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  • 1
    In: Publications of the Astronomical Society of Japan, 2008, Vol. 60(4), pp.749-769
    Description: The non-LTE state of the hydrogen gas in isothermal transonic decretion disks around a B1V star has been calculated by an iterative method in order to explore the basic physical process in the disk. This dynamical model is characterized by a density law in the equatorial plane of $\rho(R) \propto R^{-3.5}$ . The continuous radiation was calculated with the $\Lambda$ iteration in the integral form, while we adopted a single-flight escape probability for lines. We describe the non-LTE state, the radiation flow and conversion in the disk. We conclude that the stellar Balmer continuum plays a key role in the non-LTE state of the disk. An examination of the local energy gain and loss suggests that the disk temperature has double minima along the equatorial plane in the optically thick case: the intermediate region caused by deficient ultraviolet radiation and the outer Lyman $\alpha$ cooling region. We also calculated some observable quantities, such as the spectral energy distribution, the $UBV$ colors, the infrared excess and the Balmer line profiles. Our calculations with a mass-loss rate less than $10^{-10}M_{\odot}\ {\rm yr}^{-1}$ reproduce the observed continuum quantities. However, we could not obtain the large H $\alpha$ emission strength observed in Be stars. We suggest that the density gradient of the Be star disk is slower than that of an isothermal decretion disk.
    Keywords: Stars: Atmospheres ; Circumstellar Matter ; Stars: Emission - Line, Be ; Line: Profiles ; Radiative Transfer
    ISSN: 0004-6264
    E-ISSN: 2053-051X
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  • 2
    Language: English
    In: International Astronomical Union Colloquium, 2000, Vol.175, pp.701-704
    ISSN: 0252-9211
    Source: CrossRef
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  • 3
    In: Publications of the Astronomical Society of Japan, 2001, Vol. 53(6), pp.L51-L54
    Description: We observed a new dwarf nova, IX Dra, for 46 days between 2000 November 10 and 2001 June 17, and revealed that IX Dra is the fifth member of a peculiar group of SU UMa stars, called ER UMa stars. The light curve is almost perfectly identical to that of V1159 Ori: supercycle, 53 d; interval of normal outbursts, 3–4 d; duty cycle, $\sim 30\%$ ; and the outburst amplitude, 2.5 mag. From a time-series observation during the superoutbursts, we obtained a presumable superhump period of 0.067 d. We note that some clustering may exist in the period distribution of ER UMa stars. It is needed to confirm this clustering by a larger number of examples.
    Keywords: Stars: Cataclysmic Variables ; Stars: Dwarf Novae ; Stars: Individual (Ix Draconis)
    ISSN: 0004-6264
    E-ISSN: 2053-051X
    Source: Oxford University Press
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  • 4
    In: Publications of the Astronomical Society of Japan, 2014, Vol. 66(5)
    Description: Continuing the project undertaken by Kato et al. ( 2009 ), we collected times of superhump maxima for 56 SU UMa-type dwarf novae mainly observed during the 2013–2014 season and characterized these objects. We detected negative superhumps in VW Hyi and indicated that the low number of normal outbursts in some supercycles can be interpreted as a result of disk tilt. This finding, combined with the Kepler observation of V1504 Cyg and V344 Lyr, suggests that disk tilt is responsible for modulating the outburst pattern in SU UMa-type dwarf novae. We also studied the deeply eclipsing WZ Sge-type dwarf nova MASTER OT J005740.99+443101.5 and found evidence of a sharp eclipse during the phase of early superhumps. The profile can be reproduced by a combination of the eclipse of the axisymmetric disk and the uneclipsed light source of early superhumps. This finding shows the lack of evidence for a greatly enhanced hot spot during the early stage of WZ Sge-type outburst. We detected growing (stage A) superhumps in MN Dra and give a suggestion that some of SU UMa-type dwarf novae situated near the critical condition of tidal instability may show long-lasting stage A superhumps. The large negative period derivatives reported in such systems can be understood as a result of the combination of stage A and B superhumps. Two WZ Sge-type dwarf novae, AL Com and ASASSN-13ck, showed a long-lasting (plateau-type) rebrightening. In the early phase of their rebrightenings, both objects showed a precursor-like outburst, suggesting that the long-lasting rebrightening is triggered by a precursor outburst.
