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• 1
Article
In: Publications of the Astronomical Society of Japan, 1996, Vol. 48(6), pp.827-831
Description: Photometric observations of the galactic supersoft X-ray source RXJ0019.8+2156 in the B , V , R , and I bands were carried out between July and December of 1995. The observed light curves show periodic variations (Period = 15.85hr) with an amplitude of around 0.5mag in all four bands, while color curves ( B – V , V – R , and V – I ) show virtually no variation throughout the cycle. We find a secondary minimum which is highly variable in its shape from one cycle to another. The hump before the secondary minimum (phase ∼ 0.3–0.4) is brighter by about 0.1mag compared to that seen after the secondary minimum (phase ∼ 0.6–0.7). The primary minimum appears to be stable in depth on a timescale of several months. Furthermore, changes in brightness of about 0.15mag are observed from one cycle to another without detectable variation in the colors. The time scale of these irregular fluctuations is about one week or shorter.
Keywords: Accretion Disks ; Photometry ; Stars: Individual (Rx J0019. 8+2156) ; X - Rays: Binaries
ISSN: 0004-6264
E-ISSN: 2053-051X
Source: Oxford University Press
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• 2
Article
In: Nature, 2016, Vol.529(7584), p.54
Description: ブラックホール近傍から出る規則的なパターンを持つ光の変動を可視光で初めて捉えることに成功 -ブラックホールの「またたき」を直接目で観測できる機会に期待-. 京都大学プレスリリース. 2016-01-07. How black holes accrete surrounding matter is a fundamental yet unsolved question in astrophysics. It is generally believed that matter is absorbed into black holes via accretion disks, the state of which depends primarily on the mass-accretion rate. When this rate approaches the critical rate (the Eddington limit), thermal instability is supposed to occur in the inner disk, causing repetitive patterns of large-amplitude X-ray variability (oscillations) on timescales of minutes to hours. In fact, such oscillations have been observed only in sources with a high mass-accretion rate, such as GRS 1915+105 (refs 2, 3). These large-amplitude, relatively slow timescale, phenomena are thought to have physical origins distinct from those of X-ray or optical variations with small amplitudes and fast timescales (less than about 10 seconds) often observed in other black-hole binaries--for example, XTE J1118+480 (ref. 4) and GX 339−4 (ref. 5). Here we report an extensive multi-colour optical photometric data set of V404 Cygni, an X-ray transient source containing a black hole of nine solar masses (and a companion star) at a distance of 2.4 kiloparsecs (ref. 8). Our data show that optical oscillations on timescales of 100 seconds to 2.5 hours can occur at mass-accretion rates more than ten times lower than previously thought. This suggests that the accretion rate is not the critical parameter for inducing inner-disk instabilities. Instead, we propose that a long orbital period is a key condition for these large-amplitude oscillations, because the outer part of the large disk in binaries with long orbital periods will have surface densities too low to maintain sustained mass accretion to the inner part of the disk. The lack of sustained accretion--not the actual rate--would then be the critical factor causing large-amplitude oscillations in long-period systems.
Keywords: High-Energy Astrophysics ; Stars ; Sciences (General) ; Physics;
ISSN: 0028-0836
E-ISSN: 14764687
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• 3
Article
In: Publications of the Astronomical Society of Japan, 2013, Vol. 65(3)
Description: We present our photometric studies of a newly discovered optical transient, OT J012059.6 $+$ 325545, which underwent a large outburst during the period between 2010 November and 2011 January. The amplitude of the outburst was $\sim$ 8 mag. We performed simultaneous multicolor photometry using g $'$ -, $R_{\rm C}$ -, and $i'$ -band filters from the early stage of the outburst. Time-resolved photometry during its early stage revealed periodic variations with double-peaked profiles, which are referred to as early superhumps, with amplitudes of $\sim$ 0.08 mag. After rapid fading in the main outburst, we found rebrightening phenomena, which occurred at least nine times. The large amplitude of the outburst, early superhumps, and rebrightening phenomena are typical features of WZ Sge-type dwarf novae. We detected color variations within early superhump modulations, which established this objects as the second system of WZ Sge-type dwarf nova, next to V445 And. We carried out numerical calculations of the accretion disk to explain both of the modulations and the color variations of the early superhump. This modeling of the disk height supports the idea that height variations within the outer disk can produce early-superhump modulations, though we cannot rule out an idea that temperature asymmetry may also play a role.
