scholarly journals IW And-type state in IM Eridani

2019 ◽  
Vol 72 (1) ◽  
Author(s):  
Taichi Kato ◽  
Yasuyuki Wakamatsu ◽  
Naoto Kojiguchi ◽  
Mariko Kimura ◽  
Ryuhei Ohnishi ◽  
...  
Keyword(s):  
Small Amplitude ◽  
Repeated Sequence ◽  
Type Star ◽  
Dwarf Novae ◽  
Oscillation Phase ◽  
Long Cycle ◽  
Model Based ◽  
Disk Mass ◽  
Type Phase ◽  
Tilted Disk

Abstract IW And stars are a recently recognized group of dwarf novae which are characterized by a repeated sequence of brightening from a standstill-like phase with damping oscillations followed by a deep dip. Kimura et al. (2019, PASJ, submitted) recently proposed a model based on thermal-viscous disk instability in a tilted disk to reproduce the IW And-type characteristics. IM Eri experienced the IW And-type phase in 2018 and we recorded three cycles of the (damping) oscillation phase terminated by brightening. We identified two periods during the IW And-type state: 4–5 d small-amplitude (often damping) oscillations and a 34–43 d long cycle. This behavior is typical for an IW And-type star. The object gradually brightened within the long cycle before the next brightening, which terminated the (damping) oscillation phase. This observation agrees with the increasing disk mass during the long cycle predicted by the Kimura et al. model of thermal-viscous disk instability in a tilted disk. We did not, however, succeed in detecting negative superhumps, which are considered to be the signature of a tilted disk.

scholarly journals Periodically repeating fast radio bursts: Lense–Thirring precession of a debris disk?

2020 ◽  
Vol 72 (4) ◽  
Author(s):  
Wen-Cong Chen
Keyword(s):  
Magnetic Field ◽  
Rotational Energy ◽  
Radio Bursts ◽  
Spin Period ◽  
Disk Mass ◽  
Debris Disk ◽  
The Magnetic Field ◽  
Normal Magnetic Field ◽  
Current Stage ◽  
Tilted Disk

Abstract Recently, repeating fast radio bursts (FRBs) with a period of PFRB = 16.35 ± 0.18 d from FRB 180916.J0158+65 were reported. It still remains controversial how such a periodicity might arise for this FRB. In this Letter, based on an assumption of a young pulsar surrounding by a debris disk, we attempt to diagnose whether Lense–Thirring precession of the disk on the emitter can produce the observed periodicity. Our calculations indicate that the Lense–Thirring effect of a tilted disk can result in a precession period of 16 d for a mass inflow rate of 0.5–1.5 × 1018 g s−1, a pulsar spin period of 1–20 ms, and an extremely low viscous parameter α = 10−8 in the disk. The disk mass and the magnetic field of the pulsar are also constrained to be ∼10−3 M⊙ and <2.5 × 1013 G. In our model, a new-born pulsar with normal magnetic field and millisecond period would successively experience the accretion and propeller phases, and is visible as a strong radio source in the current stage. The rotational energy of such a young neutron star can provide the observed radio bursting luminosity for 400 yr.

scholarly journals Detection of the Irradiated Red Dwarf in WY Sge (Nova 1783)

1996 ◽  
Vol 158 ◽  
pp. 327-328
Author(s):  
M. W. Somers ◽  
K. Mukai ◽  
T. Naylor ◽  
F.A. Ringwald
Keyword(s):  
Optical Spectroscopy ◽  
White Dwarf ◽  
Type Star ◽  
Sufficient Information ◽  
Late Type ◽  
Dwarf Novae ◽  
System A ◽  
Late Type Star ◽  
The Face ◽  
Ir Photometry

AbstractWe present infrared (IR) photometry and optical spectroscopy of the eclipsing old nova WY Sge. According to hibernation theorists the disc in a system a few centuries after outburst should be significantly fainter than in other, more recent, old novae but similar to the discs of dwarf novae in quiescence. Despite the apparent faintness of the late type star we have sufficient information to infer that the face closest to the white dwarf (WD) is irradiated.

scholarly journals Magnetic Field Reconnection in Differentially Rotating Accretion Disks