    Keywords: Accretion, Accretion Disks ; Novae, Cataclysmic Variables ; Stars: Dwarf Novae
    ISSN: 0004-6264
    E-ISSN: 2053-051X
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  • 5
    In: Publications of the Astronomical Society of Japan, 2004, Vol. 56(sp1), pp.S99-S107
    Description: We report on the results of the QW Ser campaign, which has been continued from 2000 to 2003 by the VSNET collaboration team. Four long outbursts and many short ones were caught during this period. Our intensive photometric observations revealed superhumps with a period of $0.07700(\pm 0.00004) \,\mathrm{d}$ during all four superoutbursts, proving the SU UMa nature of this star. The recurrence cycles of the normal outbursts and the superoutbursts were measured to be $\sim 50$ days and $240(\pm 30)$ days, respectively. The change rate of the superhump period was $-5.8 \times 10^{-5}$ . The distance and the X-ray luminosity in the range of 0.5–2.4 keV are estimated to be $380(\pm60) \,\mathrm{pc}$ and $\log L_\mathrm{X} = 31.0 \pm 0.1 \,\mathrm{erg} \,\mathrm{s}^{-1}$ . These properties have typical values for an SU UMa-type dwarf nova with this superhump period.
    Keywords: Accretion, Accretion Disks ; Stars: Dwarf Novae ; Stars: Individual (Qw Ser) ; Stars: Novae, Cataclysmic Variables
    ISSN: 0004-6264
    E-ISSN: 2053-051X
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  • 6
    In: Publications of the Astronomical Society of Japan, 2001, Vol. 53(5), pp.905-914
    Description: We report here on time-resolved photometric observations of the superoutburst of a dwarf nova, RZ Leo, which occurred during 2000 December–2001 January. We reveal the following characteristics of the outburst based on our observations: long duration, large amplitude, and the existence of two types of superhumps — “early superhumps” and “normal superhumps”. In addition to the extremely low frequency of the outbursts, the characteristics of the outburst strongly indicate that RZ Leo is the fifth member of the WZ Sge-type dwarf novae. The orbital period of RZ Leo is 0.07651 d, which is remarkably longer than the “canonical” period of other WZ Sge stars ( $\sim 0.058\,\mathrm{d}$ ). The longer period indicates a non-degenerate secondary of RZ Leo, which suggests that the idea of a low quiescence viscosity due to a degenerate brown dwarf secondary may not be correct. The present discovery of RZ Leo as being a WZ Sge star provides the first clear indication that the decay of magnetic turbulence in accretion disks of quiescent WZ Sge stars plays an important role in producing the proposed low quiescent viscosity.
    Keywords: Stars: Cataclysmic Variables ; Stars: Dwarf Novae ; Stars: Individual (Rz Leo)
    ISSN: 0004-6264
    E-ISSN: 2053-051X
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  • 7
    In: Publications of the Astronomical Society of Japan, 2002, Vol. 54(2), pp.285-298
    Description: We report on photometric and spectroscopic observations of a possible halo black-hole X-ray nova, XTE J1118 $ +$ 480 ( $ =$ KV UMa) during outburst. Our photometric monitoring during the main outburst revealed that the optical maximum as well as the onset of the outburst precede those in the X-ray region. This indicates that the event was an “outside-in” type outburst and that its optical flux was dominated by viscous heating, itself, and not the effect of X-ray irradiation. Based on these results, we suggest an outburst scenario analogous to superoutbursts in SU UMa-type dwarf novae. This scenario predicts a superhump phenomenon, which we indeed detected throughout the outburst. We determined its period to be $ 0.170529\pm 0.000006 \,\mathrm{d}$ , which is slightly longer than the orbital periods suggested from spectroscopic observations. We have furthermore revealed the first evidence of a continuous period decreasing in X-ray novae. The most prominent feature in our optical spectrum is a double-peak He II 4686Å emission line having an asymmetric profile with an outstanding blue side peak. Using a Doppler mapping method, we found that the He II emission originates from the accretion disk, which particularly concentrates on the hot spot. The time that the blue peak becomes strongest corresponds to a superhump peak. This implies that we see an elongated side of an eccentric disk at that time and, hence, it may cause an asymmetric emission profile. Substituting the observed fractional superhump excess for a theoretically expected relation between it and the mass ratio, we estimate that the black-hole mass is larger than $9.5 \,{{{M}_{\odot}}}$ . XTE J1118 $ +$ 480 thus has a large mass of a compact object compared with the typical black-hole X-ray novae.