Keywords: Accretion: Accretion Disks ; Binaries: Close ; Stars: Dwarf Novae ; Stars: Individual (Ot J012059. 6 + 325545)
ISSN: 0004-6264
E-ISSN: 2053-051X
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• 4
Article
In: Monthly Notices of the Royal Astronomical Society, 2015, Vol. 455(3), pp.2712-2730
Description: We present broad-band photometric and polarimetric observations of two Type II supernovae (SNe) 2013hj and 2014G. SN 2014G is a spectroscopically classified Type IIL event, which we also confirm photometrically because its light curve shows characteristic features – a plateau slope of 2.55 mag (100 d) −1 in the V band and a duration of ∼77 d – of a generic Type IIL SN. However, SN 2013hj also shows a high plateau decline rate of 1.5 mag (100 d) −1 in the V band, similar to SNe IIL, but marginally lower than SNe IIL template light curves. Our high cadence photometric observations of SNe 2013hj and 2014G enables us to cover all characteristic phases up to the radioactive tail of optical light curves. Broad-band polarimetric observations reveal some polarization in SN 2013hj with subtle enhancement as the SN evolves towards the plateau end. However, the polarization angle remains constant throughout the evolution. This characteristic is consistent with the idea that the evolving SN with recombining hydrogen envelope is slowly revealing a more asymmetric central region of explosion. Modelling of the bolometric light curve yields a progenitor mass of ∼11 M ⊙ with a radius of ∼700 R ⊙ for SN 2013hj, while for the SN 2014G model estimated progenitor mass is ∼9 M ⊙ with a radius of ∼630 R ⊙ , both having a typical energy budget of ∼2 × 10 51  erg.
Keywords: Supernovae: General ; Supernovae: Individual: Sn 2013hj ; Supernovae: Individual: Sn 2014g ; Galaxies: Individual: Mcg - 02 - 24 - 3 ; Galaxies: Individual: Ngc 3448
ISSN: 0035-8711
E-ISSN: 1365-2966
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• 5
Article
In: Frontiers Science Series No. 26., 1999., p.45
Description: ER UMa stars are a recently recognized small subgroup of SU UMa-type dwarf novae, which are characterized by the extremely high outburst frequency and short (19--48 d) supercycles. From the current thermal-tidal disk instability scheme, they are considered to be high mass-transfer SU UMa-type dwarf novae, and comprise a link to "permanent superhumpers" below the period gap. They do not only provide an opportunity to test the applicability of thermal-tidal instability model but also pose problems on the origin of high mass-transfer in short orbital-period cataclysmic variables. A historical review of this subgroup and recent topics of ER UMa stars, the unique pattern of superhump evolution and the "helium ER UMa analog" (CR Boo), are also discussed. Comment: 10 pages, 6 figures, reproduction of the proceeding paper in 1999 for easier accessibility (Disk Instabilities in Close Binary Systems. 25 Years of the Disk-Instability Model. Proceedings of the Disk-Instability Workshop held on 27-30 October, 1998; Frontiers Science Series No. 26. Universal Academy Press, Inc., 1999., p.45.)
Keywords: Astrophysics - Solar And Stellar Astrophysics
Source: Cornell University
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• 6
Article
Language: English
In: IEEE Transactions on Industrial Electronics, April, 2007, Vol.54(2), p.1113(9)
Description: The use of robotic devices in surgical applications has been growing in recent years. Surgical robots are beginning to find applications in minimally invasive surgeries. The control issues pertaining to many of the applications of robotics to surgery are similar. In all cases, the ability to accommodate unique special-purpose mechanical designs is important, as is the ability to restrict the motions of the end-effector. Conventionally, motion constraint is attained by mechanical constraint equipments, such as bearing, linear guide, and so on. In this paper, robot motion control with a controlled supporting point (CSP) for operator aid is proposed. The method is to make the constraint without setting mechanical constraints. The merits of the proposed method are not only the simplification of mechanical equipments but also the deletion of friction at the constraint. It is easy to set the CSP at the position where the setting of mechanical supporting points is difficult. Furthermore, it is also possible to change the CSP online. This method is especially effective for the object whose position of surface is always changing. The proposed method is applied to six-degrees-of-freedom manipulators. The numerical and experimental results show the viability of the proposed method. Index Terms--Bilateral teleoperation, constraint, disturbance observer, environment quarrier, force control, haptics, motion control, surgery robot.
Keywords: Robots -- Usage ; Haptics Technology -- Usage
ISSN: 0278-0046
Source: Cengage Learning, Inc.