1985 ◽  
Vol 107 ◽  
pp. 477-482
Author(s):  
David Gilden ◽  
T. Tajima
Keyword(s):  
Magnetic Field ◽  
Accretion Disks ◽  
Hot Spots ◽  
Small Amplitude ◽  
Uniform Magnetic Field ◽  
Cataclysmic Variables ◽  
Dwarf Novae ◽  
The Magnetic Field ◽  
Viscous Stresses ◽  
Fast Reconnection

Differentially rotating accretion disks threaded by a uniform magnetic field have been numerically simulated. Fast reconnection followed by coalescence allows the magnetic field to drive small amplitude radial oscillations in the disk. These oscillations may be observable as the viscous stresses cause the disk to brighten and fade as the disk expands and contracts. Episodes of reconnection may also be observable as hot spots produced locally at the sites of coalescence. Cataclysmic variables, and in particular dwarf novae, provide a natural interpretation for these calculations.

scholarly journals On the Origin of the Abundance Anomalies in IK Peg

1996 ◽  
Vol 158 ◽  
pp. 461-462
Author(s):  
B. Smalley ◽  
K.C. Smith ◽  
D. Wonnacott
Keyword(s):  
Mass Transfer ◽  
Binary System ◽  
White Dwarf ◽  
Small Amplitude ◽  
Diffusion Processes ◽  
Type Star ◽  
Common Envelope ◽  
Radiative Diffusion ◽  
The Common ◽  
Abundance Anomalies

AbstractIK Peg is a binary system comprising a pulsating A-type star in orbit with a massive white dwarf. A detailed abundance analysis of IK Peg A has been performed. It is found that the Ca and Sc abundances are approximately solar, and the Fe-group elements slightly enhanced. IK Peg is not a classical Am star but the results are not inconsistent with its spectroscopic classification as a marginal Am star. An excess of Ba and Sr are found. These anomalies could be explained by radiative diffusion processes operating in the atmosphere of IK Peg A, even though it is undergoing small-amplitude pulsations. Alternatively, since the companion is a massive white dwarf, these anomalies could be the result of mass transfer during the common envelope phase of the binary system’s evolution.

scholarly journals Envelope-to-disk mass transport in the FUor-type young eruptive star V346 Normae

2018 ◽  
Vol 14 (S345) ◽  
pp. 320-321
Author(s):  
Á. Kóspál ◽  
P. Ábrahám ◽  
O. Fehér ◽  
F. Cruz-Sáenz de Miera ◽  
M. Takami
Keyword(s):  
Mass Transport ◽  
Velocity Structure ◽  
Accretion Rate ◽  
Central Star ◽  
Type Star ◽  
Disk Mass ◽  
Disk Material ◽  
Accretion Rates

AbstractHaving disk-to-star accretion rates on the order of 10-4M⊙/yr, FU Orionis-type stars (FUors) are thought to be the visible examples for episodic accretion. FUors are often surrounded by massive envelopes, which replenish the disk material and enable the disk to produce accretion outbursts. We observed the FUor-type star V346 Nor with ALMA at 1.3 mm continuum and in different CO rotational lines. We mapped the density and velocity structure of its envelope and analyzed the results using channel maps, position-velocity diagrams, and spectro-astrometric methods. We discovered a pseudo-disk and a Keplerian disk around a 0.1 M⊙ central star. We determined an infall rate from the envelope onto the disk of 6×10-6M⊙/yr, a factor of few higher than the quiescent accretion rate from the disk onto the star. This hints for a mismatch between the infall and accretion rates as the cause of the eruption.

On nearly-commensurable periods in the restricted problem of three bodies, with calculations of the long-period variations in the interior 2:1 case

1966 ◽  
Vol 25 ◽  
pp. 197-222 ◽  
Author(s):  
P. J. Message
Keyword(s):  
Periodic Solution ◽  
Periodic Solutions ◽  
Large Amplitude ◽  
Restricted Problem ◽  
Small Amplitude ◽  
Minor Planets ◽  
Long Period ◽  
Numerical Integrations ◽  
Period Variations ◽  
The Mean

An analytical discussion of that case of motion in the restricted problem, in which the mean motions of the infinitesimal, and smaller-massed, bodies about the larger one are nearly in the ratio of two small integers displays the existence of a series of periodic solutions which, for commensurabilities of the typep+ 1:p, includes solutions of Poincaré'sdeuxième sortewhen the commensurability is very close, and of thepremière sortewhen it is less close. A linear treatment of the long-period variations of the elements, valid for motions in which the elements remain close to a particular periodic solution of this type, shows the continuity of near-commensurable motion with other motion, and some of the properties of long-period librations of small amplitude.To extend the investigation to other types of motion near commensurability, numerical integrations of the equations for the long-period variations of the elements were carried out for the 2:1 interior case (of which the planet 108 “Hecuba” is an example) to survey those motions in which the eccentricity takes values less than 0·1. An investigation of the effect of the large amplitude perturbations near commensurability on a distribution of minor planets, which is originally uniform over mean motion, shows a “draining off” effect from the vicinity of exact commensurability of a magnitude large enough to account for the observed gap in the distribution at the 2:1 commensurability.