    Keywords: Accretion, Accretion Disks ; Binaries: Close ; Stars: Individual (Xte J1118+480)
    ISSN: 0004-6264
    E-ISSN: 2053-051X
    Source: Oxford University Press
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  • 8
    Language: English
    Description: Kyoto University (京都大学) 0048 新制・課程博士 博士(理学) 甲第14085号 理博第3332号 新制||理||1490(附属図書館) UT51-2008-L141 京都大学大学院理学研究科物理学・宇宙物理学専攻 (主査)准教授 上田 佳宏, 教授 太田 耕司, 教授 長田 哲也 学位規則第4条第1項該当
    Keywords: 400
    Source: Networked Digital Library of Theses and Dissertations
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  • 9
    In: Publications of the Astronomical Society of Japan, 2009, Vol. 61(sp2), pp.S395-S616
    Description: We systematically surveyed period variations of superhumps in SU UMa-type dwarf novae based on newly obtained data and past publications. In many systems, the evolution of the superhump period is found to be composed of three distinct stages: an early evolutionary stage with a longer superhump period, a middle stage with systematically varying periods, and a final stage with a shorter, stable superhump period. During the middle stage, many systems with superhump periods of less than 0.08 d show positive period derivatives. We present observational characteristics of these stages and give greatly improved statistics. Contrary to an earlier claim, we found no clear evidence for a variation of period derivatives among different superoutbursts of the same object. We present an interpretation that the lengthening of the superhump period is a result of the outward propagation of an eccentricity wave, which is limited by the radius near the tidal truncation. We interpret that late-stage superhumps are rejuvenated excitation of a 3:1 resonance when superhumps in the outer disk are effectively quenched. The general behavior of the period variation, particularly in systems with short orbital periods, appears to follow a scenario proposed in Kato, Maehara, and Monard ( 2008 , PASJ, 60, L23). We also present an observational summary of WZ Sge-type dwarf novae. Many of them have shown long-enduring superhumps during a post-superoutburst stage having longer periods than those during the main superoutburst. The period derivatives in WZ Sge-type dwarf novae are found to be strongly correlated with the fractional superhump excess, or consequently with the mass ratio. WZ Sge-type dwarf novae with a long-lasting rebrightening or with multiple rebrightenings tend to have smaller period derivatives, and are excellent candidates for those systems around or after the period minimum of evolution of cataclysmic variables.
    Keywords: Accretion, Accretion Disks ; Stars: Dwarf Novae ; Novae, Cataclysmic Variables
    ISSN: 0004-6264
    E-ISSN: 2053-051X
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  • 10
    Language: English
    In: Ultramicroscopy, 2011, Vol.111(12), pp.1650-1658
    Description: Although conventional electron microscopy (EM) requires samples to be in vacuum, most chemical and physical reactions occur in liquid or gas. The Atmospheric Scanning Electron Microscope (ASEM) can observe dynamic phenomena in liquid or gas under atmospheric pressure in real time. An electron-permeable window made of pressure-resistant 100 nm-thick silicon nitride (SiN) film, set into the bottom of the open ASEM sample dish, allows an electron beam to be projected from underneath the sample. A detector positioned below captures backscattered electrons. Using the ASEM, we observed the radiation-induced self-organization process of particles, as well as phenomena accompanying volume change, including evaporation-induced crystallization. Using the electrochemical ASEM dish, we observed tree-like electrochemical depositions on the cathode. In silver nitrate solution, we observed silver depositions near the cathode forming incidental internal voids. The heated ASEM dish allowed observation of patterns of contrast in melting and solidifying solder. Finally, to demonstrate its applicability for monitoring and control of industrial processes, silver paste and solder paste were examined at high throughput. High resolution, imaging speed, flexibility, adaptability, and ease of use facilitate the observation of previously difficult-to-image phenomena, and make the ASEM applicable to various fields. ► Atmospheric SEM (ASEM) observes dynamic phenomena in liquid or gas in open ASEM dish. ► Random motion and radiation-induced self-organization were observed. ► Tree-like electrochemical deposition of gold was observed on an electrode . ► Temperature-dependent phase transitions of solder were dynamically observed in air. ► Silver and solder pastes were easily and rapidly observed in air for process control.
    Keywords: SEM ; Electrochemistry ; Dynamic Observation ; Self Organization ; Asem ; Metal Paste ; Biology
    ISSN: 0304-3991
    E-ISSN: 1879-2723
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