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• 7
Article
Language: English
In: IEEE Transactions on Industrial Electronics, February 2007, Vol.54(1), pp.530-538
Description: Controlling robots in contact with the environment is an important problem in industry applications. Generally, a force sensor is used for sensing the external force. It is well known that information of a force sensor has much noise. Furthermore, unstable state is also caused by the narrow bandwidth of force information by a force sensor. This paper shows that stable contact with the environment is difficult when a force sensor is used because of its soft mechanical structure and narrow bandwidth of force sensing. In order to solve the instability of force control, the disturbance observer is implemented instead of the force sensor. The disturbance observer can observe the external force without force sensors. When the disturbance observer is implemented in a robot, a force control system does not include a soft mechanism between a robot and the environment. Since a robot can detect the environmental information directly, a wide bandwidth of force sensing is attained. In this way, this paper solves the problems of force control by considering the force sensing method without changing the control architecture, and the ability of force control is improved. Experimental results show viability of the proposed method
Keywords: Force Control ; Force Sensors ; Robot Sensing Systems ; Bandwidth ; Motion Control ; Service Robots ; Design Engineering ; Systems Engineering and Theory ; Industry Applications ; Robotic Assembly ; Acceleration Control ; Disturbance Observer ; Force Bandwidth ; Force Control ; Force Sensor ; Haptics ; Motion Control ; Engineering
ISSN: 0278-0046
E-ISSN: 1557-9948
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• 8
Article
Language: English
In: IEEE Transactions on Industrial Electronics, June 2006, Vol.53(3), pp.922-928
Description: Controlling robots in contact with the environment is an important problem in industry applications. In the conventional force control, much research has paid attention to develop novel force control systems and implemented force sensors to detect external force. This paper shows that narrow bandwidth of force sensor has a big influence on the force control system. Generally, to solve the instability in force control, the velocity feedback gain is enlarged. The system becomes unstable with small velocity feedback gain, and robot's response becomes slow with large one. Inasmuch as there is a tradeoff between the stability and the response, it is considered that force control by robots is difficult. This paper proposes a force control system with disturbance observer. It is possible to obtain the force information with wide bandwidth by using the disturbance observer. This paper shows that bandwidth of force sensing is very important for contact motion control. By using the wide bandwidth of force sensing, both stability and response are improved. Furthermore, force control is attainable by the construction of the easiest force control architecture. Therefore, the ideal zero-stiffness-force control is attained. The numerical and experimental results show viability of the proposed method.
Keywords: Bandwidth ; Force Control ; Force Sensors ; Robot Sensing Systems ; Stability ; Robot Control ; Service Robots ; Industry Applications ; Force Feedback ; Motion Control ; Bandwidth ; Control Stiffness ; Disturbance Observer ; Force Control ; Force Sensing ; Haptics ; Motion Control ; Robustness ; Engineering
ISSN: 0278-0046
E-ISSN: 1557-9948
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• 9
Article
Language: English
In: The Astrophysical Journal Letters, 2014, Vol.782(2), p.L35 (6pp)
Description: We report photometric and spectroscopic observations of the nearby Type Ia Supernova (SN Ia) 2012ht from 15.8 days to +49.1 days after B -band maximum. The decline rate of the light curve is m 15 ( B ) = 1.39 ± 0.05 mag, which is intermediate between normal and subluminous SNe Ia, and similar to that of the transitional Type Ia SN 2004eo. The spectral line profiles also closely resemble those of SN 2004eo. We were able to observe SN 2012ht at a very early phase, when it was still rising and was about three magnitudes fainter than at the peak. The rise time to the B -band maximum is estimated to be 17.6 ± 0.5 days and the time of the explosion is MJD 56277.98 ± 0.13. SN 2012ht is the first transitional SN Ia whose rise time is directly measured without using light curve templates, and the fifth SN Ia overall. This rise time is consistent with those of the other four SNe within the measurement error, even including the extremely early detection of SN 2013dy. The rising part of the light curve can be fitted by a quadratic function, and shows no sign of a shock-heating component due to the interaction of the ejecta with a companion star. The rise time is significantly longer than that inferred for subluminous SNe such as SN 1991bg, which suggests that a progenitor and/or explosion mechanism of transitional SNe Ia are more similar to normal SNe Ia rather than to subluminous SNe Ia.
Keywords: Astrophysics - Solar And Stellar Astrophysics;
ISSN: 2041-8205
E-ISSN: 2041-8213
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• 10
Article
Language: English
In: Publications of the Astronomical Society of Japan, 2001, Vol.53(1), pp.111～117
Description: Title Transcription: Superdisks in Supersoft X Ray Sources
Description: Material Type: 記事・論文
Keywords: Accretion ; Accretion Disks ; Stars ; White Dwarfs ; Supercritical Accretion ; X-Rays ; Individual(Rx J0019.8+2156)
ISSN: 00046264
E-ISSN: 2053051X
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