundances have been reviewed from the standpoint of theoretical nucleosynthesis models. It is likely that the elemental abundances except Ncould be explained either by a 1.5M⊙ single starmodel or by a binarymodel composed of 0.75M⊙ +1.5M⊙ stars. Careful examination implies that BoBn 1 has evolved from a 0.75M⊙ + 1.5M⊙ binary and experienced coalescence during the evolution to become a visible PN, similar to the other extremely metal-poor halo PN, K 648 in M 15. © 2010. The American Astronomical Society.

Murakawa K.,University of Leeds | Izumiura H.,Okayama Astrophysical Observatory
Astronomy and Astrophysics | Year: 2012

Aims. We investigate the circumstellar dust shell of the water fountain source IRAS 16342-3814. Methods. We performed two-dimensional radiative transfer modeling of the dust shell, taking into account previously observed spectral energy distributions (SEDs) and our new J-band imaging and H-and K S-band imaging polarimetry obtained using the VLT/NACO instrument. Results. Previous observations expect an optically thick torus in the equatorial plane because of a striking bipolar appearance and a large viewing angle of 30-40°. However, models with such a torus as well as a bipolar lobe and an AGB shell cannot fit the SED and the images simultaneously. We find that an additional optically and geometrically thick disk located inside a massive torus solves this problem. The masses of the disk and the torus are estimated to be 0.01 M · at the a max = 100 μm dust and 1 M · at a max = 10 μm dust, respectively. Conclusions. We discuss a possible formation scenario for the disk and torus based on a similar mechanism to the equatorial back flow. IRAS 16342-3814 is expected to undergo mass loss at a high rate. The radiation from the central star is shielded by the dust that was ejected in the subsequent mass loss event. As a result, the radiation pressure on dust particles cannot govern the motion of the particles anymore. The mass loss flow can be concentrated in the equatorial plane by help of an interaction, which might be the gravitational attraction by the companion, if it exists in IRAS 16342-3814. A fraction of the ejecta is captured in a circum-companion or circum-binary disk and the remains are escaping from the central star(s) and form the massive torus. © 2012 ESO.

Murakawa K.,University of Leeds | Izumiura H.,Okayama Astrophysical Observatory | Oudmaijer R.D.,University of Leeds | Maud L.T.,University of Leeds
Monthly Notices of the Royal Astronomical Society | Year: 2013

We investigate the circumstellar dust properties of the oxygen-rich bipolar proto-planetary nebula (PPN) IRAS 18276-1431 by means of two-dimensional radiative transfer simulations of the circumstellar dust shell. The model geometry is assumed to have a torus and an envelope which consists of a pair of bipolar lobes and a spherical asymptotic giant branch shell. The parameters of the dust and the dust shell are constrained by comparing the spectral energy distribution (SED) and near-infrared intensity and polarization data with the models. The polarization in the envelope reaches 50-60 per cent and is nearly constant in the H and KS bands in the observations. This weak wavelength dependence of the polarization can be reproduced with a grain-size distribution function for the torus: 0.05 μm ≤ a with n(a) α a-(p=5.5) exp(-a/ac = 0.3 μm). The power index p is significantly steeper than that for interstellar dust (p ~ 3). Similar results have also been found in some other PPNs and suggest that mechanisms that grind down large particles, such as sputtering, may also have acted when the dust particles formed. The spectral opacity index β is found to be 0.6 ± 0.5 from the 760 μm to 2.6 mm fluxes, which is characterized by the dust in the torus. This low value (<2) indicates the presence of large dust grains in the torus. We discuss two possible dust models for the torus. One has a size distribution function of 1.0 ≤ a ≤ amax = 5 000.0 μmwith n(a) α a-(p=5.5) and the other is 1.0 μm≤ a ≤ amax = 10 000.0 μm with n(a) α a-(p=5.5). The former has β of 0.633, but we are not able to find reasonable geometry parameters to fit the SED in the infrared. The latter has β of 1.12, but reproduces the SED better over a wide wavelength range. With this dust model, the geometric parameters are estimated as follows: the inner and outer radii are 30 and 1000 au and the torus mass is 3.0 M⊙. Given that the torii are generally not found to be rotating, a large fraction of the torus material is likely to be expanding. Assuming an expansion velocity of 15 km s-1, the torus formation time and mass-loss rate are found to be ~300 yr and ~10-2M⊙ yr-1, respectively. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Murakawa K.,Okayama Astrophysical Observatory
AIP Conference Proceedings | Year: 2012

Imaging polarimetry is a powerful technique to study circumstellar dusty environments. Detailed analyses of polarization disks allow to quantitatively evaluate the disk geometries and the dust properties. We present near-infrared (NIR) polarimetric images and radiative transfer modeling of the high-mass protostar CRL 2136 and the Herbig Be star R Mon. In CRL 2136, the data show a central star feature (IRS 1), a spot-like high polarization region towards IRS 1 (P K = 32%), and a linear polarization vector alignment along the equatorial direction around IRS 1. In our spherical grain model, the optical depth of the disk is estimated to be 210 in the V-band. With such an intermediate optical depth, the linear vector alignment and the visible central star feature can not be reproduced simultaneously. We interpret that the linear vector alignment detected in our observation is probably due to dichroism by aligned nonspherical grains. In R Mon, our NIR polarimetric data detected a butterfly-shaped polarization disk with an extension of ∼4″, low polarizations (P<2%), and a centro-symmetric vector alignment. Our radiative transfer models which reproduce these results expect a large disk radius of 3000 AU and large dust up to ∼1000.0 μm in the disk. The polarization disk traces the Keplerian rotating gas disk (∼1500 AU) comparably well and the modeled disk is much larger than typical low-mass star disks (∼100 AU). Furthermore, the dust disk is found to be geometrically thinner than the gas disk (Fuente et al. 2006) and much thicker than typical T Tauri disks. This result suggests a possible ongoing dust settling. © 2012 American Institute of Physics.

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