Representation, abstraction, and simple-minded sophisticates

2020 ◽  
Vol 43 ◽  
Author(s):  
Peter Dayan
Keyword(s):  
Decision Theory ◽  
Predictive Coding ◽  
Bayesian Decision Theory ◽  
Bayesian Decision ◽  
Model Based ◽  
Model Free

Abstract Bayesian decision theory provides a simple formal elucidation of some of the ways that representation and representational abstraction are involved with, and exploit, both prediction and its rather distant cousin, predictive coding. Both model-free and model-based methods are involved.

Quasi-Periodic Oscillations in Dwarf Novae

1979 ◽  
Vol 46 ◽  
pp. 77-88
Author(s):  
Edward L. Robinson
Keyword(s):  
Binary Systems ◽  
Outer Edge ◽  
Light Curves ◽  
Close Binary ◽  
Bright Spot ◽  
Dwarf Novae ◽  
Periodic Oscillations ◽  
High Frequencies ◽  
Short Period ◽  
Typical Time

Three distinct kinds of rapid variations have been detected in the light curves of dwarf novae: rapid flickering, short period coherent oscillations, and quasi-periodic oscillations. The rapid flickering is seen in the light curves of most, if not all, dwarf novae, and is especially apparent during minimum light between eruptions. The flickering has a typical time scale of a few minutes or less and a typical amplitude of about .1 mag. The flickering is completely random and unpredictable; the power spectrum of flickering shows only a slow decrease from low to high frequencies. The observations of U Gem by Warner and Nather (1971) showed conclusively that most of the flickering is produced by variations in the luminosity of the bright spot near the outer edge of the accretion disk around the white dwarf in these close binary systems.

Symbiotic Stars at Optical, Infrared and Radio Wavelengths

1979 ◽  
Vol 46 ◽  
pp. 125-149 ◽  
Author(s):  
David A. Allen
Keyword(s):  
Temperature Regime ◽  
Type Star ◽  
Stellar Systems ◽  
Symbiotic Stars ◽  
Lower Excitation ◽  
Definition Of ◽  
Original Type

No paper of this nature should begin without a definition of symbiotic stars. It was Paul Merrill who, borrowing on his botanical background, coined the termsymbioticto describe apparently single stellar systems which combine the TiO absorption of M giants (temperature regime ≲ 3500 K) with He II emission (temperature regime ≳ 100,000 K). He and Milton Humason had in 1932 first drawn attention to three such stars: AX Per, CI Cyg and RW Hya. At the conclusion of the Mount Wilson Ha emission survey nearly a dozen had been identified, and Z And had become their type star. The numbers slowly grew, as much because the definition widened to include lower-excitation specimens as because new examples of the original type were found. In 1970 Wackerling listed 30; this was the last compendium of symbiotic stars published.

RSCVn Stars in the Southern Hemisphere

1979 ◽  
Vol 46 ◽  
pp. 371-384 ◽  
Author(s):  
J.B. Hearnshaw
Keyword(s):  
Light Curve ◽  
Southern Hemisphere ◽  
Orbital Period ◽  
Binary Stars ◽  
Small Amplitude ◽  
Light Variation ◽  
Orbital Phase

RSCVn stars are fully detached binary stars which show intrinsic small amplitude (up to 0.3 amplitude peak-to-peak) light variations, as well as, in most of the known cases, eclipses. The spectra are F to G, IV to V for the hotter component and usually KOIV for the cooler. They are also characterised by abnormally strong H and K emission from the cooler star, or, occasionally, from both components. The orbital and light curve periods are in the range 1 day to 2 weeks. An interesting feature is the migration of the light variations to earlier orbital phase, as the light variation period is shorter than the orbital period by a few parts in 10+4to a few parts in 10+3.

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